Handbook for

Designing Roadways

for the 

Aging Population

Interchanges Roadway

Segments

Intersections

Construction/

Work Zones

HighwayRail Grade

Crossings

Handbook for Designing Roadways for the Aging Population i

FRONT MATTER

Foreword

The proportion of the United States population age 65 and over will increase significantly 

in the coming decades. The effects of aging on people as drivers and pedestrians are 

highly individual. Challenges that may impact people as they age include declining 

vision, decreased flexibility and psychomotor performance, and changes in perceptual 

and cognitive performance. Design practices that explicitly recognize these changes will 

better serve this growing segment of the nation’s population. 

This Handbook for Designing Roadways for the Aging Population provides practitioners 

with a practical information source that links aging road user performance to highway 

design, operational, and traffic engineering features. This Handbook supplements 

existing standards and guidelines in the areas of highway geometry, operations, and 

traffic control devices.

The information in this Handbook should be of interest to highway designers, traffic 

engineers, and highway safety specialists involved in the design and operation of highway 

facilities. In addition, this Handbook will be of interest to researchers concerned with 

issues of aging road user safety and mobility.

The Handbook is also available online at http://safety.fhwa.dot.gov/older_users/#training. 

Tony Furst

Associate Administrator for Safety 

Federal Highway Administration

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of 

information exchange. The U.S. Government assumes no liability for the use of the information contained in this 

document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this 

report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the 

public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the 

quality, objectivity, utility, and integrity of its information.

FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality 

improvement.
ii Handbook for Designing Roadways for the Aging Population

FRONT MATTER

1. Report No.

FHWA-SA-14-015

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Handbook for Designing Roadways for the Aging Population

5. Report Date

June 2014

6. Performing Organization Code

7. Authors 

Marcus Brewer, Debbie Murillo, Alan Pate

Authors of Previous Draft

David Harkey, Loren Staplin, Kathy Lococo, Raghavan Srinivasan, Jongdae 

Baek, Michael Daul, Hugh McGee, Michael Tantillo

8. Performing Organization Report No.

9. Performing Organization Name and Address

Texas A&M Transportation Institute Battelle

2935 Research Parkway 505 King Avenue

College Station, TX 77845 Columbus, OH 43201

Performing Organization Name and Address for Previous Draft

University of North Carolina TransAnalytics

Highway Safety Research Center 1722 Sumneytown Pike

730 ML King Blvd, CB #3430 Box 328

Chapel Hill, NC 27599 Kulpsville, PA 19443

Vanasse Hangen Brustlin, Inc.

8300 Boone Blvd., Suite 700

Vienna, VA 22182

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-12-D-00046, TO T-13005

Contract or Grant No. for Previous Draft

DTFH61-05-D-00024, TO T-10-002

12. Sponsoring Agency Name and Address

Federal Highway Administration 

Office of Safety 

1200 New Jersey Ave. S.E.

Washington, DC 20590-9898

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

15. Supplementary Notes

Government Task Manager (GTM): Rebecca Crowe

16. Abstract

The original Older Driver Highway Design Handbook was published by FHWA in 1998 (FHWA-RD-97-135). The 

2nd edition, titled Highway Design Handbook for Older Drivers and Pedestrians (FHWA-RD-01-103) was published in 

2001. This 3rd edition, under a new title, incorporates new research findings and treatments to improve the safety of the 

transportation system for the aging population.

The Handbook is divided into three sections. The first section explains how to use the Handbook to select treatments to 

address problems for aging drivers and pedestrians. The second section includes treatments for 51 proven and promising 

traffic control and design elements distributed among five categories: Intersections, Interchanges, Roadway Segments, 

Construction/Work Zones, and Highway-Rail Grade Crossings. The final section of the Handbook includes the rationale 

and supporting evidence for the treatments.

A website including all of the content of the Handbook is available at http://safety.fhwa.dot.gov/older_users/#training.

17. Key Words

Safety, Highway Design, Traffic 

Operations, Driver Age, Driver 

Performance, Pedestrian, Human 

Factors, Vision, Attention, Perception, 

Cognition, Memory, Physical Ability, Risk 

Perception, Hazard Perception

18. Distribution Statement

No restrictions. 

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

 422

22. Price

 Form DOT F 1700.7 (8-72) Reproduction of form and completed page is authorized 

Technical Report Documentation Page
Handbook for Designing Roadways for the Aging Population iii

July 10, 2013 FRONT MATTER

ii

SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol 

LENGTH

in inches 25.4 millimeters mm 

ft feet 0.305 meters m

yd yards 0.914 meters m

mi miles 1.61 kilometers km 

AREA

in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2

ac acres 0.405 hectares ha

mi2 square miles 2.59 square kilometers km2

VOLUME 

fl oz fluid ounces 29.57 milliliters mL 

gal gallons 3.785 liters L

ft3 cubic feet 0.028 cubic meters m3

yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg

T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t") 

TEMPERATURE (exact degrees) o

F Fahrenheit 5 (F-32)/9 Celsius oC

or (F-32)/1.8 

ILLUMINATION

fc foot-candles 10.76 lux lx

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS 

lbf poundforce 4.45 newtons N

lbf/in2 poundforce per square inch 6.89 kilopascals kPa 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

LENGTH mm millimeters 0.039 inches in 

m meters 3.28 feet ft 

m meters 1.09 yards yd 

km kilometers 0.621 miles mi 

AREA mm2 square millimeters 0.0016 square inches in2

m2 square meters 10.764 square feet ft2

m2 square meters 1.195 square yards yd2

ha hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi2

VOLUME 

mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft3

m3 cubic meters 1.307 cubic yards yd3

MASS 

g grams 0.035 ounces oz

kg kilograms 2.202 pounds lb

Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T

TEMPERATURE (exact degrees) o

C Celsius 1.8C+32 Fahrenheit oF

ILLUMINATION

lx lux 0.0929 foot-candles fc 

cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS 

N newtons 0.225 poundforce lbf 

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)
iv Handbook for Designing Roadways for the Aging Population

FRONT MATTER

Preface

The increasing numbers and percentages of aging persons using our nation’s streets and 

highways in the decades ahead will pose many challenges to transportation engineers 

who focus on safety and operational efficiency. According to the Administration on 

Aging, the 65-and-older age group, which numbered 39.6 million in the United States in 

2009, will grow to more than 55 million in 2020. By 2030, there will be approximately 

72.1 million aging persons, accounting for roughly one-fifth of the population of driving 

age in this country. In effect, for many aspects of road planning and design, the “design 

driver” and the “design pedestrian” of the early 21st century will likely be 65 or over.

There are important consequences of these changing demographics, and life for aging 

persons depends to an extraordinary degree on remaining independent. Independence 

requires mobility. In our society the overwhelming choice of mobility options is the 

personal automobile. Other mobility options that may be utilized include public transit 

and walking. This means that there will be a steadily increasing proportion of drivers 

and pedestrians who experience declining vision; slowed decision-making and reaction 

times; exaggerated difficulty when dividing attention between traffic demands and other 

important sources of information; and reductions in strength, flexibility, and general 

fitness.

In a proactive response to this pending surge in aging road users, the Federal Highway 

Administration (FHWA) published the Older Driver Highway Design Handbook in 1998. 

The 1998 Handbook provided highway designers and engineers with the first practical 

information source linking age-related declines in functional capabilities to enhanced 

design, operational, and traffic engineering treatments, keyed to specific roadway 

features. Experience with these enhanced treatments, including extensive feedback from 

local and State-level practitioners, led to the release of the Highway Design Handbook for 

Older Drivers and Pedestrians in 2001. Now, a third edition of this resource has been 

prepared, under a new title, which incorporates new research, expands the range of 

applications covered by the Handbook, and introduces format changes—including a webbased version—that will facilitate access and use by engineering professionals to improve 

our streets and highways in the years ahead.

Part I of this Handbook retains its focus on five broad categories of roadway features, 

each containing a number of specific design elements for which guidance is presented. 

The top priority is intersections, reflecting aging drivers’ most serious and enduring 

crash problem area, as well as the greatest exposure to risk for pedestrians. Next, welldocumented difficulties with merging/weaving and lane changing maneuvers focus 

attention on interchanges. Roadway segments, with an emphasis on curves and passing 

zones, plus highway construction/work zones, are included due to heightened tracking 

(steering) demands that may increase a driver’s workload along with an increased 

potential for unexpected events that require a rapid response. Finally, highway-rail grade 

crossings merit consideration as sites where conflicts are rare, and thus unexpected, and 

where problems of detection (with passive controls) may be exaggerated due to sensory 

losses with advancing age. 
Handbook for Designing Roadways for the Aging Population v

FRONT MATTER

The treatments presented in Part I are followed by a more lengthy section, Part II, 

presenting the rationale and supporting evidence. Within each of these two major 

Handbook sections, material is organized in terms of five subsections, corresponding 

to the categories of roadway features noted above. Preceding the treatments, a chapter 

titled “How To Use This Handbook” explains codes used throughout the document 

to cross-reference the Manual on Uniform Traffic Control Devices (MUTCD), A Policy 

on Geometric Design of Highways and Streets (the Green Book) and other manuals and 

guides. In addition, a guide for interpreting graphics used in the Handbook and a table 

for translating speeds and distances into “preview times” for driver decision and response 

selection are presented; and, a structured approach to help engineering professionals 

decide when to implement Handbook treatments is described. A supplementary 

discussion about how to determine the visibility of roadway elements is appended to this 

edition of the Handbook. The Handbook concludes with a glossary providing definitions 

of selected terms and a reference list.

Most of the treatments in this Handbook are based on supporting evidence drawn from 

a comprehensive review of field and laboratory research addressing human factors and 

highway safety. The supporting information presented in Part II represents the latest 

relevant information and data available to the authors at the time the document was 

assembled. Some research findings have been carried forward from previous Handbooks, 

while other findings are new since the release of the 2001 Handbook. A number of 

additional treatments were considered but ultimately dropped or deferred because of gaps 

or deficiencies in the supporting studies. This edition also includes some “Promising 

Practices”—treatments that are being used by one or more agencies, which although 

they have not been evaluated formally, are generally believed to benefit the aging 

population of roadway users based on subjective assessment by the staff participating in 

the development of this Handbook. This conservative approach also dictated that the 

Handbook’s treatments relate to the demonstrated performance deficits of normally aging

drivers and pedestrians. It deserves mention that diminished capabilities that result from 

the onset of Alzheimer’s disease and related dementias, which may afflict over 10 percent 

of those age 65 and older and over 40 percent of those age 85 and older, are not explicitly 

targeted in these guidelines. Neither are the compromises in performance that are 

associated with drowsiness, fatigue or distraction.

This resource can be applied preemptively to enhance safety wherever there are aging 

road users in a given jurisdiction, or it may be employed primarily as a “problem solver” 

at crash sites. The implementation of these treatments will translate into real gains 

in safety and mobility for our nation’s aging citizens, and indeed for all users of our 

surface transportation system. Readers of this Handbook must note, however, that the 

treatments presented in this Handbook do not constitute a new standard of required 

practice. The final decision about when and where to apply the treatments presented 

in this Handbook remains at the discretion of State and local design and engineering 

professionals.
vi Handbook for Designing Roadways for the Aging Population

FRONT MATTER

Acknowledgements

The quality and usefulness of the Handbook for Designing Roadways for the Aging 

Population is a direct result of the many highway engineering practitioners and 

researchers who provided their comments and suggestions to the authors of this edition 

of the Handbook, as well as the previous two editions. The authors wish to acknowledge 

the following individuals for their assistance and support in making this third edition a 

success:

•	 Gene Amparano, FHWA Resource Center

•	 Mark Doctor, FHWA Resource Center

•	 Keith Harrison, FHWA Resource Center

•	 Ken Kochevar, FHWA California Division

•	 Fred Ranck, formerly with FHWA Resource Center

•	 Rebecca Crowe, FHWA Office of Safety

•	 Dick Schaffer, formerly with FHWA Office of Safety

•	 Scott Wainwright, formerly with FHWA Office of Operations

•	 Kevin Sylvester, FHWA Office of Operations, MUTCD Team

•	 Chris Monk, NHTSA

•	 Esther Wagner, NHTSA

•	 Brian Chodrow, NHTSA

•	 Mary Stahlihut, Iowa Department of Transportation

•	 Gail Holley, Florida Department of Transportation

•	 Charlene M. Wilder, Federal Transit Administration

The authors would also like to acknowledge Charlie Zegeer, Laura Sandt, and Carl 

Sundstrom of the FHWA Pedestrian and Bicycle Information Center for their input to the 

pedestrian treatments included in the Handbook.
Handbook for Designing Roadways for the Aging Population vii

FRONT MATTER

Table of Contents

Foreword i

Preface iv

Acknowledgements vi

Abbreviations and Acronyms x

Chapter 1. How to Use this Handbook 1

Organization of the Handbook 1

Time-Speed-Distance Table 5

Knowing When to Implement these Recommendations 5

Part I. Treatments 11

Chapter 2. Intersections 13

1. Intersecting Angle (Skew) 19

2. Receiving Lane (Throat) Width 20

3. Channelization 20

4. Intersection Sight Distance 22

5. Offset Left-Turn Lanes 23

6. Delineation of Edge Lines and Curbs 26

7. Curb Radius 27

8. Left-Turn Traffic Control for Signalized Intersections 28

9. Right-Turn Traffic Control for Signalized Intersections 29

10. Street Name Signs 31

11. Stop and Yield Signs 33

12. Lane Assignment on Intersection Approach 34

13. Traffic Signals 35

14. Intersection Lighting 37

15. Pedestrian Crossings 38

16. Roundabouts 41

17. Right-Turn Channelization Design 45

18.	 Combination Lane-Use/Destination Overhead Guide Signs 46

19. Signal Head Visibility 46

20. High-Visibility Crosswalks 47

21. Supplemental Pavement Marking for Stop and Yield Signs 47

22. Reduced Left-Turn-Conflict Intersections 48

23. Accessible Pedestrian Signal (APS) Treatments 49

24. Flashing Yellow Arrow 49

Chapter 3. Interchanges 51

25. Exit Signs and Markings 54

26. Freeway Entrance Traffic Control Devices 56

27. Delineation 57

28. Acceleration/Deceleration Lane Design 58

29. Interchange Lighting 60

30. Restricted or Prohibited Movements 60
viii Handbook for Designing Roadways for the Aging Population

FRONT MATTER

31. Advance Pavement (Route Shield) Markings at Major Freeway Junctions 62

32. Wrong-Way Driving Countermeasures 63

Chapter 4. Roadway Segments 65

33. Horizontal Curves 68

34. Vertical Curves 70

35. Passing Zones 71

36. Lane Control Devices 72

37. Lane Drop Markings 73

38. Contrast Markings on Concrete Pavement 74

39. Utilize Highly Retroreflective Marking Material 75

40. Curve Warning Markings 75

41. Road Diets 76

42. High Friction Surface Treatments 76

Chapter 5. Construction/Work Zones 77

43. Signing and Advance Warning 79

44. Portable Changeable (Variable) Message Signs 81

45.	 Channelization (Path Guidance) 82

46. Delineation of Crossovers/Alternate Travel Paths 84

47. Temporary Pavement Markings 85

48. Increased Letter Height for Temporary Work Zone Signs 86

49. Work Zone Road Safety Audit (WZRSA) 86

Chapter 6. Highway-Rail Grade Crossing 87

50. Passive Traffic Control Devices 90

51. Lighting 91

Part II. Rationale and Supporting Evidence 93

Chapter 7. Intersections 95

1. Intersecting Angle (Skew) 96

2. Receiving Lane (Throat) Width 99

3. Channelization 102

4. Intersection Sight Distance 107

5. Offset Left-Turn Lanes 122

6. Delineation of Edge Lines and Curbs 129

7. Curb Radius 132

8. Left-Turn Traffic Control for Signalized Intersections 135

9. Right-Turn Traffic Control for Signalized Intersections 148

10. Street Name Signs 152

11. Stop and Yield Signs 160

12. Lane Assignment on Intersection Approach 170

13. Traffic Signals 173

14. Intersection Lighting 181

15. Pedestrian Crossings 185

16. Roundabouts 197

17. Right-Turn Channelization Design 215
Handbook for Designing Roadways for the Aging Population ix

FRONT MATTER

18.	 Combination Lane-Use/Destination Overhead Guide Signs 215

19. Signal Head Visibilty 216

20. High-Visibility Crosswalks 216

21. Supplemental Pavement Markings for Stop and Yield Signs 217

22. Reduced Left-Turn Conflict Intersections 218

23. Accessible Pedestrian Signal (APS) Treatments 219

24. Flashing Yellow Arrow 220

Chapter 8. Interchanges 223

25. Exit Signs and Markings 224

26. Freeway Entrance Traffic Control Devices 235

27. Delineation 238

28. Acceleration/Deceleration Lane Design 243

29. Interchange Lighting 248

30. Restricted or Prohibited Movements 252

31. Advance Pavement (Route Shield) Markings at Major Freeway Junctions 257

32 Wrong-Way Driving Countermeasures 257

Chapter 9. Roadway Segments 259

33. Horizontal Curves 260

34. Vertical Curves 272

35. Passing Zones 277

36. Lane Control Devices 281

37. Lane Drop Markings 284

38. Contrast Markings on Concrete Pavement 284

39. Utilize Highly Retroreflective Marking Material 285

40. Curve Warning Markings 285

41. Road Diets 286

42. High Friction Surface Treatments (HFSTs) 287

Chapter 10. Construction/Work Zones 289

43. Signing and Advance Warning 290

44. Portable Changeable (Variable) Message Signs 300

45.	 Channelization (Path Guidance) 313

46. Delineation of Crossovers/Alternate Travel Paths 318

47. Temporary Pavement Markings 323

48. Increased Letter Height for Temporary Work Zone Signs 328

49. Work Zone Road Safety Audits 329

Chapter 11. Highway-Rail Grade Crossings 331

50. Passive Traffic Control Devices 332

51. Lighting 343

Appendix A. Supplemental Technical Notes 345

Appendix B. Photograph and Image Credits 349

Appendix C. Glossary 357

Appendix D. References 369
x Handbook for Designing Roadways for the Aging Population

FRONT MATTER

Abbreviations and Acronyms

AAAFTS American Automobile Association Foundation for Traffic Safety

AADT annual average daily traffic

AASHTO American Association of State and Highway Transportation Officials

ASTM American Society for Testing and Materials

ATSSA American Traffic Safety Services Association

cd candela

CIE Commission Internationale de l’Eclairage

CIL complete interchange lighting

CMS changeable message sign

CSSB concrete safety-shaped barrier

DS diverge steering

DSD decision sight distance

FARS Fatality Analysis Reporting System

FHWA Federal Highway Administration

fL footlambert

GSA gap search and acceptance

IA initial acceleration

IIHS Insurance Institute for Highway Safety

ISD intersection sight distance

ISBL in-service brightness level

ISTEA Intermodal Surface Transportation Efficiency Act

ITE Institute of Transportation Engineers

LI legibility index

LPI leading pedestrian interval

MOE measure of effectiveness

MRVD minimum required visibility distance

MSC merge steering control

MUTCD Manual on Uniform Traffic Control Devices for Streets and Highways

NCHRP National Cooperative Highway Research Program

NHTSA National Highway Traffic Safety Administration

NTOR no turn on red
Handbook for Designing Roadways for the Aging Population xi

FRONT MATTER

NTSB National Transportation Safety Board

PIL partial interchange lighting

PMD post-mounted delineator

PRT perception-reaction time

RT reaction time

RPM raised pavement markers

RTOR right turn on red

SC steering control

SCL speed-change lane

SSD stopping sight distance

STV small target visibility

SU single unit (truck)

TCD traffic control device

TRB Transportation Research Board

TVA transient visual adaptation

TWLTL two-way, left-turn lane

VC visual clear
xii Handbook for Designing Roadways for the Aging Population
Handbook for Designing Roadways for the Aging Population 1

CHAPTER 1

How to Use this Handbook

Organization of the Handbook

The Handbook consists of two parts. Part I includes recommended treatments for 33 

traffic control or geometric design elements divided among five categories. The five 

categories of treatment are as follows:

•	 Intersections,

•	 Interchanges,

•	 Roadway Segments,

•	 Construction/Work Zones, and

•	 Highway-Rail Grade Crossings.

These treatments are recommended because they have been shown through research to 

be a benefit to the aging road user. In addition, 18 “Promising Practice” treatments are 

included. These are treatments being utilized by transportation agencies that should 

benefit aging road users as determined by a subjective assessment by staff participating 

on the development of this Handbook. Current trends indicate these practices have a 

positive impact on aging road user safety. These promising treatments are placed at the 

end of each category to which they apply. 

Part II includes the rationale and supporting evidence for each of the treatments. This 

part of the Handbook is also divided into these same five categories.

The treatments for each design element are presented as shown in Figure 1 and consist of 

the following components:

Category — At the top of each page is a header showing the category of treatment 

(i.e., Intersections, Interchanges, Roadway Segments, Construction Work Zones and 

Highway-Rail Grade Crossings).

Design Element — Each element has a unique number for quick reference to the Table of 

Contents.

Treatments — Each treatment within a design element is clearly identified by a unique 

letter, followed by a recommendation on how that treatment should be used.

Figure(s) — Many of the concepts described in the treatments are illustrated in 

figures—as photographs, figures extracted from the MUTCD or other publications, 

or as drawings. The drawings are for illustrative purposes only; they are not to 

scale and should not be used for design purposes. It is important to note that the 

lettering styles, arrows and symbols used in this Handbook are not always consistent 

with those prescribed in the MUTCD. When employing treatments included in this 

Handbook, only MUTCD-approved lettering styles, arrows and symbols should be used. 

Additionally, any highway agency wishing to implement a treatment that has not been 
2 Handbook for Designing Roadways for the Aging Population

CHAPTER 1—HOW TO USE THIS HANDBOOK

included in the most recent edition of the MUTCD, and thus denoted by a relationship 

code of “5” (see Table 1), must request experimentation approval from the FHWA.

References and Relationship Codes — References placed below each treatment indicate 

its relationship (by a numeric relationship code) to the design guides most frequently 

referenced by practitioners, as determined by the Handbook authors. A legend is 

provided at the bottom of each treatment page to remind users (in an abbreviated format) 

of the meaning of the numerical values. The complete definitions for these relationship 

codes are provided in Table 1.

Handbook for Designing Roadways for the Aging Population 31

CHAPTER 2 INTERSECTIONS

1: most conservative

2: 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: 

10 Street Name Signs 

A. Letter Heights and Sign Border

To accommodate the reduction in visual acuity associated with increasing 

age, minimum letter heights of 6 in for uppercase letters and 4.5 in for 

lowercase letters are recommended for use on ground-mounted street-name 

signs (MUTCD D3-1, as shown in Figure 18) on all roads where the posted 

speed limit is at or below 25 mph. On all roads where the posted speed limit 

is greater than 25 mph, letter heights of 8 in for uppercase letters and 6 in for 

lowercase letters should be used. 

intersections as a supplement to ground-mounted street-name signs. Minimum 

letter heights of 12 in for uppercase letters and 9 in for lowercase letters are 

recommended by the MUTCD. 

In the design of street-name signs, the use of larger letter heights may require 

necessary to minimize sign panel size while accommodating the larger letter 

size.

 References: MUTCD:1, NCHRP 500-9:4

B. Advance Street-Name Plaque

Wherever an advance intersection warning sign is installed (MUTCD W2 

series) it should be accompanied by an advance street name plaque (W16-8P 

or W16-8aP) using minimum letter heights of 6 in for uppercase letters and 

sign (MUTCD W3 series) is installed on a multi-lane approach, an advance 

street name plaque (W16-8P or W16-8aP), using the same minimum letter 

heights described above, should be considered. 

 References: MUTCD:2, NCHRP 500-9:4

C. Advance Street-Name Sign

control sign (with accompanying advance street-name plaque), the use 

of advance street-name signs (MUTCD D3-2) for major intersections is 

recommended, with turn bays to provide adequate preparation time for any 

lane change and/or turning maneuvers (see Figure 20).

 References: MUTCD:1, NCHRP 500-9:1

Figure 18. (MUTCD D3-1)

Figure 19. Intersection 

Warning W2-1 Sign and 

W16-8P Supplemental 

Advance Street Name 

Plaque

Figures — gures 

are used throughout 

the guide to 

illustrate the 

recommendations. 

They are numbered 

for easy reference.

Relationship Codes — each 

recommendation includes numbered 

references to supporting information 

in the design guides most frequently 

used by practitioners. A legend at the 

bottom of the page denes the 

relationship codes.

Treatment — each recommended 

treatment is identied with a letter 

for quick reference.

Category — identies the 

current section of the guide.

Design Element — each design 

element is numbered to allow 

for quick reference.

Figure 1. Elements included for each Handbook treatment
Handbook for Designing Roadways for the Aging Population 3

CHAPTER 1—HOW TO USE THIS HANDBOOK

Table 1. Definitions for the relationship codes between the recommendations and existing design guides or other 

manuals.

Code Definition

1 Handbook treatment selects the most conservative design value among present options in the standard manual/

guideline. (Example: Using a larger sign size identified as an “option” in the MUTCD).

2 Handbook treatment indicates the preferred design value where a discrepancy exists among two or more manuals/

guidelines. (Example: Limit skew to 75° as per TEH instead of 60° as per Green Book).

3 Handbook treatment extends a current practice to a new application or operation. (Example: Use of fluorescent 

sheeting on wrong-way control signing, for increased conspicuity).

4

Handbook treatment advances a specific design value or concept where only general guidance now exists, or provides 

more detailed or more stringent design criteria than are currently specified. (Example: It is recommended that an advance 

street-name plaque be used wherever an advance intersection warning sign is installed. The use of this supplemental 

plaque is an option per engineering judgment in the 2009 MUTCD.) 

5

Handbook treatment is permissible at this time only in accordance with the provisions of MUTCD Section 1A.10, 

Interpretations, Experimentations, Changes and Interim Approvals. These treatments represent advances in technology 

which research indicates will result in improved safety and efficiency of operations. (Example: It is recommended that 

the Roundabout Circulation Plaque (R6-5P) be placed immediately below the R1-2 Yield sign on both sides of the road 

at each entrance to a roundabout.)

The design guides, manuals, and other resources referenced by the relationship codes in 

the treatments and throughout the Handbook are shown in Table 2. The most current 

published edition of each guide was consulted in the preparation of the Handbook, 

with the exceptions as noted. The latest version of the MUTCD can be accessed at 

http://mutcd.fhwa.dot.gov.

In addition to the design guides shown in Table 2, there are a number of other resources 

and supporting tools available to assist in improving the roadway environment for aging 

(and all) road users. Some key resources include:

•	 Interactive Highway Safety Design Model (IHSDM): A suite of software analysis 

tools for evaluating safety and operational effects of geometric design decisions on 

two-lane rural highways (http://www.fhwa.dot.gov/research/tfhrc/projects/safety/

comprehensive/ihsdm/).

•	 Highway Safety Manual (HSM), 1st Edition, Volumes 1, 2 and 3, 2010: This resource 

provides safety knowledge and tools to facilitate improved decision-making based on 

safety performance (http://www.highwaysafetymanual.org).

•	 SafetyAnalyst: Analytical tools for use in the decision-making process to identify and 

manage a system-wide program of site-specific improvements to enhance highway 

safety by cost-effective means (http://www.safetyanalyst.org/).

•	 Human Factors Guidelines for Road Systems, NCHRP Report 600: This report 

is designed to help non-experts in human factors to consider more effectively the 

roadway user’s capabilities and limitations in the design and operation of highway 

facilities (http://www.trb.org/Main/Blurbs/167909.aspx). 

•	 NCHRP Report 500: Guidance for Implementation of the AASHTO Strategic

Highway Safety Plan: A series of guides to assist transportation agencies in reducing 

specific types of crashes in targeted emphasis areas outlined in the AASHTO Strategic 

Highway Safety Plan (http://www.trb.org/main/blurbs/152868.aspx).
4 Handbook for Designing Roadways for the Aging Population

CHAPTER 1—HOW TO USE THIS HANDBOOK

•	 Pedestrian Road Safety Audit Guidelines and Prompt Lists: A guide for 

conducting formal safety examinations of future roadway projects or inservice facilities with a focus on identifying and addressing pedestrian 

safety concerns (http://www.walkinginfo.org/library/details.cfm?id=3955). 

Similarly, a guide is available for conducting more general road safety audits 

(http://safety.fhwa.dot.gov/rsa/). 

•	 AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities:

Guidelines are included for the construction and design of sidewalks, street crossings,

and many aspects of pedestrian trails. The document is available for purchase at 

https://bookstore.transportation.org/. 

•	 PEDSAFE: Pedestrian Safety Guide and Countermeasure Selection System: This

interactive system is intended to help practitioners choose the most appropriate 

engineering, education, and enforcement countermeasures to address pedestrian 

safety and mobility issues (www.walkinginfo.org/pedsafe). 

For additional resources, visit the FHWA Office of Safety web site at 

http://safety.fhwa.dot.gov/.

Table 2. Abbreviations used for the references cited in the recommendation chapters.

Abbreviation Key Reference Citation

Green Book A Policy on Geometric Design of Highways and Streets (Green Book). American Association of State Highway 

and Transportation Officials, 2011.

HCM Highway Capacity Manual. Transportation Research Board, 2010. 

MUTCD Manual on Uniform Traffic Control Devices for Streets and Highways. (2009 Edition). Federal Highway 

Administration, 2009.

NCHRP 279 Intersection Channelization Design Guide, (NCHRP Report 279). National Cooperative Highway Research 

Program, 1985. 

NCHRP 500-9 Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, Volume 9: A Guide for Reducing 

Collisions Involving Older Drivers, (NCHRP Report 500, Volume 9). National Cooperative Highway Research 

Program, 2004.

NCHRP 672 NCHRP Report 672, Roundabouts: An Informational Guide (Second edition).

NCHRP 674 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities, 

(NCHRP Report 674). National Cooperative Highway Research Program, 2010. 

RLH FHWA Lighting Handbook, Federal Highway Administration, 2012.

RRX Railroad-Highway Grade Crossing Handbook, Revised 2nd Edition. Federal Highway Administration, 2007.

TEH Traffic Engineering Handbook, 5th Edition. Institute of Transportation Engineers, 2009.
Handbook for Designing Roadways for the Aging Population 5

CHAPTER 1—HOW TO USE THIS HANDBOOK

Time-Speed-Distance Table

A number of treatments presented in the Handbook identify the placement of a device 

or treatment in terms of the preview time that should be provided to the driver for its 

application. These values are typically expressed in seconds, such that the recommended 

placement of the device or treatment depends upon the speed at which traffic is moving. 

To facilitate application of Handbook treatments of this nature, Table 3 provides the 

advance placement distance needed to achieve a desired preview time at a particular 

operating speed.

Knowing When to Implement these 

Recommendations

Implementation of the treatments in this Handbook provide benefits for design 

challenges that disproportionately affect aging road users due to changes in functional 

ability experienced with normal aging. These may be most urgently needed where a crash 

problem with aging drivers or pedestrians has already been demonstrated; however, the 

greater benefit arguably lies in designing safer new roads and identifying and modifying 

problems with existing roads before statistics reveal a crash problem. Not only does this 

practice minimize the risk and severity of crashes, it minimizes the need for remedial 

works after construction, thus reducing the whole-life cost of projects. This is the central 

premise of the road safety audit process supported by FHWA and it holds the key for 

applying the Handbook treatments as well. 

Table 3. Advance placement distances required to achieve desired preview times at designated operating speeds.

Preview Time 

(seconds)

Operating Speed (mph)

30 35 40 45 50 55 60 65 70 75 80 

2.5 110 128 147 165 183 202 220 238 257 275 293 

3.0 132 154 176 198 220 242 264 286 308 330 352 

3.5 154 180 205 231 257 282 308 334 359 385 411 

4.0 176 205 235 264 293 323 352 381 411 440 469 

4.5 198 231 264 297 330 363 396 429 462 495 528 

5.0 220 257 293 330 367 403 440 477 513 550 587 

5.5 242 282 323 363 403 444 484 524 565 605 645 

6.0 264 308 352 396 440 484 528 572 616 660 704 

6.5 286 334 381 429 477 524 572 620 667 715 763 

7.0 308 359 411 462 513 565 616 667 719 770 822 

7.5 330 385 440 495 550 605 660 715 770 825 880 

8.0 352 411 469 528 587 645 704 763 822 880 939 
6 Handbook for Designing Roadways for the Aging Population

CHAPTER 1—HOW TO USE THIS HANDBOOK

The engineering enhancements described in this document should benefit all road users. 

Special justification may be required for implementation of Handbook practices. This 

section was developed to support engineering judgment in this regard. It suggests a 

three-step procedure using checklist responses plus brief written comments, as explained 

below. A set of optional worksheets for documenting each step is also provided.

Step 1: Problem Identification [see Project Review Worksheet on page 7]

During the planning stage for each project, practitioners are asked to determine whether 

a problem with the safe use of the facility by aging road users currently exists or may 

reasonably be expected based on current and projected use patterns. Using the first 

worksheet that follows this discussion, problem identification can be accomplished by 

checking YES or NO to the following four questions:

Q1. “Is there a demonstrated crash problem with aging road users?”

Q2. “Has any aspect of design or operations at the project location been associated with 

complaints to local, municipal, or county-level officials from aging road users or are 

you aware of a potential safety concern for aging road users at this location, either 

through observation, agency documentation, or engineering judgment?” 

Q3. “Is this project located on a direct link to a travel origin or destination for which, 

in the judgment of local planning/zoning authorities or other local officials, aging 

persons constitute a significant proportion of current users?” 

Q4. “Is the project located in a census tract or zip code designation that has experienced 

an increase in the proportion of (non-institutionalized) residents age 65 and older, 

for the most recent period in which the population was sampled?”

To answer these questions, practitioners will need to obtain reliable crash data from 

the appropriate division or bureau of their departments of transportation. At least the 

three most recent years for which data are available should be examined, and the data 

should be sorted by age, at a minimum. Sources of information outside of the State DOT 

also may be required to answer the problem identification questions. Potential sources 

include, but are not limited to:

•	 Local government officials/Board of Supervisors/city council representatives.

•	 Local and State police.

•	 The (State) Department of Aging and/or county Area Agency on Aging.

•	 The (State) Department of Health and Human Services and Department of Public

Welfare.

•	 The regional planning commission.

Step 2: Identification of Design Elements and Treatments [see worksheet on page 9]

For each project where a practitioner has answered YES to one or more of the problem 

identification questions in Step 1, the next step is consider all categories (i.e., intersection, 

interchanges, roadway segments, construction/work zones, and highway-rail grade 

crossings) on the facility. Then, for each category, consider each design element and 

treatment that could be applied. For each one, the engineer should indicate whether the 
Handbook for Designing Roadways for the Aging Population 7

CHAPTER 1—HOW TO USE THIS HANDBOOK

Project Review Worksheet

Project Title/ID: _______________________________________________________________

Person Completing Worksheet: __________________________________________________ Date: ________________________

Q1. “Is there a demonstrated crash problem with aging road users?” YES ■ NO ■

Source(s) Date of Contact

Q2. “Has any aspect of design or operations at the project location been associated with 

complaints to local, municipal, or county-level officials from aging road users or are you 

aware of a potential safety concern for aging road users at this location, either through 

observation, agency documentation, or engineering judgment?”

YES ■ NO ■

Source(s) Date of Contact

Q3. “Is this project located on a direct link to a travel origin or destination for which, in the 

judgment of local planning/zoning authorities or other local officials, aging persons 

constitute a significant proportion of current users?”

YES ■ NO ■

Source(s) Date of Contact

Q4. “Is the project located in a census tract or zip code designation that has experienced an 

increase in the proportion of (non-institutionalized) residents age 65 and older, for the most 

recent period in which the population was sampled?”

YES ■ NO ■

Source(s) Date of Contact

REPRODUCE THIS PAGE AS NEEDED
8 Handbook for Designing Roadways for the Aging Population

CHAPTER 1—HOW TO USE THIS HANDBOOK

Step 3: Implementation Decision [see worksheet on page 10]

To begin Step 3, each Handbook treatment identified as a candidate for implementation in 

Step 2 should be properly referenced [e.g., 5D(1)]. Next, any factors relating to increased 

costs (for an enhanced treatment), added approvals that may be needed, or any other 

special considerations that impact implementation may be noted in separate columns on 

the worksheet. The final step is then to proceed to an implementation decision. This is 

recorded as a judgment by the engineer as to whether implementation of the candidate 

countermeasure is recommended. The engineer’s judgment is indicated by a check in the 

space next to YES or NO in the last column on the worksheet, accompanied by his/her 

initials for verification. Additional comments should be entered as deemed appropriate.

recommended practice differs from standard State or local practices, and if yes, what 

additional benefits are expected to result from implementing the applicable Handbook

treatment(s). One possible example of how such worksheet entries could be made is 

shown in Table 4. 

Category Design Element

Applicable 

Handbook

Treatment

Differs From 

Existing 

State or Local 

Practice?

If YES...

NO YES Explain Difference Identify Expected 

Benefits

Intersections 1. Intersecting 

Angle (Skew)

(1C) Skewed 

Signalized 

Intersection

✔ According to MUTCD 

warrants, there is 

“adequate” sight 

distance and fewer than 

3 RTOR crashes annually 

on approach.

Should reduce the 

difficulty for aging 

drivers to check for 

approaching traffic, and 

also reduce aggressive 

behavior of following 

drivers who don’t 

accept an aging driver’s 

decision not to turn on 

red.

Intersections 10. Street-Name 

Signs 

(10A) Letter 

Heights and Sign 

Border

✔

Intersections 16. Roundabouts (16C) Splitter 

Islands

✔

Intersections 24. Flashing Yellow 

Arrow

(Promising 

Practice for 

permissive left 

turns)

✔ Current practice 

uses a green ball for 

permissive left turns.

Should improve the 

ability of aging drivers 

to correctly recognize 

when permissive left 

turns are allowed.

Construction/

Work Zones

43.Signing and 

Advance 

Warning

(43C) Sign 

Sheeting

✔

Table 4. Example of Completed Design Elements and Treatments Worksheet.
Handbook for Designing Roadways for the Aging Population 9

CHAPTER 1—HOW TO USE THIS HANDBOOK

Identification of Design Elements and 

Treatments Worksheet

Project Title/ID: _______________________________________________________________________________________________

Person Completing Worksheet: __________________________________________________ Date: ________________________

Identify design elements for which a treatment exists in the Handbook and the applicable treatments. 

Then, (a) describe differences between the treatment and standard practice, and (b) list benefits 

expected to result from implementing the Handbook.

Category Design Element

Applicable 

Handbook

Treatment

Differs From 

Existing State or 

Local Practice?

If YES...

NO YES Explain Difference Identify Expected 

Benefits

REPRODUCE THIS PAGE AS NEEDED
10 Handbook for Designing Roadways for the Aging Population

CHAPTER 1—HOW TO USE THIS HANDBOOK

Implementation Worksheet

Project Title/ID: _______________________________________________________________________________________________

Person Completing Worksheet: __________________________________________________ Date: ________________________

List each treatment identified as a candidate for implementation. Document whether additional 

approval is needed (i.e., Environmental, Regulatory, etc.), and whether increased costs or other 

special considerations may affect implementation. Based on these considerations, decide whether 

implementation can be recommended, add your initials, and add supplemental comments as 

appropriate.

Treatment

Implementation Considerations

Implementation Recommended?

Added Costs? Added 

Approvals? Other

NO_______ Initials _________

YES ______

Comments:

NO_______ Initials _________

YES ______

Comments:

NO_______ Initials _________

YES ______

Comments:

REPRODUCE THIS PAGE AS NEEDED
Handbook for Designing Roadways for the Aging Population 11

Treatments

Overview

This section of the Handbook is organized in the following categories: 

Chapter 2 — Intersections, 

Chapter 3 — Interchanges, 

Chapter 4 — Roadway Segments, 

Chapter 5 — Construction/Work Zones, and 

Chapter 6 — Highway-Rail Grade Crossings. 

Within each chapter (category), the design elements being presented are listed. 

This listing is then followed by a concise discussion summarizing the key issues 

for the aging population. Then, for each design element, the treatments being 

recommended are presented. After all of the numbered design elements are 

presented, then the “Promising Practice” treatments are provided. These are 

treatments that designers and engineers should consider, recognizing that these 

are being used by one or more agencies, which, though they have not been 

evaluated formally, are generally believed to benefit the aging population based on 

a subjective assessment by staff participating in the development of the Handbook. 

PART I 
12 Handbook for Designing Roadways for the Aging Population
Handbook for Designing Roadways for the Aging Population 13

CHAPTER 2

Intersections

This section of the Handbook provides treatments for 16 different design elements in order 

to accommodate the needs and enhance the performance of road users with age-related 

diminished capabilities as they approach and negotiate intersections. Also, after the last 

element, eight additional promising practices are provided. Drawings are for illustrative 

purposes only; they are not to scale and should not be used for design purposes. 

Proven Practices

1. Intersecting Angle (Skew)

2. Receiving Lane (Throat) Width

3. Channelization

4. Intersection Sight Distance 

5. Offset Left-Turn Lanes 

6. Delineation of Edge Lines and Curbs 

7. Curb Radius 

8. Left-Turn Traffic Control for Signalized Intersections 

9. Right-Turn Traffic Control for Signalized Intersections 

10. Street Name Signs 

11. Stop and Yield Signs 

12. Lane Assignment on Intersection Approach 

13. Traffic Signals 

14. Intersection Lighting 

15. Pedestrian Crossings 

16. Roundabouts

Promising Practices

17. Right Turn Channelization Design

18.	 Combination Lane-Use/Destination Overhead Guide Signs

19. Signal Head Visibility

20. High Visibility Crosswalks 

21. Supplemental Pavement Markings for Stop and Yield Signs 

22. Reduced Left-Turn-Conflict Intersections

23. Accessible Pedestrian Signal (APS) Treatments 

24. Flashing Yellow Arrow

The single greatest concern in accommodating aging road users, both drivers and pedestrians, 

is the ability of these persons to negotiate intersections safely. For at least two decades, 

safety experts have keyed on relationships of age and road user type (driver or pedestrian) to 

understand injury and fatal crash experience at intersections in the United States. The findings 

of one widely cited analysis of nationwide crash data (Hauer, 1988) are shown in Figure 2. 
14 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

The figure illustrates that aging drivers and aging pedestrians are involved in a higher 

percentage of injury and fatal incidents at intersections. 

These same relationships endure today. A higher proportion of passenger vehicle drivers 

age 70 and older are involved in fatal multiple-vehicle crashes at intersections (40%) than 

drivers younger than age 70 (22%) (IIHS, 2007). While the number of fatalities, both 

overall and among aging road users, has declined in recent years, people age 65 and older 

are still involved in a disproportionate share of fatalities compared to the population as a 

whole (see Table 5). The number of aging drivers has increased substantially, making up 

a larger share of the driving population. Therefore, while people age 65 and older make 

up about 13 percent of the nation’s population, they represent about 16 percent of drivers, 

16 percent of driver fatalities, and 19 percent of pedestrian fatalities (FARS, 2013). These 

findings reinforce a long-standing recognition that driving situations involving complex 

speed-distance judgments under time constraints—the typical scenario for intersection 

operations—are more problematic for aging road users than for their younger counterparts. 

Other studies within the large body of evidence showing dramatic increases in intersection 

crash involvements as driver age increases have associated specific crash types and vehicle 

movements with particular age groups, linked in some cases to the driving task demands for 

a given maneuver (Campbell, 1993; Council and Zegeer, 1992; Staplin and Lyles, 1991).

Complementing crash analyses and observational studies with subjective reports of 

intersection driving difficulties, a statewide survey of 664 aging drivers by Benekohal, et 

al. (1992) found that the following activities become more difficult for drivers as they grow 

older (with proportion of drivers responding in parentheses): 

•	 Reading street signs in town (27 percent).

•	 Driving across an intersection (21 percent).

Figure 2. 

Percentage of 

crashes involving 

drivers and 

pedestrians by age 

at intersections 

(Hauer, 1988)

100

90

80

70

60

50

40

30

20

10

0

Injuries Fatalities

Percentage of Incidents Occurring at Intersections (%)

Drivers

100

90

80

70

60

50

40

30

20

10

0

Injuries Fatalities

Percentage of Incidents Occurring at Intersections (%)

Pedestrians

60

48

37

18

65+

26-64

Driver Age

65+

26-64

Pedestrian Age

51

26

33

18

60
Handbook for Designing Roadways for the Aging Population 15

CHAPTER 2—INTERSECTIONS

Table 5. Involvement of the Older Population in Traffic Fatalities by Gender, 2002 and 2011 (FARS, 2013)

2002 2011 Percentage Change, 

2002–2011

Total Age 65+

Percentage 

of Total Total Age 65+

Percentage 

of Total Total Age 65+

Population (Thousands)

Total 287,625 35,522 12.4 311,592 41,394 13.3 8 17

Male 141,231 14,764 10.5 153,291 17,943 11.7 9 22

Female 146,395 20,758 14.2 158,301 23,451 14.8 8 13

Drivers Involved in Fatal Crashes

Total* 58,113 6,323 10.9 43,668 5,469 12.5 -25 -14

Male 42,377 4,340 10.2 31,806 3,769 11.8 -25 -13

Female 14,999 1,982 13.2 11,209 1,700 15.2 -25 -14

Driver Fatalities

Total* 26,659 3,984 14.9 20,753 3,402 16.4 -22 -15

Male 19,859 2,704 13.6 15,868 2,316 14.6 -20 -14

Female 6,799 1,279 18.8 4,881 1,086 22.2 -28 -15

Total Traffic Fatalities

Total* 43,005 6,680 15.5 32,367 5,401 16.7 -25 -19

Male 29,466 3,840 13.0 22,860 3,261 14.3 -22 -15

Female 13,529 2,838 21.0 9,499 2,140 22.5 -30 -25

Occupant Fatalities

Total* 37,375 5,541 14.8 27,060 4,417 16.3 -28 -20

Male 25,491 3,154 12.4 19,053 2,617 13.7 -25 -17

Female 11,875 2,386 20.1 8,000 1,800 22.5 -33 -25

Pedestrian Fatalities

Total* 4,851 1,064 21.9 4,432 845 19.1 -9 -21

Male 3,298 619 18.8 3,086 522 16.9 -6 -16

Female 1,552 444 28.6 1,345 323 24.0 -13 -27

Passenger Vehicle Occupant Fatalities

Total* 32,843 5,314 16.2 21,253 3,970 18.7 -35 -25

Male 21,431 2,959 13.8 13,811 2,208 16.0 -36 -25

Female 11,403 2,354 20.6 7,435 1,762 23.7 -35 -25

Motorcyclist Fatalities

Total 3,270 96 2.9 4,612 301 6.5 41 214

Male 2,961 89 3.0 4,181 285 6.8 41 220

Female 309 7 2.3 431 16 3.7 39 129

Pedalcyclist Fatalities

Total 665 56 8.4 677 90 13.3 2 61

Male 592 53 9.0 578 82 14.2 -2 55

Female 73 3 4.1 99 8 8.1 36 167

* Total includes unknown gender.
16 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

•	 Finding the beginning of a left-turn lane at an intersection (20 percent).

•	 Making a left turn at an intersection (19 percent).

•	 Following pavement markings (17 percent).

•	 Responding to traffic signals (12 percent).

Benekohal et al. (1992) also found that the following highway features become more 

important to drivers as they age (with proportion of drivers responding in parentheses): 

•	 Lighting at intersections (62 percent).

•	 Pavement markings at intersections (57 percent).

•	 Number of left-turn lanes at an intersection (55 percent).

•	 Width of travel lanes (51 percent).

•	 Concrete lane guides (raised channelization) for turns at intersections (47 percent).

•	 Size of traffic signals at intersections (42 percent).

Comparisons of responses from drivers ages 66–68 versus those age 77 and older showed 

that the older group had more difficulty following pavement markings, finding the 

beginning of the left-turn lane, and driving across intersections. Similarly, the level of 

difficulty for reading street signs and making left turns at intersections increased with age. 

Turning left at intersections was perceived as a complex driving task. This was made more 

difficult when raised channelization providing visual cues was absent, and only pavement 

markings designated which were through lanes versus turning lanes ahead. For the oldest 

age group, pavement markings at intersections were the most important item, followed by 

the number of left-turn lanes, concrete guides, and intersection lighting. A study of aging 

road users completed in 1996 provides evidence that the single most challenging aspect of 

intersection negotiation for this group is performing left turns during the permissive signal 

phase (Staplin, et al., 1997). 

During focus group discussions (Benekohal et al., 1992), aging drivers reported that 

intersections with too many islands are confusing; raised curbs that are unpainted 

(unmarked) are difficult to see; and textured pavements (rumble strips) are of value as a 

warning of upcoming raised medians, approaches to (hidden or flashing red) signals, and 

the roadway edge/shoulder lane boundary. Study subjects indicated a clear preference for 

turning left on a protected arrow phase, rather than making permissive-phase turns. When 

turning during a permissive phase of signal operation, they reported waiting for a large gap 

before making a turn, which frustrates drivers behind them. A key finding was the need for 

more time to react.

Additional insight into the problems aging drivers experience at intersections was provided 

by focus group responses from 81 aging drivers (Staplin et al., 1997). The most commonly 

reported problems are listed below: 

•	 Difficulty in turning their heads at skewed (non-90-degree) angles to view

intersecting traffic. 

•	 Difficulty in smoothly performing turning movements at tight corners.

•	 Hitting raised concrete barriers such as channelizing islands in the rain and at night.
Handbook for Designing Roadways for the Aging Population 17

CHAPTER 2—INTERSECTIONS

•	 Finding oneself positioned in the wrong lane—especially a “turn-only” lane—

during an intersection approach, due to poor visibility (maintenance) of pavement 

markings or the obstruction of roadside signs designed to inform drivers of 

intersection traffic patterns. 

•	 Difficulty at the end of an auxiliary (right) turn lane in seeing potential conflicts

well and quickly enough to smoothly merge with adjacent-lane traffic. 

•	 Merging with adjacent-lane traffic at a pavement width reduction, when the lane

drop occurs near (i.e., within 500 ft of) an intersection. 

For aging pedestrians, age-related diminished capabilities may make it more difficult to 

negotiate intersections. Aging pedestrians face a variety of concerns, including decreased 

visual acuity, increased risk of falls, slowed walking and crossing speeds, and decreased 

ability to judge safe gaps and avoid turning vehicles. 

Lighting and visibility at intersections are increasingly important to pedestrians as they 

age. In a survey of aging pedestrians (average age of 75) involved in crashes, 63 percent 

reported that they failed to see the vehicle that hit them, or to see it in time to take evasive 

action (Sheppard and Pattinson, 1986). Knoblauch, et al. (1995) noted that difficulty

seeing a vehicle against a (complex) street background may occur with vehicles of certain 

colors, causing them to blend in with their background. Reductions in visual acuity 

make it more difficult for aging pedestrians to read the crossing signal as well (Bailey, et 

al., 1992).

With increasing age, there is a concurrent loss of physical strength, joint flexibility, 

agility, balance, coordination and motor skills, and stamina. These losses contribute 

to difficulty negotiating curbs and an increased risk of falling as a result of undetected 

surface irregularities in the pavement and inaccurate estimation of curb heights (Clark, 

Lord, and Webster, 1993). 

The physical limitations of aging pedestrians result in a greater likelihood to delay before 

crossing; to wait for longer gaps between vehicles before attempting to cross the road 

(Tobey, Shungman, and Knoblauch, 1983); to spend more time at the curb; to take longer

to cross the road (Hoxie and Rubenstein, 1994; Knoblauch, Nitzburg, Dewar, et al., 1995);

and to make more head movements before and during crossing (Wilson and Grayson,

1980). Parsonson (1992) reported that the State of Delaware has found that pedestrians do 

not react well to the short WALK and long flashing DONT WALK timing pattern.

Turning vehicles are also a concern for aging pedestrians. The loss of peripheral vision 

and “useful field of view” increases an aging pedestrian’s chances of not detecting 

approaching and turning vehicles from the side. The analysis by Council and Zegeer 

(1992) included an examination of vehicle-pedestrian crashes and the collision types in 

which aging pedestrians were over-involved. The results showed aging pedestrians to be 

overrepresented in both right- and left-turn crashes. The young-elderly (ages 65-74) were 

most likely to be struck by a vehicle turning right, whereas the old-elderly (age 75 and 

older) were more likely to be struck by a left-turning vehicle. 

Together, these findings from research on aging road users reinforce the overriding 

design principles to “clarify” and “simplify” traffic operations at intersections. By 
18 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

providing appropriate advance information about route choices and destinations, clearly 

identifying lane assignments for allowed maneuvers, and implementing conspicuous and 

easily comprehensible sign and signal displays for traffic control, engineers can manage 

workload during intersection approach and negotiation in a manner that benefits road 

users of all ages. Likewise, the need for intersection geometrics to unambiguously convey 

path, direction, and speed is universal, and such “positive guidance” is an explicit goal of 

the treatments presented in this chapter.
Handbook for Designing Roadways for the Aging Population 19

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

1 Intersecting Angle (Skew)

The HSM (page 10-32) defines skew angle as: “intersection skew angle (in 

degrees); the absolute value of the difference between 90 degrees and the 

actual intersection angle.

A. Unrestricted Right-of-Way

In the design of new facilities or redesign of existing facilities where 

right-of-way is not restricted, all intersecting roadways should meet at a 

90-degree angle (as indicated in Figure 3). 

References: Green Book:1, NCHRP 279:1, TEH:1, NCHRP 500-9:1

B. Restricted Right-of-Way

In the design of new facilities or redesign of existing facilities where 

right-of-way is restricted, intersecting roadways should meet at an angle 

of not less than 75 degrees (as indicated in Figure 4).

References: TEH:2

C. Skewed Signalized Intersections

At skewed signalized intersections where the approach leg to the left 

intersects the driver’s approach leg at an angle of less than 75 degrees, 

prohibit right turn on red (RTOR) (see Figure 5). 

References: TEH:4, MUTCD:2

The rationale and supporting evidence for these treatments 

begins on page 96 of the Handbook.

PROVEN PRACTICES

Figure 3. Example 90° angle 

of intersection

Figure 4. Example 75° angle 

of intersection

90

75

Figure 5. Skewed signalized intersection with 

prohibition of right turn on red
20 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

2 Receiving Lane (Throat) Width

A. Minimum Width

Wherever practical, a minimum receiving throat width of 16 ft is 

recommended. The total width may include a travel lane of 11 to 12 ft and a 

paved shoulder or bicycle lane of 4 to 5 ft as shown in Figure 6. 

References: NCHRP 279:2, TEH:2

The rationale and supporting evidence for this treatment begins on page 99 of 

the Handbook.

3 Channelization 

A. Left- and Right-Turn Lanes

Raised channelization with sloping curbs (see Figure 7) is recommended over 

channelization accomplished through the use of pavement markings alone 

(flush) for left- and right-turn lane treatments at intersections on all roadways 

with operating speeds of less than 45 mph.

References: Green Book:4, NCHRP 279:4, TEH:4, MUTCD:4, NCHRP 500-9:4

B. Retroreflective Markings

Where raised channelization is implemented at intersections (see Figure 7) the 

median and island curb sides and curb horizontal surfaces should be treated 

with retroreflectorized markings, such as edge lines, painted curbs, or raised 

Figure 6. Recommended receiving lane width

11–12 ft 4–5 ft

Travel

Lane

Bicycle Lane /

Paved Shoulder

16 ft

Recommended Receiving Lane Width
Handbook for Designing Roadways for the Aging Population 21

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

pavement markers, and be maintained at a minimum luminance contrast level* 

as follows: 

B-1. With overhead lighting, a contrast of at least 2.0.

B-2. Without overhead lighting, a contrast of at least 3.0. 

Contrast should be calculated according to this formula:

Luminance contrast (C) = 

Luminancestripe - Luminancepavement 

Luminancepavement 

*  Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which 

is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often 

described as brightness)—especially at night—this may vary greatly for the same object or marking 

depending upon such factors as the location and intensity of the source of illumination, and the angle at 

which a driver views it. 

References: MUTCD:4, NCHRP 500-9:4

C. Acceleration Lane

If right-turn channelization is present at an intersection, an acceleration lane 

providing for the acceleration characteristics of passenger cars as delineated in 

AASHTO (2011) specifications is recommended for operating speeds of 

45 mph or greater.

References: Green Book:4

D. Sloping vs. Vertical Curbs

The use of sloping curbs rather than vertical curbs (see Figure 7) for 

channelization is recommended, except where the curbs surround a 

pedestrian refuge area or are being used for access control. Vertical 

curbs should also not be used for channelization on high-speed (i.e., 

45 mph or greater) roadways.

References: Green Book:4, NCHRP 279:4

E. Pedestrian Refuge Island

If right-turn channelization is present and pedestrian traffic may be 

expected based on surrounding land use, it is recommended that an 

adjacent pedestrian refuge island, conforming to MUTCD (2009) and 

AASHTO (2011) specifications, be provided.

References: Green Book:1, NCHRP 279:3, MUTCD:1 Figure 7. Vertical Curb (top), 

Sloping Curb (bottom)
22 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

F. Median Channelization

To reduce unexpected midblock conflicts with opposing vehicles, the use 

of channelized left-turn lanes in combination with continuous raisedcurb medians is recommended instead of center, two-way, left-turn lanes 

(TWLTL) for new construction or reconstruction where average daily traffic 

volumes exceed 20,000 vehicles per day, or for remediation where there is a 

demonstrated crash problem, or wherever a need is demonstrated through 

engineering study.

References: Green Book:4, NCHRP 279:4

The rationale and supporting evidence for these treatments begins on page 102 of 

the Handbook.

4 Intersection Sight Distance

A. Gap Value

It is recommended that a gap of no less than 8.0 s, plus 0.5 s for each additional 

lane crossed, be used in intersection sight distance (ISD) calculations to 

accommodate the slower decision-making and maneuver times of aging drivers 

for the following cases:

•	 Cases B1, B2, and B3 – stop-control on the minor road,

•	 Cases C1 and C2 – yield control on the minor road,

•	 Case D - signalized with permissive left-turn phases and/or where RTOR is

permitted and/or which are placed on flashing operations at night, and 

•	 Case F - left turns from a major roadway.

Note: Cases refer to the intersection control cases defined in the AASHTO 

Green Book (2011).

References: Green Book:1

The rationale and supporting evidence for these treatments begins on page 107 of 

the Handbook.
Handbook for Designing Roadways for the Aging Population 23

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

5 Offset Left-Turn Lanes

A. Full Offset – Opposing Cars

Left-turn lanes should be positively offset (as shown in Figure 8) at least 4 ft to 

the left of the opposing left-turn lane to achieve the desired sight distance for 

the left-turning driver. This will provide a margin of safety for aging drivers 

who, as a group, do not position themselves to the far left within the lane and 

within the intersection before initiating a left turn. 

References: Green Book:1, NCHRP 279:4, TEH:4, NCHRP 500-9:4

B. Full Offset – Opposing Heavy Trucks

At intersections where engineering judgment indicates a high probability 

of heavy trucks as the opposing left-turning vehicles, the positive offset is 

recommended to be 5.5 ft to achieve the desired sight distance.

References: Green Book:4, NCHRP 279:4, TEH:4, NCHRP 500-9:4

C. Minimum Offset

At locations where the full offset distances cannot be obtained, it is 

recommended that the minimum offset distances shown in Table 6 be provided 

to achieve minimum required sight distances according to design speed. It is 

recommended that the “Opposing Truck” values be used where the opposing 

left-turn traffic includes a moderate to heavy volume of large trucks. 

References: Green Book:4, NCHRP 279:4, TEH:4, NCHRP 500-9:4

Figure 8. Left-turn lanes with positive offset
24 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Table 6. Minimum offset distances for left-turn lanes.

Design Speed (mph) Minimum Offset (ft)

Opposing Car Opposing Truck

≤ 30 0.8 3.0

35 1.4 3.5

40 1.8 3.8

45 2.1 4.1

50 2.4 4.2

55 2.6 4.4

60 2.7 4.5

65 2.8 4.6

70 2.9 4.7

1 ft = 0.305 m

D. Signs and Markings

At intersections where the left-turn lane treatment results in channelized offset 

left-turn lanes (e.g., a parallel or tapered left-turn lane between two medians), 

the following countermeasures (see Figure 9) are recommended to reduce 

the potential for wrong-way maneuvers by drivers turning left from a stopcontrolled intersecting minor roadway: 

D-1. Largest practical sign sizes as specified in the MUTCD (2009) for 

DIVIDED HIGHWAY CROSSING, WRONG WAY, DO NOT ENTER,

KEEP RIGHT, and ONE WAY signs.

References: TEH:4, MUTCD:3, NCHRP 500-9:4

D-2. For the signs listed above, use prismatic retroreflective sheeting, to 

provide increased sign conspicuity and legibility for older drivers. 

Ensure these signs are replaced before they meet the minimum sign 

retroreflectivity levels, which includes white on red signs having a 

contrast ratio of at least 3:1. 

References: MUTCD:1, NCHRP:4

D-3. Retroreflective lane-use arrows.

References: MUTCD:1, NCHRP 500-9:4

D-4. Retroreflective pavement marking extensions of the center line that 

scribe a path through the turn, except where extensions for opposing 

movements cross. 

References: MUTCD:3, NCHRP 500-9:4
Handbook for Designing Roadways for the Aging Population 25

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

1

4

3

6

1 Left-Turn Arrow

(Lane-use pavement marking)

2 Median Nose Delineation

4 Raised Channelization

6 Raised Crossing Island

for Pedestrians

Optional Signs

(For medians less than 30ft wide)

5

Channelization Accomplished 

Using Retroreective 

Pavement Markings

3 Wrong-Way Arrow 

Pavement Marking

5

2

Figure 9. Recommended signs and markings for intersections with channelized offset left-turn lanes
26 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

D-5. Placement of 23.5-ft- long retroreflective wrong-way arrows in the 

through lanes at locations determined to have a special need, as specified 

in the MUTCD (2009), Sections 3B.19 and 2E-50.

References: MUTCD:3, NCHRP 500-9:4

D-6. Delineation of median noses using retroreflective treatments to increase 

their visibility and improve driver understanding of the intersection 

design and function.

References: Green Book:1, MUTCD:2, NCHRP 500-9:4

E. Pedestrian Accommodations

At intersections where there are high pedestrian volumes, and the offset leftturn treatment results in a crossing width that would require a pedestrian 

walking at 3.0 ft/s to cross in two stages, the following is recommended to 

create a pedestrian crossing island (or refuge area), as shown in Figure 10:

E-1. Flush (painted) channelization is used to separate the left-turn lane and 

adjacent through lanes.

E-2. Raised channelization with a vertical curb and a minimum width of 

6 ft is used to separate the left-turn lane from opposing travel lanes. 

While a 6-ft width is the minimum, there are advantages to providing 

wider islands where possible. Sloped curbs should be used instead of 

vertical curbs for channelization on high-speed (i.e., 45 mph or greater) 

roadways.

References: Green Book:1, MUTCD:2

The rationale and supporting evidence for these treatments begins on page 122 of 

the Handbook.

6 Delineation of Edge Lines and Curbs 

A. Visibility

A minimum in-service luminance contrast level between the marked edge of 

the roadway and the road surface should be maintained as follows: 

A-1. At intersections with overhead lighting, a contrast of 2.0 or higher.

A-2. At intersections without overhead lighting, a contrast of 3.0 or higher.

Figure 10. Pedestrian Crossing 

Island (or Refuge Area)

6ft minimum 

width
Handbook for Designing Roadways for the Aging Population 27

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Contrast should be calculated according to this formula:

Luminance contrast (C) = 

Luminancestripe - Luminancepavement 

Luminancepavement

*  Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which 

is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often 

described as brightness)—especially at night—this may vary greatly for the same object or marking 

depending upon such factors as the location and intensity of the source of illumination, and the angle at 

which a driver views it. 

References: MUTCD:4, RLH:4

B. Intersection Curbs

Curbs at intersections (including median islands and other raised 

channelization) should be delineated on their vertical face and at least a 

portion of the top surface, in addition to the provision of a marked edge 

line on the road surface (see Figure 11). 

The use of a Keep Right (R4-7 Series) or a Double Arrow (W12-1) sign

with the addition of a low-mounted Type 1 Object Marker (OM1-1) near 

the median and channelizing island noses, respectively, could also be 

helpful to aging road users. These signs are optional and can be used if 

they are warranted. Since markings primarily supplement signing, this 

treatment should be placed in addition to the signing available for these 

locations.

References: Green Book:1, MUTCD:1

The rationale and supporting evidence for these treatments begins on page

129 of the Handbook.

7 Curb Radius 

A. Simple Radius

Where roadways intersect at 90 degrees and are joined with a simple radius 

curve, a corner curb radius in the range of 25 ft to 30 ft is recommended to: 

(a) facilitate vehicle turning movements, (b) moderate the speed of turning 

vehicles, and (c) avoid unnecessary lengthening of pedestrian crossing 

distances (see Simple Curve in Figure 12). 

References: AASHTO:1, NCHRP 279:1

Figure 11. Raised median 

island with yellow marking 

on the vertical face and top 

surface
28 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

B. Accommodation of Heavy Vehicles

When it is necessary to accommodate turning movements by large trucks, the 

use of offsets, tapers, and compound curves is recommended in place of larger 

simple radii (e.g., 75 ft or more) to minimize pedestrian crossing distances (see 

Figure 12).

References: AASHTO:1, NCHRP 279:4, TEH:4

The rationale and supporting evidence for these treatments begins on page 132 of 

the Handbook.

8 Left-Turn Traffic Control for 

Signalized Intersections

A. Protected-Only Left-Turn Phasing

The use of protected-only left-turn operations is recommended for all leftturning movements, whenever appropriate. In particular, protected-only 

left-turn phasing should be considered where minimum intersection sight 

distance requirements are not achieved through the use of offset left-turn lanes 

(see Design Element 5) or other geometric design features, or where a pattern of 

permissive left-turn crashes occurs. 

References: Green Book:4, TEH:1, MUTCD:1

Figure 12. Comparison of curb radii

20ft Curve

with 1:10 Tapers and

2.5 ft Offsets

3-Centered

Compound Curve

Radius = 100 ft, 20 ft,

100 ft

Simple Curve

25 ft Radius
Handbook for Designing Roadways for the Aging Population 29

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

B. Permissive Left-Turn Signing

If circular green is used as the permissive 

indication of a protected/permissive leftturn, consistent use of the MUTCD R10-12 

sign, (LEFT TURN YIELD ON GREEN ) 

is recommended, with overhead placement 

preferred at the intersection adjacent to the 

left-turn signal face (see Figure 13). 

References: TEH:4, MUTCD:1

C. Advance Signing

Where practical, an additional R10-12 

sign (i.e., in addition to the R10-12 sign adjacent to the signal face) should 

be placed in advance of the intersection to advise left-turning drivers of 

permissive signal operation. The sign should be displayed at a 3-s preview 

distance before the intersection, or at the beginning of the left-turn lane, 

as per engineering judgment, accompanied by an AT SIGNAL (R10-31P)

supplemental plaque as shown in Figure 14. [See time-speed-distance table on 

page 5.] 

References: AASHTO:3, MUTCD:1, NCHRP 500-9:4

D. Lead versus Lag Phasing

A leading protected left-turn phase is recommended wherever protected leftturn signal operation is implemented (as opposed to a lagging protected leftturn phase). 

References: TEH:2, MUTCD:2

The rationale and supporting evidence for these treatments begins on page 135 of 

the Handbook.

9 Right-Turn Traffic Control for 

Signalized Intersections 

A Turn Prohibition

At signalized intersections where a right turn on red is prohibited, a 

supplemental NO TURN ON RED sign, using the MUTCD R10-11 design 

as shown in Figure 15, should be placed at a location on either the near or 

opposite side of the intersection where, per engineering judgment, it will 

be most conspicuous. This supplemental NO TURN ON RED sign is in 

Figure 13. MUTCD R10-12 sign adjacent to left-turn signal 

face

Figure 14. (MUTCD R10-31P)

Figure 15. (MUTCD R10-11)
30 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

addition to the MUTCD recommended practice of installing an R10-11 series 

sign near the appropriate signal head. 

References: TEH:4, MUTCD: 1

B. Skewed Signalized Intersections

At skewed signalized intersections where the approach leg to the left intersects 

the driver’s approach leg at an angle of less than 75 degrees (as illustrated in 

Figure 16), prohibit right turn on red (RTOR).

References: TEH:4, MUTCD:1

C. Pedestrian Protection

The posting of MUTCD standard R10-15 signs, Turning Vehicles Yield to 

Pedestrians (shown in Figure 17) is recommended wherever engineering 

judgment indicates a clear potential for right-turning vehicles to come into 

conflict with crossing pedestrians. (Note that a yellow background color may 

be used instead of fluorescent yellow-green for this sign.)

References: MUTCD:1

The rationale and supporting evidence for these treatments begins on page 148 of 

the Handbook. 

Figure 16. Skewed signalized intersection with prohibition of right turn on red

Figure 17. (MUTCD R10-15)
Handbook for Designing Roadways for the Aging Population 31

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

10 Street Name Signs 

A. Letter Heights and Sign Border

To accommodate the reduction in visual acuity associated with increasing 

age, minimum letter heights of 6 in for uppercase letters and 4.5 in for 

lowercase letters are recommended for use on ground-mounted street-name 

signs (MUTCD D3-1, as shown in Figure 18) on all roads where the posted 

speed limit is at or below 25 mph. On all roads where the posted speed limit 

is greater than 25 mph, letter heights of 8 in for uppercase letters and 6 in for 

lowercase letters should be used. 

The use of overhead-mounted street-name signs is recommended at major 

intersections as a supplement to ground-mounted street-name signs. Minimum 

letter heights of 12 in for uppercase letters and 9 in for lowercase letters are 

recommended by the MUTCD. 

In the design of street-name signs, the use of larger letter heights may require 

a larger sign panel. The border may be eliminated on street-name signs if 

necessary to minimize sign panel size while accommodating the larger letter 

size.

References: MUTCD:1, NCHRP 500-9:4

B. Advance Street-Name Plaque

Wherever an advance intersection warning sign is installed (MUTCD W2 

series) it should be accompanied by an advance street name plaque (W16-8P 

or W16-8aP) using minimum letter heights of 6 in for uppercase letters and 

4.5 in for lowercase letters (see Figure 19). Where an advance traffic control 

sign (MUTCD W3 series) is installed on a multi-lane approach, an advance 

street name plaque (W16-8P or W16-8aP), using the same minimum letter 

heights described above, should be considered. 

References: MUTCD:2, NCHRP 500-9:4

C. Advance Street-Name Sign

In the absence of an advance intersection warning sign or advance traffic 

control sign (with accompanying advance street-name plaque), the use 

of advance street-name signs (MUTCD D3-2) for major intersections is 

recommended, with turn bays to provide adequate preparation time for any 

lane change and/or turning maneuvers (see Figure 20).

References: MUTCD:1, NCHRP 500-9:1

Figure 18. (MUTCD D3-1)

Figure 19. Intersection 

Warning W2-1 Sign and 

W16-8P Supplemental 

Advance Street Name 

Plaque
32 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

D. Directional Street-Name Sign

When different street names are used for different directions of travel on a 

crossroad, the names should be separated and accompanied by directional 

arrows on both advance and intersection street-name signs, as shown in 

Figure 20. 

References: MUTCD:1

E. Retroreflectivity

For ground-mounted street-name signs installed at intersections in areas 

of intensive land use, complex design features, and heavy traffic, prismatic 

retroreflective sheeting that provides for high retroreflectance should be 

used to provide increased sign conspicuity and legibility for aging drivers. 

The sheeting should be replaced well before it reaches the minimum levels 

designated in the current MUTCD (Section 2A.08 in the 2009 MUTCD).

References: MUTCD:1

The rationale and supporting evidence for these treatments begins on page 152 of 

the Handbook.

Figure 20. (MUTCD D3-2)

Scott Blvd Lincoln Ave
Handbook for Designing Roadways for the Aging Population 33

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

11 Stop and Yield Signs

Treatments to improve the safe use of intersections by aging drivers, where the 

need for stop control or yield control has already been determined, include the 

following: 

A. Sign Size

The use of standard size (30-in for single lane applications, 36-in for multi-lane 

applications) STOP (R1-1) and standard size (36-in for single lane applications, 

48-in for multi-lane applications, 60-in for freeway applications) YIELD (R1-2) 

signs, as a minimum, is required by the 2009 MUTCD wherever these devices 

are implemented, with the option of using larger R1-1 (36-in for single lane 

applications, or 48-in in any location) signs where engineering judgment 

indicates that greater emphasis or visibility is required.

References: MUTCD:1

B. Retroreflectivity

A minimum sign background (red area) retroreflectivity level (i.e., coefficient of 

retroreflection [RA]) for STOP (R1-1) and YIELD (R1-2) signs is as follows:

B-1. 12 cd/lux/m2 for roads with operating speeds lower than 40 mph.

B-2. 24 cd/lux/m2 for roads with operating speeds of 40 mph or higher. 

Signs with an RA below these levels should be replaced.

References: TEH:4, MUTCD:1

C. Supplemental Warning Sign

The use of a 30-in x 18-in supplemental warning sign panel (MUTCD

W4-4P) as illustrated in Figure 21, mounted below the STOP (R1-1) 

sign, is recommended for two-way stop-controlled intersection sites 

selected on the basis of crash experience, where the sight triangle is 

restricted, and wherever a conversion from four-way stop to two-way 

stop operations is implemented.

References: MUTCD:1

D. Location of Stop Ahead Sign

A STOP AHEAD sign (MUTCD W3-1, as shown in Figure 22) should be used 

where the distance at which the STOP sign is visible is less than the AASHTO 

stopping sight distance (SSD) at the operating speed, plus an added preview 

 Figure 21. (MUTCD W4-4P)
34 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

distance of at least 2.5 s. [See time-speed-distance table on page 5.]

References: Green Book:4, TEH:4, MUTCD:1, NCHRP 500-9:4

E. Transverse Treatments and Supplemental Pavement Markings

Utilize supplemental pavement markings on approaches to stop-controlled 

or yield-controlled intersections where engineering judgment indicates a 

special need due to sight restrictions, high approach speeds, or a history of 

ran-stop-sign crashes. “STOP AHEAD” pavement markings to supplement 

STOP AHEAD signs and triangular pavement markings to supplement 

YIELD AHEAD signs are described in MUTCD Section 3B.20 and Figure 32. 

Transverse pavement striping or rumble strips may also be considered where 

high approach speeds are a concern.

References: TEH:4, NCHRP 500-9:3

The rationale and supporting evidence for these treatments begins on page 160 of 

the Handbook.

12 Lane Assignment on 

Intersection Approach

A. Lane-Use Control Signs

The consistent overhead placement of lane-use control signs (MUTCD

R3-5 and R3-6 series) at intersections on a signal mast arm or span wire is 

recommended, as illustrated in Figure 23. 

References: MUTCD:1

B. Advance Signs and Markings

The consistent posting of lane-use control signs (MUTCD R3 series) plus 

application of lane-use arrow pavement markings at a preview distance 

of at least 5 s (at operating speed) in advance of a signalized intersection 

is recommended, regardless of the specific lighting, channelization, or 

delineation treatments implemented at the intersection. [See time-speeddistance table on page 5.] R3-5 and R3-6 series signs should be mounted 

overhead wherever practical.

References: MUTCD:4

The rationale and supporting evidence for these treatments begins on page 170 of 

the Handbook.

Figure 22. (MUTCD W3-1)
Handbook for Designing Roadways for the Aging Population 35

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Handbook for Designing Roadways for the Aging Population 35

CHAPTER 2—INTERSECTIONS

13 Traffic Signals

A. Visibility

To ensure visibility and conspicuity of the traffic signal, the following is 

recommended:

A-1. A maintained performance level of 200 cd for peak intensity for both 

8-in and 12-in signals.

A-2. Use of 12-in signals in all cases except the few limited situations in which 

the MUTCD allows the use of 8-in signals. 

References: MUTCD:1

B. All-Red Clearance Interval

To accommodate age differences in perception-reaction time, an all-red 

clearance interval should be consistently implemented, with length determined 

according to the Institute of Transportation Engineers (2013) expressions given 

below:

B-1. Where pedestrian traffic is prohibited, or no pedestrian crossing facilities 

are provided, use:

r = 

W + L

1.47V

Figure 23. Mast-arm mounted lane-use control signs
36 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

B-2. Where pedestrian crossing facilities are provided, use:

r = 

P + L

1.47V

where: 

r = length of red clearance interval, to the nearest 0.1 s. 

W = width of intersection (ft), measured from the near-side stop line to the far 

edge of the conflicting traffic lane along the actual vehicle path. 

P = width of intersection (ft), measured from the near-side stop line to the far 

side of the farthest conflicting pedestrian crosswalk along the actual vehicle 

path. 

L = length of vehicle (recommended as 20 ft) 

V = approach speed of the vehicle (mph) 

References: MUTCD:2

C. Backplates

Backplates with retroreflective borders should be considered as part of efforts 

to systemically improve safety performance at signalized intersections. Use 

backplates with traffic signals on all roads with operating speeds of 40 mph 

or higher. The use of backplates with signals is also recommended on roads 

with operating speeds lower than 40 mph where engineering judgment 

indicates a need due to the potential for sun glare problems, site history, or 

other variables. Yellow retroreflective borders, shown in Figure 24, may be 

used as an option to improve visibility of the illuminated face of the signal. 

The yellow retroreflective strip should have a minimum width of 1 inch and 

a maximum width of 3 inches and be placed along the perimeter of the face 

of a signal backplate to project a rectangular appearance at night. The yellow 

retroreflective strip should have a minimum width of 1 inch and a maximum 

width of 3 inches and be placed along the perimeter of the face of a signal 

backplate to project a rectangular appearance at night.

References: MUTCD:4

The rationale and supporting evidence for these treatments begins on page 173 of 

the Handbook.
Handbook for Designing Roadways for the Aging Population 37

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

CHAPTER 2—INTERSECTIONS

14 Intersection Lighting

A. Fixed Installations

Wherever feasible, fixed lighting installations are recommended as follows: 

A-1. Where the potential for wrong-way movements is indicated through 

crash experience or engineering judgment.

A-2. Where twilight or nighttime pedestrian volumes are high.

A-3. Where shifting lane alignment, turn-only lane assignment, or a 

pavement-width transition forces a path-following adjustment at or near 

the intersection.

References: Green Book:4, RLH:4

B. Maintenance

Regular cleaning of lamp lenses, and lamp replacement when output has 

degraded by 20 percent or more of peak performance (based on hours of 

service and manufacturer’s specifications), are recommended for all fixed 

lighting installations at intersections.

References: RLH:4

The rationale and supporting evidence for these treatments begins on page 181 of 

the Handbook.

Figure 24. Yellow retroreflective backplates
38 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

CHAPTER 2—INTERSECTIONS

15 Pedestrian Crossings

A. Walking Speed

To accommodate the aging pedestrian who typically has a shorter stride, slower 

gait, and delayed “start-up” time before leaving from a position further back 

from the curb at signalized crossings, the joint application of the following 

practices is recommended:

A-1.	 Use a walking speed of 3.0 ft/s to calculate total crossing time (WALK

interval plus pedestrian clearance interval). 

A-2. Measure crossing distance from a location 6 ft back from the curb or 

travel lane edge to the far side of the travel way being crossed.

References: Green Book:2, NCHRP 279:2, MUTCD:1

B. Channelized Right-Turn Lane

For pedestrian crossings where the right-turn lane is 

channelized, it is recommended that:

B-1. An adjacent pedestrian refuge island 

conforming to MUTCD (2009) and AASHTO 

(2011) specifications be provided.

B-2. If a crosswalk is within the channelized area, 

it should be located approximately one car 

length from the yield line for the intersection 

(see Figure 25), which will allow drivers on the 

approach leg to look for and yield to pedestrians 

before reaching the intersecting roadway and 

scanning for gaps in traffic. 

References: Green Book:4, NCHRP 279:4, TEH:4, 

MUTCD:2

C. Educational Signs

Where engineering judgment deems there to be a need 

to improve understanding of pedestrian signals, it is 

recommended that educational signs be posted near the crosswalk as follows:

C-1. For single stage crossings, use MUTCD R10-3b, R10-3c, R10-3e, R10-3f, 

R10-3g, or R10-3i as shown in Figure 26.

References: MUTCD: 2

Figure 25. Pedestrian crossing at channelized 

right-turn lane
Handbook for Designing Roadways for the Aging Population 39

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 26. (MUTCD R10-3 Series)

R10-3f R10-3g R10-3h

R10-3e

R10-3i

R10-3b R10-3c R10-3d

C-2. For two-stage crossings using a median refuge island, use MUTCD R10-

3d or R10-3h (see Figure 26) on the corners of the intersection and the 

placards defined above on the median refuge island.

References: MUTCD: 2

D. Turning Vehicles Yield to Pedestrians Sign

The posting of the MUTCD R10-15 sign (see Figure 27) is recommended 

wherever engineering judgment indicates a clear potential for right-turning 

vehicles to come into conflict with crossing pedestrians. 

References: MUTCD:1

E. Leading Pedestrian Interval

At intersections with high turning-vehicle volumes and no turn on red 

(NTOR) control for traffic moving parallel to a marked crosswalk, a leading 

pedestrian interval (LPI), timed to allow slower walkers to cross at least one 

moving lane of traffic is recommended to reduce conflicts between pedestrians 

and turning vehicles. The length of the LPI, which should be at least 3 s, may be 
40 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

calculated using the formula: 

LPI = (ML + PL + 6.0)/3.0

where: 

LPI = seconds between onset of the WALK signal for pedestrians and the green

indicator for vehicles.

ML = width of moving lane in ft 

PL = width of parking lane (if any) in ft

6.0 = distance in ft back from the edge of the curb to the assumed starting 

location for pedestrians 

3.0 = walking speed in ft/s

References: MUTCD:1

F. Countdown Signal

Countdown pedestrian signals (see Figure 28) should be installed at all 

signalized intersections where pedestrian signals are warranted. The 2009 

MUTCD requires the use of countdown pedestrian signals when the pedestrian 

change interval is greater than 7s. 

References: MUTCD: 1

The rationale and supporting evidence for these treatments begins on page 185 of 

the Handbook.

Figure 27. Recommended placement of MUTCD R10-15 sign

Figure 28. Countdown 

pedestrian signal
Handbook for Designing Roadways for the Aging Population 41

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

16 Roundabouts 

There are features of roundabout intersections that can benefit aging drivers and 

be a beneficial treatment over a traditional stop- or signal-controlled intersection 

if properly designed to meet the needs of that location. When properly designed, 

roundabouts are low-speed intersections, which provide benefits to aging drivers 

and pedestrians alike. In addition, roundabouts effectively eliminate severe 

right-angle crashes. Any crashes that do occur are typically low-angle (i.e., 

sideswipe) crashes at reduced speeds. The low-speed features associated with 

roundabouts eliminate the problems associated with making unprotected left turns 

at intersections. It is therefore recommended that roundabouts be considered as 

part of the engineering study in the design of new intersections and the redesign of 

existing intersections. 

Treatments for preferred practices when a State or local highway authority has 

determined through engineering study to install a modern roundabout during 

construction or reconstruction of an intersection include the following (see 

Figure 29): 

A. Number of Lanes

Unless required by operational needs, it is recommended that roundabout 

installations be limited to one-lane entrances and exits and one lane of 

circulating traffic.

References: NCHRP 672:1

B. Pedestrian Crossings

Pedestrian crossings at single-lane roundabouts should be set back a minimum 

of 25 ft from the yield lines and include a crossing island of at least 6 ft in 

width. 

References: NCHRP 672:1

C. Splitter Islands

To control for wrong-way movements, calm traffic, and provide a pedestrian 

refuge for all roundabout categories, raised splitter islands should be used, as 

opposed to pavement markings, to delineate the channelization. The pedestrian 

crosswalk area should be designed at street level (crosswalk cut through a 

splitter island).

References: NCHRP 672:1
42 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 29. Key geometric design elements and traffic control devices for roundabouts

Inscribed

Circle Diameter

(optional)

(optional)

(optional)

Central Island

Apron

Splitter Island

Exit

Radius

Entry

Radius

Exit 

Width

Departure

Width

Approach

Width Entry

Width

Circulatory

Roadway Width

Yield Line
Handbook for Designing Roadways for the Aging Population 43

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

D. Conspicuity

To enhance the conspicuity of roundabouts in all categories, the sides and tops 

of curbs on the splitter islands and the central island should be treated with 

retroreflective markings, and be maintained at a minimum luminance contrast 

level* as follows: 

D-1. At roundabouts with overhead lighting, a contrast of 2.0 or higher.

D-2. At roundabouts without overhead lighting, a contrast of 3.0 or higher. 

Contrast should be calculated according to this formula: 

Luminance contrast (C) = 

Luminancestripe - Luminancepavement 

Luminancepavement 

* Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which 

is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often 

described as brightness)—especially at night—this may vary greatly for the same object or marking 

depending upon such factors as the location and intensity of the source of illumination, and the angle at 

which a driver views it. 

References: NCHRP 672:4

E. Advance Warning Sign

The use of an advance roundabout warning sign (W2-6), as shown in Figure 30, 

is recommended on all approaches to a roundabout.

References: MUTCD:1

F. Directional Signs

The use of a Roundabout Directional Arrow sign (R6-4 series) is 

recommended to direct traffic counter-clockwise around the central 

island. This sign display should be placed on the central island in direct 

view of a driver’s entry point, as shown in Figure 31, (if different than at the 

centerline of the approaching roadway). 

References: MUTCD:1

Figure 30. (MUTCD W2-6)
44 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

G. Roundabout Circulation Plaque

The Roundabout Circulation Plaque (R6-5P) should be placed immediately 

below the R1-2 Yield sign on both sides of the road at each entrance to a 

roundabout (see Figure 32).

References: MUTCD:5

The rationale and supporting evidence for these treatments begins on page 197 of 

the Handbook.

Figure 31. Roundabout directional arrow sign

Central

Island

Figure 32. Placement of Roundabout Circulation Plaques

(Optional)

Central

Island
Handbook for Designing Roadways for the Aging Population 45

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

PROMISING PRACTICES

These are treatments being utilized by transportation agencies that should benefit 

aging road users as determined by a subjective assessment by staff participating on the 

development of this Handbook. Current trends indicate these practices have a positive 

impact on aging road user safety.

17 Right-Turn Channelization Design

Right-turn channelization with tighter turning radii to reduce turning speeds to 

approximately 17 to 18 mph, decrease pedestrian crossing distances, and optimize 

the right-turning motorists’ line of sight should be considered during design, as 

shown in the Preferred example on the right of Figure 33. Designs such as those on 

the left of Figure 33 are potentially problematic as drivers have to turn their heads 

farther to see oncoming traffic. The short curve radius should be between 25 and 

40 ft, and the long curve radius should be between 150 and 275 ft. Traffic control 

devices at the end of the channelization should be visible to vehicles entering the 

channelized lane. 

References: NCHRP 674:1

The rationale and supporting evidence for these treatments can be found beginning 

on page 215 of this Handbook.

Figure 33. Right-Turn Channelization Design

142°

112°

Angle

30° 55-60°

30° 20°

30°

High speed,

low visibility,

head turner

14 –18 mph,

good visibility

PREFERRED
46 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 34. Combination Lane 

Use/Destination Guide Sign 

(MUTCD D15-1)

OR

18 Combination Lane-Use/Destination 

Overhead Guide Signs

At intersections where complex design features or heavy traffic is present, 

and specific guidance advising roadway users which lane is necessary for 

their intended destination, combination lane use/destination signs (D15-1) 

should be used. These signs are typically used as overhead combination lane 

use destination guide signs and are described in Section 2D.33 of the 2009 

MUTCD (see Figure 34).

References: MUTCD:1

The rationale and supporting evidence for these treatments can be found 

beginning on page 215 of this Handbook.

19 Signal Head Visibility

Place all required signal heads overhead and centered over each lane instead of 

placing them on pedestal poles (see Figure 35). Supplemental signal heads may be 

placed on pedestal posts as needed. Do not 

place a signal head that displays a circular 

green indication over or directly in front of a 

left-turn lane. Instead, place a shared signal 

face over the lane line between the left-turn 

and through lane, or slightly to the right of it, 

or place a separate signal face over the center 

of the left turn lane that uses a flashing yellow 

arrow as the permissive indication.

References: MUTCD: 1

The rationale and supporting evidence for 

these treatments can be found beginning on 

page 216 of this Handbook. Figure 35. Example Of One Signal Head Per Lane
Handbook for Designing Roadways for the Aging Population 47

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 36. High-Visibility (“Ladder”) Crosswalk

20 High-Visibility Crosswalks

To allow drivers to more easily see pedestrians in a marked 

crosswalk, high-visibility crosswalk marking patterns 

should be utilized. Two examples of such markings include 

white diagonal lines at a 45 degree angle to the crosswalk 

or the ”ladder” crosswalk design shown in Figure 36.

References: MUTCD: 1

The rationale and supporting evidence for these treatments 

can be found beginning on page 216 of this Handbook.

21 Supplemental Pavement Marking 

for Stop and Yield Signs

Utilize “STOP AHEAD” word pavement markings to supplement stop ahead signs 

(W3-1) and “YIELD AHEAD” word pavement markings or yield ahead triangle 

symbol pavement markings to supplement yield ahead signs (W3-2). See Section 

3B.20 of the 2009 MUTCD and Figure 37.

References: MUTCD: 1

The rationale and supporting evidence for these treatments can be found beginning 

on page 217 of this Handbook.

Figure 37. Yield Ahead Triangle Symbols

A - Posted or Statutory Speed Limit of 45 mph or greater B - Posted or Statutory Speed Limit of less than 45 mph

6 ft

36

inches

20 ft

8 inches

Direction of travel

6 ft

30

inches

13 ft

Direction of travel

8 inches
48 Handbook for Designing Roadways for the Aging Population

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 38. Diagram of Median U-Turn Intersection

Figure 39. Diagram of Restricted Crossing U-Turn Intersection

Crossing

Merging

Diverging

Vehicle Paths

Crossing

Merging

Diverging

Vehicle Paths

22 Reduced Left-TurnConflict Intersections

A class of innovative intersection designs accommodate left-turns in unique ways, 

which greatly reduce, if not eliminate, unprotected left-turns at the intersection. 

Designs such as the median U-turn intersection (see Figure 38) and restrictedcrossing U-turn (RCUT) intersection (see Figure 39) have features that minimize 

the operational delay and potential for crashes due to left turns. Other intersection 

designs that are increasingly common include the displaced left-turn (DLT) 

intersection and the diverging diamond interchange (DDI). These innovative 

intersection designs should be considered for suitability during the engineering 

study for new and reconstructed intersections.

The rationale and supporting evidence for these treatments can be found beginning 

on page 218 of this Handbook.
Handbook for Designing Roadways for the Aging Population 49

CHAPTER 2—INTERSECTIONS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 40. (MUTCD 

R10-32P)

Indicates Flashing

Figure 41. Typical arrangements of signal faces with flashing yellow arrow 

indications for permissive left-turn movements

23 Accessible Pedestrian Signal 

(APS) Treatments

A. Pushbutton-Activated Extended Pedestrian Crossing Phase

At crosswalks frequently used by aging pedestrians, consider inclusion of 

pushbutton-activated extension of the pedestrian crossing phase, using the 

required signage described by the MUTCD, as shown in Figure 40. 

B. Passive Pedestrian Detection

Use of passive pedestrian detection to help aging pedestrians who have 

difficulty using the pushbutton or to detect pedestrians within the crosswalk 

that may need more time to complete the crossing maneuver. Passive 

pedestrian detection uses sensors to detect the presence of pedestrians and 

register a pedestrian call with the signal system; as a result, the pedestrian does 

not have to push a button to request a WALK signal or extended crossing time.

The rationale and supporting evidence for these treatments can be found beginning 

on page 219 of this Handbook.

24 Flashing Yellow Arrow

The flashing yellow arrow (see Figure 41) is the recommended signal indication for 

permissive left-turn movements at signalized intersections. 

The rationale and supporting evidence for these treatments begins on page 220 of 

the Handbook.
50 Handbook for Designing Roadways for the Aging Population
Handbook for Designing Roadways for the Aging Population 51

CHAPTER 3

Interchanges

This section of the Handbook provides treatments for highway design elements in six areas 

to enhance the performance of aging drivers at interchanges. Also, after the last design 

element, two promising practice treatments are presented. Drawings are for illustrative 

purposes only; they are not to scale and should not be used for design purposes.

Proven Practices

25. Exit Signs and Markings

26. Freeway Entrance Traffic Control Devices

27. Delineation

28. Acceleration/Deceleration Lane Design

29. Interchange Lighting

30. Restricted or Prohibited Movements 

Promising Practices

31. Route Shield Markings at Major Freeway Junctions

32. Wrong-Way Driving Countermeasures

Overall, freeways are characterized by the highest safety level (lowest fatality rates) when 

compared with other types of highways in rural and urban areas (AAA Foundation for 

Traffic Safety, 1995). At the same time, freeway interchanges have design features that 

have been shown to result in safety and operational issues. Taylor and McGee (1973)

reported that erratic maneuvers are a common occurrence at freeway exit ramps, and 

that the number of crashes there is four times greater than at any other freeway location. 

Two decades later, Lunenfeld (1993) reiterated that most freeway crashes and directional 

uncertainty occur in the vicinity of interchanges.

Distinct patterns in the occurrence of freeway interchange crashes emerge in studies that 

look specifically at driver age. Staplin and Lyles (1991) conducted a statewide (Michigan) 

analysis of the crash involvement ratios and types of violations for drivers in four age 

groups: age 76 and older; ages 56 to 75; ages 27 to 55; and age 26 and younger. Using 

induced-exposure methods to gauge crash involvement levels, this analysis showed that 

drivers over age 75 were overrepresented as the driver at fault in merging and weaving 

crashes near interchange ramps. With respect to violation types, the older driver groups 

were cited most frequently for failing to yield and for improper use of lanes. Similarly, 

Harkey, Huang, and Zegeer’s study (1996) of the pre-crash maneuvers and contributing 

factors in aging driver freeway crashes indicated that aging drivers were much more likely 

than younger drivers to be merging or changing lanes, or passing/overtaking prior to a 

crash, and that aging drivers’ failure to yield was the most common contributing factor. 

These data raise concerns about the use of freeway interchanges by aging drivers. Broader 

demographic and societal changes suggest that the dramatic growth in aging driver 

freeway travel between 1977 and 1988 reported by Lerner and Ratté (1991) will continue 

and even accelerate in the years ahead.
52 Handbook for Designing Roadways for the Aging Population

CHAPTER 3—INTERCHANGES

Age differences in interchange crashes and violations may be understood in terms of 

driving task demands and age-related diminished driver capabilities. The exit gore area 

is a transitional area that requires a major change in tracking. A driver (especially in an 

unfamiliar location) must process a large amount of directional information during a 

short period of time and at high speeds, while maintaining or modifying his/her position 

within the traffic stream. When drivers must perform guidance and navigation tasks 

in close proximity, the chances increase that they will become overloaded and commit 

errors (Lunenfeld, 1993). Erratic maneuvers resulting from driver indecisiveness in such 

situations include encroaching on the gore area, and even backing up on the ramp or 

the through lane. When weaving actions are required, the information-processing task 

demands for both entry and exit maneuvers are further magnified.

On a population basis, the age-related diminished capabilities that contribute most 

to aging drivers’ difficulties at freeway interchanges include losses in vision and 

information-processing ability, and decreased physical flexibility in the neck and upper 

body. Specifically, aging adults show declines in static and dynamic acuity, increased 

sensitivity to glare, poor night vision, and reduced contrast sensitivity (McFarland, et 

al., 1960; Weymouth, 1960; Richards, 1972; Pitts, 1982; Sekuler, Kline, and Dismukes,

1982; Owsley, Sekuler, and Siemsen, 1983). These sensory losses are compounded by the 

following perceptual and cognitive deficits, the first two of which are recognized as being 

especially critical to safety: reduction in the ability to rapidly localize the most relevant 

stimuli in a driving scene; reduction in the ability to efficiently switch attention between 

multiple targets; reduction in working memory capacity; and reduction in processing 

speed (Avolio, Kroeck, and Panek, 1985; Plude and Hoyer, 1985; Ponds, Brouwer, and

van Wolffelaar, 1988; Brouwer, et al., 1990; Brouwer, et al., 1991). The most important 

physical losses are reduced range of motion (head and neck), which impairs visual search, 

and slowed response time to execute a vehicle control movement, especially when a 

sequence of movements—such as braking, steering, and accelerating to weave and then 

exit a freeway—is required (Smith and Sethi, 1975; Goggin, Stelmach, and Amrhein,

1989; Goggin and Stelmach, 1990; Hunter-Zaworski, 1990; Staplin, Lococo, and Sim,

1990; Ostrow, Shaffron, and McPherson, 1992).

One result of these age-related diminished capabilities is demonstrated by a driver who 

waits when merging and entering freeways at on-ramps until he/she is alongside traffic, 

then relies on mirror views of overtaking vehicles on the mainline to begin searching 

for an acceptable gap (McKnight and Stewart, 1990). Exclusive use of mirrors to check

for gaps, and slowing or stopping to look for a gap, increase the likelihood of crashes 

and have a negative effect on traffic flow. Malfetti and Winter (1987), in a critical 

incident study of merging and yielding problems, reported that aging drivers on freeway 

acceleration lanes merged so slowly that traffic was disrupted, or they stopped completely 

at the end of the ramp instead of attempting to approach the speed of the traffic flow 

before entering the mainline. In a survey of 692 aging drivers, 25 percent reported 

that they stop on a freeway entrance ramp before merging onto the highway, and 17 

percent indicated that they have trouble finding a large enough gap in which to merge 

onto the mainline (Knoblauch, Nitzburg, and Seifert, 1997). Thirty-four percent of the

respondents ages 50 to 72, and 26 percent of the respondents ages 73 to 97, responded that 

they wish entrance lanes were longer. In Lerner and Ratté’s research (1991), aging drivers 
Handbook for Designing Roadways for the Aging Population 53

CHAPTER 3—INTERCHANGES

in focus group discussions commented that they experienced difficulty maintaining 

vehicle headway because of slower reaction times, difficulty reading signs, fatigue, 

mobility limitations, a tendency to panic or become disoriented, and loss of daring 

or confidence. Merging onto the freeway was the most difficult maneuver discussed. 

Needed improvements identified by these aging drivers included the elimination of 

weaving sections and short merge areas, which would facilitate the negotiation of onramps at interchanges. Improvements identified to ease the exit process included better 

graphics, greater use of sign panels listing several upcoming exits, and other methods to 

improve advance signing for freeway exits. 

The intersection of interchange entrance and exit ramps with surface streets often creates 

an environment that is unfriendly and sometimes unsafe for pedestrians. Motorists often 

have a low yield rate at these locations and are traveling at moderately high speeds. These 

factors place vulnerable pedestrians, including aging pedestrians, in a compromised 

state when crossing at these locations. There has been very little research performed on 

specific roadway treatments for pedestrians at interchanges. As a result, there are not 

specific treatments included in this chapter. However, the treatments included in Chapter 

2 for intersections may be considered and applied where engineering judgment deems it 

appropriate to increase driver awareness of pedestrians, slow vehicle speeds, and improve 

pedestrian mobility. 
54 Handbook for Designing Roadways for the Aging Population

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

25 Exit Signs and Markings

A. Letter Size

The calculation of letter size requirements for signs at interchanges and on 

their approaches based on an assumption of a minimum specific ratio of 1 inch 

of letter height per 30 feet of legibility distance is recommended for new or 

reconstructed installations and for sign replacement. 

References: TEH:4, MUTCD:1

B. Mixed-Case Lettering

To increase the reading distance of all highway destination signs, it is required 

by the 2009 MUTCD that mixed-case lettering be used for destination and 

street names.

References: MUTCD:1

C. Overhead Arrow-per-Lane Sign

The MUTCD recommends Overhead Arrow-per-Lane guide signs to be used 

on all new or reconstructed freeways and expressways as described in MUTCD

Sections 2E.20 and 2E.21, whereby the number of arrow shafts appearing on 

the sign matches the number of lanes on the roadway at the location of the sign 

(see Figure 42).

Figure 42. Example Overhead Arrow-per-Lane Sign

PROVEN PRACTICES
Handbook for Designing Roadways for the Aging Population 55

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Freeway and expressway splits or multi-lane exit interchanges that 

contain an interior option lane in which traffic can either leave 

the route or remain on the route, or choose either destination at 

a split, from the same lane should use overhead arrow-per-lane 

guide signs rather than diagrammatic guide sign designs. Overhead 

arrow-per-lane guide signs have been shown to be superior to either 

conventional guide signs or diagrammatic guide signs because they 

convey positive direction about which destination and direction 

each approach lane serves, particularly for the option lane, which is 

otherwise difficult to clearly sign.

References: MUTCD:1

D. Retroreflective Sheeting

Microprismatic retroreflective sheeting should be used on overhead 

and ground-mounted guide signs (in place of Type III sheeting). The 

use of Clearview® font, in conjunction with retroreflective sheeting, 

should be considered because it may further enhance positive 

contrast legends if used appropriately.

References: MUTCD:4, MUTCD:5

The rationale and supporting evidence for these treatments can be found 

beginning on page 224 of this Handbook.
56 Handbook for Designing Roadways for the Aging Population

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

26 Freeway Entrance Traffic 

Control Devices 

A. Guide Sign

A 48-in x 30-in guide sign panel with the legend Freeway Entrance (see Figure 

43), using a minimum letter height of 8 in, should be consistently used in 

situations where freeway entrance and exit ramps are adjacent to one another 

(such as at a partial cloverleaf interchange) and placed as described in Section 

2D.46 and shown in Figure 2D-14 of the MUTCD.

References: MUTCD:1

B. Adjacent Entrance/Exit Ramps

Where adjacent entrance and exit ramps intersect with a crossroad, the use 

of a median separator, either painted or preferably raised, is recommended, 

with the nose of the separator delineated with yellow 

retroreflectorized markings and extending as close to the 

crossroad as practical without obstructing the turning 

path of vehicles (see Figure 44). Where engineering 

judgment determines the need for the median nose to 

be set back from the intersection, the setback distance 

should be treated by a 12-in or wider yellow stripe. In 

addition, a KEEP RIGHT (R4-7) sign should be posted on

the median separator nose, if it is raised. 

References: MUTCD:4

Figure 43. (MUTCD 

D13-3)

Figure 44. Recommended signs and markings 

for adjacent entrance/exit ramps at a crossroad 

intersection
Handbook for Designing Roadways for the Aging Population 57

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

C. Diagrammatic Entrance Sign

For diagrammatic guide signs depicting lane use for 

entry to a freeway from an urban multilane arterial, 

maximum visibility is achieved through overhead 

sign placement. Where this is not feasible, two 

advance ground-mounted diagrammatic guide signs 

should be used, one placed at 0.5 mi and the second 

placed at 0.25 mi in advance of the interchange (see 

Figure 45).

References: MUTCD:4

The rationale and supporting evidence for these 

treatments can be found beginning on page 235 of this 

Handbook.

27 Delineation 

A. Delineators/Raised Pavement Markers

Delineation in the 

vicinity of the exit gore 

at non-illuminated and 

partially illuminated 

interchanges should 

include, as a minimum, 

raised pavement markers 

and retroreflective postmounted delineators as 

shown in Figure 46.

References: Green Book:4, 

MUTCD:4

White Raised 

Pavement Markers

(snowplowable raised pavement

markers may be used where

appropriate for conditions,

spacing of 20 ft)

Object Marker

[Optional]

Type 1 (OM1-2)

Yellow Partially Retroreflective 

Flexible Posts

(Begin posts > 5 s before start 

of exit maneuver point,

spacing of 100 ft)

White Post

Delineators

(spacing of 10–20 ft)

Yellow Post

Delineators

(spacing of 10–20 ft)

Figure 46. Recommended raised pavement markers and post-mounted 

delineators at an exit gore

Figure 45. Advance ground-mounted 

diagrammatic sign
58 Handbook for Designing Roadways for the Aging Population

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

B. Object Marker

Where engineering judgment has identified a hazardous gore area (e.g., 

containing a ditch) or other special visibility need, the minimum treatments 

described above should be supplemented by adding Type 1 object markers to 

the exit gore sign post as illustrated in Figure 46.

References: Green Book:4, TEH:3, MUTCD:1

C. Chevrons/Post-Mounted Delineators

Post-mounted delineators and/or chevrons should be applied to delineate the 

controlling curvature on exit ramps, as illustrated in Figure 47.

References: MUTCD:3

The rationale and supporting evidence for these treatments can be found beginning 

on page 238 of this Handbook.

28 Acceleration/Deceleration 

Lane Design

A. Entrance Ramp Geometry

A parallel (rather than a taper) design for entrance ramp geometry is 

recommended, as shown in Figure 48. AASHTO recognizes the operational 

and safety benefits of long acceleration lanes provided by parallel type 

entrances. A long acceleration lane provides more time for merging drivers to 

find an opening in the through-traffic stream. A parallel style entrance lane 

length of at least 1,200 ft, plus a taper, is desirable. 

References: Green Book:1

B. Location of Exit Ramps

The AASHTO (2011) decision sight distance values should be consistently 

applied in locating ramp exits downstream from sight-restricting vertical or 

horizontal curvature on the mainline (instead of locating ramps based on 

stopping sight distance formulas).

References: Green Book:2

The rationale and supporting evidence for these treatments can be found beginning 

on page 243 of this Handbook.

Figure 47. Placement of 

chevrons on the controlling 

curve of an exit ramp
Handbook for Designing Roadways for the Aging Population 59

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 48. Recommended markings for acceleration lanes from entrance 

ramps onto freeways

A

0.5 A

MIN. 

A - Parallel Acceleration Lane B - Tapered Acceleration Lane

Optional normal width 

dotted white lane line 

or dotted extension of 

right-hand edge line 

downstream beyond 

the “0.5 A MIN.” point

Optional normal width 

dotted extension of 

right-hand edge line

Normal width dotted 

white lane line for at 

least half the length 

of the full-width 

acceleration lane 

plus taper

Wide or normal width 

solid white lane line 

(optional, variable 

length) or normal 

width dotted white 

lane line

Theoretical gore

Theoretical gore

Full lane width

White

channelizing lines

White

channelizing lines

Optional white 

chevron markings 

in neutral area

Physical gore

Physical gore

Neutral area

Edge of 

through lane

PREFERRED

Legend

 Direction of travel

A Length of acceleration 

lane plus taper

B Distance from physical 

gore to downstream end 

of full width acceleration 

lane
60 Handbook for Designing Roadways for the Aging Population

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

29 Interchange Lighting

A. Complete versus Partial Lighting

Complete interchange lighting (CIL) is the preferred practice, but where a CIL 

system is not feasible to implement, a partial interchange lighting (PIL) system 

comprised of two high-mast installations (e.g., 60- to 150-ft- high structures 

with 3 to 12 luminaires per structure) per ramp is recommended, with one 

fixture located on the inner ramp curve near the gore, and one fixture located 

on the outer curve of the ramp, midway through the controlling curvature.

References: Green Book:4, RLH:4

The rationale and supporting evidence for this treatment can be found beginning 

on page 248 of this Handbook.

30 Restricted or Prohibited Movements

A. Signing Practices

To meet overriding concerns for enhanced conspicuity of signing for prohibited 

movements, the following countermeasures should be used where DO NOT 

ENTER (R5-1) and WRONG WAY (R5-1a) signs are used:

A-1.	 For enhanced conspicuity of DO NOT ENTER (R5-1) and WRONG

WAY (R5-1a) signs placed on freeway ramps, use larger than minimum 

MUTCD sizes for freeway applications with corresponding increases in 

letter size. 

References: MUTCD:4

A-2. To provide increased sign conspicuity and legibility for aging drivers, use 

retroreflective fluorescent red sheeting materials that provide for high 

retroreflectance overall.

References: MUTCD:1

A-3. Where engineering judgment indicates an exaggerated risk of wrong-way 

movement crashes, both the R5-1 and R5-1a signs should be installed 

on both sides of the ramp, placed in accordance with the MUTCD (see 

Figure 49). 

References: MUTCD:4
Handbook for Designing Roadways for the Aging Population 61

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

A-4. Where all other engineering 

options have been tried 

or considered, lowering 

sign height to maximize 

brightness under low-beam 

headlight illumination is 

recommended by mounting 

the signs 36 in above the 

pavement (measured from the 

road surface to the bottom 

of the sign), or the lowest 

value above 36 in that is 

practical when the presence 

of snow, vegetation, or other 

obstructions is taken into 

consideration.

References: MUTCD: 2

B. Pavement Markings

B-1. The application of 23.5-ft 

long wrong-way arrow 

pavement markings near the 

terminus on all exit ramps is 

recommended (see Figure 49). 

B-2. Where engineering judgment 

indicates a need for increased 

conspicuity, wrong-way arrow 

pavement markings should be supplemented with red/white bidirectional 

retroreflective raised pavement markers.

References: MUTCD:3

The rationale and supporting evidence for these treatments can be found beginning 

on page 252 of this Handbook.

Exit Ramp

Entrace Ramp

Legend

Direction of travel

Wrong-way arrows

Optional

Figure 49. Recommended signing for restricted movements on an 

exit ramp
62 Handbook for Designing Roadways for the Aging Population

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

These are treatments being utilized by transportation agencies that should benefit 

aging road users as determined by a subjective assessment by staff participating on the 

development of this Handbook. Current trends indicate these practices have a positive 

impact on aging road user safety. 

31 Advance Pavement (Route Shield) 

Markings at Major Freeway Junctions 

At major freeway interchanges and route splits, route shield markings should be 

used in the lanes approaching the split to guide drivers to the correct approach lane 

(see Figure 50). The placement of this type of marking should be just prior to the 

location of the advance guide signs.

References: MUTCD:1

The rationale and supporting evidence for these treatments can be found beginning 

on page 257 of this Handbook.

Figure 50. Route Shield Markings At Freeway Junctions

PROMISING PRACTICES
Handbook for Designing Roadways for the Aging Population 63

CHAPTER 3—INTERCHANGES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

32 Wrong-Way Driving Countermeasures

The NTSB’s FARS analysis determined that drivers over the age of 70 are overrepresented in fatal wrong-way crashes (NTSB, 2013). Additional treatments 

to counter wrong-way driving by aging drivers (e.g., improved lighting, 

channelization, signs and markings in addition to those in Treatment 30) should 

be considered where exit ramps intersect with surface streets. Road owners could 

employ the use of a Road Safety Audit (RSA) to examine the performance of the 

interchange and determine appropriate countermeasures to employ. A WrongWay Driving (WWD) Prompt list is available to focus specific attention on wrongway driving issues and contributing factors. The prompt list has been developed 

in a similar framework to the broader RSA prompt lists contained in Chapter 

8 of the FHWA RSA Guidelines document. The prompts are only an aid to the

RSA team and they are not intended to cover all conditions or circumstances an 

RSA team may encounter. The American Traffic Safety Services Association also 

provides a publication that describes promising practices in wrong-way driving 

countermeasures (ATSSA, 2012); a review of that document should be included 

during the consideration of potential WWD treatments to implement.

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 257 of this Handbook.
64 Handbook for Designing Roadways for the Aging Population
Handbook for Designing Roadways for the Aging Population 65

CHAPTER 4

Roadway Segments

This section of the Handbook provides treatments to enhance the performance of aging 

drivers for the following design elements associated with roadway segments. Also, 

after the last element, six promising practice treatments are provided. Drawings are 

for illustrative purposes only; they are not to scale and should not be used for design 

purposes.

Proven Practices

33. Horizontal Curves 

34. Vertical Curves

35. Passing Zones

36. Lane Control Devices 

Promising Practices

37. Lane Drop Markings

38. Contrast Markings on Concrete Pavement

39. Utilize Highly Retroreflective Marking Material 

40. Curve Warning Markings

41. Road Diets

42. High Friction Surface Treatments

Crashes on horizontal curves have been recognized as a considerable safety problem for 

many years. Crash studies indicate that roadway curves experience a higher crash rate 

than tangents, with rates ranging from one-and-a-half to four times higher than tangents 

(Glennon, Neuman, and Leisch, 1985; Zegeer, et al., 1990; Neuman, 1992). Lerner and

Sedney (1988) reported anecdotal evidence that horizontal curves present problems for 

aging drivers. Also, analyses of crash data in Michigan found that aging drivers were 

involved in crashes on horizontal curves as a result of driving too fast for the curve or, 

more significantly, because they were surprised by the curve alignment (Lyles, et al., 

1997). In reviewing literature on driver behavior on rural road curves, Johnston (1982) 

reported that horizontal curves that are less than 1960 ft in radius on two-lane rural 

roads, and those requiring a substantial reduction in speed from that prevailing on the 

preceding tangent section, were disproportionately represented among crash sites.

Successful curve negotiation depends on the choice of appropriate approach speed and 

adequate lateral positioning through the curve. Many studies have shown that loss-ofcontrol crashes result from an inability to maintain a lateral position through the curve 

because of excessive speed, with inadequate deceleration in the approach zone. These 

problems, in turn, stem from a combination of factors, including poor anticipation 

of vehicle control requirements, induced by the driver’s prior speed, and inadequate 

perception of the demands of the curve.
66 Handbook for Designing Roadways for the Aging Population

CHAPTER 4—ROADWAY SEGMENTS

Many studies report a relationship between horizontal curvature (and the degree 

of curvature) and the total percentage of crashes by geometric design feature on the 

highways. The reasons for these crashes are related to the following inadequate driving 

behaviors:

•	 Deficient skills in negotiating curves, especially those of more than 3 degrees

(Eckhardt and Flanagan, 1956). 

•	 Exceeding the design speed on the curve (Messer, Mounce, and Brackett, 1981).

•	 Exceeding the design of the vehicle path (Glennon and Weaver, 1971; Good, 1978).

•	 Failure to maintain appropriate lateral position in the curve (McDonald and Ellis,

1975).

•	 Incorrect anticipatory behavior of curve speed and alignment when approaching

the curve (Messer et al., 1981; Johnston, 1982).

•	 Inadequate appreciation of the degree of hazard associated with a given curve

(Johnston, 1982). 

With respect to vertical curves, design policy is based on the need to provide drivers 

with adequate stopping sight distance (SSD). That is, enough sight distance must exist to 

permit drivers to see an obstacle soon enough to stop for it under some set of reasonable 

worst-case conditions. The parameters that determine sight distance on crest vertical 

curves include the change of grade, the length of the curve, the height above the ground 

of the driver’s eye, and the height of the obstacle to be seen. SSD is determined by the 

driver’s reaction time, design speed, and deceleration rate. Current practice assumes 

an obstacle height of 2.0 ft and controlled braking rather than locked-wheel braking 

(AASHTO, 2004). Minimum lengths of crest vertical curves are based on sight distance 

and driver comfort. These criteria do not currently include adjustments for age-related 

effects in driving performance measures, which would suggest an even more conservative 

approach. At the same time, the general lack of empirical data demonstrating benefits for 

limited sight-distance countermeasures has led some to propose liberalization of model 

criteria, such as obstacle height (Neuman, 1989; Fambro, Fitzpatrick, and Koppa, 1997). 

Standards and criteria for sight distance, horizontal and vertical alignment, and 

associated traffic control devices are based on the following driver performance 

characteristics: detection and recognition time, perception-reaction time, decision and 

response time, time to perform brake and accelerator movements, maneuver time, and 

(if applicable) time to shift gears. However, these values have typically been based on 

driving performance (or surrogate driving measures) of the entire driving population, 

or have been formulated from research biased toward younger (college age) as opposed 

to aging driver groups. The models underlying these design standards and criteria 

therefore have not, as a rule, included variations to account for slower reaction time 

or other performance deficits consistently demonstrated in research on aging driver 

response capabilities. In particular, diminished visual performance (reduced acuity 

and contrast sensitivity), physical capability (reduced strength to perform control 

movements and sensitivity to lateral force), cognitive performance (attentional deficits 

and declines in choice reaction time in response to unpredictable stimuli), and perceptual 

abilities (reduced accuracy of processing speed-distance information as required for 
Handbook for Designing Roadways for the Aging Population 67

CHAPTER 4—ROADWAY SEGMENTS

gap judgments) combine to make the task of negotiating the highway design elements 

addressed in this section more difficult and less forgiving for aging drivers.

With the increasing need to provide more capacity on freeways and urban arterials, 

more jurisdictions are moving to the use of reversible lanes to accommodate peakperiod traffic flows. The control of wrong-way movements on these facilities may be 

accomplished through the use of lane control signals (LCS), which provide real-time 

information to motorists about which lanes are open (green downward arrow), which 

are closed (red X) and which lanes are about to be closed (yellow X) either because of 

an incident downstream or because the lane is a reversible lane. Drivers should vacate 

lanes designated with a yellow X and should not enter lanes designated with a red X. Safe 

and effective responses to these indications by aging drivers hinge upon visual target 

detection and recognition processes that decline with advancing age.
68 Handbook for Designing Roadways for the Aging Population

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

PROVEN PRACTICES

33 Horizontal Curves

A. Edge Lines

White edge lines on horizontal curves (see Figure 51) are to be maintained at 

the following in-service contrast levels:

A-1. On highways without median separation of opposing directions of 

traffic, the recommended minimum in-service contrast level for 

edgelines on horizontal curves is 5.0.

A-2. On highways where median barriers effectively block the drivers’ 

view of oncoming headlights or where median width exceeds 50 ft, 

the recommended minimum in-service contrast level for edgelines on 

horizontal curves is 3.75.

Contrast should be calculated according to this formula:

Luminance contrast (C) = 

Luminancestripe - Luminancepavement 

Luminancepavement

* Luminance is the amount of light reflected from an object. This is different from retroreflectivity, which 

is a property of a material. While increasing retroreflectivity generally results in higher luminance, (often 

described as brightness)—especially at night—this may vary greatly for the same object or marking 

depending upon such factors as the location and intensity of the source of illumination, and the angle at 

which a driver views it. 

References: MUTCD: 4

Figure 51. White edge lines, centerline RPMs, and chevrons on a horizontal curve
Handbook for Designing Roadways for the Aging Population 69

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

B. Retroreflective Pavement Markers 

The use of retroreflective raised pavement markers (RPMs) is recommended to 

improve the visibility of surface delineation treatments on horizontal curves in 

the following situations where demands on motorists for path maintenance and 

vehicle guidance are increased:

B-1. For curves with radii greater than 1640 ft and less than 3280 ft, it is 

recommended that standard centerline markings be supplemented with 

RPMs installed at standard spacing (i.e., 40 ft apart), and that they be 

applied for a distance of 5 s of driving time (at 85th percentile speed) 

on the approach to the curve and continued throughout the length of 

the curve. [See time-speed-distance table on page 5.] The Highway 

Safety Manual cites a negative effect on roadway crashes for some drivers 

when RPM’s are installed on curves with radii less than 1640 feet. 

B-2. Where engineering judgment indicates that nighttime wet pavement 

visibility for surface delineation treatments is a priority for safe 

operations, regardless of curve radius, the use of RPMs is recommended.

References: MUTCD: 4

C. Post-Mounted Delineators

In addition to the installation of chevron alignment signs (W1-8) as specified 

in the MUTCD, roadside post-mounted delineators should be installed on 

horizontal curves with approximate uniform spacing as shown in Table 7.

References: MUTCD: 2

Table 7. Recommended spacing for post-mounted delineators.

Radius of Curve 

(Feet)

Approximate Spacing 

(Feet)

< 600 40

700 75

800 80

900 85

> 1000 90
70 Handbook for Designing Roadways for the Aging Population

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Note: Spacing for curves greater than 600 ft based on the following formula 

from the MUTCD (Table 3D-1):

English: S = 3(R-50)0.5

Where:

S = approximate spacing on curve (ft)

R = radius (ft)

D. Pavement Width

On two-lane rural roads, the combined (lane plus shoulder) paved width in 

one direction should be at least 18 ft throughout the length of the curve for a 

horizontal curve with a radius less than 1900 ft.

References: Green Book: 4

The rationale and supporting evidence for this treatment can be found beginning 

on page 260 of this Handbook.

34 Vertical Curves

A. Perception-Reaction Time

To accommodate the exaggerated decline among aging drivers in response to 

unexpected hazards, strict adherence to a perception-reaction time (PRT) of at 

least 2.5 sec for a roadway hazard obscured by the vertical curvature should be 

used in the design of new and reconstructed facilities.

References: Green Book: 1

B. Passive Warning Sign

Where a need has been determined for installation or replacement of a device 

to warn motorists that sight distance is restricted by a crest vertical curve, 

use the 30-in x 30-in HILL BLOCKS VIEW sign (MUTCD W7-6) with an 

Advisory Speed plaque (MUTCD W13-1P) as shown in Figure 52. 

References: MUTCD: 2

C. Active Warning Sign

If a signalized intersection is obscured by vertical curvature in a manner that 

the signal becomes visible at a preview distance of 8 s or less (at operating 

speed), then it is recommended that, in addition to the standard advance 

signal warning sign (MUTCD W3-3), a BE PREPARED TO STOP warning 

sign (MUTCD W3-4) and WHEN FLASHING plaque (MUTCD W16-13) 

Figure 52. (MUTCD

W7-6 and W13-1P)
Handbook for Designing Roadways for the Aging Population 71

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

be used along with a warning beacon interconnected with the traffic signal 

controller (see Figure 53). The yellow warning beacon should be activated at a 

sufficient interval prior to the onset of the yellow signal phase and sustained 

after the onset of the green signal phase to take into account the end of queues 

experienced during peak traffic conditions, as determined through engineering 

study. [See time-speed-distance table on page 5.]

References: MUTCD: 2

The rationale and supporting evidence for these treatments can be found beginning 

on page 272 of this Handbook.

35 Passing Zones 

A. Passing Sight Distance

To accommodate age-related difficulties in judging gaps and longer decisionmaking and reaction times exhibited by aging drivers, use the most 

conservative minimum required passing sight distance (PSD) values from the 

2009 MUTCD, Table 3B-1. See Table 8. 

References: Green Book: 2, TEH: 2, MUTCD: 1

Table 8. Minimum passing sight distances for no-passing zone markings.

85th-Percentile or Posted or 

Minimum Passing

Statutory Speed Limit 

Sight Distance

25 mph 450 feet

30 mph 500 feet

35 mph 550 feet

40 mph 600 feet

45 mph 700 feet

50 mph 800 feet

55 mph 900 feet

60 mph 1,000 feet

65 mph 1,100 feet

70 mph 1,200 feet

B. Pennant

Use of the MUTCD oversized (48-in x 64-in x 64-in) NO PASSING ZONE

pennant (W14-3), or the standard size (36 in x 48 in x 48 in) using fluorescent 

yellow retroreflective sheeting, is recommended as a high-conspicuity 

supplement to conventional centerline pavement markings at the beginning of 

no passing zones (see Figure 54).

References: MUTCD: 1, MUTCD: 3

Figure 53. (MUTCD

W3-4 and W16-13)

Figure 54. (MUTCD 

W14-3)
72 Handbook for Designing Roadways for the Aging Population

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

C. Passing Lanes

To the extent feasible for new or reconstructed two-lane facilities, the 

implementation of passing/overtaking lanes (in each direction) at intervals of 

no more than 3.1 mi is recommended.

References: Green Book: 4, TEH: 4

The rationale and supporting evidence for these treatments can be found beginning 

on page 277 of this Handbook.

36 Lane Control Devices

A. Pixel Specifications

To increase the legibility distance of overhead lane-control signal indications 

for prohibited movements (red X), use a double-stroke arrangement of 

pixels that are small (approximating 0.15 in diameter) and closely spaced 

(approximating 0.70 in center-to-center), as shown in Figure 55.

References: MUTCD: 4

The rationale and supporting evidence for these treatments can be found beginning 

on page 281 of this Handbook.

Figure 55. Lane Control 

Signal (adapted from 

Ullman et al. 1996)
Handbook for Designing Roadways for the Aging Population 73

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

These are treatments being utilized by transportation agencies that should benefit 

aging road users as determined by a subjective assessment by staff participating on the 

development of this Handbook. Current trends indicate these practices have a positive 

impact on aging road user safety. 

37 Lane Drop Markings

To provide additional guidance where a through lane becomes a mandatory turn 

lane at an intersection or becomes a mandatory exit lane at an interchange, a 

“dotted” lane line should be used to separate the continuing through lane from the 

mandatory turn or mandatory exit lane, as described in Section 3B.04 of the 2009 

MUTCD and as shown in Figure 56.

References: MUTCD:1

The rationale and supporting evidence for these treatments can be found beginning 

on page 284 of this Handbook.

PROMISING PRACTICES

Figure 56. Dotted Lane Line Markings at Freeway Lane Drop
74 Handbook for Designing Roadways for the Aging Population

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

38 Contrast Markings on 

Concrete Pavement

Contrast markings should be used wherever the pavement color is light to 

increase visibility of pavement markings (see MUTCD Section 3A.05 and 

Figure 57).

References: MUTCD:1

The rationale and supporting evidence for these treatments can be found 

beginning on page 284 of this Handbook.

Figure 57. Contrast Markings on Light Colored Pavement
Handbook for Designing Roadways for the Aging Population 75

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

39 Utilize Highly Retroreflective 

Marking Material 

To maintain visibility under adverse driving conditions, use highly retroreflective 

marking material.

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 285 of this Handbook.

40 Curve Warning Markings

Curve warning pavement markings, such as shown in Figure 58, should be 

considered as a supplement to curve warning signs at horizontal curves identified 

as a safety problem.

References: TEH: 4, FHWA:2, MUTCD:5

The rationale and supporting evidence for these treatments can be found beginning 

on page 285 of this Handbook.

Figure 58. Curve Warning Markings (MUTCD:5)
76 Handbook for Designing Roadways for the Aging Population

CHAPTER 4—ROADWAY SEGMENTS

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

41 Road Diets

The classic roadway reconfiguration commonly referred to as a “road diet” involves 

converting an undivided four-lane roadway into three lanes made up of two 

through lanes and a center two-way left turn lane. An example of a completed road 

diet is shown in Figure 59. When performing an evaluation or road safety audit of 

a roadway segment that may be redesigned or reconstructed, a road diet should be 

included among the options to be considered.

References: HCM:1

The rationale and supporting evidence for these treatments can be found beginning 

on page 286 of this Handbook.

42 High Friction Surface Treatments

High friction surface treatments (HFST) are the site-specific application of very 

high quality polish-resistant, abrasion-resistant aggregates bonded to the pavement 

surface using a polymer binder that restores and maintains pavement friction where 

the need for a safer pavement surface is the greatest.

HFSTs are recommended on horizontal and vertical curves (such as the example 

shown in Figure 60), at intersections, at on and off-ramps, on bridge decks, locations 

prone to frequent rain, snow, or ice, or where additional side friction is beneficial.

References: Green Book:1

The rationale and supporting evidence for these treatments can be found beginning 

on page 287 of this Handbook.

Figure 59. Example of Road Diet Figure 60. High Friction Surface Treatment on a 

Horizontal Curve
Handbook for Designing Roadways for the Aging Population 77

CHAPTER 5

Construction/Work Zones

This section of the Handbook provides treatments to enhance the performance of aging 

drivers as they approach and travel through construction/work zones, keyed to five specific 

design elements. Also, after the last element, two promising practices treatments are 

provided. Drawings are for illustrative purposes only; they are not to scale and should not 

be used for design purposes. 

Proven Practices

43. Signing and Advance Warning

44. Portable Changeable (Variable) Message Signs

45.	 Channelization (Path Guidance)

46. Delineation of Crossovers/Alternate Travel Paths

47. Temporary Pavement Markings

Promising Practices

48. Increased Letter Height for Temporary Work Zone Signs

49. Work Zone Road Safety Audit (WZRSA)

Highway construction and maintenance zones deserve special consideration with respect 

to aging driver needs because of their strong potential to violate driver expectancy. 

Alexander and Lunenfeld (1986) properly emphasized that driver expectancy is a key factor 

affecting the safety and efficiency of all aspects of the driving task. Consequently, it is 

understandable that crash analyses consistently show that more crashes occur on highway 

segments containing construction zones than on the same highway segments before the 

zones were implemented (Juergens, 1972; Graham, Paulsen, and Glennon, 1977; Lisle, 1978;

Nemeth and Migletz, 1978; Paulsen, Harwood, and Glennon, 1978; Garber and Woo, 1990;

Hawkins, Kacir, and Ogden, 1992).

Work-zone traffic control must provide adequate notice to motorists that describes the 

condition ahead, the location, and the required driver response. Once drivers reach a 

work zone, pavement markings, signing, and channelization must be conspicuous and 

unambiguous in providing guidance through the area. The National Transportation Safety 

Board (NTSB, 1992) stated that the MUTCD guidelines concerning signing and other 

work-zone safety features provide more than adequate warning for a vigilant driver, but 

may be inadequate for an inattentive or otherwise impaired driver. It is within this context 

that functional deficits associated with normal aging, as described below, may place aging 

drivers at greater risk when negotiating work zones.

In a crash analysis at 20 case-study work-zone locations, among the most frequently listed 

contributing factors were driver attention errors and failure to yield the right-of-way 

(Pigman and Agent, 1990). Aging drivers are most likely to demonstrate these deficits. 

Research on selective attention has documented that aging adults respond much more 

slowly to stimuli that are unexpected (Hoyer and Familant, 1987), suggesting that aging 

adults could be particularly disadvantaged by changes in roadway geometry and operations 
78 Handbook for Designing Roadways for the Aging Population

CHAPTER 5—CONSTRUCTION/WORK ZONES

such as those found in construction zones. There is also research indicating that aging 

adults are more likely to respond to new traffic patterns in an “automatized” fashion, 

resulting in more frequent driver error (Fisk, McGee, and Giambra, 1988). To respond

in situations that require decisions among multiple and/or unfamiliar alternatives, with 

unexpected path-following cues, drivers’ actions are described by complex reaction times

that are longer than reaction times in simple situations with expected cues. In Mihal 

and Barrett’s analysis (1976) relating simple, choice, and complex reaction time to crash 

involvement, only an increase in complex reaction time was associated with crashes. The 

relationship with driver age was most striking: the correlation between complex reaction 

time and crash involvement increased from r = 0.27 for the total analysis sample (all ages) 

to r = 0.52 when only aging adults were included. Such data suggest that in situations 

where there is increased complexity in the information to be processed by drivers—such 

as in work zones—the most relevant information must be communicated in a dramatic 

manner to ensure that it receives a high priority by aging individuals.

Compounding their exaggerated difficulties in allocating attention to the most relevant 

aspects of novel driving situations, diminished visual capabilities among aging drivers 

are well documented (McFarland, Domey, Warren, and Ward, 1960; Weymouth, 1960; 

Richards, 1972; Pitts, 1982; Sekuler, Kline, and Dismukes, 1982; Owsley, Sekuler, and

Siemsen, 1983; Wood and Troutbeck, 1994). Deficits in static and dynamic acuity and 

contrast sensitivity, particularly under low-luminance conditions, make it more difficult 

for them to detect and read traffic signs, to read variable message signs, and to detect 

pavement markings and downstream channelization devices. Olson (1988) determined 

that for a traffic sign to be noticed at night in a visually complex environment, its 

reflectivity must be increased by a factor of 10 to achieve the same level of conspicuity 

as in a low-complexity environment. Mace (1988) asserted that the minimum required 

visibility distance—the distance from a traffic sign required by drivers in order to detect 

the sign, understand the situation, make a decision, and complete a vehicle maneuver 

before reaching a sign—is increased significantly for aging drivers due to their poorer 

visual acuity and contrast sensitivity, coupled with inadequate sign luminance and legend 

size. Other age-related deficits cited by Mace (1988) include lowered driver alertness, 

slower detection time in complex roadway scenes due to distraction from irrelevant 

stimuli, increased time to understand unclear messages such as symbols, and slower 

decision making.

In a mail survey of 1,329 AARP members ages 50 to 97, conducted to identify aging 

driver freeway needs and capabilities, 21 percent of the respondents indicated that they 

have problems with accurately judging distances in construction zones (Knoblauch,

Nitzburg, and Seifert, 1997). These drivers reported additional problems in negotiating 

work zones, including congestion/traffic; lack of adequate warning; narrow lanes; lane 

closures and lane shifts; and difficulty staying in their lane.
Handbook for Designing Roadways for the Aging Population 79

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

43 Signing and Advance 

Warning

A. Flashing Yellow Arrow Panel

At construction/maintenance work zones on high-speed 

roadways (where the posted speed limit is 45 mph or 

greater) and divided highways, the consistent use of a 

flashing arrow panel located at the taper for each lane 

closure is recommended as shown in Figure 61.

References: MUTCD:4

B. Lane Closure Advance Signing

In implementing advance signing for lane closures as per 

MUTCD Part 6, it is recommended that:

A supplemental (portable) changeable message sign 

(CMS) displaying the one-page (phase) message LEFT 

(RIGHT, CENTER) LANE CLOSED should be placed

0.5 to 1.0 mile upstream of the lane closure taper (see 

Figure 62).

OR

Redundant static signs should be used, with a minimum 

letter height of 8 in and fluorescent orange retroreflective 

sheeting, where both the first upstream sign (e.g., W20-

1) and the second sign (e.g., W20-5) encountered by 

the driver are equipped with flashing warning lights 

throughout the entire time period of the lane closure (see 

Figure 63).

References: TEH:4, MUTCD:4

Shoulder taper

Work vehicle

Truck-mounted

attenuator

(optional)

Figure 62. Changeable message sign 

upstream of lane closure taper

Figure 61. Flashing arrow panel at lane 

closure taper

PROVEN PRACTICES
80 Handbook for Designing Roadways for the Aging Population

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

C. Sign Sheeting

To increase the legibility distance of ground-mounted work-zone signs, the use 

of fluorescent orange is recommended over the use of beaded high-intensity 

orange sheeting.

References: MUTCD:1, NCHRP 500-9:4

D. Legibility Distance

A minimum specific ratio of 1 inch of letter height per 30 feet of legibility 

distance should be used.

References: TEH:4, MUTCD:1

The rationale and supporting evidence for these treatments can be found beginning 

on page 290 of this Handbook.

Figure 63. Redundant static signs upstream of lane closure taper
Handbook for Designing Roadways for the Aging Population 81

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

44 Portable Changeable 

(Variable) Message Signs

A. Number of Phases

The MUTCD requires that no more than two phases be used on a 

changeable message sign (CMS). If a message cannot be conveyed in two 

phases, multiple CMSs and/or a supplemental highway advisory radio 

message should be used; alternatively, the action statement only may be 

presented on a single page/phase. 

References: TEH:2, MUTCD:4

B. Display Time

Each phase of a CMS message should be displayed for a minimum of 3 s.

References: MUTCD:1

C. Units of Information

C-1. It is recommended that no more than one unit of information be 

displayed on a single line on a CMS, and no more than three units 

should be displayed for any single phase. A unit of information is one 

or more words that answers a specific question (e.g., What happened? 

Where? What is the effect on traffic? What should the driver do?).

References: MUTCD:4

C-2. For CMS messages split into two phases, a total of no more than four 

unique units of information should be presented.

References: TEH:4, MUTCD:4

D. Sign Content

When a CMS is used to display a message in two phases, the problem and 

location statements should be displayed during phase 1 and the effect or 

action statement during phase 2, as illustrated in Figure 64. 

If legibility distance restrictions rule out a two-phase display, the use of 

abbreviations [as specified in the MUTCD (FHWA, 2007)] plus elimination 

of the problem statement is the recommended strategy to allow for the 

presentation of the entire message in one phase, as illustrated in Figure 65. 

References: TEH:4, MUTCD:4

Figure 64. Phase 1 (Top) 

and Phase 2 (Bottom)

LEFT

LANE

CLOSED

ROAD

2 MILES

WORK

 Figure 65. Use of 

approved abbreviation 

in one-phase message

LEFT LN

CLOSED

IN 2 MI
82 Handbook for Designing Roadways for the Aging Population

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

E. Legibility

For superior legibility:

E-1. Only single-stroke lettering should be used for displays of alphanumeric 

characters on portable CMSs with the conventional 5- x 7-pixel matrix; 

double-stroke lettering should be avoided.

References: MUTCD:4

E-2 As new portable CMSs are procured by a highway agency, the 

performance specifications of such devices should include a minimum 

character width-to-height ratio of 0.7 (complete character) and a 

maximum stroke width-to-height ratio of 0.13.

References: MUTCD:4

F. Sign Height

Portable changeable message signs should be elevated to a height sufficient 

to be seen across multiple lanes of (same-direction) traffic by approaching 

passenger car drivers.

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 300 of this Handbook.

45 Channelization (Path Guidance)

A. Device Dimensions

The following minimum dimensions or properties for channelizing 

devices used in highway work zones are recommended to 

accommodate the needs of aging drivers:

A-1 Traffic cones—36 in high, with two bands of retroreflective 

material totaling at least 12 in wide for nighttime operations. (see 

Figure 66)

References: MUTCD:4

A-2 Tubular markers—42 in high, with a single band of 

retroreflective material at least 12 in wide for nighttime operations.

References: MUTCD:4

6 inches

2 inches

3 to 4 inches

6 inches

Retroreflective

band

36 inches

Figure 66. Traffic cone for nighttime 

work zone operations
Handbook for Designing Roadways for the Aging Population 83

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

A-3 Vertical (striped) panels—12 in wide.

References: MUTCD:1

A-4 Barricades—12-in x 36-in minimum dimension.

References: MUTCD:2

A-5 Drums—18 in x 36 in, with high-brightness sheeting for the orange and 

white retroreflective stripes (as per MUTCD guidelines). 

References: MUTCD:4

B. Device Spacing

Channelizing devices through work zones (in non-crossover applications) 

should be spaced at no more than a distance in feet equal to the speed 

limit through the work zone in miles per hour (e.g., in 40-mph work zone, 

channelizing devices should be spaced no farther apart than 40 ft). Where 

engineering judgment indicates a special need for speed reduction where 

there is horizontal curvature or through the taper for a lane closure, spacing 

of channelizing devices at a distance in feet equal to no more than half of the 

speed limit in miles per hour is recommended (e.g., in a 40-mph zone, space 

the devices no farther apart than 20 ft). 

References: MUTCD:4

C. Reflectors

The use of side reflectors with cube-corner lenses or reflectors (facing the 

driver) mounted on top of concrete safety-shaped barriers and related 

temporary channelizing barriers is recommended, spaced (in feet) at no more 

than the construction zone speed limit (in miles per hour) through a work 

zone.

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 313 of this Handbook.
84 Handbook for Designing Roadways for the Aging Population

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

46 Delineation of Crossovers/

Alternate Travel Paths

A. Positive Barriers

Use positive barriers in transition zones and positive separation 

(channelization) between opposing two-lane traffic throughout a crossover, 

for intermediate- and long-term-duration work zones, for all roadway classes 

except residential.

References: MUTCD:1

B. Device Spacing

A maximum spacing (in feet) of one-half the construction zone speed limit 

(in miles per hour) for channelizing devices (other than concrete barriers) is 

recommended in transition areas, and through the length of the crossover, and 

in the termination area downstream (where operations as existed prior to the 

crossover resume).

References: MUTCD:4

C. Reflectors

Use side reflectors with cube-corner lenses spaced (in feet) at no more than the 

construction zone speed limit (in miles per hour) on concrete channelizing 

barriers in crossovers (or alternately, the use of retroreflective sheeting on 

plastic glare-control louvers [paddles] placed in crossovers).

References: MUTCD:4

D. Screens

It is recommended for construction/work zones on high-volume roadways 

that glare-control screens be mounted on top of temporary traffic barriers that 

separate two-way motor vehicle traffic, when used in transition and crossover 

areas, at a spacing of not more than 24 in.

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 318 of this Handbook.
Handbook for Designing Roadways for the Aging Population 85

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

47 Temporary Pavement Markings

A. Raised Pavement Markers

Where temporary pavement markings shorter than the 10-ft standard length 

are implemented, it is recommended that a raised pavement marker be placed 

at the center of the gap between successive markings. 

References: MUTCD:2

The rationale and supporting evidence for this treatment can be found beginning 

on page 323 of this Handbook.
86 Handbook for Designing Roadways for the Aging Population

CHAPTER 5—CONSTRUCTION/WORK ZONES

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 67. Temporary work 

zone sign with increased 

letter height

These are treatments being utilized by transportation agencies that should benefit 

aging road users as determined by a subjective assessment by staff participating on the 

development of this Handbook. Current trends indicate these practices have a positive 

impact on aging road user safety.

48 Increased Letter Height for 

Temporary Work Zone Signs

It is recommended that some “action” words on temporary work zone signs on 

portable sign stands have a minimum letter height of 8 in. (see Figure 67)

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 328 of this Handbook.

49 Work Zone Road Safety 

Audit (WZRSA)

The Work Zone Road Safety Audit Guidelines and Prompt Lists provide a process

for individuals or agencies performing formal work zone safety examinations 

to improve the safety of workers and all roadway users, including the aging 

population. This document includes guidance on conducting Road Safety 

Audits (RSA) at all phases of work zone planning, design and deployment, and 

considerations for each project phase. The guidelines and prompt lists explain the 

importance of the Work Zone RSA and navigate the practitioner through the RSA 

process. 

References: MUTCD:4

The rationale and supporting evidence for these treatments can be found beginning 

on page 329 of this Handbook.

PROMISING PRACTICES
Handbook for Designing Roadways for the Aging Population 87

CHAPTER 6

Highway-Rail Grade Crossing

This section of the Handbook provides treatments to enhance the performance of aging 

drivers at highway-rail grade crossing, keyed to two specific proven practices: 

Proven Practices

50. Passive Traffic Control Devices

51. Lighting

There are no promising practice treatments for this element. Drawings are for illustrative 

purposes only; they are not to scale and should not be used for design purposes.

According to the Federal Railroad Administration (FRA, 2014), there were 1,967 highwayrail grade crossing crashes in 2012, resulting in 233 fatalities and 941 injuries. An FRA 

report found 55 percent of such incidents in 2012 occurred during the day, 29 percent 

occurred at night, and 16 percent occurred during dusk/dawn. Fifty-six percent of the 

crashes in 2012 occurred at crossings with passive controls. In a U. S. Department of 

Transportation Office of Inspector General report (June 2004), driver error was cited as the

probable cause of the crash in 94 percent of vehicle crashes at highway grade crossings for 

the previous ten years. 

Klein, Morgan, and Weiner (1994) analyzed Fatality Analysis Reporting System (FARS)

data from 1975 to 1992 to determine the characteristics of drivers involved in fatal crashes 

at highway-rail grade crossings, and the circumstances under which such crashes occurred. 

This analysis indicated that drivers ages 25 to 34 are involved in the highest percentage 

(almost 25 percent) of all fatal rail crossing crashes, followed by drivers ages 16 to 20 

(approximately 18 percent). Drivers in these age groups also show the highest involvement 

in all fatal crashes and all fatal intersection crashes, based on crash frequency data 

uncorrected for exposure. By contrast, drivers ages 65 to 74 were involved in 6.5 percent of 

fatal railroad crossing crashes and drivers ages 74 and older account for almost 5 percent of 

the railroad crossing fatalities. Again, these data do not reflect level of exposure. However, 

the data show that the percentage of drivers ages 65 to 74 who are involved in fatal rail 

crossing crashes is slightly more than the percentage of drivers in this age group who are 

involved in all fatal crashes (4.6 percent) and about the same as those involved in fatal 

intersection crashes (6.2 percent), which is the maneuver category for which aging drivers 

are most at risk. Notably, the proportion of aging drivers involved in highway-rail grade 

crossing crashes at night is higher than the proportion of aging drivers in vehicle-involved 

crashes at night, suggesting special problems associated with the use of these facilities 

under reduced visibility conditions.

There are several age-related diminished capabilities that may make the task of safely 

negotiating highway-rail grade crossing more difficult for aging drivers. Well-documented 

losses in visual acuity and contrast sensitivity with advancing age (Burg, 1967; Ball and 

Owsley, 1991; Ball, et al., 1993; Decina and Staplin, 1993) may delay substantially the 

detection of critical elements such as the standard crossbuck or warning symbol during a 

motorist’s approach to a crossing, and may preclude detection of a train actually present 
88 Handbook for Designing Roadways for the Aging Population

CHAPTER 6—HIGHWAY-RAIL GRADE CROSSING

at the crossing until impact is imminent, especially at night. While the analyses of 

Klein et al. (1994) paint a compelling picture of young males engaging in intentionally

risky behavior as a significant component of the crash problem at rail crossings, the 

technical literature suggests that willful noncompliance with traffic control devices by 

aging drivers at these sites will not be a major problem—if they (visually) detect and 

comprehend the advisory, warning, and regulatory information conveyed by these 

devices in time to respond safely. 

Expectancy also plays a role in where and when drivers look for trains, and consequently, 

train detection (Raslear, 1995). A driver who is familiar with a crossing and rarely or 

never encounters a train during the time period he or she uses the crossing is more likely 

to miss seeing a train than either the driver who is unfamiliar with the crossing and 

therefore has no expectations about train frequency, or the driver who is familiar with the 

crossing and frequently encounters trains during the time period that he or she crosses 

the tracks. Drivers who don’t expect trains do not look for them. As a consequence, per 

train, crash rates are higher for crossings with the lowest frequency of trains (Raslear, 

1995). Enhancing the conspicuity and comprehension of design elements at passive 

crossings, plus the use of signing that orients drivers’ attention toward trains and advises 

drivers on the appropriate action to be taken, are thus top priorities.

Comprehension of highway-rail crossing traffic control devices and performance of 

related information-processing tasks may be expected to pose disproportionate difficulty 

for aging drivers. Although the crossbuck sign is a regulatory sign that serves as an 

implied YIELD sign, researchers consistently report that drivers do not understand the 

message it is intended to convey (Bridwell, et al., 1993; Fambro, et al., 1997). 

Furthermore, assuming that a driver has been properly alerted to the need to search for 

an approaching train by design elements upstream and at the crossing, has slowed, and 

has begun to actively scan the tracks in each direction, the perception-reaction time 

(PRT) for a decision either to stop or to proceed, plus the subsequent execution of a brake 

or accelerator response, draw upon abilities found to slow significantly among the elderly 

(Staplin and Fisk, 1991; Goggin, Stelmach, and Amrhein, 1989; Stelmach, Goggin, and

Amrhein, 1988). Whereas AASHTO (2011) uses a PRT of 2.5 s for calculating the sight 

triangle at passive grade crossings, over two decades ago, Gordon, McGee, and Hooper

(1984) recommended that a full second be added to this design value to accommodate the 

85th percentile driver. With the ever-increasing number and percentage of aging drivers, 

the need to refocus attention on this issue is urgent.

Additional insight is provided by Leibowitz (1985), who showed that inaccurate 

judgments of train speed and distance may make drivers’ decisions to cross hazardous, 

due to perceptual illusions. Most drivers are not aware of the effects of the illusions of 

perspective, train size, and velocity (e.g., the bigger the object, the slower it appears to be 

moving), and this results in unsafe crossing decisions. Kinnan (1993) states that, in most

cases, the driver believes the decision to cross is a rational one; most motorists seriously 

underestimate the risk because they can’t properly gauge the speed of the train or its 

distance from the crossing. This problem will only be exacerbated by the age-related 
Handbook for Designing Roadways for the Aging Population 89

CHAPTER 6—HIGHWAY-RAIL GRADE CROSSING

decline in the ability to integrate speed and distance information, as reported by Staplin, 

Lococo, and Sim (1993) for the judgment of gaps at intersections. 

Finally, age-related hearing loss may contribute to a failure to detect a train approaching 

a crossing. According to government statistics (DHHS, 1994), approximately 30 to 35 

percent of people ages 65 to 75 have a hearing loss, increasing to 40 percent for persons 

over the age of 75. Janke (1994) reported that totally deaf males have more crashes than 

their non-deaf counterparts, and drivers who wear hearing aids have an increased risk of 

crashing compared to drivers who do not wear them (excluding individuals who formerly 

wore hearing aids then discarded them, who had an even worse driving record). Thus, 

auditory train signals may not be completely effective as a secondary warning system for 

visually impaired drivers or drivers who neglect to properly scan at rail crossings if they 

are also hearing impaired. At the same time, data show that audible warnings can help 

reduce nighttime crashes, as evidenced by the 195 percent increase in collisions in Florida 

as a result of a nighttime whistle ban between 10:00 p.m. and 6:00 a.m. (Kinnan, 1993). 

Raslear’s (1995) crash prediction model indicates that the use of the train whistle reduces 

the field of visual search from 180° to 10°, which, in turn, reduces the visual search 

time by a factor of 18. By decreasing visual search time, the train whistle decreases the 

probability of a crash.

Though few studies have directly measured the effectiveness of countermeasures for 

aging drivers in this arena, sufficient data exist to explain performance errors among the 

population at large to support highway-rail grade crossing design element treatments for 

passive crossing control devices that offer the greatest promise to improve safety for aging 

road users.
90 Handbook for Designing Roadways for the Aging Population

CHAPTER 6—HIGHWAY-RAIL GRADE CROSSING

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

Figure 68. Recommended placement of post-mounted delineators

Post-mounted

Delineators

 50 ft spacing

(with high performance 

retroreflective sheeting)

PROVEN PRACTICES

50 Passive Traffic Control Devices

A. Post-Mounted Delineators

For rural passive grade crossings that are not illuminated, it is 

recommended that the approach be delineated with post-mounted 

delineators spaced 50 ft or closer together on the right shoulder, from 

the location of the Railroad Advance Warning sign (W10-1) to the 

crossbuck, and extending an equal distance beyond the crossbuck (as 

illustrated in Figure 68).

References: RRX:4

The rationale and supporting evidence for these treatments can be found 

beginning on page 332 of this Handbook.
Handbook for Designing Roadways for the Aging Population 91

CHAPTER 6—HIGHWAY-RAIL GRADE CROSSING

1: most conservative

2: preferred among differing guides 

5: permissible only in accordance with MUTCD section 1A.10, 

Interpretations, Experimentations, and Changes

REFERENCES LEGEND See pages 3 and 4 for full description of codes and acronyms of cited design guides.

3: new application of current practice

4: more specific, detailed or stringent 

51 Lighting

A. Luminaire Type/Alignment

Illumination at a crossing may be effective in reducing nighttime 

collisions. Illuminating most crossings is technically feasible because 

more than 90 percent of all crossings have commercial power available. 

Illumination may be effective under the following conditions:

•	 Nighttime train operations.

•	 Low train speeds.

•	 Blockage of crossings for long periods at night.

•	 Collision history indicating that motorists often fail to detect trains or

traffic control devices at night.

•	 Horizontal and/or vertical alignment of highway approach such that

vehicle headlight beam does not fall on the train until the vehicle has 

passed the safe stopping distance.

•	 Long dark trains, such as unit coal trains.

•	 Restricted sight or stopping distance in rural areas.

•	 Humped crossings where oncoming vehicle headlights are visible

under trains.

•	 Low ambient light levels.

•	 A highly reliable source of power.

Luminaires may provide a low-cost alternative to active traffic control 

devices on industrial or mine tracks where switching operations are 

carried out at night.

Luminaire supports should be placed in accordance with the principles in 

the Roadside Design Guide and NCHRP Report 350. If they are placed in

the clear zone on a high-speed road, they should be breakaway.

References: RLH:4, RRX:4, MUTCD:4

The rationale and supporting evidence for these treatments can be found 

beginning on page 343 of this Handbook.
92 Handbook for Designing Roadways for the Aging Population
Handbook for Designing Roadways for the Aging Population 93

Rationale and 

Supporting Evidence

Overview

This section of the Handbook is organized in terms of the same category of highway 

features as the treatments: 

Chapter 7 – Intersections,

Chapter 8 – Interchanges,

Chapter 9 – Roadway Segments,

Chapter 10 – Construction/Work Zones, and 

Chapter 11 – Highway-Rail Grade Crossings.

Within each of these five chapters (category), subsections are organized in terms of 

design elements with unique geometric, operational, and/or traffic control characteristics, 

also consistent with the treatments. Also, the rationale for the additional “Promising 

Practices” treatments included under Intersections, Interchanges, Roadway Segments and 

Construction/Work Zones is presented at the end of their respective chapters.

At the beginning of each subsection within a class of highway features, reference material 

for a particular design element is introduced using a cross-reference table. This table 

relates the discussion in that subsection—as well as the associated treatments, presented 

earlier—to entries in standard reference manuals consulted by practitioners in this area. 

Principal among these reference manuals are the following:

•	 Manual on Uniform Traffic Control Devices, Editions 2009 and 2003. (Note to 

reader: if the discussion refers to MUTCD material found in the revisions to 

2003 published in 2007, the citation will be MUTCD 2003a.)

•	 A Policy on Geometric Design of Highways and Streets [the Green Book], 2011); 

•	 Traffic Engineering Handbook (TEH, 2009). 

Other standard references with more restricted applicability, which also appear in the 

cross-reference tables for selected design elements, include the following:

•	 Intersection Channelization Design Guide, NCHRP Report No. 279, (Neuman, 

1985).

PART II 
94 Handbook for Designing Roadways for the Aging Population

•	 Roundabouts: An Informational Guide, Second Edition, NCHRP Report 672, 

(Rodegerdts, et al., 2010).

•	 Roundabouts: An Informational Guide (FHWA, 2000).

•	 Roadway Lighting Handbook (FHWA, 1978). 

•	 Railroad-Highway Grade Crossing Handbook (FHWA, 2007).

•	 Highway Capacity Manual (TRB, 2010).

•	 A Guide for Reducing Collisions Involving Older Drivers, NCHRP Report No. 

500-Volume 9, (Potts et al, 2004).

Material in this part of the Handbook represents, to as great an extent as possible at the 

time of its development, the results of empirical work with aging driver or pedestrian 

samples for investigations with the specific highway features of interest. Naturalistic 

and controlled field studies were given precedence, augmented by laboratory simulations 

employing traffic stimuli and relevant situational cues. Crash data are cited as 

appropriate. In addition, some citations reference studies showing effects of design 

changes, where the predicted impact on (aging) driver performance is tied logically to 

the results of research on age-related differences in detection, comprehension, response 

selection, maneuver execution, or other capability needed to safely negotiate the design 

element.
Handbook for Designing Roadways for the Aging Population 95

CHAPTER 7

Intersections

The following discussion presents the rationale and supporting evidence for Handbook

treatments pertaining to these 24 proven and promising practices:

Proven Practices

1. Intersecting Angle (Skew)

2. Receiving Lane (Throat) Width

3. Channelization

4. Intersection Sight Distance 

5. Offset Left-Turn Lanes 

6. Delineation of Edge Lines and Curbs 

7. Curb Radius 

8. Left-Turn Traffic Control for Signalized Intersections 

9. Right-Turn Traffic Control for Signalized Intersections 

10. Street Name Signs 

11. Stop and Yield Signs 

12. Lane Assignment on Intersection Approach 

13. Traffic Signals 

14. Intersection Lighting 

15. Pedestrian Crossings 

16. Roundabouts

Promising Practices

17. Improved Design for Right-Turn Channelization

18.	 Combination Lane-Use/Destination Overhead Guide Signs

19. Signal Head Visibilty

20. High-Visibility Crosswalks

21. Supplemental Pavement Markings for Stop and Yield Signs 

22. Reduced Left-Turn Conflict Intersections 

23. Accessible Pedestrian Signal (APS) Treatments

24. Flashing Yellow Arrow
96 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

1 Intersecting Angle (Skew)

Table 9. Cross-References of Related Entries for Intersecting Angle (Skew).

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500- 

Volume 9

(2004)

NCHRP 279 

Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Sections 2B.54, 

4D.06, 4D.09, 

4D.12, 4D.13

Pg. 5-9, Final Paragraph

Pg. 9-5, 3rd bullet item

Pg. 9-10, Final Paragraph

Pgs. 9-19, 9-20, Sect. 9.3.3 Multileg Intersections

Pgs. 9-25 through 9-27, Sect. 9.4.2 Alignment

Pgs. 9-57 through 9-63, Tables 9-15 and 9-16

Pg. 9-82, Sect. on Oblique-Angle Turns

Pgs. 9-97 through 9-99, Sects. on Divisional 

Islands, Refuge Islands, & Island Size and 

Designation

Pg. 9-98 Figure 9-37

Pg. 9-112, Sect. on Oblique-Angle Turns with 

Corner Islands

Pgs. 9-113 through 9-114 Table 9-18

Pg. 9-54, Sect. 9.5.4 Effect of Skew

Pg. 9-55, Figure 9-22

Pgs. 9-151 through 9-153, Sect. 9.8.5 Effect of 

Skew

Pg. 9-152 through 9-153, Table 9-28

Pgs. V-25-V-26, 

Sect. on Strategy

3.1 B10: Reduce 

Intersection Skew 

Angle

Pg. 19, Top fig.

Pg. 21, Item 5

Pg. 25, Para. 2

Pg. 30, Para. 1 & top three 

figs.

Pg. 31, Para. 3 & bottom 

left fig.

Pgs. 42-44, Sect. on Angle 

of Intersection

Pg. 45, Fig. 4-5

Pg. 71, Top two figs.

Pgs. 100-105, Intersct. 

Nos. 7 -9

Pgs. 148-149, Intersct. 

No. 35

Pg. 243, 5th Principle

Pg. 243, Sect. on 

Alignment Design

PROVEN PRACTICES

There is broad agreement that right-angle intersections are the preferred design. 

Decreasing the angle of the intersection makes detection of and judgments about 

potential conflicting vehicles on crossing roadways much more difficult. In addition, 

the amount of time required to maneuver through the intersection increases, for both 

vehicles and pedestrians, due to the increased pavement area. However, there is some 

inconsistency among reference sources concerning the degree of skew that can be 

safely designed into an intersection. The Green Book states that although a right-angle 

crossing normally is desired, an angle of 60 degrees provides most of the benefits that are 

obtained with a right-angle intersection. Subsequently, factors to adjust intersection sight 

distances for skewness are suggested for use only when angles are less than 60 degrees 

(AASHTO, 2011). However, another source on subdivision street design states that: 

“Skewed intersections should be avoided, and in no case should the angle be less than 75 

degrees” (Institute of Transportation Engineers [TEH], 1984). The Traffic Engineering 

Handbook (TEH, 1999) states that: “Crossing roadways should intersect at 90 degrees 

if possible, and not less than 75 degrees.” It further states that: “Intersections with 
Handbook for Designing Roadways for the Aging Population 97

CHAPTER 7—INTERSECTIONS

severe skew angles (e.g., 60 degrees or less) often experience operational or safety problems. 

Reconstruction of such locations or institution of more positive traffic control such as 

signalization is often necessary.” With regard to intersection design issues on two-lane rural 

highways, TEH (1999) states that: “Skew angles in excess of 75 degrees often create special 

problems at stop-controlled rural intersections. The angle complicates the vision triangle for 

the stopped vehicle; increases the time to cross the through road; and results in a larger, more 

potentially confusing intersection.”

Skewed intersections pose particular problems for aging drivers. Many aging drivers 

experience a decline in head and neck mobility, which accompanies advancing age and may 

contribute to the slowing of psychomotor responses. Joint flexibility, an essential component 

of driving skill, has been estimated to decline by approximately 25 percent in aging adults 

due to arthritis, calcification of cartilage, and joint deterioration (Smith and Sethi, 1975). A 

restricted range of motion reduces an aging driver’s ability to effectively scan to the rear and 

sides of his or her vehicle to observe blind spots, and similarly may be expected to hinder 

the timely recognition of conflicts during turning and merging maneuvers at intersections 

(Ostrow, Shaffron, and McPherson, 1992). For aging drivers, diminished physical capabilities 

may affect their performance at intersections designed with acute angles by requiring them to 

turn their heads further than would be required at a right-angle intersection. This obviously 

creates more of a problem in determining appropriate gaps. For aging pedestrians, the longer 

exposure time within the intersection becomes a major concern.

Isler, Parsonson, and Hansson (1997) measured the maximum head rotation of 20 drivers in 

each of four age groups: less than age 30; ages 40 to 59; ages 60 to 69; and age 70 and older, 

as well as their horizontal peripheral visual field. The oldest subjects exhibited an average 

decrement of approximately one-third of head range of movement compared with the 

youngest group of subjects. The mean maximum head movement (in one direction) was 86 

degrees for the youngest drivers, 72 degrees for drivers ages 40 to 59, 67 degrees for drivers 

ages 60 to 69, and 59 degrees for drivers age 70+. In addition, the percentage of drivers with 

less than 30 degrees of horizontal peripheral vision increased with increases in age, from 15 

percent of the younger driver sample to 65 percent of the drivers age 70+. Three of the oldest 

drivers had less than 50 degrees of head movement and two of these drivers also had less than 

20 degrees of horizontal peripheral vision. 

In a survey of aging drivers conducted by Yee (1985), 35 percent of the respondents reported 

problems with arthritis and 21 percent indicated difficulty in turning their heads to scan 

rearward while driving. Excluding vision/visibility problems associated with nighttime 

operations, difficulty with head turning placed first among all concerns mentioned by aging 

drivers participating in a focus group conducted by Staplin, Harkey, Lococo, and Tarawneh 

(1997) to examine problems in the use of intersections where the approach leg meets the main 

road at a skewed angle, and/or where channelized right-turn lanes require an exaggerated 

degree of head/neck rotation to check for traffic conflicts before merging. Comments 

about this geometry centered around the difficulty aging drivers experience turning their 

heads at angles less than 90 degrees to view traffic on the intersecting roadway, and several 

participants reported an increasing reliance on outside rearview mirrors when negotiating 

highly skewed angles. However, they reported that the outside mirror is of no help when the 

roads meet at the middle angles (e.g., 40 to 55 degrees) and a driver is not flexible enough to 

physically turn to look for traffic. 
98 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

In an observational field study conducted as a part of the same project, Staplin et al. 

(1997) found that approximately 30 percent of young/middle-aged drivers (ages 25–45) 

and young-old drivers (ages 65–74) used their mirrors in addition to making head checks 

before performing a right-turn-on-red (RTOR) maneuver at a skewed intersection (a 

channelized right-turn lane at a 65-degree skew). By comparison, none of the drivers age 

75 and older used their mirrors; instead, they relied solely on information obtained from 

head/neck checks. In this same study, it was found that the likelihood of a driver making 

an RTOR maneuver is reduced by intersection skew angles that make it more difficult for 

the driver to view conflicting traffic.

The practical consequences of restricted head and neck movement on driving 

performance at T-intersections were investigated by Hunter-Zaworski (1990), using a 

simulator to present videorecorded scenes of intersections with various levels of traffic 

volume and sight distance in a 180-degree field of view from the driver’s perspective. 

Drivers in two subject groups, ages 30–50 and 60–80, depressed a brake pedal to watch 

a video presentation (on three screens), then released the pedal when it was judged safe 

to make a left turn; half of each age group had a restricted range of neck movement 

as determined by goniometric measures of maximum (static) head-turn angle. Aside 

from demonstrating that skewed intersections are hazardous for any driver with a neck 

movement impairment, this study found that maneuver decision time increased with 

both age and level of impairment. Thus, the younger drivers in this study were able to 

compensate for their impairments, but aging drivers both with and without impairments 

were unable to make compensations in their (simulated) intersection response selections.

Older and younger driver performance was compared at 10 intersections (5 improved 

and 5 unimproved) to test the effectiveness of FHWA’s recommendations for intersection 

design to accommodate aging road users (Classen et al., 2007). Thirty-nine drivers 

ages 25 to 45 and 32 drivers ages 65 to 85 drove an instrumented vehicle on urban and 

residential streets in Gainesville, FL, accompanied by a front-seat driving evaluator who

recorded behavioral errors. The course took approximately 1 hour to complete, and 

included driving through 5 sets of improved and unimproved intersections. One set of 

intersections included roadways that met at a 90-degree angle (improved) and roadways 

that met at an angle less than 75 degrees (unimproved). Both kinematic data (vehicle 

control responses during the turn phase including longitudinal and lateral accelerations, 

yaw, and speed) and behavioral data (driving errors including vehicle position, lane 

maintenance, speed, yielding, signaling, visual scanning, adjustment to stimuli/traffic 

signs, and left-turn gap acceptance) were recorded. With the exception of speed during 

the turn, kinematic measures showed significantly better performance associated with 

the improved intersection, and there were significantly fewer behavioral errors with the 

improved design. The improved design was associated with lesser side forces, indicating 

improved lateral stability, and fewer deviations from the idealized curved path during the 

turn, indicating greater vehicle stability. There were no significant differences between 

age groups for either the kinematics measures or the behavioral measure. 

These research findings reinforce the desirability of providing a 90-degree intersection 

geometry and support the TEH (1984) recommendation establishing a 75-degree 

minimum as a practice to accommodate age-related performance deficits, benefiting both 

older as well as younger drivers.
Handbook for Designing Roadways for the Aging Population 99

CHAPTER 7 CHAPTER 7—INTERSE INTERSECTIONS

2 Receiving Lane (Throat) Width

Table 10. Cross-References of Related Entries for Receiving Lane (Throat) Width. 

Applications in Standard Reference Manuals

AASHTO

Green Book

(2011)

NCHRP 279 Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Pgs. 3-97 through 3-106, Sect. 3.3.11 Widths for 

Turning Roadways at Intersections

Pg. 9-55, Section 9.6.1 Types of Turning Roadways, 

Para. 1 

Pg. 9-97, Final Two Paragraphs

Pg. 9-98, Figure 9-37

Pg. 10, Table 2-4

Pg. 57, Para. 5, 1st Bullet

Pg. 58, Fig. 4-20

Pg. 63, Sect. on Lane Widths

Pg. 69, Sect. on Width of Roadways

Pg. 73, Fig. 4-29

Pg. 107, Fig. c

Pg. 113, Fig. a

Pg. 115, Figs. d- e

Pg. 120, Item 3

Pg. 122, Item 2

Pg. 125, Intersct. No. 19

Pg. 381, Para. 2

Lane widths are addressed in the Intersection Channelization Design Guide (Neuman,

1985). A recommendation for (left) turning lanes, which also applies to receiving lanes, 

is that “12-ft widths are desirable, (although) lesser widths may function effectively and 

safely. Absolute minimum widths of 9 ft should be used only in unusual circumstances, 

and only on low-speed streets with minor truck volumes.” Similarly, the TEH (1984) 

guidelines suggest a minimum lane width of 11 ft and specify 12 ft as desirable. These 

guidelines suggest that wider lanes be avoided due to the resulting increase in pedestrian 

crossing distances. However, the TEH guidelines provide a range of lane widths at 

intersections from 9 ft to 14 ft, where the wider lanes would be used to accommodate 

larger turning vehicles, which have turning paths that sweep a path from 13.6 ft for a 

single-unit truck or bus up to 20.6 ft for a semitrailer. Thus, wider (12-ft) lanes used to 

accommodate (right) turning trucks also are expected to benefit (left) turning drivers. 

Further increases in lane width for accommodation of heavy vehicles may result in 

unacceptable increases in (aging) pedestrian crossing times, however.

Results of field observation studies conducted by Firestine, Hughes, and Natelson (1989) 

found that trucks turning on urban roads encroached into other lanes on streets with 

widths of less than 12 ft. They noted that on rural roads, lanes wider than 12 ft or 13 ft 

allowed oncoming vehicles on the cross street to move further right to avoid trucks, and 

shoulders wider than 4 ft allowed oncoming vehicles a greater margin of safety. Lane 

widths are addressed in the Intersection Channelization Design Guide (Neuman, 1985). 

A recommendation for (left) turning lanes, which also applies to receiving lanes, is that 

“12-ft widths are desirable, (although) lesser widths may function effectively and safely. 

Absolute minimum widths of 9 ft should be used only in unusual circumstances, and 

only on low-speed streets with minor truck volumes.” 
100 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Figure 69. Turning Path Taken by Left-Turning Vehicles (from Staplin et al., 1997)

Turning Path Descriptors

1 Encroach into Opposing CrossTraffic Stream

2, 3 

and 4

Proper Turning from Different 

Points within the Intersection

5 Left Turn from a Position Requiring 

a Greater-than-90-Degree Turn to 

Enter the Cross-Street

Design recommendations for lane width at intersections follow from consideration of 

vehicle maneuver requirements and their demands on drivers. Positioning a vehicle 

within the lane in preparation for turning has long been recognized as a critical task 

(McKnight and Adams, 1970). Swinging too wide to lengthen the turning radius and

minimize rotation of the steering wheel (“buttonhook turn”) while turning left or right 

is a common practice of drivers who lack strength (including aging drivers) or are 

physically limited (McKnight and Stewart, 1990).

Two factors can compromise the ability of aging drivers to remain within the boundaries 

of their assigned lane during a left turn. One factor is the diminishing ability to share 

attention (i.e., to assimilate and concurrently process multiple sources of information 

from the driving environment). The other factor involves the ability to turn the steering 

wheel sharply enough, given the speed at which they are traveling, to remain within the 

boundaries of their lanes. Some aging drivers seek to increase their turning radii by 

initiating the turn early and rounding-off the turn. The result is either to cut across the 

apex of the turn, conflicting with vehicles approaching from the left, or to intrude upon a 

far lane in completing the turn. 

In an observational field study conducted to determine how aging drivers (age 65 

and older) compare with younger drivers during left-turn operations under varying 

intersection geometries, one variable that showed significant differences in older and 

younger driver behavior was turning path (Staplin, Harkey, Lococo, and Tarawneh, 

1997). Aging drivers encroached into the opposing lane of the cross street (see Figure 69, 

turning path trajectory number 1) when making the left turn more often than younger 

drivers at the location where the throat width (equivalent to the lane width) measured 

12 ft. Where the throat width measured 23 ft, which consisted of a 12-ft lane and an 11-ft 
Handbook for Designing Roadways for the Aging Population 101

CHAPTER 7—INTERSECTIONS

shoulder, there was no significant difference in the turning paths. The narrower throat 

width resulted in higher encroachments by aging drivers, who physically may have more 

difficulties maneuvering their vehicles through smaller areas. 

In a study comparing older and younger driver performance at improved and 

unimproved intersections to test the effectiveness of FHWA’s recommendations for 

intersection design to accommodate aging road users, Classen et al. (2007) included an 

intersection where a left-turning vehicle had an extended receiving lane width of at least 

12 ft and a forgiving shoulder of 4 ft and an intersection where the receiving lane was less 

than 12 ft and there was no forgiving shoulder. In this study, 39 drivers ages 25 to 45, and 

32 drivers ages 65 to 85 drove an instrumented vehicle on urban and residential streets in 

Gainesville, FL, accompanied by a front-seat driving evaluator who recorded behavioral

errors. The course took approximately 1 hour to complete, and included driving through 

five sets of improved and unimproved intersections. Both kinematic data (vehicle 

control responses during the turn phase including longitudinal and lateral accelerations, 

yaw, and speed) and behavioral data (driving errors including vehicle position, lane 

maintenance, speed, yielding, signaling, visual scanning, adjustment to stimuli/traffic 

signs, and left-turn gap acceptance) were recorded. There were significantly fewer 

behavioral errors with the improved design. The improved design was associated with 

lesser side forces and fewer deviations from the idealized curved path during the turn, 

indicating improved lateral control and greater vehicle stability. The increased speed 

at the improved intersection indicated greater control and confidence during turning. 

There were no significant differences between age groups for either the kinematics 

measures or the behavioral measures. The authors concluded that the guidelines for 

extended receiving lane width at intersections are effective for driver safety, and improve 

the performance of older as well as younger drivers. 

In a retrospective site-based review and crash analysis, that included a detailed 

investigation of over 400 crashes involving drivers age 65 years and older at 62 sites in 

Australia, absence of a minimum receiving lane width of 12 ft with a 4 ft shoulder was a 

contributing factor in 8 percent of the crashes (Oxley, et al., 2006). 

These data sources indicate that a 12-ft lane width provides the most reasonable tradeoff 

between the need to accommodate aging drivers, as well as larger turning vehicles, 

without penalizing the aging pedestrian in terms of exaggerated crossing distance.
102 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

3 Channelization 

The spatial visual functions of acuity and contrast sensitivity are important in the ability 

to detect/recognize downstream geometric features such as pavement width transitions, 

channelized turning lanes, island and median features across the intersection, and any 

non-reflectorized raised elements at intersections. Visual acuity (the ability to see highcontrast, high-spatial-frequency stimuli, such as black letters on a white eye chart) shows 

a slow decline beginning at approximately age 40, and marked acceleration at age 60 

(Richards, 1972). Approximately 10 percent of men and women between ages 65 and 75 

have (best corrected) acuity worse than 20/30, compared with roughly 30 percent over 

the age of 75 (Kahn, et al., 1977). A driver’s response to intersection geometric features

is influenced in part by the processing of high-spatial-frequency cues—for example, the 

characters on upstream advisory signs—but it is the larger, often diffuse edges defining 

lane and pavement boundaries, curb lines, and raised median barriers that are the targets 

with the highest priority of detection for safety. Aging persons’ sensitivity to visual 

contrast (the ability to see objects of various shapes and sizes under varying levels of 

contrast) also declines beginning around age 40, then declines steadily as age increases 

(Owsley, Sekuler, and Siemsen, 1983). Poor contrast sensitivity has been shown to relate 

to increased crash involvement for drivers age 66 and older, when incorporated into a 

battery of vision tests also including visual acuity and horizontal visual field size (Decina 

and Staplin, 1993).

The effectiveness of channelization from a safety perspective has been documented in 

several studies. An evaluation of Highway Safety Improvement Program projects showed 

that channelization produced an average benefit-cost ratio of 4.5 (FHWA, 1996). In this 

evaluation, roadway improvements consisting of turning lanes and traffic channelization 

resulted in a 47 percent reduction in fatal crashes, a 26 percent reduction in nonfatal 

injury crashes, and a 27 percent reduction in combined fatal plus nonfatal injury crashes, 

at locations where before and after exposure data were available. 

One of the advantages of using curbed medians and intersection channelization is that it 

provides a better indication to motorists of the proper use of travel lanes at intersections. 

In a set of studies performed by the California Department of Public Works investigating 

the differences in crash experience with raised channelization versus channelization 

accomplished through the use of flush pavement markings, the findings were as 

follows: raised traffic islands are more effective than flush marked islands in reducing 

frequencies of night crashes, particularly in urban areas; and little difference is noted 

in the effectiveness of raised versus marked channelizing islands at rural intersections 

(Neuman, 1985). 

One of the most common uses of channelization is for the separation of left-turning 

vehicles from the through-traffic stream. The safety benefits of left-turn channelization 

have been documented in several studies. A study by McFarland, et al. (1979) showed 

that crashes at signalized intersections where a left-turn lane was added, in combination 

with and without a left-turn signal phase, were reduced by 36 percent and 15 percent, 

respectively. At non-signalized intersections with marked channelization separating 

the left-turn lane from the through lane, crashes were reduced for rural, suburban, and 

urban areas by 50, 30, and 15 percent, respectively. When raised channelization devices 
Handbook for Designing Roadways for the Aging Population 103

CHAPTER 7—INTERSECTIONS

Table 11. Cross-references of Related Entries for Channelization.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

FHWA Lighting 

Handbook (2012)

NCHRP 500- 

Volume 9

(2004)

NCHRP 279 

Intersection

Channelization

Design Guide 

(1985)

Traffic Engineering 

Handbook

(2009)

Sections 1A.13, 

3B.03, 3B.05, 

3B.09, 3B.10, 

3B.20, 3B.23, 

3C.02, 3C. 03, 3E. 

01, 3G.01, 3H.01, 

3I.01 through 

3I.06, 5G.03

Pg. 4-35, Para. 4

Pg. 7-31, Final two paragraphs

Pg. 7-32, Fig. 7-7

Pgs. 9-12 through 9-14, Sect. 

on Channelized Three-Leg 

Intersections

Pgs. 9-15 through 9-19, Sect. on 

Channelized Four-Leg Intersections

Pgs. 9-95 through 9-112, 

Sects. on Channelizing Islands, 

Divisional Islands, Refuge Islands, 

Island Size and Designation, 

Island Delineation and Approach 

Treatment & Right-Angle Turns 

With Corner Islands

Pgs. 9-8 through 9-10, 

Introductory portion of Sect. 

9.3 Types and Examples of 

Intersections Pgs. 9-92 through 

9-94, Sect. 9.6.2 Channelization

Pgs. 9-182 through 9-183 Sect. 

9.11.7 Midblock Left Turns on 

Streets with Flush Medians

Pg. 71, Para. 1-3

Pg. 77, Fig. 47

Pgs. V-23 through V-25, 

Sect. on Strategy 3.1 

B9: Replace Painted 

Channelization with Raised 

Channelization (P)

Pg. 1, Paras. 2-3

Pg. 21, Fig. 3-1

Pg. 24, Bottom fig.

Pg. 25, Para. 3

Pg. 26, Top fig.

Pg. 28, Middle fig.

Pg. 32, Middle fig.

Pg. 34, Para. 1 & bottom 

fig.

Pg. 35, Bottom left fig.

Pg. 38, Middle fig.

Pg. 39, Paras. 2-3 & top 

two figs.

Pg. 69, Sect. on Traffic 

Islands

Pg. 74, Fig. 4-30

Pgs. 75-76, Para. 1 on 1st 

pg. & Sects. on Guidelines 

for Design of Traffic Islands, 

Guidelines for Selection of 

Island Type, & Guidelines 

for Design of Median 

Islands

Pg. 79, Fig. 4-34

Pgs. 94- 95, Intersct. No. 4

Pgs. 102-103, Intersct. 

No. 8

Pgs. 106-113, Intersct. 

Nos. 10-13

Pgs. 116-117, Intersct. 

No. 15

Pgs. 132-133, Intersct. 

No. 22

Pgs. 138-139, Intersct. 

No. 29

Pgs. 148-153, Intersct. 

Nos. 35-37

Pgs. 243, Sect. on Principles 

of Channelization

Pg. 247, Sect. on Traffic 

Island Design

Pg. 381, Para. 1
104 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

were used, the crash reductions were 60, 65, and 70 percent in rural, suburban, and urban 

areas, respectively. Consistent findings were reported in Hagenauer, et al. (1982).

Important considerations in choosing to implement raised versus marked channelization 

include operating speed and type of maneuver (i.e., left turn versus right turn). Left-turn 

channelization separating through and turning lanes may, because of its placement, 

constitute a hazard when a raised treatment is applied, especially on high-speed facilities. 

Detection and avoidance of such hazards requires visual and response capabilities known 

to decline significantly with advancing age.

In this same vein, it was reported in Transportation Research Circular 382

(Transportation Research Board, 1991) that the aging driver, having poorer vision, slower 

physical reaction time, lower degree of awareness, and reduced ability to maneuver the 

vehicle, is more likely to be negatively affected by a raised median than is the average 

driver; and, because medians are fixed objects, when they are struck they pose a serious 

threat of loss of control, especially for aging drivers. The typical curbed median offers 

low to no contrast with the adjacent pavement and is difficult to reflectorize at night. 

Low-beam headlight limitations coupled with reduced vision of the aging driver 

compounds the visibility problem. In addition, raised medians and raised corner islands, 

when used together, often create turning path options at complex intersections that are 

confusing to the average driver, and disproportionately so for the aging one. Thus, to 

realize the safety benefits channelization can provide, it is particularly important to 

ensure the visibility of raised surfaces for (aging) drivers with diminished vision, so these 

road users can detect the channelizing devices and select their paths accordingly.

Another benefit in the use of channelization is the provision of a refuge for pedestrians. 

Refuge islands are a design element that can aid aging pedestrians who have slow walking 

speeds. With respect to the Hagenauer et al. (1982) study cited earlier, Hauer (1988) 

stated that because channelization in general serves to simplify an otherwise ambiguous 

and complex situation, the channelization of an existing intersection might enhance 

both the safety and mobility of aging persons, as well as enhance the safety of other 

pedestrians and drivers. However, in designing a new intersection, he stated that the 

presence of islands is unlikely to offset the disadvantage of large intersection size for the 

pedestrian.

Staplin, et al. (1997) conducted a field study evaluating four right-turn lane geometries to 

examine the effect of channelized right-turn lanes and the presence of skew on right-turn 

maneuvers made by drivers of different ages. One hundred subjects divided across three 

age groups drove their own vehicles around test routes using the local street network in 

Arlington, VA. The three age groups were ages 25–45, ages 65–74, and age 75 and older. 

As diagrammed in Figure 70, the four right-turn lane geometries were:

a) A non-channelized 90-degree intersection where drivers had the chance to 

make a right turn on red (RTOR) around a 40-ft radius. This site served as 

control geometry to examine how channelized intersections compare with nonchannelized intersections.

b) A channelized right-turn lane at a 90-degree intersection with an exclusive use 

(acceleration) lane on the receiving street. Under this geometric configuration, 

drivers did not need to stop at the intersection and they were removed from 
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CHAPTER 7—INTERSECTIONS

the conflicting traffic upon entering the cross street. They had the opportunity 

to accelerate in their own lane on the cross street and then change lanes 

downstream when they perceived that it was safe to do so.

c) A channelized right-turn lane at a 65-degree skewed intersection without an 

exclusive use lane on the receiving street.

d) A channelized right-turn lane at a 90-degree intersection without an exclusive 

use lane on the receiving street. Under this geometry, drivers needed to check 

the conflicting traffic and complete their turn into a through traffic lane on the 

cross street. 

The right-turn maneuver at all locations was made against two lanes carrying through 

(conflicting) traffic. The two through lanes were the only ones that had a direct 

effect on the right-turn maneuver. All intersections were located on major or minor 

arterials within a growing urban area, where the posted speed limit was 35 mph. All 

intersections were controlled by traffic signals with yield control on the three channelized 

intersections.

The results indicated that right-turn channelization affects the speed at which drivers 

make right turns and the likelihood that they will stop before making a RTOR. Drivers, 

especially younger drivers (ages 25–45), turned right at speeds 3–5 mph higher on 

intersection approaches with channelized right-turn lanes than they did on approaches 

with non-channelized right-turn lanes.

At the non-channelized intersection, 22 percent of drivers age 25–45, 5 percent of the 

drivers age 65–74, and none of the drivers age 75 and older performed a RTOR without 

a stop. On approaches with channelized right-turn lanes, drivers age 25–74 were much 

less likely to stop before making a RTOR. Where an acceleration lane was available, 

65 percent of young/middle-aged drivers continued through without a complete stop, 

compared with 55 percent of drivers age 65–74 and 11 percent of drivers 75 and older. 

Female drivers age 75 and older always stopped before a RTOR. The increased mobility 

exhibited by the two younger groups of drivers at the channelized right-turn lane 

locations was not, however, exhibited by the drivers age 75 and older, who stopped in 

19 of the 20 turns executed at the channelized locations. Also, questionnaire results 

indicated drivers perceived that making a right turn on an approach with a channelized 

Figure 70. Intersection Geometries Examined in a Field Study of Right-Turn Channelization (Staplin et al., 1997)
106 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

right-turn lane without an acceleration lane on the cross street was more difficult than at 

other locations, and even more difficult than at skewed intersections.

Regarding channelization for mid-block left-turn treatments, Bonneson and McCoy 

(1997) evaluated the safety and operational effects of three mid-block left-turn 

treatments: raised curb medians; two-way, left turn-lanes; and undivided cross sections. 

Traffic flow data were collected during 32 field studies in eight cities in four States, and 

3-year crash histories for 189 street segments were obtained from cities in two States. The 

studies were conducted on urban or suburban arterial segments, and therefore treatments 

can only be applied to such environments that include the following criteria: traffic 

volume exceeding 7,000 vehicles per day; speed limit between 30 and 50 mph); spacing 

of at least 350 ft between signalized intersections; direct access from abutting properties; 

no angle curb parking (parallel parking is acceptable); located in or near a populated 

area (e.g., population of 20,000 or more); no more than six through lanes (three in each 

direction); and arterial length of at least 0.75 mi.

In terms of annual delays to major-street left-turn and through vehicles, the raised-curb 

treatment has slightly higher delays than the TWLTL treatment at the highest left-turn 

and through volumes, which results from the greater likelihood of bay overflow for the 

raised-curb median treatment under high-volume conditions. The undivided cross 

section has significantly higher delays than the raised-curb treatment for all nonzero 

combinations of left-turn and through volume.

Looking at crash frequencies as a function of mid-block channelization treatment, the 

raised curb median treatment is associated with the fewest crashes of all three treatment 

types. Differences between the crash frequencies for TWLTL treatments vs. undivided 

cross sections are affected by whether or not parallel parking is allowed on the undivided 

cross section. When parallel parking is allowed on the undivided cross section, the 

undivided cross section is associated with significantly more crashes than the TWLTL 

treatment. However, when parallel parking is not allowed, the TWLTL has about the 

same crash frequency as the undivided cross section at lower traffic volumes.

In general, at mid-block locations, the raised-curb median treatment was associated with 

fewer crashes than the undivided cross section and TWLTL, especially for average daily 

traffic demands greater than 20,000 vehicles per day. Also, a benefit of the raised-curb 

median is that it provides a pedestrian refuge.

Bonneson and McCoy (1997) provide a set of six tables to use as guidelines in considering 

the conversion of an undivided cross section to a raised curb median, or to a TWLTL, 

and conversion from a TWLTL to a raised-curb median treatment. In these tables, it is 

recommended that the existing treatment remain in place when the benefit-cost ratio (in 

terms of delay and safety) is less than 1.0, and when the benefit-cost ratio exceeds 2.0, it is 

recommended that the engineer consider adding the alternative treatment.

Bonneson and McCoy (1997) do not report crash frequencies by driver age for one 

treatment versus another. However, approximately one-fifth of the aging drivers 

participating in focus group studies conducted by Staplin, et al. (1997) reported that 

using center two-way left turn lanes (TWLTL), was confusing, risky, and made them 

uncomfortable, because at times they came face-to-face with an opposing left-turner, 
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CHAPTER 7—INTERSECTIONS

and both drivers were stranded. Also mentioned was the difficulty seeing the pavement 

markings in poor weather (night, fog, rain) when they are less visible, and particularly 

when they are snow-covered. Drivers referred to TWLTL’s as “suicide lanes.” In the same 

research study, Staplin et al. (1997) reported on a crash analysis that revealed ways in 

which aging drivers failed to use a TWLTL correctly: a TWLTL was not used for turning 

at all; and the TWLTL was entered too far in advance of where the turn was to be made. 

4 Intersection Sight Distance

Because intersections define locations with the highest probability of conflict between 

vehicles, adequate sight distance is particularly important. Not surprisingly, a number 

of studies have shown that sight distance problems at intersections usually result in a 

higher crash rate (Mitchell, 1972; Hanna, Flynn, and Tyler, 1976; David and Norman, 

1979). The need for adequate sight distance at an intersection is best illustrated by a quote 

from the Green Book: “The driver of a vehicle approaching an intersection should have 

an unobstructed view of the entire intersection, including any traffic-control devices, 

and sufficient lengths along the intersecting highway to permit the driver to anticipate 

and avoid potential collisions” (AASHTO, 2011, p. 9-28). AASHTO values (for both 

uncontrolled and stop-controlled intersections) for available sight distance are measured 

from the driver’s eye height (currently 3.5 ft above the roadway surface) to the object to be 

seen (currently 3.5 ft above the surface of the intersecting road). 

Table 12. Cross-references of Related Entries for Intersection Sight Distance.

Applications in Standard Reference Manuals

AASHTO

Green Book

(2011)

FHWA 

Lighting Handbook 

(2012)

NCHRP 279 

Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Pgs. 3-6 through 3-8, Sect. 3.2.3 Decision Sight 

Distance

Pg. 5-21, Para. 6

Pg. 5-22, Para. 1

Pg. 6-9, Para. 7

Pg. 9-25, Para. 2

Pg. 9-27, Para. 2

Pgs. 9-27 through 9-28, Sect. 9.4.3 Profile

Pgs. 9-28 through 9-55, Sect. 9.5 Intersection Sight 

Distance

Pg. 9-123, Sect. 9.6.7 Stopping Sight Distance at 

Intersections for Turning Roadways

Pgs. 9-186 through 9-192, Sect. 9.12.4 Sight 

Distance

Pgs. 10-104 through 10-105, Sects. on Terminal 

Location and Sight Distance, Ramp Terminal Design, 

& Distance Between a Free-flow Terminal and 

Structure

Pg. 20, Figure 8 Pg. 1, Item , 1st bullet

Pg. 10, Table 2-4

Pgs. 13-14, Sect. on Sight 

Distance

Pg. 15, Para. 1

Pg. 27, Bottom right fig.

Pg. 30, 2nd fig. from bottom

Pg. 31, Para. 3

Pg. 35, Para. 3 & bottom 

right fig.

Pg. 44, Para. 6, item 1 

Pg. 45, Table 4-2

Pg. 63, Para. 3, item 3

Pg. 75, Last item 4

Pgs. 99-103, Intersct. Nos. 

6-8

Pgs. 106-111, Intersct. Nos. 

10-12

Pgs. 223-224, Sect. on 

Intersection Sight Distance

Pg. 466, Para. 3

Pg. 631, Sect. on Intersection 

Sight Distance
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CHAPTER 7—INTERSECTIONS

Sight distances at an intersection can be reduced by a number of deficiencies, including 

physical obstructions too close to the intersection, severe grades, and poor horizontal 

alignment. The alignment and profile of an intersection have an impact on the sight 

distance available to the driver and thus affect the ability of the driver to perceive 

the actions taking place both at the intersection and on its approaches. Since proper 

perception is the first key to performing a safe maneuver at an intersection, it follows that 

sight distance should be maximized; this, in turn, means that the horizontal alignment 

should be straight and the gradients as flat as practical. Horizontal curvature on the 

approaches to an intersection makes it difficult for drivers to determine appropriate 

travel paths, because their visual focus is directed along lines tangential to these paths. 

Kihlberg and Tharp (1968) showed that crash rates increased 35 percent for highway

segments with curved intersections over highway segments with straight intersections. 

Limits for vertical alignment at intersections suggested by AASHTO (2011) and Institute 

of Transportation Engineers (1984) are 3 and 2 percent, respectively.

Harwood, et al. (1993) stated that the provision of intersection sight distance (ISD) 

is intended to give drivers an opportunity to obtain the information they need to 

make decisions about whether to proceed, slow, or stop in situations where potentially 

conflicting vehicles may be present. They noted that while it is desirable to provide a 

reasonable margin of safety to accommodate incorrect or delayed driver decisions, there 

are substantial costs associated with providing sight distances at intersections; therefore, 

it is important to understand the derivation of ISD requirements and why it is reasonable 

to expect a safety benefit from tailoring this design parameter to the needs of aging 

drivers.

Traditionally, the need for—as well as the basis for calculating—sight distance at 

intersections has rested upon the notion of the sight triangle. As excerpted from NCHRP 

Report 383, the diagram shown in Figure 71 effectively illustrates how different driver 

decisions during a (minor) road approach to an intersection (with a major road) depend 

upon the planned action. The driver’s first decision is to either stop or to continue 

through the intersection (with a turning or a crossing maneuver) according to the type 

of traffic control information he or she perceives. A red signal or a stop sign results in 

a “stop” decision; all other types of information are functionally equivalent at this stage 

of driver decision making, translating into a “yield” decision. That is, drivers’ decisions 

at this stage are dichotomous: (1) slow down and prepare to stop, regardless of traffic on 

the major road, or (2) based on their view of the major road, either slow down, maintain 

speed, or accelerate as required to safely complete their intended maneuver. For drivers 

who are required to stop, their decision to proceed after the stop also is based on a 

view of traffic on the major road, but at a point much closer to the intersection. The 

contrasting sight lines and sight triangles defined by the position of a driver who must 

stop before proceeding at the intersection, versus one who may proceed without stopping, 

conditional on the intersecting (major) road traffic, are clearly indicated in Figure 71.

For purposes of describing driver decision making, the diagram in Figure 71 may apply 

to varying aspects of intersection operations in all Cases A through F as per AASHTO 

(2011) classification. For Case F, however, where a driver is turning left from a major road 

at an intersection or driveway, the decision process and corresponding sight distance 

requirements are defined differently. The sight lines in this case are affected by the 
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CHAPTER 7—INTERSECTIONS

Figure 71. Sight Distance for Left and Right Turns for Passenger Car Drivers at Yield-Control 

Intersections (Harwood et al., 1993)

presence, type (passenger versus heavy vehicle), and location (positioned or un-positioned 

in the intersection) of opposing left-turning traffic, and by the lateral offset of the 

opposite left-turn lanes themselves. These relationships are illustrated in Figure 72 from 

McCoy, Navarro, and Witt (1992).

The rationale for treatments pertaining to intersection sight distance requirements will 

proceed as follows. First, driver age differences in cognitive and physical capabilities that 

are relevant to ISD issues will be discussed. Then, research efforts that have attempted 

to quantify the safety impact of providing adequate sight distance are summarized, plus 

studies examining the appropriate values for specific components used when calculating 

sight distance in the AASHTO gap acceptance models. Much of the research cited was 

conducted on the basis of the PRT models that were included in the Green Book prior to 

2001. The discussion emphasizes the need for an increased value of PRT, which translates 

to a need for an increased gap using the current AASHTO models.

Older road users do not necessarily react more slowly to events that are expected, but 

they take significantly longer to make decisions about the appropriate response than 

younger road users, and this difference becomes more exaggerated in complex situations. 

Although the cognitive aspects of safe intersection negotiation depend upon a host 

of specific functional capabilities, the net result is response slowing. There is general 

consensus among investigators that older adults tend to process information more slowly 

than younger adults, and that this slowing transcends the slower reaction times (Anders, 

Fozard, and Lillyquist, 1972; Eriksen, Hamlin, and Daye, 1973; Waugh, Thomas, and 

Fozard, 1978; Salthouse and Somberg, 1982; Byrd, 1984). Of course, a conflict must be 

seen before any cognitive processing of this sort proceeds. Therefore, any decrease in 
110 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

available response time because of sight distance restrictions will pose disproportionate 

risks to aging drivers. Slower reaction times for older versus younger adults when 

response uncertainty is increased has been demonstrated by Simon and Pouraghabagher 

(1978), indicating a disproportionately heightened degree of risk when aging road users 

are faced with two or more choices of action. Also, research has shown that aging 

persons have greater difficulty in situations where planned actions must be rapidly 

altered (Stelmach, Goggin, and Amrhein, 1988). The difficulty aging persons experience

in making extensive and repeated head movements further increases the decision and 

response times of aging drivers at intersections.

David and Norman (1979) quantified the relationship between available sight distance 

and the expected reduction in crashes at intersections. The results of this study showed 

that intersections with shorter sight distances generally have higher crash rates. Using 

these results, predicted crash reduction frequencies related to ISD were derived as shown 

in Table 13.

Other studies have attempted to show the benefits to be gained from improvements to 

ISD (Mitchell, 1972; Strate, 1980). Mitchell conducted a before-and-after analysis, with 

a period of one year on each end, of intersections where a variety of improvements were 

implemented. The results showed a 67 percent reduction (from 39 to 13) in crashes where 

obstructions that inhibited sight distance were removed; this was the most effective of 

the implemented improvements. Strate’s analysis examined 34 types of improvements 

made in Federal Highway Safety Program projects. The results indicated that sight 

distance improvements were the most cost-effective, producing a benefit-cost ratio of 

5.33:1. A report on the FHWA Highway Safety Improvement Programs (1996) indicates 

that improvements in intersection sight distance have a benefit-cost ratio of 6.1 in 

Figure 72. Spatial 

relationships that 

determine available 

sight distance 

(McCoy et al., 1992)
Handbook for Designing Roadways for the Aging Population 111

CHAPTER 7—INTERSECTIONS

reducing fatal and injury crashes. In these analyses, fatal crashes were reduced by 56 

percent and nonfatal injury crashes by 37 percent after sight distance improvements were 

implemented.

Collectively, the studies described above indicate a positive relationship between 

available ISD and a reduction in crashes, though the amount of crash reduction that can 

be expected by a given increase in sight distance may be expected to vary according to 

the maneuver scenario and existing traffic control at the intersection. Procedures for 

determining appropriate ISDs are provided by AASHTO for various levels of intersection 

control and the maneuvers to be performed. The scenarios defined are as follows: 

•	 Case A: Intersections with No Control. ISD for vehicles approaching

intersections with no control, at which vehicles are not required to stop, but may 

be required to adjust speed.

•	 Case B: Intersections with Stop Control on the Minor Road.

° B1: Left Turn from the Minor Road. ISD for a vehicle on a stop-controlled 

approach on the minor road to accelerate from a stopped position and turn 

left onto the major road.

° B2: Right Turn from the Minor Road. ISD for a vehicle on a stop-controlled 

approach on the minor road to accelerate from a stopped position and turn 

right onto the major road.

° B3: Crossing Maneuver from the Minor Road. ISD for a vehicle on a stopcontrolled approach on the minor road to accelerate from a stopped position 

and cross the major road.

•	 Case C: Intersections with Yield Control. ISD for vehicles on a minor-road

approach controlled by a yield sign.

° C1: Crossing Maneuver from the Minor Road. ISD for a vehicle on a yieldcontrolled approach on the minor road to cross the major road.

° C2: Left or Right Turn from the Minor Road. ISD for a vehicle on a yieldcontrolled approach on the minor road to turn left or right onto the major 

road.

•	 Case D: Intersections with Traffic Signal Control. ISD for two-way flashing

operations should be determined by Case B guidance.

•	 Case E: Intersections with All-Way Stop Control. ISD for a vehicle on any

approach determined by the location of the first vehicle on all other approaches.

Table 13. Expected Reduction in Number of Crashes per Intersection Per Year (David 

and Norman, 1979).

AADT* 

(1000s)

Intersection Sight Distance (ft)

20-49 50-99 > 100

< 5 0.18 0.20 0.30

5 – 10 1.00 1.30 1.40

10 – 15 0.87 2.26 3.46

> 15 5.25 7.41 11.26

* Annual average daily traffic entering the intersection
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CHAPTER 7—INTERSECTIONS

•	 Case F: Left Turns from the Major Road. ISD for a vehicle making a left-turn

across the lanes used by opposing traffic. 

Prior to 2001, perception-reaction time (PRT) was a key component in determining 

ISD in all cases defined according to AASHTO (1994). The discussion of this value is 

still present in chapters 2 and 3 of the Green Book under “Reaction Time” and “Brake 

Reaction Time,” respectively (AASHTO, 2011). Results of several studies (e.g., Normann, 

1953; Johansson and Rumar, 1971) are cited, and in conclusion, the 2.5-s value is selected 

since it was found to be adequate for approximately 90 percent of the overall driver 

population. Controlled field studies and simulator studies involving aging drivers have 

confirmed that brake reaction times to unexpected hazards (e.g., a barrel rolling into the 

road in front of the driver, a vehicle turning in front of a driver who is traveling straight 

through an intersection) are not significantly different as a function of age, and that 

virtually all response times are captured by the current 2.5-s AASHTO design parameter 

for brake perception-response time (Lerner, et al., 1995; Kloeppel, et al., 1995). 

With respect to at-grade intersections, the 1994 Green Book recommended the following 

values of PRT for ISD calculations. In Case I, the PRT is assumed to be 2.0 s plus an 

additional 1.0 s to actuate braking, although the “preferred design” uses stopping sight 

distance (SSD) as the ISD design value (which incorporates a PRT of 2.5 s). In Case II, 

SSD is the design value; thus, the PRT is 2.5 s. For all Case III scenarios and Cases IV 

and V, the PRT is assumed to be 2.0 s. Refer to Table 14 to cross-reference the 1994 vs. 

2011 intersection scenarios.

Table 14. Cross-Reference for 1994 and 2011 Intersection Sight Distance Cases (AASHTO, 2011; 

AASHTO, 1994).

Scenario AASHTO 2011 Case 1994 AASHTO Case

No control Case A Case I

Stop control on minor road Case B Case III

Left turn maneuver B1 III-B

Right turn maneuver B2 III-C

Crossing maneuver B3 III-A

Yield control on minor road Case C Case II

Crossing maneuver C1

Left or right turn maneuver C2

Traffic signal control Case D Case IV

All-way stop control Case E Not included

Left turn from major road Case F Case V

Regarding PRT for Cases III and V, the value of 2.0 s assumed by AASHTO (1994) 

represents the time necessary for the driver to look in both directions of the roadway, to 

perceive that there is sufficient time to perform the maneuver safely, and to shift gears, 

if necessary, prior to starting. This value is based on research performed by Johansson 

and Rumar (1971). The PRT is defined as the time from the driver’s first look for possible 

oncoming traffic to the instant the car begins to move. Some of these operations are 

done simultaneously by many drivers, and some operations, such as shifting gears, may 

be done before searching for intersecting traffic or may not be required with automatic 
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CHAPTER 7—INTERSECTIONS

transmissions. AASHTO states that a value of 2.0 s is assumed to represent the time 

taken by the slower driver.

A critique of these values questioned the basis for reducing the PRT from 2.5 s used in 

SSD calculations to 2.0 s in the Case III ISD calculations (Alexander, 1989). As noted 

by the author, “The elements of PRT are: detection, recognition, decision, and action 

initiation.” For SSD, this is the time from object or hazard detection to initiation 

of the braking maneuver. Time to search for a hazard or object is not included in 

the SSD computation, and the corresponding PRT value is 2.5 s. Yet, in all Case III 

scenarios, the PRT has been reduced to 2.0 s and now includes a search component 

which was not included in the SSD computations. Alexander pointed out that a driver 

is looking straight ahead when deciding to perform a stopping maneuver and only has 

to consider what is in his/her forward view. At an intersection, however, the driver 

must look forward, to the right, and to the left. This obviously takes time, especially 

for those drivers with lower levels of physical dexterity, e.g., aging drivers. Alexander 

(1989) proposed the addition of a “search time” variable to the current equations for 

determining ISD, and use of the PRT value currently employed in the SSD computations 

(i.e., 2.5 s) for all ISD computations. Neuman (1989) also argued that a PRT of 2.5 s for 

SSD may not be sufficient in all situations, and can vary from 1.5 s to 5.0 s depending on 

the physical state of the driver (alert versus fatigued), the complexity of the driving task, 

and the location and functional class of the highway.

A number of research efforts have been conducted to determine appropriate PRT values 

for use in ISD computations. Hostetter, et al. (1986) examined the PRT of 124 subjects 

traversing a 3-hour test circuit which contained scenarios identified above as Cases II, 

IIIA, IIIB, and IIIC. For the Case II (yield control) scenario, the results showed that in 

over 90 percent of the trials, subjects reacted in time to meet the SSD criteria established 

and thus the 2.5-s PRT value was adequate. With respect to Case III scenarios, the 

PRT was measured from the first head movement after a stop to the application of 

the accelerator to enter the intersection. The mean and 85th percentile values for all 

maneuvers combined were 1.82 s and 2.7 s, respectively. The results also showed that the 

through movement produced a lower value than the mean, while the turning maneuvers 

produced a higher value. These results led to conclusions that the 2.0-s criteria for Case 

IIIA be retained and that the PRT value for the Case III turning maneuvers (B and C) be 

increased from 2.0 to 2.5 s. One other result, which is applicable to the current effort, was 

that no significant differences were found with respect to age, (i.e., increased PRTs were 

needed to accommodate all drivers).

Fambro, et al. (1998) found significant differences in mean perception-brake 

response times as a function of age and gender, with aging drivers and female drivers 

demonstrating longer response times. They conducted three separate on-road studies 

to measure driver perception-brake response time to several stopping sight distance 

situations. Studies were conducted on a closed course as well as on an open roadway. In 

one study conducted on the closed course, subjects drove an instrumented test vehicle 

belonging to the Texas Transportation Institute (TTI), and in another closed course 

study they drove their own vehicles. In the open roadway study, they drove their own 

vehicles. Seventeen younger drivers (age 24 or under) and 21 older drivers (age 55 or 

older) participated in trials that required them to brake in response to expected and 
114 Handbook for Designing Roadways for the Aging Population

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unexpected events, that included a barrel rolling off of a pickup truck parked next to the 

roadway, an illuminated LED on the windshield, and a horizontal blockade that deployed 

ahead of them on the roadway. Across all expected-object, perception-brake response 

time trials, the mean response time for younger drivers was 0.52 s and the mean response 

time for older drivers was 0.66 s. For these “expected” trials, the mean perception brakeresponse time for males was 0.59 s and for females was 0.63 s. For the unexpected-object, 

perception-brake response trials, longer response times were demonstrated for trials 

where subjects drove their own vehicles, compared to those in which they drove TTI’s 

vehicle. The study authors suggested that subjects were more relaxed and unsuspecting 

when driving their own vehicles. The mean response time across studies (controlled and 

open road, own vehicle and research vehicle) for the unexpected object was 1.1 s; the 95th 

percentile perception-brake response time was 2.0 s. 

Based on this finding, Fambro et al. (1998) concluded that AASHTO’s 2.5-s perceptionbrake reaction time value is appropriate for highway design, when stopping sight distance 

is the relevant control. However, they note that at locations or for geometric features 

where something other than stopping sight distance is the relevant control, different 

perception-reaction times may be appropriate. For example, longer perception-reaction 

times may be appropriate for intersection or interchange design where more complex 

decisions and driver speed and/or path correction are required.

Another effort examined the appropriateness of the PRT values currently specified by 

AASHTO for computing SSD, vehicle clearance interval, sight distance on horizontal 

curves, and ISD (McGee and Hooper, 1983). With respect to ISD, the results showed

the following: for Case I, the driver is not provided with sufficient time or distance to 

take evasive action if an opposing vehicle is encountered; and for Case II, adequate sight 

distance to stop before arriving at the intersection is not provided despite the intent of 

the standard to enable such action. With respect to the PRT values, recommendations 

include increasing the 2.0-s and 2.5-s values used in Case I and Case II calculations, 

respectively, to 3.4 s. It was also recommended that the PRT value for Case III scenarios 

be redefined.

Although there is no consensus from the above studies on the actual values of PRT 

that should be employed in the ISD computations, there is a very clear concern as to 

whether the current values are meeting the needs of aging drivers. Since aging drivers 

tend to take longer in making a decision, especially in complex situations, the need to 

further evaluate current PRT values is underscored. Slowed visual scanning of traffic 

on the intersecting roadway by aging drivers has been cited as a cause of near misses 

of (crossing) crashes at intersections during on-road evaluations. In the practice of 

coming to a stop, followed by a look to the left, then to the right, and then back to the left 

again, the aging driver’s slowed scanning behavior allows approaching vehicles to have 

closed the gap by the time a crossing maneuver finally is initiated. The traffic situation 

has changed when the aging driver actually begins the maneuver, and drivers on the 

main roadway are often forced to adjust their speed to avoid a collision. Hauer (1988) 

stated that “the standards and design procedures for intersection sight triangles should 

be modified because there is reason to believe that when a passenger car is taken as the 

design vehicle, the sight distance is too short for many aging drivers, who take longer to 

make decisions, move their heads more slowly, and wish to wait for longer gaps in traffic.”
Handbook for Designing Roadways for the Aging Population 115

CHAPTER 7—INTERSECTIONS

In a retrospective site-based review and crash analysis that included a detailed 

investigation of over 400 crashes involving drivers age 65 years and older at 62 sites in 

Australia, Oxley, et al. (2006) identified an insufficient perception-reaction time for 

intersection sight distance (e.g., a value less than 2.5 s) as a contributing factor in 23 

percent of the crashes. This was particularly problematic at intersections controlled by 

stop and yield signs. The study authors suggest that these findings provide strong support 

for the argument that longer sight distances at intersections are required to accommodate 

older drivers, to give them more time to select a safe gap in which to turn across, enter, or 

cross traffic.

In contrast, research conducted by Lerner, et al. (1995) concluded that, based on older 

driver performance, no changes to design PRT values were recommended for ISD, SSD, 

or decision sight distance (DSD), even though the 85th percentile J values exceeded the 

AASHTO 2.0-s design standard at 7 of the 14 sites. The J value equals the sum of the PRT 

time and the time to set the vehicle in motion, in seconds. No change was recommended 

because the experimental design represented a worst-case scenario for visual search and 

detection (drivers were required to begin their search only after they had stopped at the 

intersection and looked inside the vehicle to perform a secondary task). Naylor and 

Graham (1997), in a field study of older and younger drivers waiting to turn left at stopcontrolled intersections (Case IIIB), similarly concluded that the current AASHTO value 

of 2.0 s is adequate for the PRT (J-value) used in calculating intersection sight distance at 

these sites.

Lerner et al. (1995) conducted an on-road experiment to investigate whether the assumed 

values for Case III driver PRT used in AASHTO design equations adequately represent 

the range of actual PRT for aging drivers. Approximately 33 subjects in each of three 

driver age groups were studied: ages 20–40, ages 65–69, and age 70 and older. Drivers 

operated their own vehicles on actual roadways, were not informed that their response 

times were being measured, and were naive as to the purpose of the study (i.e., they 

were advised that the purpose of the experiment was to judge road quality and how this 

relates to aspects of driving). The study included 14 data collection sites on a 56-mi route. 

Results showed that the aging drivers did not have longer PRT than younger drivers, and 

in fact the 85th percentile PRT closely matched the AASHTO design equation value of 

2.0 s. The 90th percentile PRT was 2.3 s, with outlying values of 3 to 4 s. The median 

daytime PRT was approximately 1.3 s. Interestingly, it was found that typical driver 

actions did not follow the stop/search/decide maneuver sequence implied by the model; 

in fact, drivers continued to search and appeared ready to terminate or modify their 

maneuver even after they had begun to move into the intersection. This finding resulted 

in the study authors’ conclusion that the behavioral model on which ISD is based is 

conservative. 

Harwood, et al. (1996) evaluated current AASHTO policy on ISD for Cases I, II, 

III, IV, and V during performance of NCHRP project 15-14(1), based on a survey of 

current highway agencies’ practices and a consideration of alternative ISD models and 

computational methodologies, as well as findings from observational studies for selected 

cases. Although this work culminated in recommendations for minimum distances for 

the major and minor legs of the sight triangle for all cases, driver age was not included 

as a study variable; therefore, specific values for these design elements were not included 
116 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

within the treatments presented in this Handbook, nor is an exhaustive discussion of 

these materials included in this section. The results of the Harwood et al. (1996) analyses 

pertaining to ISD for Case IIIB and IIIC—and by extension for Case V—are of particular 

interest, however, in the interpretation of related findings from an aging driver field 

study in this area. These analysis outcomes are reviewed below.

Prior to the 1990 AASHTO Green Book, the issue of ISD for a driver turning left off of a 

major roadway onto a minor roadway or into an entrance (Case V) was not specifically 

addressed. In the 1990 Green Book, the issue was addressed at the end of the Case III 

discussions in two paragraphs. In the 1994 Green Book, these same paragraphs have been 

placed under a new condition referred to as Case V. The equation used for determining 

ISD for Case V was simply taken from the Case IIIA (crossing maneuver at a stopcontrolled intersection) and Case IIIB (left-turn maneuver from a stop-controlled minor 

road onto a major road) conditions, with the primary difference between the cases being 

the distance traveled during the maneuver. A central issue in defining the ISD for Case 

V involves a determination of whether the tasks that define ISD for Cases IIIA and IIIB 

are similar enough to the tasks associated with Case V to justify using the same equation, 

which follows:

ISD=0.28 V (J +ta)

where:

ISD = intersection sight distance (m).

V = design speed on the major roadway (km/h).

J = time required to search for oncoming vehicles, to perceive that there is 

sufficient time to make the left turn, and to shift gears, if necessary, prior to 

starting (J is assumed to be 2.0 s).

ta = time required to accelerate and traverse the distance to clear traffic in the 

approaching lane(s); obtained from Figure IX-33 in the 1994 AASHTO 

Green Book.

For Case IIIA (crossing maneuver), the sight distance is calculated based on the need to 

clear traffic on the intersecting roadway on both the left and right sides of the crossing 

vehicle. For Case IIIB (left turn from a stop), sight distance is based on the requirement 

to first clear traffic approaching from the left and then enter the traffic stream of vehicles 

from the right. It has been demonstrated that the perceptual judgments required of 

drivers in both of these maneuver situations increase in difficulty when opposing through 

traffic must be considered.

The perceptual task of turning left from a major roadway at an unsignalized intersection 

or during a permissive signal phase at a signalized intersection requires a driver 

to make time-distance estimates of a longitudinally moving target as opposed to a 

laterally moving target. Lateral movement (also referred to as tangential movement) 

describes a vehicle that is crossing an observer’s line of sight, moving against a changing 

visual background where it passes in front of one fixed reference point after another. 

Longitudinal movement, or movement in depth, results when the vehicle is either 
Handbook for Designing Roadways for the Aging Population 117

CHAPTER 7—INTERSECTIONS

coming toward or going away from the observer. In this case there is no change in visual 

direction, only subtle changes in the angular size of the visual image, typically viewed 

against a constant background. Longitudinal movement is a greater problem for drivers 

because the same displacement of a vehicle has a smaller visual effect than when it moves 

laterally—that is, lateral movement results in a much higher degree of relative motion 

(Hills, 1980). 

In comparison with younger subjects, a significant decline for older subjects has been 

reported in angular motion sensitivity. In a study evaluating the simulated change 

in the separation of taillights indicating the overtaking of a vehicle, Lee (1976) found 

a threshold elevation greater than 100 percent for drivers’ ages 70–75 compared with 

drivers ages 20–29 for brief exposures at night. Aging persons may in fact require twice 

the rate of movement to perceive that an object is approaching, versus maintaining a 

constant separation or receding, given a brief duration (2.0 s) of exposure. In related 

experiments, Hills (1975) found that aging drivers required significantly longer time to 

perceive that a vehicle was moving closer at constant speed: at 19 mph, decision times 

increased 0.5 s between ages 20 and 75. This body of evidence suggests that the 2.0-s PRT 

(i.e., variable J in the ISD equation above) used for Cases III and V may not be sufficient 

for the task of judging gaps in opposing through traffic by aging drivers. A revision of 

Case V to determine a minimum required sight distance value which more accurately 

reflects the perceptual requirements of the left-turn task may therefore be appropriate. 

Harwood et al. (1996) suggested that at locations where left turns from the major road are 

permitted at intersections and driveways, at unsignalized intersections, and at signalized 

intersections without a protected turn phase, sight distance along the major road should 

be provided based on a critical gap approach, as was recommended for left and right 

turns from the minor road at stop-controlled intersections. The Gap Acceptance model

developed and proposed to replace the 1994 AASHTO ISD model is:

ISD = 1.47 VG

where:

ISD = intersection sight distance (feet).

V = operating speed on the major road (mph).

	 G	 =	 the specified critical gap (in seconds); equal to 5.5 s for crossing one

opposing lane plus an additional 0.5 s for each additional opposing lane. 

Field data were collected in the NCHRP study to better quantify the gap acceptance 

behavior of passenger car and truck drivers, but only for left- and right-turning 

maneuvers from minor roadways controlled by a STOP sign (Cases IIIB and C). In the 

Phase I interim report produced during the conduct of the NCHRP project, Harwood 

et al. (1993) reported that the critical gap currently used by the California Department 

of Transportation is 7.5 s. When AASHTO Case IIIB ISD criteria were translated to 

time gaps in the major road traffic stream, the gaps ranged from 7.5 s (220 ft at a 20-mph 

operating speed to 15.2 s (1,560 ft) at a 70-mph operating speed. Harwood et al. (1993) 

stated that the rationale for gap acceptance as an ISD criterion is that drivers safely accept 

gaps much shorter than 15.2 s routinely, even on higher speed roadways. 
118 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

In developing the Gap Acceptance model for Case V, Harwood et al. (1996) relied on data

from studies conducted by Kyte (1995) and Micsky (1993). Kyte (1995) recommended a

critical gap value of 4.2 s for left turns from the major road by passenger cars for inclusion 

in the unsignalized intersection analysis procedures presented in the Highway Capacity 

Manual (Transportation Research Board, 1994). A constant value was recommended 

regardless of the number of lanes to be crossed; however, a heavy-vehicle adjustment 

of 1.0 s for two-lane highways and 2.0 s for multilane highways was recommended. 

Harwood et al. (1996) reported that Micsky’s 1993 evaluation of gap acceptance behavior 

for left turns from the major roadway at two Pennsylvania intersections resulted in 

critical gaps with a 50 percent probability of acceptance (determined from logistic 

regression) of 4.6 s and 5.3 s. Using the rationale that design policies should be more 

conservative than operational criteria such as the Highway Capacity Manual, Harwood 

et al. (1996) recommended a critical gap for left turns from the major roadway of 5.5 s, 

and an increase in the critical gap to 6.5 s for left turns by single-unit trucks and to 7.5 s 

for left turns by combination trucks. In addition, if the number of opposing lanes to be 

crossed exceeds one, an additional 0.5 s per additional lane for passenger cars and 0.7 s 

per additional lane for trucks was recommended.

It is important to note that the NCHRP study did not consider driver age as a variable. 

However, Lerner et al. (1995) collected judgments about the acceptability of gaps in traffic 

as a function of driver age for left turn, right turn, and through movements at stopcontrolled intersections. While noting that these authors found no significant differences 

between age groups in the total time required to perceive, react, and complete a maneuver 

in a related Case III PRT study, the Lerner et al. (1995) findings indicate that younger 

drivers accept shorter gaps than older drivers. The 50th percentile gap acceptance point 

was about 7 s (i.e., if a gap is 7 s long, only about half of the subjects would accept it). 

The 85th percentile point was approximately 11 s. The oldest group required about 1.1 s 

longer than the youngest group. 

Staplin, et al. (1997) conducted an observational field study of driver performance as a 

function of left-turn lane geometry and driver age at four locations where the main road 

operating speed was 35 mph. The mean left-turn critical gap sizes across all sites, for 

drivers who had positioned their vehicles within the intersection, were as follows: 5.90 s 

for the young/middle-aged (ages 25–45) females; 5.91 s for the young/middle-aged males; 

6.01 s for the young-old (ages 65–74) females; 5.84 s for the young-old males; 6.71 s for the 

old-old (age 75 and older) females; and 6.55 s for the old-old males. Prominent trends 

indicated that aging drivers demonstrated larger critical gap values at all locations. The 

young/middle-aged and young-old groups were not significantly different from each 

other; however, both were significantly different from the old-old group. Critical gap data 

were not collected in this study for drivers who did not position themselves within the 

intersection, but it is important to note that the older drivers were less likely to position 

themselves within the intersection than the young and middle-aged drivers.

Critical gap sizes displayed in a laboratory simulation study in the same project, where 

oncoming vehicles traveling at 35 mph were viewed on a large screen display in correct 

perspective, ranged from 6.4 s to 8.1 s for young/middle-aged drivers and from 5.8 to 

10.0 s for drivers age 75 and older. This increase in size and variability of the critical gap 

for left turns by aging drivers suggests that the value for G in the Gap Acceptance model
Handbook for Designing Roadways for the Aging Population 119

CHAPTER 7—INTERSECTIONS

must be increased to accommodate this user group, beyond levels recommended in 

NCHRP 383 (where the performance of aging drivers, per se, was not at issue). 

The culmination of this work was a rigorous exercise of competing models and 

theoretical approaches for calculating sight distance requirements. As reported by Staplin 

et al. (1997), several different sight distance models were exercised using data collected 

in the observational field study. This study was conducted at four intersections which 

differed in the amount that the opposite left-turn lanes were offset. The goal was to 

determine which model(s), including existing and modified 1994 AASHTO models and 

a Gap Acceptance model (which is the current 2004 AASHTO model) best predicted the

data observed in the field. 

Several data elements collected in the field received special attention. One of these data 

elements was the maneuver time of the left-turning driver. This time is equivalent to ta

in the 1994 AASHTO model, as shown in Figure IX-33 in the AASHTO (1994) Green 

Book. These times were measured at each of four intersections included in the study, 

for positioned and un-positioned drivers. That is, separate maneuver-time measures 

were obtained, depending on whether the drivers positioned themselves within the 

intersection prior to turning. Staplin et al. (1997) found no significant differences in 

maneuver time as a function of age for the drivers turning left at the four intersections 

studied (which had distances ranging from 84 to 106 ft). Maneuver times for drivers 

positioned within the intersection versus unpositioned drivers, however, were 

significantly different. Since aging drivers less frequently positioned themselves in the 

field study, the design value for this factor (maneuver time) should be based on that 

obtained for unpositioned drivers.

A comparison between 1994 AASHTO values and the 95th percentile clearance times 

demonstrated by positioned drivers and unpositioned drivers in this study is presented 

in Table 15. In Table 15, the “positioned” vehicles were located within the intersection, 

approaching the median or centerline of the cross street. The “unpositioned” vehicles 

were at or behind the stop line or end of the left-turn bay. (See Figure 76, located in the 

discussion for Design Element 5 — Offset Left Turn Lanes, for an illustration of driver 

positioning within an intersection).

Table 15. Comparison of Clearance Times Obtained in the Staplin et al. (1997) Field Study with 1994 

AASHTO Green Book Values Used in Sight Distance Calculations.

Vehicle Location Measure

Left-Turn Lane Geometry

-14 ft

Offset 

-3 ft

Offset 

0 ft

Offset 

+6 ft

Offset

Positioned Distance Traveled (ft) 70 ft 67 ft 64 ft 70 ft 

Positioned 95th Percentile Clearance 

Time (s) From Field Study 3.8 s 3.9 s 3.9 s 3.9 s

Positioned AASHTO Clearance Time (s) 

From Figure IX-33 5.1 s 5.0 s 5.0 s 5.1 s

Unpositioned Distance Traveled (ft) 106 ft 98 ft 84 ft 88 ft 

Unpositioned 95th Percentile Clearance 

Time (s) From Field Study 6.7 s 6.4 s 6.6 s 5.7 s

Unpositioned AASHTO Clearance Time (s) 

From Figure IX-33 6.5 s 6.2 s 5.9 s 6.0 s
120 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Figure 73. Comparison of Required Intersection Sight 

Distance Values from the Modified AASHTO Model 

(with J = 2.5 S) and the Gap Acceptance Model (with 

Gap Values of 5.5 S, 7.0, 7.5 S, and 8.0 S)

A detailed discussion of the outputs from the model 

exercise is provided in the publication Intersection 

Geometric Design and Operational Guidelines for Older

Drivers and Pedestrians (Staplin, et al. 1997). However, 

the most significant result for purposes of this discussion 

is as follows: the required sight distances computed 

using a modified 1994 AASHTO model (where PRT 

was increased to 2.5 s) produced values that were most 

predictive of actual field operations. 

Thus, when ISD is calculated using the AASHTO model 

as it relates to drivers turning left from a major roadway, 

there is evidence that the PRT value should be increased 

to 2.5 s to provide adequate sight distance. The Gap

Acceptance model, on the other hand, produced sight 

distance values that were approximately 23 percent 

shorter than the current AASHTO model that uses 

a PRT of only 2.0 s. If the Gap Acceptance model is

going to be used, particularly where there are significant 

volumes of aging left-turning drivers, an adjustment 

factor applied to increase the sight distance to better 

accommodate this driver age group therefore appears 

warranted.

To determine what adjustment is most appropriate in 

this regard, a set of analyses were performed in which 

the goal was to identify a value of G that would yield

required sight distance values meeting or exceeding 

those derived from the modified AASHTO model 

formula (i.e., where J = 2.5 s). By extension, this 

result would also best match the behavior of drivers 

75 and older observed in the field study. Very simply, 

alternate values for G were substituted into the gap

formula for calculating minimum required sight distance (1.47VG). These included 5.5

s, as recommended by Harwood et al. (1996), as well as values which increase in 0.5 s 

increments. The results of these calculations for alternate values of G, beginning at 7.0 s,

are plotted against the required sight distance calculated using the modified AASHTO 

formula [1.47V(J+ ta); where J=2.5 s and ta is obtained from Table IX-33 in the 1994 Green 

Book] in Figure 73. As shown in this figure, a gap of 8.0 s affords sight distance for leftturning drivers that equals or exceeds the requirements calculated using the modified 

AASHTO model for major road design speeds from 20 to 70 mph.

Finally, in a driving simulator study, Yan, Radwan, and Guo (2007) evaluated the effects

of age, gender, and major road speed on drivers’ left turn gap acceptance judgments 

at stop-controlled intersections. The study sample included 28 younger subjects (ages 

20 to 30), 21 middle-aged subjects (ages 31 to 55), and 14 older subjects (ages 56 to 

83). Subjects “drove” along the minor road and stopped at a stop sign at a major road, 
Handbook for Designing Roadways for the Aging Population 121

CHAPTER 7—INTERSECTIONS

with approaching vehicle speeds of either 25 mph or 55 mph. Vehicle gap sizes ranged 

from 1 to 16 s. The driver’s task was to wait at the stop sign on the minor road for an 

appropriate gap to turn into on the major road. 

In general, older drivers accepted larger gaps than young and middle-aged drivers (7.94 s 

vs. 6.29 s and 6.20 s, respectively) and females accepted larger gaps than males (6.93 s 

vs. 6.38 s, respectively). Oncoming vehicle speed played an important role in the gap 

size accepted by drivers, with drivers accepting smaller gaps for the higher major road 

approach speed than for the lower approach speed scenario. This implies that drivers 

show more sensitivity to oncoming vehicle distance than to oncoming vehicle approach 

speed. An interaction effect between age and speed showed that for the lower approach 

speed scenario (25 mph), the older drivers accepted larger gaps (females =10.99 s; males 

8.76 s) than the young drivers (females =7.56 s; males = 6.35 s) and middle-aged drivers 

(females = 6.97 s; males = 6.60 s). However, for the higher-speed approach (55 mph), the 

minimum gaps accepted by the older drivers (females = 7.11 s; males = 6.23 s) were not 

significantly larger than the younger drivers (females = 6.0 s; males = 5.26 s). During 

the process of turning, older drivers turned the steering wheel slower and used smaller 

acceleration rates to achieve the major road traffic speed than young and middle-aged 

drivers. The larger gaps that drivers accepted, the slower their accelerations to turn onto 

the road, reflecting older drivers’ conservative driving attitude. Speed reduction rates of 

following vehicles (to accommodate the turning vehicle) were higher for all driver ages 

when turning into higher-speed traffic than into lower- speed traffic. However, older 

drivers contributed to more speed reduction rates on the major road than young and 

middle-aged drivers, with older females causing the highest speed reduction rates of 

following vehicles. 

The finding that older drivers did not select larger gaps than younger drivers at higher 

speed roads indicates that they rely exclusively on perceived distance to make gap 

acceptance judgments. This puts them at a higher crash risk, because at the same time 

they are causing a shorter separation from the following vehicle, they are steering slower 

and accelerating slower than the younger drivers, and causing more effects on major road 

traffic. This suggests that at stop-controlled intersections, older drivers— in particular, 

older female drivers—are more likely to collide with speeding vehicles approaching on 

the major road.
122 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

5 Offset Left-Turn Lanes

Table 16. Cross-References of Related Entries for Offset Left-Turn Lanes.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 – 

Volume 9

(2004)

NCHRP 279 

Intersection

Channelization

Design Guide 

(1985)

Traffic Engineering 

Handbook

(2009)

Sections 1A.13 (median, 

regulatory sign, delineator, 

stop line, & wrong-way 

arrow), 2A.23, 2B.03, 2B.37, 

2B.38, 2B.40, 2B.41, 2B.42, 

3B.04,3B.11, 3B.16, 3B.20, 

3B.23, 3F.03, 3G.01, 3I.04 

through 3I.06 

Table 2B-1

Figures 2A-3, 2B-14 through 

2B-16, 2B-18,d 2B-19, 3B-13 

a, b & d, 3B-23, 3B-27

Pg. 2-39, Para. 3

Pgs. 9-99 through 9-105, 

Sects. on Island Size and 

Designation & Island 

Delineation and Approach 

Treatment

Pgs. 9-133 through 9-138, 

Sects. on Median Left-Turn 

Lanes, Median End Treatment, 

& Offset Left-Turn Lanes

Pgs. V-19-V-21, Sect. on 

Strategy 3.1 B6:Provide 

Offset Left-Turn Lanes at 

Intersections (T)

Pg. 1, 1st bullet

Pg. 3, 2nd col., Para. 5

Pg. 6, Table 2-1

Pg. 10, Table 2-4 & 2nd 

col., Para. 3

Pg. 14, Sect. on Decision 

Sight Distance

Pg. 17, Middle fig.

Pg. 29, Para. 1

Pg. 34, Para. 1 and top 

fig.

Pg. 35, Paras. 2-3

Pg. 60, Middle fig.

Pgs. 631, Sect. on 

Intersection Sight Distance

Pg. 246, Para. 5

Studies examining crashes involving aging drivers and the types of maneuvers being 

performed just prior to the collision have consistently found this group to be overinvolved in left-turning crashes at both rural and urban signalized intersections and 

have indicated that failure to yield the right-of-way (as the turning driver) was the 

principal violation type (Staplin and Lyles, 1991; Council and Zegeer, 1992). Underlying 

problems for the maneuver errors include the misjudgment of oncoming vehicle speed, 

misjudgment of available gap, assuming the oncoming vehicle was going to stop or turn, 

and simply not seeing the other vehicle. Joshua and Saka (1992) noted that sight distance 

problems at intersections which result from queued vehicles in opposite left-turn lanes 

pose safety and capacity deficiencies, particularly for unprotected (permissive) left-turn 

movements. These researchers found a strong correlation between the offset for opposite 

left-turn lanes—i.e., the distance from the inner edge of a left-turn lane to the outer edge 

of the opposite left-turn lane—and the available sight distance for left-turning traffic. 

The alignment of opposite left-turn lanes and the horizontal and vertical curvature on 

the approaches are the principal geometric design elements that determine how much 

sight distance is available to a left-turning driver. Operationally, vehicles in the opposite 

left-turn lane waiting to turn left can also restrict the (left-turning) driver’s view of 

oncoming traffic in the through lanes. The level of blockage depends on how the opposite 

left-turn lanes are aligned with respect to each other, as well as the type/size of vehicles 

in the opposing queue. Restricted sight distance can be minimized or eliminated by 

offsetting opposite left-turn lanes so that left-turning drivers do not block each other’s 

view of oncoming through traffic. When the two left-turn lanes are exactly aligned, 

the offset distance has a value of zero. Negative offset describes the situation where the 
Handbook for Designing Roadways for the Aging Population 123

CHAPTER 7—INTERSECTIONS

opposite left-turn lane is shifted to the left. Positive offset describes the situation where the 

opposite left-turn lane is shifted to the right. Figure 74 illustrates the relationships between 

the opposite left-turn lanes for negative and positive offset lane geometry. Positive offset 

left-turn lanes and aligned left-turn lanes provide greater sight distances than negative 

offset left-turn lanes, and a positive offset provides greater sight distance than the aligned 

configuration. 

Aging drivers may experience greater difficulties at intersections as the result of diminished 

visual capabilities such as depth and motion perception, as well as diminished attentionsharing (cognitive) capabilities. Studies have shown that there are age differences in depth 

and motion perception. Staplin, Lococo, and Sim (1993) found that the angle of stereopsis 

(seconds of arc) required for a group of drivers age 75 and older to discriminate depth using 

a commercial vision tester was roughly twice as large as that needed for a group of drivers 

ages 18 to 55 to achieve the same level of performance. However, while accurate perception 

of the distance to geometric features delineated at intersections—as well as to potentially 

hazardous objects such as islands and other raised features—is important for the safe use 

of these facilities, relatively greater attention by researchers has been placed upon motion 

perception, where dynamic stimuli (usually other vehicles) are the primary targets of 

interest. It has been shown that aging persons require up to twice the rate of movement 

to perceive that an object is approaching, and they require significantly longer to perceive 

that a vehicle is moving closer at a constant speed (Hills, 1975). A study investigating 

causes of aging driver over-involvement in turning crashes at intersections, building on the 

previously reported decline for detection of angular expansion cues, did not find evidence 

of overestimation of time-to-collision (Staplin et al., 1993). At the same time, a relative 

insensitivity to approaching (conflict) vehicle speed was shown for older versus younger 

drivers; this result was interpreted as supporting the notion that older drivers rely primarily 

or exclusively on perceived distance—not time or velocity—to perform gap acceptance 

judgments, reflecting a reduced ability to integrate time and distance information with 

increasing age. Thus, a principal source of risk at intersections is the error of an older, 

turning driver when judging gaps in front of fast vehicles. 

In a retrospective site-based review and crash analysis that included a detailed investigation 

of over 400 crashes involving drivers age 65 years and older at 62 sites in Australia, limited 

or restricted sight distance at right turns (equivalent to left turns in the U.S.) contributed 

to 23 percent of the crashes, and restricted sight distance plus a lack of right-turn offsets 

(i.e., left-turn offsets in the U.S.) contributed to an additional 10 percent of the crashes 

(Oxley, et al., 2006). 

Figure 74. Alignment of Left-Turn Lanes for Negative and Positive Offset
124 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Several studies examining the minimum required sight distance for a driver turning left 

from a major roadway to a minor roadway, as a function of major road design speed, have 

provided data necessary to determine: (1) the left-turn lane offset value needed to achieve 

the minimum required sight distance; and (2) the offset value that will provide unlimited 

sight distance. A fundamental premise in these studies, which are described below, is 

that it is not the amount of left-turn lane offset per se, but rather the sight distance that a 

given level of offset provides that should be the focus of any recommendations pertaining 

to the design of opposite left-turn lanes.

In a study conducted by McCoy, Navarro, and Witt (1992), guidelines were developed for 

offsetting opposite left-turn lanes to eliminate the left-turn sight distance problem. All 

minimum offsets specified in the guidelines are positive. For 90-degree intersections on 

level tangent sections of four-lane divided roadways, with 12-ft wide left-turn lanes in 16-

ft wide medians with 4-ft wide medial separators, the following conclusions were stated 

by McCoy et al. (1992): (1) a 2-ft positive offset provides unrestricted sight distance when 

the opposite left-turn vehicle is a passenger car, and (2) a 3.5-ft positive offset provides 

unrestricted sight distance when the opposite left-turn vehicle is a truck, for design 

speeds up to 70 mph.

Harwood, et al. (1995) conducted an observational field study and a crash analysis to 

develop design policy recommendations for the selection of median width at rural and 

suburban divided highway intersections based on operational and safety considerations. 

They found that at rural unsignalized intersections, both crashes and undesirable driving 

behaviors decrease as median width increases. However, at suburban signalized and 

unsignalized intersections, crashes and undesirable behaviors increase as the median 

width increases. At suburban intersections, it is therefore suggested that the median 

should not generally be wider than necessary to accommodate pedestrians and the 

appropriate median left-turn treatment needed to serve current and anticipated future 

traffic volumes. Harwood et al. stated that wider medians generally have positive effects 

on traffic operations and safety; however, wider medians can result in sight restrictions 

for left-turning vehicles due to the presence of opposite left-turn vehicles. The most 

common solution to this problem is to offset the left-turn lanes, using either parallel 

offset or tapered offset left-turn lanes.

Figure 75 compares conventional left-turn lanes with these two alternative designs. As 

noted by Harwood et al. (1995), parallel and tapered offset left-turn lanes are still not 

common, but are used increasingly to reduce the risk of crashes due to sight restrictions 

from opposite left-turn vehicles. Parallel offset left-turn lanes with 12-ft widths can be 

constructed in raised medians with widths as narrow as 24 ft, and can be provided in 

narrower medians if restricted lane widths or curb offsets are used or a flush median is 

provided (Bonneson, McCoy, and Truby, 1993). Tapered offset left-turn lanes generally 

require raised medians of 24 ft or more in width. 

For separation of the left-turn lane from through traffic in alternative designs such as 

those discussed above, the practitioner must choose between raised channelization 

and channelization accomplished through the use of pavement markings. As noted 

earlier, left-turn channelization separating through and turning lanes may, because 

of its placement, constitute a hazard when a raised treatment is applied, especially on 
Handbook for Designing Roadways for the Aging Population 125

CHAPTER 7—INTERSECTIONS

high-speed facilities. Detection and avoidance of such hazards requires visual and 

response capabilities known to decline significantly with advancing age, supporting 

recommendations for treatments to improve the contrast for these channelizing features 

at intersections (see Design Element 3 — Channelization).

As discussed in some detail under Design Element 4 — Intersection Sight Distance, 

Staplin, et al. (1997) performed a laboratory study, field study, and sight distance 

analysis to measure driver age differences in performance under varying traffic and 

operating conditions, as a function of varying degrees of offset of opposite left-turn 

lanes at suburban arterial intersections. Research findings indicated that an increase 

in sight distance through positively offsetting left-turn lanes can be beneficial to leftturning drivers, particularly aging drivers. In the field study, where left-turn vehicles 

needed to cross the paths of two or three lanes of conflicting traffic (excluding parking 

lanes) at 90-degree, four-legged intersections, four levels of offset of opposite left-turn 

lane geometry were examined. These levels include: (a) 6-ft “partial positive” offset, 

(b) aligned (no offset) left-turn lanes, (c) 3-ft “partial negative” offset, and (d) 14-ft “full 

negative” offset. All intersections were located within a growing urban area where the 

posted speed limit was 35 mph. Additionally, all intersections were controlled by trafficresponsive semi-actuated signals, and all left-turn maneuvers were completed during the 

permissive left-turn phase at all study sites. 

In the analysis of the field study lateral positioning data, it was found that the partial 

positive offset and aligned locations had the same effect on the lateral positioning 

behavior of drivers. Drivers moved approximately 5 ft to the left when there was a large 

negative offset, clearly indicating that sight distance was limited. There was a significant 

difference between the partial negative offset geometry and the partial positive offset 

or aligned geometries, suggesting a need for longer sight distance when opposite leftturn lanes are even partially negatively offset. The fact that aging drivers (and females) 

were less likely to position themselves (i.e., pull into the intersection) in the field studies 

highlights the importance of providing adequate sight distance for unpositioned drivers, 

Figure 75. 

Alternative LeftTurn Treatments for 

Rural and Suburban 

Divided Highways 

(Bonneson et al., 

1993)
126 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

for all left-turn designs. Vehicle positioning refers to the location within an intersection 

at which a left-turning vehicle waits for an acceptable gap in the opposing through traffic 

stream; specifically, at issue is the positioning behavior of drivers attempting to make 

a left turn through the conflicting through traffic while being opposed or blocked by 

at least one vehicle trying to make a left-turn maneuver from the opposite direction. 

The restriction of sight distance for an unpositioned versus a positioned driver at an 

intersection with aligned left-turn lanes is shown in Figure 76.

Shechtman et al. (2007) compared older and younger driver performance at improved 

and unimproved intersections in a high-fidelity, virtual reality driving simulator to test 

the effectiveness of FHWA’s recommendations for intersection designs to accommodate 

older road users. In this study, 19 drivers ages 25 to 45, and 20 drivers ages 65 to 85 

viewed visual representations of actual intersections on urban and residential streets in 

Gainesville, FL, and made braking, accelerating, and steering responses using controls

integrated into an actual vehicle. A driving evaluator sat in the car and recorded 

behavioral errors as subjects “drove” through 8 intersections. One of the improved 

intersections included left-turn lanes offset at 4 to 5 feet to improve the sight distance of 

oncoming vehicles by the left-turning driver. The comparison unimproved intersection 

included aligned left-turn lanes, which resulted in restricted sight distance. Both 

kinematic data (vehicle control responses during the turn phase including longitudinal 

and lateral accelerations, yaw, and speed) and behavioral data (driving errors including 

vehicle position, lane maintenance, speed, yielding, signaling, visual scanning, 

adjustment to stimuli/traffic signs, and left-turn gap acceptance) were recorded. Gap

acceptance was also evaluated for left turns. Of the kinematic measures, only maximum 

yaw was reduced for the improved intersection, for both older and younger drivers, 

indicating better lateral control of the vehicle for the offset left-turn lanes compared to 

the aligned left-turn lanes. There were no differences in the other kinematic measures 

when comparing the two age groups. There were no differences in behavioral errors 

between the two intersections or between the two age groups. These findings suggest 

that both older and younger drivers may benefit from increased sight distance offered 

by offsetting left turn lanes, with better lateral control of their vehicles when negotiating 

these intersections.

Figure 76. Sight 

Distance Restrictions 

for a Positioned and 

Unpositioned LeftTurning Driver at an 

Aligned Intersection 

with an Opposing LeftTurning Vehicle
Handbook for Designing Roadways for the Aging Population 127

CHAPTER 7—INTERSECTIONS

Several issues were raised in the research conducted by Staplin et al. (1997) regarding 

the adequacy of the 1994 AASHTO and new intersection sight distance (ISD) models for 

a driver turning left from a major roadway. The researchers exercised alternative sight 

distance models, including the 1994 AASHTO Case V model using 2.0 s for perceptionreaction time (PRT), a modified 1994 AASHTO model using a 2.5-s PRT, and a Gap

Acceptance model proposed in NCHRP 383 by Harwood, et al. (1996). The new Gap

Acceptance model relies on a critical gap value in place of PRT and maneuver time. A 

detailed description of the model parameters and output can be found in the FHWA 

report entitled Intersection Geometric Design and Operational Guidelines for Older

Drivers and Pedestrians (Staplin et al., 1997). Of particular significance was the finding 

that the modified 1994 AASHTO model with the longer PRT of 2.5 s was the model most 

predictive of actual field operations. Also of significance was the dramatic decrease in 

required sight distance that occurred with the gap acceptance model compared with 

the traditional AASHTO model. Across all intersections and all design speeds, the 

required sight distance was approximately 23 percent less using the gap acceptance 

model. However, this was expected since the rationale behind the use of a gap acceptance 

model (cf. Harwood et al., 1996), in place of the 1994 AASHTO model, is the fact that 

drivers are commonly observed accepting shorter gaps than those implied by the 1994 

AASHTO model. As discussed under Design Element 4, subsequent analyses established 

a recommendation for use of an 8.0-s gap size (plus 0.5 s for each additional lane crossed) 

to adjust the Gap Acceptance to accommodate aging driver needs for increased sight

distance.

Regardless of which model is used to compute ISD for drivers turning left off a major 

roadway, a practical countermeasure to increase the sight distance is through positive 

offset of left-turn lanes. As shown in the study by Staplin et al. (1997), such designs result 

in significantly better performance on the part of all drivers, but especially for aging 

drivers. Prior work by McCoy et al. (1992) examined the issue of offset left-turn lanes, 

and developed an approach that could be used to compute the amount of offset that is 

required to minimize or eliminate the sight restriction caused by opposing left-turn 

vehicles. 

This approach, incorporating the parameters represented in the intersection diagram 

shown earlier in Figure 72 (see Design Element 4 — Intersection Sight Distance), was 

applied to the intersections in the study by Staplin et al. (1997) to determine the amount 

of offset that would be required when using the modified 1994 AASHTO model (i.e., 

J = 2.5 s). The left-turn lane offsets required to achieve the minimum required sight 

distances calculated using this model are shown in Figure 77, in addition to the offsets 

required to provide unrestricted sight distance. Based on intersections examined in the 

study, the offset necessary to achieve unrestricted sight distance for opposing left-turning 

cars is 4.1 ft and for opposing left-turning trucks is 5.6 ft.

Finally, the potential for wrong-way maneuvers, particularly by aging drivers, at 

intersections with positive offset channelized left-turn lanes was raised during a panel 

meeting comprised of aging driver experts and highway design engineers, during 

the conduct of the research performed by Staplin et al. (1997). The concern expressed 

was that drivers turning left from the minor road may turn too soon and enter the 

channelized left-turn lane, instead of turning around both medians. Similar concern 
128 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

was raised by highway engineers surveyed by Harwood et al. (1995) during the conduct 

of NCHRP project 15-14(2). These authors reported that the potential for wrong-way 

movements by opposing-direction vehicles entering the left-turn roadway is minimal if 

proper signing and pavement markings are used. 

Researchers studying wrong-way movements at intersections—particularly the 

intersection of freeway exits with secondary roads—have found that such movements 

resulted from left-turning vehicles making an early left turn rather than turning around 

the nose of the median, and have proposed and tested several countermeasures. Scifres 

and Loutzenheiser (1975) reported that indistinct medians are design elements that 

reduce a driver’s ability to see and understand the overall physical and operational 

features of an intersection, increasing the frequency of wrong-way movements. They 

suggested delineation of the median noses to increase their visibility and improve driver 

understanding of the intersection design and function. Also, increasing the conspicuity 

of ONE WAY, WRONG WAY, and DO NOT ENTER signs by using larger-than-standard

(MUTCD) size signs, and using retroreflective sheeting on these signs that provides 

for high brightness at the wide observation angles typical of the sign placements and 

distances at which these signs are viewed (e.g., 1.0+ degrees) will be of benefit to drivers, 

particularly those with age-related diminished visual and attentional capabilities. 

Parsonson and Marks (1979) found that the use of the two-piece, 23.5-ft arrow pavement 

marking (wrong-way arrow) was effective in preventing wrong-way entries onto freeway 

exit ramps in Georgia. Later work in this State found a benefit of pulling the nose back

from the intersection, and extending the median line from the nose to the intersection 

using painted markings and raised retroreflectors; this treatment reduced the frequency 

of impacts with the median by turning vehicles, particularly trucks (per feedback 

provided by State engineers during a training workshop conducted by Handbook authors 

on August 6–7, 1998).

Figure 77. Left-Turn Lane 

Offset Design Values 

Necessary to Achieve 

Unrestricted Sight 

Distances Calculated 

with Either the Modified 

AASHTO Model (J = 2.5 s) 

or the Gap Acceptance 

Model (G = 8.0 s)
Handbook for Designing Roadways for the Aging Population 129

CHAPTER 7—INTERSECTIONS

6 Delineation of Edge Lines and Curbs 

Table 17. Cross-References of Related Entries for Delineation of Edge Lines and Curbs.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Roadway Lighting 

Handbook 

(1978)

NCHRP 279 

Intersection

Channelization

Design Guide 

(1985)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, Edge Line 

Markings, Island, & Object 

Marker

Sects. 2C.63 through 2C.65

Sect. 3A.06

Sects. 3B.09, 3B.10, 3B.11, 

3B.13, & 3B.23

Sect. 3G.01

Sect. 3H.01

Sects. 3I.01 through 3I.06

Pg. 2-39, Para. 3

Pg. 3-176, Paras. 3-4

Pgs. 4-17 through 4-19, Sect. on Curb 

Configurations

Pg. 6-15, Para. 3

Pg. 7-32, Para. 3

Pg. 9-19, Para. 2

Pg. 9-18, Fig. 9-9B

Pgs. 9-99 through 9-105, Sects. on Island 

Size and Designation & Island Delineation 

and Approach Treatment

Pgs. 9-106 through 9-112, Sect. on RightAngle Turns with Corner Islands

Pg. 9-148, Sect. on Shape of Median End

Pgs. 694-696, Figs. 9-55 through 9-58

Pg. 9-133, Paras. 5-6

Pgs. 9-134 through 9-136, Figs. 9-50 & 9-51

Pgs. 9-137, Sect. on Median End Treatment

Pg. 2, 2nd col, Para. 1

Pg. 3, Para. 4

Pg. 4, 1st bullet

Pg. 9, Sect. on Contrast

Pg. 17, Form 1

Pg. 21, Table 1

Pg. 24, Example Form 1

Pgs. 29-30, Sect. on 

Adverse Geometry and 

Environment Warrant

Pg. 31, Item, A

Pg. 24, Para. 1

Pg. 35, Para. 2 & bottom 

left fig.

Pg. 39, All figs.

Pg. 66, 2nd col., Para. 1

Pgs. 69 & 75, Sects. on 

Traffic Islands & Guidelines for Selection of 

Island Type

Pg. 74, Fig. 4-31

Pg. 76, Item 1

Pgs. 102-103, Intersct. 

No. 8

Pg. 382, Sect. on 

Centerline and Edge Line 

Markings

Pg. 573, Sect. on Marking 

of Curb Extensions and 

Edge Islands

Pg. 391-392, Sect. 

on Older Drivers and 

Pedestrians

The discrimination at a distance of gross highway features, as opposed to the fine detail 

contained in a sign message, governs drivers’ perceptions of intersection geometric 

elements. Thus, the conspicuity of such elements as curbs, medians, and obstacles, 

as well as all raised channelization, is of paramount importance in the task of safely 

approaching and choosing the correct lane for negotiating an intersection, as well as 

avoiding collisions with the raised surfaces. During the conduct of their driving task 

analysis, McKnight and Adams (1970a, 1970b) identified five driving tasks related

specifically to the conspicuity of intersection geometric elements: (1) maintain correct 

lateral lane position; (2) survey pavement markings; (3) survey physical boundaries; (4) 

determine proper lane position for the intended downstream maneuver; and (5) search 

for path guidance cues. The visual/perceptual requirement common to the performance 

of these tasks is contrast sensitivity: for detecting lane lines, pavement word and symbol 

markings, curbs and roadway edge features, and median barriers.

Aging drivers’ decreased contrast sensitivity, reduced useful field of view, increased 

decision time—particularly in response to unexpected events—and slower vehicle control 

movement execution combine to put these highway users at greater crash risk when 

approaching and negotiating intersections. The smaller the attentional demand required 

of a driver to maintain the correct lane position for an intended maneuver, the greater 
130 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

the attentional resources available for activities such as the recognition and processing of 

traffic control device messages and detection of conflict vehicles and pedestrians. 

A variety of conspicuity-enhancing treatments are mandated in current practice. The 

MUTCD (section 3B.10, Approach Markings for Obstructions) specifies that pavement 

markings shall be used to guide traffic away from fixed objects (such as median islands 

and raised channelization islands) within a paved roadway. Section 3B.23 (Curb 

Markings) states that retroreflective solid yellow markings should be placed on the curbs 

of islands that are located in the line of traffic flow where the curb serves to channel 

traffic to the right of the obstruction, and that retroreflective solid white markings 

should be used (on curbs) when traffic may pass on either side of the island. Section 

3G.01 (Colored Pavements) describes the use of colored pavements as traffic control

devices, where yellow shall be used for median islands and white for channelizing 

islands, and section 3I.03 (Island Marking Application) describes the use of pavement 

and curb markings; object markers; and delineators for island marking application. 

Supplementary treatments, and requirements for in-service brightness levels for certain 

elements contained in existing guidelines, are presently at issue.

The conspicuity of curbs and medians, besides aiding in the visual determination of how 

an intersection is laid out, is especially important when medians are used as pedestrian 

refuges. Care must be taken to ensure that pedestrian refuges are clearly signed and 

made as visible as possible to passing motorists.

Research findings describing driver performance differences directly affecting the use of 

pavement markings and delineation focus upon (age-related) deficits in spatial vision. In 

a pertinent laboratory study conducted by Staplin, Lococo, and Sim (1990), two groups of 

subjects (ages 19–49 and 65–80) viewing a series of ascending and descending brightness 

delineation targets were asked to report when they could just detect the direction of 

roadway curvature at the horizon (roadway heading)—left versus right—from simulated 

distances of 100 ft and 200 ft. Results showed that the older driver group required a 

contrast of 20 percent higher than the younger driver group to achieve the discrimination 

task in this study.

To describe the magnitude of the effects of age and visual ability on delineation 

detection/recognition distance and retroreflective requirements for threshold detection 

of pavement markings, a series of analyses using the Ford Motor Company PC DETECT 

computer model (Matle and Bhise, 1984) yielded the stripe contrast requirements shown 

in Table 18 (ADI Limited, 1991). PC DETECT is a headlamp seeing-distance model that 

uses the Blackwell and Blackwell (1971, 1980) human contrast sensitivity formulations 

to calculate the distance at which various types of targets illuminated by headlamps first 

become visible to approaching drivers, with 

and without glare from opposing headlights. 

The top 5 percent of 25-year-olds (the bestperforming younger drivers) and bottom 5 

percent of 75-year-olds (the worst-performing 

older drivers) were compared in this analysis.

Blackwell and Taylor (1969) conducted a study 

of surface pavement markings employing 

Table 18. Contrast Requirements for Edge Line Visibility at 400 ft 

With 5-S Preview at a Speed of 55 mph, as Determined by PC 

Detect Computer Model (ADI, 1991).

Driver age group/

% accommodated Worst-case glare No glare

Age 25 / top 5% 0.11 0.05

Age 75 / bottom 5% 7.21 3.74
Handbook for Designing Roadways for the Aging Population 131

CHAPTER 7—INTERSECTIONS

an interactive driving simulator, plus field evaluations. They concluded that driver 

performance —measured by the probability of exceeding lane limits—was optimized 

when the perceived brightness contrast between pavement markings and the roadway 

was 2.0. A study by Allen, O’Hanlon, and McRuer (1977) also concluded that delineation 

contrast should be maintained above a value of 2.0 for adequate steering performance 

under clear night driving conditions. In other words, because contrast is defined as 

the difference between target and background luminance, divided by the background 

luminance alone, these studies have asserted that markings must appear to be at least 

three times as bright as the road surface. Also, because these studies were not specifically 

focused on the accommodation of aging drivers—particularly the least capable members 

of this group—the contrast requirements defined in the 1991 modeling studies and 

analyses, as presented in Table 18, are accorded greater emphasis. Taking the indicated 

value for the least capable 5 percent of 75-year-olds into account, as well as the prior 

field evaluations, a contrast requirement of 3.0 for pavement markings appears most 

reasonable.

It is important to note that, whether luminance is measured in metric or English units 

[candelas per square meter (cd/m2

) or footlamberts (fL)], contrast is a dimensionless 

number; thus the present recommendations as well as the calculation of contrast level are 

independent of the unit of measure.

Finally, inadequate conspicuity of raised geometric features at intersections has been 

brought to the attention of researchers during the conduct of several focus group studies 

involving aging drivers. Subjects reported difficulty knowing where to drive, due to 

missing or faded roadway lines on roadway edges and delineation of islands and turning 

lanes. They also reported hesitating during turns, because they did not know where 

to aim the vehicle (Staplin, Lococo, and Sim, 1990). In another focus group, subjects 

suggested that the placement of advance warning pavement markings be located as far 

in advance of an intersection as practicable (Council and Zegeer, 1992). Drivers ages 

66–77 and older participating in focus group discussions conducted by Benekohal, et 

al. (1992), reported that intersections with too many islands are confusing because it 

is hard to find which island the driver is supposed to go around. Raised curbs that are 

unmarked are difficult to see, especially in terms of height and direction, and result in 

people running over them. These aging drivers stated that they would prefer to have 

rumble strips in the pavement to warn them of upcoming concrete medians and to warn 

them about getting too close to the shoulder. In other focus group discussions conducted 

to identify intersection geometric design features that pose difficulty for aging drivers 

and pedestrians (Staplin, et al., 1997), drivers mentioned that they have problems seeing 

concrete barriers in the rain and at night, and characterized barriers as “an obstruction 

waiting to be hit.” 

An inventory of the materials and devices commonly employed to delineate roadway 

edges, curbs, medians, and obstacles includes: retroreflective paint or tape, raised 

pavement markers (RPM’s), post-mounted delineators (PMD’s), object markers, and 

chevron signs.
132 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

7 Curb Radius

Table 19. Cross-References of Related Entries for Curb Radius.

Applications in Standard Reference Manuals

AASHTO

Green Book

(2011)

NCHRP 279 Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Pgs. 9-83 through 9-92, 

Sects. on Effect of Curb Radii 

on Turning Paths & Effect of 

Curb Radii on Pedestrians

Pg. 9-96, Paras. 1-2

Pgs. 9-141 through 9-149, 

Sect. 9.8.2 Control Radii for 

Minimum Turning Paths

Pgs. 9-149 through 9-151, 

Sect. on Median Openings 

Based on Control Radii for 

Design Vehicles

Pg. 1, 2nd bullet

Pg. 6, Paras. 4-5

Pg. 10, Table 2-4

Pg. 20, Bottom fig.

Pg. 21, 2nd col, Item 4 & Fig. 3-1

Pg. 22, 2nd fig from bottom of pg.

Pg. 23, Bottom right fig.

Pg. 26, Bottom fig.

Pg. 35, Para. 2

Pg. 36, Middle fig. & associated notes

Pg. 38, Middle fig. & associated notes

Pgs. 66-69, Sects. on Corner Radius 

Design & Radius of Turn

Pgs. 70-73, Figs. 4-27 through 4-29

Pg. 77, Fig. 4-32

Pg. 83, Sects. on Driveways Along Major 

Arterials and Collectors & Consideration of 

Pedestrians

Pgs. 84-87, Figs. 4-37 through 4-39

Pgs. 93-94, Intersct. No. 2

Pgs. 96-97, Intersct. No. 4

Pgs. 122-125, Intersct. Nos. 18-19

Pgs. 128-129, Intersct. No. 20B

Pgs. 132-135, Intersct. Nos. 22-23

Pg. 247, Sect. on Curb 

RadiusParas. 5-6

Pg. 254, first bullet

Recommendations for this design element address the radius of the curb that joins the 

curbs of adjacent approaches to an intersection. The size of the curb radius affects the 

size of vehicle that can turn at the intersection, the speed at which vehicles can turn, 

and the width of intersection that must be crossed by pedestrians. If curb radii are too 

small, lane encroachments resulting in traffic conflicts and increased crash potential can 

occur. If the radii are too large, pedestrian exposure may be increased (although, if large 

enough, refuge islands may be provided). The procedures used in the design of curb radii 

are well detailed in the Green Book (AASHTO, 2011).

McKnight and Stewart (1990) identified the task of positioning a vehicle in preparation

for turning as a critical competency. A significant problem identified in a task analysis to 

prioritize aging drivers’ problems with intersections is carrying out the tight, right-turn 

maneuver at normal travel speed on a green light (Staplin, et al., 1994). The problems 

are somewhat moderated when right turns are initiated from a stop, because the turn 

can be made more slowly, which reduces difficulties with short radii. Aging drivers may 

seek to increase the turning radius by moving to the left before initiating the turn, often 

miscommunicating an intention to turn left and encouraging following drivers to pass 

on the right. Or, they may initiate the turn from the correct position, but swing wide 

into a far lane in completing the turn in order to lengthen the turning radius and thus 

minimize rotation of the steering wheel. Encroaching upon a far lane can lead to conflict 

with vehicles approaching from the right or, on multilane roads, oncoming drivers 

turning to their left at the same time. The third possibility is to cut across the apex of 

the turn, possibly dragging the rear wheels over the curb. Each of these shortcomings in 

lanekeeping can be overcome by a channelized right-turn lane or wider curb radii. 
Handbook for Designing Roadways for the Aging Population 133

CHAPTER 7—INTERSECTIONS

Chu (1994) found that relative to middle-aged drivers (ages 25–64), older drivers (age 65 

and older) tend to drive larger automobiles and drive at slower speeds. Although large 

heavy cars are associated with a crash fatality rate that is less than one-quarter of that 

associated with the smallest passenger cars (Insurance Institute for Highway Safety, 1991) 

and are, therefore, a wise choice for older drivers who are more frail than their middleaged counterparts, large vehicles have larger turning radii, which may exacerbate the 

problems older drivers exhibit in lanekeeping during a turn. Roberts and Roberts (1993) 

reported that common arthritic illnesses such as osteoarthritis, which affects more than 

50 percent of the elderly population, and rheumatoid arthritis, affecting 1 to 2 percent, 

are relevant to the tasks of turning and gripping the steering wheel. A hand deformity 

caused by either osteoarthritis or rheumatoid arthritis may be very sensitive to pressure, 

making the driver unwilling to apply full strength to the steering wheel or other controls. 

In an assessment of 83 drivers with arthritis, Cornwell (1987) found that 83 percent of 

the arthritic group used both hands to steer, 7 percent used the right hand only, and 

10 percent the left hand only; in this study, more than one-half of the arthritic group 

required steering modifications, either in the form of power steering or other assistive 

device such as a smaller steering wheel. 

The Intersection Channelization Design Guide (Neuman, 1985) states that intersections 

on high-speed roadways with smooth alignment should be designed with sufficient 

radii to accommodate moderate- to high-speed turns. At other intersections, such as in 

residential neighborhoods, low-speed turns are desirable, and smaller corner radii are 

appropriate in these cases. Additionally, selection of a design vehicle is generally based 

on the largest standard or typical vehicle type that would regularly use the intersection. 

For example, a corner radius of 50 ft will accommodate moderate-speed turns for all 

vehicles up to WB-50 (combination truck/large semitrailer with an overall length of 

55 ft). However, many agencies are designing intersections along their primary systems 

to accommodate a 70 ft, single trailer design vehicle (C-70). Table 4-8 (p. 66) of the 

Intersection Channelization Design Guide provides guidelines for the selection of a design 

vehicle. It further specifies in Table 4-9 the operational characteristics for various corner 

radii. For example, a corner radius of less than 5 ft is not appropriate even for P design 

vehicles (passenger cars), whereas a corner radius of 20–30 ft will accommodate a lowspeed turn for P vehicles, and a crawl-speed turn for SU vehicles (single unit truck, 30 ft 

in length) with minor lane encroachment. 

Of equal importance to the right-turning design vehicle in determining curb radii is a 

consideration of pedestrian crossing time, particularly in urban areas. Smaller corner 

radii (less than 30 ft) can decrease right-turn speeds and reduce open pavement area for 

pedestrians crossing the street. A consideration of vehicle turning speed and pedestrian 

crossing distance can contribute to the safe handling of vehicle/pedestrian crossing 

conflicts (Neuman, 1985). Hauer (1988) noted that “the larger the curb-curve radius, 

the larger the distance the pedestrian has to cover when crossing the road. Thus, for a 

sidewalk whose centerline is 6 ft from the roadway edge, a 15-ft corner radius increases 

the crossing distance by only 3 ft. However, a 50-ft radius increases this distance by 26 ft, 

or 7 s of additional walking time.” Hauer further stated that the following are widely held 

concerns with the widening of curb radii: (1) the longer the crossing distance, the greater 

the hazard to pedestrians, even though there may be space for refuge islands when the 

corner radius is large enough; (2) larger curb radii may induce drivers to negotiate the 
134 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

right turn at a higher speed; and (3) the larger the radius, the wider the turn, which 

makes it more difficult for the driver and the pedestrian to see each other. For these 

reasons, the safety of aging persons at intersections, particularly pedestrians, may be 

adversely affected when large curb radii are provided. 

In focus group discussions with 46 drivers ages 65–74 (young-old group) and 35 drivers 

age 75 and older (old-old group), 74 percent of drivers in each age group reported that 

tight intersection corner radii posed difficulty in maneuvering through the intersection 

for the following reasons: (1) there are visibility problem with sharp corners; (2) drivers 

sometimes hit curbs and median barriers; and (3) with sharp turns, trucks turning left 

into the adjacent opposing traffic lane end up face-to-face with drivers, requiring them 

to back up (Staplin, et al. 1997). Approximately 24 percent of the young-old drivers and 

34 percent of the old-old drivers suggested that medium rounding is sufficient to facilitate 

turning maneuvers and is safer than very broadly rounded corners because the latter 

encourages high-speed turns. 

In a design preference study using slides to depict varying radii of corner curb cuts, four 

alternative curb geometries were presented to 30 drivers ages 65–74 (young-old group) 

and 30 drivers age 75 and older (old-old group) (Staplin et al., 1997). The four alternative 

geometries (depicted in Figure 78) were: (1) a simple circular radius of 18 ft; (2) a simple 

circular radius of 12 m; (3) a simple circular radius of 48 ft; and (4) a three-sided/

truncated curve with the center side measuring 54 ft. The alternatives were identically 

ranked by both groups of drivers: Alternative 3 was consistently preferred, Alternative 

4 placed second, Alternative 2 placed third, and Alternative 1 was least preferred. Both 

young-old and old-old drivers in this study were most concerned about ease of turning, 

citing the better 

maneuverability 

and less chance of 

hitting the curb as 

their primary basis of 

response. The second 

most common—

but also strongly 

weighted—reason 

for the preference 

responses of both 

groups related to 

the degree of visibility of traffic on intersecting roadways, possibly explaining the slight 

preference for Alternative 2 over Alternative 1. Alternatives 3 and 4 both are described 

by corner curb line geometries offering ease of turning and good visibility; however, 

isolated responses to the truncated corner geometry (Alternative 4) indicated concerns 

that providing too much room in the right-turn path might result in a lack of needed 

guidance information and could lead to a maneuver error, and that it could be harder to 

detect pedestrians with this design.

In a field study conducted as part of the same project, three intersections providing 

right-turn curb radii of 40 ft, 25 ft, and 15 ft were evaluated to examine the effects of curb 

radii on the turning paths of vehicles driven by drivers in three age groups. One hundred 

Figure 78. Alternative Curb Radii Evaluated in Laboratory Preference Study of Intersection 

Geometries (Staplin et al., 1997)
Handbook for Designing Roadways for the Aging Population 135

CHAPTER 7—INTERSECTIONS

8 Left-Turn Traffic Control for 

Signalized Intersections

subjects divided across three age groups drove their own vehicles around test routes using 

the local street network in Arlington, VA. The three age groups were “young/middleaged” (ages 25–45), which contained 32 drivers; “young-old” (ages 65–74), containing 

36 drivers; and “old-old” (age 75 and older), containing 32 drivers. The speed limit was 

35 mph and all intersections were located on major or minor arterials within a growing 

urban area. Data were only collected for turns executed on a green-signal phase.

Analysis of the free-flow speeds showed that all factors (age, gender, and geometry), and 

their interactions, were significant. Mean free-flow speeds were highest at the largest 

(40 ft) curb radius location, for all age groups. A consistent finding showed that the 

slowest mean free-flow speeds were measured at the 15 ft curb radius location for all age 

groups. Thus, larger curb radii increased the turning speeds of all drivers, with young/

middle-aged and young-old drivers traveling faster than old-old drivers when making 

right turns.

Crash analyses have shown that aging drivers, ages 56–75 and age 76 and older, are 

overinvolved in left-turn maneuvers at signalized intersections, with failure to yield 

right-of-way or disregarding the signal the principal violation types (Staplin and Lyles, 

1991; Council and Zegeer, 1992). Old-elderly drivers (age 75 and older) were more likely 

than younger drivers (ages 30–50) to be involved in left-turn crashes at urban signalized 

intersections, and both young-elderly (ages 65–74) and old-elderly were more likely to be 

involved in left-turn crashes at rural signalized intersections. In both cases, the crashinvolved older drivers were more likely to be performing a left-turn maneuver than the 

younger drivers. In addition, Stamatiadis, Taylor, and McKelvey (1991) found that the

relative crash involvement ratios for aging drivers were higher at two-phase (no turning 

phase) signalized intersections than for multiphase (includes turn arrow) signalized 

intersections. This highlights problems aging drivers may have determining acceptable 

gaps and maneuvering through traffic streams when there is no protective phase. 

Further, crash percentages increased significantly for aging drivers when an intersection 

contained flashing controls, as opposed to conventional (red, yellow, green) operations. 

In this analysis, the greatest crash frequency at signalized intersections occurred on 

major streets with five lanes, followed closely by roadways containing four lanes. These 

configurations were most often associated with low-speed, high-volume urban locations, 

where intersection negotiation requires more complex decisions involving more conflict 

vehicles and more visually distracting conditions. Not surprisingly, Garber and

Srinivasan’s (1991) analysis of 7,000 intersection crashes involving drivers ages 50–64 

and age 65 and older, found that the provision of a protected left-turn phase will aid in 

reducing the crash rates of the elderly at signalized intersections.

The change in the angular size of a moving object, such as an approaching vehicle 

observed by a driver about to turn left at an intersection, provides information crucial to 

gap judgments (i.e., speed and distance). Age-related declines (possibly exponential) in 

the ability to detect angular movement have been reported. Aging persons may in fact 
136 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Table 20. Cross-References Of Related Entries For Left-Turn Traffic Control For Signalized Intersections.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500–

Volume 9

(2004)

NCHRP 279 

Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Figs. 3B-13b, c, d, 3B-24, 

& 3B-27

Sect. 1A.13, Approach, 

Intersection, Lane-Use 

Control Signal, Regulatory 

Sign, Sign Legend, & Traffic 

Control Signal, Table 2B-1

Sects. 2B.18 through 

2B.22, 2B.52, 2B.53, 3B.08 

& 3B.20 

Sect. 4D.04 through 4D. 

20, 4D.25 through 4D.31

Sects. 4M.02 through 

4M.04

Pg. 3-176, Para. 4

Pgs. 9-15 through 9-19, 

sect. on Channelized FourLeg Intersections

Pg. 10-38, Para. 1

Pg. 10-39, Fig. 10-17

Pgs. 10-42 through 10-47, 

Sect. on Single-Point 

Diamond Interchanges

Pgs. V-12-V-14, Sect. on 

Strategy 3.1 B2: Provide 

Advance Guide Signs and 

Street Name Signs (T)

Pgs. V-18-V-19, Sect. on 

Strategy 3.1 B5: Provide 

More Protected Left-Turn 

Signal Phases at HighVolume Intersections (P)

Pg. 1, Item 3, 4th bullet

Pg. 3, 2nd col., Para. 3

Pg. 21, Fig. 3-1

Pg. 28, Top fig.

Pg. 29, Top left fig.

Pg. 34, Top fig. & 

associated notes

Pg. 37, Top left fig.

Pg. 48, Para. 5 & Table 4-3 

Pg. 49, Paras. 1, 2, & 4 and 

2nd col, item 2

Pg. 54, Fig. 4-16, bottom 

left photo

Pg. 57, Sects. on Double 

Left-Turn Lanes—

Guidelines for Use & Design 

of Double Left-Turn Lanes

Pgs. 58-60, Figs. 4-20 & 

4-21

Pgs. 100-101, Intersct. 

No. 7

Pgs. 104-119, Intersct. 

Nos. 9-16

Pgs. 132-135, Intersct. Nos. 

22-23

Pg. 144, Intersct. No. 33

Pgs. 148-151, Intersct. 

Nos. 35-36

Pgs. 245-246

Pgs. 462-465, Sect. on 

Turn Lanes

Pg. 413-415, Sect. on Left 

Turns

Pgs. 632-634, Sect. on 

Turn Restrictions

require twice the rate of movement than younger persons to perceive that an object is 

approaching, given a brief (2.0 s) duration of exposure. Also, older persons participating 

in laboratory studies have been observed to require significantly longer intervals than 

younger persons to perceive that a vehicle was moving closer at constant speed: at 19 

mph, decision times increased 0.5 s between ages 20 and 75 (Hills, 1975). 

Compounding this age-related decline in motion perception, some research has 

indicated that, relative to younger subjects, older subjects underestimate approaching 

vehicle speeds (Hills and Johnson, 1980). Specifically, Scialfa, et al. (1991) showed that 

older adults tend to overestimate approaching vehicle velocities at lower speeds and 

underestimate at higher speeds, relative to younger adults. Staplin, Lococo, and Sim 

(1993), while investigating causes of aging driver over-involvement in turning crashes 
Handbook for Designing Roadways for the Aging Population 137

CHAPTER 7—INTERSECTIONS

at intersections, did not find evidence of overestimation of time-to-collision by aging 

drivers in their perception of the closing distance between themselves and another vehicle 

approaching either head-on or on an intersecting path. However, a relative insensitivity 

to approach (conflict) vehicle speed was shown for older versus younger drivers, in that 

younger drivers adjusted their gap judgment of the “last safe moment” to proceed with 

a turn appropriately to take higher approach speeds into account, while older drivers 

as a group failed to allow a larger gap for a vehicle approaching at 60 mph than for one 

approaching at 30 mph. The interpretation of this and other data in this study was that 

aging drivers rely primarily or exclusively on perceived vehicle separation distance to 

reach maneuver “go/no go” decisions, reflecting a reduced ability to integrate time and 

distance information with increasing age. Thus, a principal source of risk at intersections 

is the error of an aging, turning driver in judging gaps in front of fast vehicles. 

Aside from (conflict vehicle) motion detection, an additional concern is whether there 

are age differences in how well drivers understand the rules under which the turns 

will be made—that is, whether aging drivers have disproportionately greater difficulty 

in understanding the message that is being conveyed by the signal and any ancillary 

(regulatory) signs. If the signals and markings are not understood, at a minimum there 

may be delay in making a turn or, in the worst case, a crash could result if a protected 

operation is assumed where it does not exist. 

A driver comprehension analysis conducted in a laboratory setting with drivers 30–60 

years of age and older showed that green displays (those with the circular green indication 

alone, green arrow alone, or combinations of circular green and green arrow on the 

left-turn signal) were correctly interpreted with widely varying frequency, depending 

on the signals shown for the turning and through movements (Curtis, Opiela, and 

Guell, 1988). In most cases, performance declined as age increased; aging drivers were

correct approximately half as often as the youngest drivers. Most driver errors, and 

especially aging driver errors, indicated signal display interpretations that would result 

in conservative behavior, such as stopping and/or waiting. Overall, green arrows were 

better understood than circular green indications. Conversely, red and yellow arrows were 

less comprehensible than circular red and circular yellow indications. Potentially unsafe 

interpretations were found for red arrow displays in protected-only operations. The yellow 

arrow display was more often treated as a last chance to complete a turn when compared 

with a circular yellow indication. Driver errors were most frequent in displays that 

involved flashing operations, and multiple faces with different colors illuminated on the 

left-turn signal head, and in particular, different colors on the turn and through signals.

More specifically, Curtis et al. (1988) found that the circular green indication under 

permissive control was correctly interpreted by approximately 60 percent of the 

subjects. For protected-only operations, the green arrow (with circular red for through 

movement) was correctly answered by approximately 75 percent of drivers. For protected/

permissive operation, the circular green alone was correctly answered by only 50 percent 

of the respondents, while the green arrow in combination with the circular green had 

approximately 70 percent correct responses. When the circular green with the green 

arrow was supplemented by the R10-12 sign LEFT TURN YIELD ON GREEN , only 

34 percent of drivers answered correctly. This test result suggests that the MUTCD

recommended practice may result in some driver confusion, as test subjects answered 
138 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

correctly more often when the sign was not present, even when the effects of regional 

differences in familiarity with the sign were considered. Apparently reinforcing this 

notion, the Maryland State Highway Administration (MSHA, 1993) reported a higher 

rate of left-turn collisions at three intersections where the R10-12 sign was installed than 

at three intersections where the sign was not installed. Unfortunately, driver age was 

not a study variable; also, medians were present (only) at sites with the R10-12 signs, 

and differences between sites in terms of signal phasing, traffic volumes and delays, and 

alignment and other aspects of intersection geometry, though noted, were not described. 

Other researchers have found improved driver comprehension with the use of the R10-12 

sign, compared to other messages informing drivers of the decision rule for protected/

permissive operations, as described later in this section.

When Hummer, Montgomery, and Sinha (1990) evaluated motorists’ understanding of 

left-turn signal alternatives, they found that the protected-only signal was by far the best 

understood, permissive signals were less understood, and the protected/permissive the 

least understood. When a circular green for through traffic and a green arrow for left 

turns were displayed, the protected signal was clearly preferred over the permissive and 

protected/permissive signals, and the leading signal sequence was preferred more often 

than the lagging sequence. Respondents stated that the protected-only signal caused less 

confusion, was safer, and caused less delay than the permissive and protected/permissive 

signals. It should be noted, however, that while aging persons were in the sample of 

drivers studied, they made up a very small percentage (8 of 402) and differences were 

hard to substantiate. 

Knoblauch, et al. (1995) examined the lack of understanding associated with a variety

of protected and permissive left-turn signal displays. They found that many drivers, 

both younger and older, do not understand the protected/permissive signal phasing, 

and they suggested that efforts to improve motorist comprehension of left-turn signal 

phasing should be targeted at the entire driving population. In focus group discussions, 

many aging drivers reported that they avoid intersections that do not have a protectedonly phase or those where the time allowance for left turns was too short. In addition, 

the situation where the green arrow eventually turns to a circular green was generally 

confusing and not appreciated by the aging participants. Among the recommendations 

made by the aging drivers were:

•	 Provide as many protected left-turn opportunities as possible.

•	 Standardize the sequence for the left-turn green arrow so that it precedes solid

green or red.

•	 Lengthen the protected left-turn signal.

•	 Lengthen the left-turn storage lanes so that turning traffic does not block

through traffic.

•	 Make traffic signal displays more uniform across the United States, including the

warning or amber phase.

•	 Standardize the position and size of signals.

•	 Provide traffic lights overhead and to the side at major intersections.
Handbook for Designing Roadways for the Aging Population 139

CHAPTER 7—INTERSECTIONS

•	 Paint a yellow line in the pavement upstream of the signal in a manner that,

if the driver has not reached the line before the light has turned yellow, he/she 

cannot make it through before the red light.

•	 Provide borders (backplates) around lights to minimize the effects of glare.

•	 Eliminate holiday decorations located overhead at intersections, because they are

often green and red and may be confusing near signal faces.

Bonneson and McCoy (1994) also found a decreased understanding of protected and 

permissive left-turn designs with increased age, in a survey conducted in Nebraska 

with 1,610 drivers. In this study, the overlap phase (left-turn green arrow and through 

circular green illuminated) was the least understood by drivers wishing to turn left, 

with only one-half of the respondents answering correctly; most of the respondents who 

erred chose the safer course of action, which was to wait for a gap in oncoming traffic. 

In terms of signal head location, 4 to 5 percent more drivers were able to understand 

the protected/permissive display when it was centered in the left-turn lane (exclusive) as 

opposed to having the head located over the lane line (shared). Although the difference 

was statistically significant, Bonneson and McCoy point out that the difference may be 

too small to be of practical significance. In terms of lens arrangement, significantly more 

drivers understood both the permissive indication and the protected/MUTCD indication 

(left-turn green arrow and through circular red) in vertical and horizontal arrangements 

than in the cluster arrangement. Comparisons between the protected/MUTCD

indication and a modified protected indication (green arrow with no circular red), 

showed that for the horizontal protected/permissive designs, 25 percent more drivers 

were able to understand the protected indication when the circular red was not shown 

with the green arrow, and for the vertical and cluster protected/permissive designs, 

12 percent more drivers understood the modified protected indication. The point is that 

from an operational perspective, hesitancy as a result of misunderstanding will decrease 

the level of service and possibly result in crash situations. 

Noyce and Kacir (2002) conducted a survey of 2,465 drivers in 8 locations across the U.S.

to determine driver understanding of simultaneous traffic signal indications in protected 

left turn displays. Drivers ranged in age from less than 25 to 65 and older, with 7 percent 

of the sample over age 65. The survey included 200 different scenarios, of which 68 

contained protected left-turn indications. Drivers were shown photographs of left turn 

displays from various signalized intersections around the country. Each photograph was 

taken from approximately the driver’s eye location as if the driver were positioned as the 

first left-turn vehicle in queue in an exclusive left-turn lane. Animated signal displays 

were created and replaced the existing signal displays in each photograph. Five-section 

protected and permissive left-turn (PPLT) displays in the protected phase illuminated 

both the green-arrow and through movement (green-ball or red-ball) indications as 

required by MUTCD. The four and three section displays presented only the green 

arrow. The drivers were asked to respond to the following question by selecting either 

GO, YIELD-wait for gap, STOP-then wait for gap, or STOP: “If you want to turn left, and

you see the traffic signals shown, you would....”. The time duration for each response was 

also recorded. 
140 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

In the Noyce and Kacir (2002) study, age played a significant role in the percentage of

correct responses when green arrow and red ball indications were shown simultaneously: 

for drivers less than 24 years of age, 75 percent of responses were correct, and for drivers 

over the age of 65, 62 percent of responses were correct. The majority of incorrect 

responses to the 5-section displays with the green arrow and red ball indications were 

“stop, then wait for gap,” demonstrating some confusion with the simultaneously 

illuminated indications. Compared to this, for the 65+ age group, when green arrow 

was shown with green ball, 86 percent of responses were correct, and when green arrow 

was shown without a green or red ball, 89 percent of responses were correct. When 

the green-arrow and red-ball indications were shown simultaneously in the 5-section 

signal display, driver understanding was lowest with the horizontal arrangement. The 

authors indicate that locating the green arrow to the right of the red-ball indication in a 

5-section horizontal display arrangement appears to provide confusion. For the 5-section 

horizontal display with green arrow and red ball, only 49 percent of drivers age 65 and 

older gave the correct answer. 

Regarding the response times to the signals in the Noyce and Kacir (2002) study, the

average response increased with driver age. The 3- and 4-section displays showing only 

the green arrow, had average driver response times ranging from 3 s for the under-24 age 

group to 6 s for the over-65 group. However, the difference was more pronounced with 

the 5-section horizontal display showing a green arrow and red ball simultaneously; in 

this display, the under-24 age group had an average response time of 5 s, and the over-65 

age group had an average response time of 10 s. The average response time for drivers 

over age 65 was 8 s for the 5-section cluster and vertical displays showing green-arrow 

and red-ball indications simultaneously. The average response time for the 5-section 

signal displays showing green-arrow and green-ball indications simultaneously was 

not different from that for the 3- and 4-section displays showing the green-arrow only 

indication. 

The authors recommended that in a 5-section horizontal display, the green arrow and red 

ball should not be illuminated simultaneously.

An analysis of sign use by Bonneson an McCoy (1994) compared the exclusive cluster 

lens arrangement over the left-turn lane and exclusive vertical lens arrangement over 

the through lanes with and without the use of an auxiliary sign (LEFT TURN YIELD 

ON GREEN ). Overall, the results indicated that driver understanding of the display 

increased by about 6 percent when there was no sign, though a closer examination of 

these data revealed that the specific operation signaled by the display was critical. For the 

permissive indication, the sign appeared to help driver understanding, whereas during 

the overlap and protected indications it appeared to confuse drivers.

Numerous studies have found that: (1) protected left-turn control is the safest, with 

protected/permissive being less safe than protected, but safer than permissive (Fambro 

and Woods, 1981; Matthais and Upchurch, 1985; Curtis et al., 1988); and (2) transitions 

from protected-only operations to protected/permissive operations experience crash 

increases (Cottrell and Allen, 1982; Florida Section of Institute of Transportation 

Engineers, 1982; Cottrell, 1985; Warren, 1985; Agent, 1987). According to Fambro and 

Woods (1981), for every left-turn crash during a protected phase, 10 would have occurred 
Handbook for Designing Roadways for the Aging Population 141

CHAPTER 7—INTERSECTIONS

without protection. Before-and-after studies where intersections were changed from 

protected to permissive control have shown four- to seven-fold increases in left-turn 

crashes (Florida Section of Institute of Transportation Engineers, 1982; Agent, 1987).

Hallmark and Mueller (2004) conducted a crash analysis to evaluate the impact 

of different types of left-turn phasing on older and younger drivers at high-speed 

intersections in Iowa. The sample included 101 intersections with at least one intersecting 

roadway with a speed limit of 45 mph or higher. Data from 2001 to 2003 were included. 

The induced exposure method was used to determine crash rate for drivers in three 

different age groups: 14-24 years old, 25-64 years old, and 65 years and older. Crash rate 

was calculated by dividing the number of drivers that were credited with a crash in a 

certain age group by the estimated million entering vehicles (MEV) by approach for that 

age group. Poisson regression was used to model the relationship between left-turn crash 

rates with age group, type of phasing (protected, permissive, and protected/permissive), 

and other site characteristics including opposing volume. Older drivers had the highest 

left-turn crash rates of all age groups for all types of phasing. For older drivers as well 

as middle-aged drivers, crash rates were highest at the intersections with protected/

permissive phasing, followed by permissive phasing. For the younger drivers, crash 

rates were highest with permissive phasing, followed by protected/permissive phasing. 

Protected left-turn phasing produced the lowest crash rates for all three age groups. 

Drivers may have difficulties with both protected/permissive and permissive phasing 

since left turns can be made during the permissive phase of both types of phasing. 

This may be the result of difficulties judging gaps. The high crash rate for protected/

permissive phasing may also be a reflection of driver misunderstanding of protected/

permissive signal displays. Protected/permissive phasing resulted in the most severe 

crashes for all age groups (as determined by a severity index) of the three phasing options. 

Further investigation into these results did not provide any insight into the reasons for 

the increased severity. Hallmark and Mueller (2004) indicated that left-turn volumes 

were not included in this study (hence the decision to use induced exposure); that may 

be one of the reasons why protected/permissive phasing performed worse compared to 

permissive phasing. Based on their study findings, the authors recommend protective 

phasing for use at high-speed intersections (e.g., those 45 mph or higher).

In a retrospective site-based review and crash analysis that included a detailed 

investigation of over 400 crashes involving drivers age 65 years and older at 62 sites in 

Australasia, the lack of separate traffic control for left-turn movements against oncoming 

traffic (i.e., no protected turn phase) contributed to 23 percent of the crashes (Oxley, et al., 

2006). 

Shechtman et al. (2007) found that both older and younger drivers may benefit from 

the implementation of protected left turn phasing at intersections, resulting in less 

need for hard accelerations to successfully maneuver across oncoming traffic at an 

intersection (particularly for older drivers), and better lateral control of their vehicles 

when negotiating intersections. They compared older and younger driver performance 

at improved and unimproved intersections in a high-fidelity, virtual reality driving 

simulator to test the effectiveness of FHWA’s recommendations for intersection design 

to accommodate aging road users. In this study, 19 drivers ages 25 to 45, and 20 

drivers ages 65 to 85 viewed visual representations of actual intersections on urban 
142 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

and residential streets in Gainesville, FL, and made braking, accelerating, and steering

responses using controls integrated into an actual vehicle. A driving evaluator sat in 

the car and recorded behavioral errors as subjects “drove” through 8 intersections. 

One of the improved intersections was a signalized intersection with separate signals 

for each lane, with a leading protected left-turn phase indicated by a green arrow, and 

redundant upstream signing. The comparison unimproved intersection was signalized, 

but did not have separate signals for each lane, nor a protected left-turn phase or 

redundant signing. The simulator scenario was programmed so that gap acceptance 

at the unimproved intersection was tested as follows: drivers experienced oncoming 

traffic with one relatively short gap followed by more traffic and eventually a long gap 

without any oncoming traffic. Acceptance of the first gap required a rapid increase in 

speed for successful negotiation. There was no gap acceptance task at the improved 

intersection controlled by the protected left-turn phase. Both kinematic data (vehicle 

control responses during the turn phase including longitudinal and lateral accelerations, 

yaw, and speed) and behavioral data (driving errors including vehicle position, lane 

maintenance, speed, yielding, signaling, visual scanning, adjustment to stimuli/traffic 

signs, and left-turn gap acceptance) were recorded. 

Of the kinematic measures recorded by Shechtman et al. (2007), maximum yaw and 

maximum forward acceleration were significantly reduced for the improved intersection, 

for both older and younger drivers, indicating better lateral control of the vehicle, and 

more stable forward acceleration. Maximum lateral acceleration approached significance 

with greater values for the unimproved intersection (indicating poorer lateral control 

during the turn). There were no differences in maximum speed between the improved 

and unimproved intersection. Older drivers had significantly higher forward acceleration 

than the younger drivers, indicating a “panicked” attempt to successfully drive through 

the gap in oncoming traffic at the unimproved intersection. There were no differences in 

behavioral errors between the two intersections or between the two age groups.

Williams, Ardekani, and Asante (1992) conducted a mail survey of 894 drivers in Texas 

to assess motorists’ understanding of left-turn signal indications and accompanying 

auxiliary signs. Drivers older than age 65 had the highest percentage of incorrect 

responses (35 percent). Results of the various analyses are as follows: (1) the use of a 

green arrow for protected-only left turns produced better comprehension than the use of 

a circular green indication, even when the circular green indication was accompanied by 

an auxiliary sign; (2) for a five-section signal head configuration, the display of a green 

left-turn arrow in isolation produced better driver understanding than the simultaneous 

display of a circular red indication and a green left-turn arrow; (3) the LEFT TURN 

YIELD ON GREEN auxiliary sign was associated with the smallest percentage of 

incorrect responses, compared with the LEFT TURN ON GREEN AFTER YIELD

sign, the PROTECTED LEFT ON GREEN sign, and the LEFT TURN SIGNAL sign;

and (4) the percentage of incorrect responses was 50 percent lower in the presence of a 

circular red indication compared with a red arrow; the red arrow was often perceived to 

indicate that a driver may proceed with caution to make a permissive left turn. 

In another study conducted by Curtis et al. (1988), it was found that the Delaware 

flashing red arrow was not correctly answered by any subject. The incorrect responses 

indicated conservative interpretations of the signal displays which would probably be 
Handbook for Designing Roadways for the Aging Population 143

CHAPTER 7—INTERSECTIONS

associated with delay and may also be related to rear-end collisions. Drivers interpreted 

the Delaware signal as requiring a full stop before turning, because a red indication 

usually means “stop,” even though the signal is meant to remind motorists to exercise 

caution but not necessarily to stop unless opposing through traffic is present. Hulbert, 

Beers, and Fowler (1979) found a significant difference in the percentage of drivers 

younger than age 49 versus those older than age 49 who chose the correct meaning of the 

red arrow display. Sixty-one percent of the drivers older than age 49 chose “no turning 

left” compared with 76 percent of those younger than age 49. Although other research 

has concluded that the left-turn arrow is more effective than the circular red in some 

left-turn situations in particular jurisdictions where special turn signals and exclusive 

turn lanes are provided (Noel, Gerbig, and Lakew, 1982), drivers of all ages will be better

served if signal indications are consistent. 

Hawkins, Womack, and Mounce (1993) surveyed 1,745 drivers in Texas to evaluate driver 

comprehension of selected traffic control devices. The sample contained 88 drivers age 65 

and older. Three alternative signs describing the left-turn decision rule were evaluated: 

(1) R10-9, PROTECTED LEFT ON GREEN ARROW (in the Texas MUTCD but not the 

national MUTCD); (2) R10-9a, PROTECTED LEFT ON GREEN (in the Texas MUTCD

but not the national MUTCD); and (3) R10-12, LEFT TURN YIELD ON GREEN . 

The R10-12 sign did the best job of the signs in the survey informing the driver of a 

permissive left-turn condition, with 74.5 percent choosing the desirable response. Of 

those who responded incorrectly, 13.6 percent responded that they would wait for the 

green arrow, and 4.3 percent made the dangerous interpretation that the left turn was 

protected when the circular green was illuminated. Incorrect responses were more often 

made by drivers age 65 and older. 

The decisional processes drawing upon working memory crucial to safe performance at 

intersections may be illustrated through a study of alternative strategies for presentation 

of left-turn traffic control messages (Staplin and Fisk, 1991). This study evaluated the 

effect of providing advance left-turn information to drivers who must decide whether 

or not they have the right-of-way to proceed with a protected turn at an intersection. 

Younger (mean age of 37) and older (mean age of 71) drivers were tested using slide 

animation to simulate dynamic approaches to intersection traffic control displays, with 

and without advance cueing of the “decision rule” (e.g., LEFT TURN MUST YIELD ON 

GREEN ) during the intersection approach. Without advance cueing, the decision rule 

was presented only on a sign mounted on the signal arm across the intersection as per 

standard practice, and thus was not legible until the driver actually reached the decision 

point for the turning maneuver. Cueing drivers with advance notice of the decision rule 

through a redundant upstream posting of sign elements significantly improved both the 

accuracy and latency of all drivers’ decisions for a “go/no go” response upon reaching the 

intersection, and it was of particular benefit to the older test subjects. Presumably, the 

benefit of upstream “priming” is derived from a reduction in the requirements for serial 

processing of concurrent information sources (sign message and signal condition) at the 

instant a maneuver decision must be completed and an action performed. 

Stelmach, Goggin, and Garcia-Colera (1987) found that aging adults were particularly

impaired when preparation was not possible, showing disproportionate response slowing 

when compared with younger subjects. When subjects obtained full information about 
144 Handbook for Designing Roadways for the Aging Population

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an upcoming response, reaction time (RT) was faster in all age groups. Stelmach et al. 

(1987) concluded that aging drivers may be particularly disadvantaged when they are 

required to initiate a movement in which there is no opportunity to prepare a response. 

Preparatory intervals and length of precue viewing times are determining factors in 

age-related differences in movement preparation and planning (Goggin, Stelmach, and

Amrhein, 1989). When preparatory intervals are manipulated in a way that aging adults 

have longer stimulus exposure and longer intervals between stimuli, they profit from the 

longer inspection times by performing better and exhibiting less slowness of movement 

(Eisdorfer, 1975; Goggin et al., 1989). Since aging drivers benefit from longer exposure to

stimuli, Winter (1985) proposed that signs should be spaced farther apart to allow drivers 

enough time to view information and decide what action to take. Increased viewing time 

will reduce response uncertainty and decrease aging drivers’ RT.

Differences in maneuver decisions reported by Staplin and Fisk (1991) illustrate both the 

potential problems aging drivers may experience at intersections due to working memory 

deficits, and the possibility that such consequences of normal aging can to some extent 

be ameliorated through improved engineering design practices. Staplin and Fisk (1991) 

also showed that aging drivers had higher error rates and increased decision latencies 

for situations where the left turn was not protected. In particular, the most problematic 

displays were those with only one steady illuminated signal face (circular green) 

accompanied by a sign that indicated that it was not safe to proceed into the intersection 

with the assumption of right-of-way (LEFT TURN YIELD ON GREEN ). A correct 

response to this combination depends on the inhibition of previously learned “automatic” 

responses; a signal element with one behavior (go) was incorporated into a traffic control 

display requiring another, conflicting behavior. 

Several evaluations of a novel left-turn display for the permissive phase—the flashing 

yellow arrow (FYA)— have been conducted. Brehmer, et al. (2003) conducted a 

laboratory study using 2,465 drivers in 4 age groups: < age 24 (27%); 25-44 (44%); 

45-65 (21%); and 66+ (7%). Photographs of existing signalized intersections were 

presented to drivers at driver license centers using laptop computers. Combinations 

of protected left-turn indications, permissive left-turn indications, through-movement 

indications, and protected/permissive left-turn signal display arrangements were shown 

against these background intersection scenes. Each driver was randomly presented with 

30 of the 200 unique scenarios developed for the study. Subjects were instructed to use 

the computer keyboard to select which of four options was appropriate if the person 

wanted to turn left and saw the traffic signals presented. The four options were: (1) GO,

(2) YIELD and wait for gap, (3) STOP then wait for gap, and (4) STOP. Measures of 

effectiveness included percent of correct responses to the study scenarios and response 

time. Response time data were collected as a surrogate measure of driver understanding 

(longer response times would connote lower levels of driver understanding). Aging 

drivers provided the fewest correct responses across all display combinations of all age 

groups: Age 66+ = 67.3% correct, age 45-65 = 71.1% correct; age 24-44 = 73.1% correct, 

age 24=72.2% correct. Drivers age 66+ had longer response times (2 to 4 seconds of 

additional time) compared to drivers less than age 24. For the permissive indications 

across all age groups, the circular green ball had the fewest correct responses at 50.4%, 

followed by the flashing red arrow (55.6% correct) and the flashing yellow arrow 
Handbook for Designing Roadways for the Aging Population 145

CHAPTER 7—INTERSECTIONS

(56.6% correct). The flashing red ball had the highest correct response rate (63.8%), 

followed by the flashing yellow ball (61.7%). Response times were faster for the flashing 

permissive indications than for the solid indications, and circular indications were better 

understood than arrow indications. Drivers age 66+ had low correct response rates 

(29%) for the permissive circular green ball when shown with the red through indication. 

Seventy percent of drivers age 66+ responded correctly to the flashing circular red 

permissive left-turn indication. Although the correct response rate (across age groups) 

was higher for the flashing yellow arrow than for the steady green ball, there were 2 other 

indications that had even higher percent-correct response rates than the flashing yellow 

arrow: the flashing red ball and the flashing yellow ball. 

More recently, Noyce, Bergh, and Chapman (2007) conducted a field study of crashes 

using 50 signalized intersections with at least 1 year of data after the implementation of 

flashing yellow arrow. Out of the 50 signalized intersections where the flashing yellow 

arrow was introduced, in 5 of the locations the phasing was permissive and the round 

green was replaced by flashing yellow arrow. Twenty-one of the signalized intersections 

had protected/permissive left-turn (PPLT) phasing, where the round green was replaced 

by flashing yellow arrow. In the remaining intersections, fully protected phasing was 

replaced by PPLT with a flashing yellow arrow. Crashes before the implementation of 

flashing yellow arrow was compared with crashes after the implementation of flashing 

yellow arrow. Safety was not improved at the intersections where fully protected 

phasing was replaced by PPLT phasing with flashing yellow arrow. These intersections 

experienced a change in phasing and hence, it is not possible to determine if flashing 

yellow arrow was effective. No conclusions could be made regarding the safety effect 

of replacing the green ball with flashing yellow arrow at the five intersections with 

permissive phasing. Safety was improved at the 21 intersections that operated on PPLT 

phasing where the green ball was replaced with the flashing yellow arrow. Although this 

study indicates that the flashing yellow arrow was effective in reducing crashes at PPLT 

locations, this result is based on a limited sample of intersections. It is also not clear if 

the empirical Bayes method used a reference group to account for bias due to regression 

to the mean and to account for changes in traffic volume. In addition, it is not clear if 

driver age was considered in this evaluation.

The FYA research noted above targets apparent deficits in the comprehension of the 

conventional green ball for permissive turning operations at intersections, which has 

been discussed elsewhere in this section. At the same time, concerns have been raised 

about confusion by aging motorists regarding the meaning of arrow signal indications 

elsewhere in this Handbook. Given the positive experience of some practitioners who

are early adopters of this treatment, further FYA research is a high priority. Such 

investigations could well lead to a Handbook recommendation to adopt this practice, 

pending reliable evidence that shows a) comprehension rates that equal or exceed those 

of other viable substitutes for the steady green ball; and b) an absence of performance 

penalties or safety problems for “young-old” as well as “old-old” drivers upon their 

initial encounters with such displays, under naturalistic conditions. In particular, it is 

important to rule out the possibility that the FYA will be (mis)perceived as the timing out 

of a protected left turn phase, which could actually increase the potential for injurious 

angle crashes.
146 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Next, Hummer, Montgomery, and Sinha (1991) evaluated leading and lagging signal 

sequences using a survey of licensed drivers in Indiana, an examination of traffic 

conflicts, an analysis of crash records, and a simulation model of traffic flow, to 

evaluate motorists’ understanding and preference for leading and lagging schemes as 

well as determining the safety and delay associated with each scheme. Combinations 

of permissive and protected schemes included: (1) protected-only/leading, in which 

the protected signal is given to vehicles turning left from a particular street before the 

circular green is given to the through movement on the same street; (2) protected-only/

lagging, in which the green arrow is given to left-turning vehicles after the through 

movements have been serviced; (3) protected/permissive, in which protected left turns 

are made in the first part of the phase and a circular green indication allows permissive 

turns later in the phase; and (4) protected/permissive, in which unprotected turns are 

allowed in the first part of the phase and protected left turns are accommodated later 

in the phase. The protected-only/leading and protected/permissive schemes are known 

as “leading,” and the protected-only/lagging and permissive/protected are known as 

“lagging” schemes. Of the 402 valid responses received, 248 respondents preferred 

the leading, 59 preferred the lagging sequence, and 95 expressed no preference. The 

most frequent reasons given for preference of the leading sequence were: it is more like 

normal; it results in less delay; and it is safer. There are apparent tradeoffs here, however; 

the leading sequence was associated with a higher conflict rate with pedestrians and a 

higher rate of run-the-red conflicts (drivers turning left during the clearance interval for 

opposing traffic), while the intersections with a lagging sequence were associated with 

a significantly higher rate of indecision conflicts than the leading intersections due to 

violations in driver expectancy. Overall, it is judged that consistency in signal phasing 

across intersections within a jurisdiction, as well as across jurisdictions, should be a 

priority, and that use of a leading protected left-turn phase offers the most benefits. A 

discussion of countermeasures for the protection of pedestrians may be found in the 

material that presents the Rationale and Supporting Evidence for Design Element 15 – 

Pedestrian Crossings. 

Upchurch (1991) compared the relative safety of 5 types of left-turn phasing using 

Arizona Department of Transportation crash statistics for 523 intersection approaches, 

where all approaches had a separate left-turn lane, 329 approaches had two opposing 

lanes of traffic, and 194 approaches had three opposing lanes. The five types of left-turn 

phasing included (1) permissive, (2) leading protected/permissive, (3) lagging protected/

permissive, (4) leading protected-only, and (5) lagging protected-only. For the 495 

signalized intersections in the State highway system, most samples represented a 4-year 

crash history (1983–1986). For the 132 signalized intersections in 6 local jurisdictions 

in Arizona, samples ranged from 4 months to 4 years, all between 1981 and 1989. When 

the crash statistics were stratified by various ranges of left-turn volume and various 

ranges of opposing volume (vehicles per day), the following observations and conclusions 

were made for sample sizes greater than five, eliminating any conclusions about lagging 

protected-only phasing:

•	 Leading protected-only phasing had the lowest left-turn crash rate in almost

every case. This was true in every left-turn volume range and every opposing 

volume range except one (19 out of 20 cases). Lagging protected/permissive was 

the exception for three opposing lanes and left-turn volumes of 0–1,000.
Handbook for Designing Roadways for the Aging Population 147

CHAPTER 7—INTERSECTIONS

•	 When there were two lanes of opposing traffic, lagging protected/permissive

tended to have the worst crash rate.

•	 When there were three lanes of opposing traffic, leading protected/permissive

tended to have the worst crash rate.

•	 When there were two lanes of opposing traffic, the order of safety (crash rate

from best to worst) was leading protected-only, permissive, leading protected/

permissive, and lagging protected/permissive. However, there was a small 

difference in the crash rate among the last three types of phasing.

•	 When there were three lanes of opposing traffic, the order of safety (crash rate

from best to worst) was leading protected-only, lagging protected/permissive, 

permissive, and leading protected/permissive.

Upchurch (1991) compared the crash experience of 194 intersections that had been 

converted from one type of phasing to another in a simple before-and-after design. For 

each conversion, four years of before-crash data and four years of after-crash data were 

used, where available. At approaches having two opposing lanes of traffic, the statistics 

for conversions from permissive to leading protected/permissive and vice versa reinforced 

each other, suggesting that leading protected/permissive is safer than permissive. At 

approaches having three opposing lanes of traffic, the statistics for conversions from 

leading protected-only to leading protected/permissive and vice versa reinforced each 

other, suggesting that leading protected-only is safer than leading protected/permissive.

Parsonson (1992) stated that a lagging left-turn phase should be used only if the bay 

provides sufficient storage, as any overflow of the bay during the preceding throughmovement will spill into the adjacent through lane, blocking it. A lag should also be 

reserved for those situations in which opposing left-turn movements (or U-turns) are 

safe from the left-turn trap (or are prohibited). The “left-turn trap” occurs when the 

left-turning driver’s right-of-way is terminated, while the opposing (oncoming) approach 

continues with a green arrow and an adjacent through movement. Thus, left-turning 

drivers facing a yellow indication are trapped; they believe that the opposing traffic will 

also have a yellow signal, allowing them to turn on the yellow or immediately after. 

Since the opposing traffic is not stopping, the turning driver is faced with a potentially 

hazardous situation. Locations where the left-turn trap is not a hazard include 

T-intersections, and those where the left turn (or U-turn) opposing the green arrow is 

prohibited or is allowed only on a green arrow (protected-only phasing). In addition, 

driver expectancy weighs heavily in favor of leading left turns, and driver confusion over 

lagging left turns results in losses in start-up time.
148 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

9 Right-Turn Traffic Control for 

Signalized Intersections

The right-turn-on-red (RTOR) maneuver provides increased capacity and operational 

efficiency at a low cost (Institute of Transportation Engineers [TEH], 1999). However, 

traffic control device violations and limited sight distances need to be addressed in order 

to reduce the potential for safety problems. TEH concluded that a significant proportion 

of drivers do not make a complete stop before executing an RTOR, and a significant 

portion of drivers do not yield to pedestrians. In a review of the literature on RTOR 

laws and motor vehicle crashes, Zador (1984) reported findings that linked RTOR to 

a 23 percent increase in all right-turning crashes, a 60 percent increase in pedestrian 

crashes, and a 100 percent increase in bicyclist crashes. Analysis of police crash reports 

in four States indicated that drivers who are stopped at a red light are looking left for a 

gap in traffic and do not see pedestrians and bicyclists coming from their right (Preusser, 

Leaf, DeBartolo, and Levy, 1982). Eldritch (1989) noted that, adding to the adverse effects 

RTOR has on pedestrian crashes, many motorists persist in making right turns on red 

even when there is a sign that prohibits the maneuver.

Data describing the safety impact of RTOR were provided by Compton and Milton 

(1994) in a report to Congress by the National Highway Traffic Safety Administration. 

Using the Fatality Analysis Reporting System (FARS) data and data from four State 

files for 1989–1992, it was concluded that RTOR crashes represented a small proportion 

of the total number of traffic crashes in the four States (0.05 percent) and of all fatal 

(0.03 percent), injury (0.06 percent), and signalized-intersection crashes (0.40 percent). 

FARS data showed that approximately 84 fatal crashes per year occurred involving a 

right-turning vehicle at an intersection where RTOR is permitted; however, because the 

status of the traffic signal indication is not available in this database, the actual number of 

fatal crashes that occurred when the signal was red is not known. Slightly less than oneTable 21. Cross-References of Related Entries for Right-Turn Traffic Control for Signalized Intersections.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 279 Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, Intersection, 

Right-of-Way [Assignment], Sign 

Legend, & Traffic Control Signal 

(Traffic Signal)

Table 2B-1

Sects. 2B.18 through 2B.22, 

2B.46, 2B. 52 through 2B. 54

Sects. 3B.08 & 3B.21

Figs. 3B-13b and d, 3B-24, 

3B-27

Sects. 4D.04 through 4D.17, 

4D.22 through 4D.31

Pg. 3-176, Para. 4

Pg. 7-43, Paras. 3-5

Pgs. 9-15 through 9-19, sect. 

on Channelized Four-Leg 

Intersections

Pg. 9-51, Para. 2

Pg. 3, 2nd col, Para. 2

Pg. 37, Para. 2 & top right fig. 

Pgs. 61-65, Sect. on Exclusive 

Right-Turn Lanes

Pg. 100-101, Intersct. No. 7

Pgs. 106-113, Intersct. Nos. 

10-13

Pgs. 124-125, Intersct. No. 19

Pgs. 132-135, Intersct. Nos. 

22-23

Pgs. 148-149, Intersct. No. 35

Pgs. 245-246

Pgs. 462-465, Sect. on Turn 

Lanes

Pg. 413-415, Sect. on Left Turns

Pgs. 632-634, Sect. on Turn 

Restrictions
Handbook for Designing Roadways for the Aging Population 149

CHAPTER 7—INTERSECTIONS

half of these crashes involved a pedestrian (44 percent), 10 percent involved a bicyclist, 

and 33 percent involved one vehicle striking another. Although no data on the age of 

the drivers involved in RTOR crashes were provided, there are reasons for concern that 

increasing problems with this maneuver may be observed with the dramatic growth in 

the number of aging drivers in the United States.

The difficulties that aging drivers are likely to experience making right turns at 

intersections are a function of their diminishing gap-judgment abilities, reduced 

neck/trunk flexibility, attention-sharing deficits, slower acceleration profile, and their 

general reduction in understanding traffic control devices compared with younger 

drivers. Right-turning drivers face possible conflicts with pedestrians, and restrictions 

in the visual attention of aging drivers may allow pedestrian and vehicular traffic to go 

unnoticed. The fact that pedestrians may be crossing the side street, where they enter 

the path of the right-turning vehicle, places a burden upon the driver to search the 

right-turning path ahead. The result is the need to share attention between oncoming 

vehicles approaching from the left and pedestrians in the path to the right. Limitations 

in the range of visual attention, frequently referred to as “useful field of vision,” further 

contribute to the difficulty of aging drivers in detecting the presence of pedestrians or 

other vehicles near the driver’s path. Aging drivers, who may have greater difficulty 

maintaining rapid eye movements and associated head movements, are less likely to make 

correct judgments on the presence of pedestrians in a crosswalk or on their walking 

speed (Habib, 1980).

Researchers have identified that the right-turn maneuver is more problematic for aging 

drivers compared with young or middle-aged drivers, presumably as a result of agerelated diminished visual, cognitive, and physical capabilities. Knoblauch, et al. (1995)

conducted an analysis of right-angle, left-turning, right-turning, side-swipe, and rearend crashes at intersections in Minnesota and Illinois for the time period of 1985–1987, 

comparing crash proportions and characteristics of “middle-aged” drivers ages 30–50, 

“young-elderly” drivers ages 65–74, and “old-elderly” drivers age 75 and older. Turning 

right accounted for 35.8, 39.3, and 42.9 percent, respectively, of the middle-aged, 

young-elderly, and old-elderly drivers’ crashes at urban locations. It appears that, for 

right-turning crashes, the middle-aged driver is most likely crossing the intersection 

on a green signal and the older drivers are turning right on a red signal in front of the 

oncoming middle-aged driver. Similar patterns emerged from examination of the rural 

signalized-intersection pre-crash maneuvers, with middle-aged drivers most often 

traveling straight, and older drivers most often turning left or right. Looking at the 

contributing factors in angle and turning collisions for both rural and urban signalized 

locations, the middle-aged group was much more likely to be characterized by the police 

officer as having exhibited “no improper driving.” This occurred in 65 percent of the 

crashes involving this age group, compared with 30.7 percent of the young-elderly, and 

13.4 percent of the old-elderly. The two elderly groups were more likely to be cited for 

failing to yield (42.0 percent of the old-elderly, 31.9 percent of the young-elderly, and 

10.9 percent of the middle-aged); disregarding the traffic control device (30.7 percent of 

the old-elderly, 22.0 percent of the young-elderly, and 10.3 percent of the middle-aged); 

and driver inattention (8.2 percent of the old-elderly, 8.9 percent of the young-elderly, and 

6.4 percent of the middle-aged). 
150 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Knowledge testing has indicated that, compared with younger drivers, older drivers are

less familiar with the meaning of traffic control devices and relatively new traffic laws 

(McKnight, Simone, and Weidman, 1982). “Newness” of traffic laws, in this regard,

relates not to the period of time that has elapsed since the device or law was implemented, 

but the low frequency with which drivers come in contact with the situation. Aging 

drivers may not encounter right turn on red after stop (RTOR), no turn on red (NTOR), 

or red right-turn arrow situations on a daily basis, due to the significantly lower 

amount and frequency of driving in which they are engaged. The demonstrated lack 

of understanding for the red right-turn arrow (Hulbert, Beers, and Fowler, 1979) and 

increased violations associated with this display (Owolabi and Noel, 1985) would be of 

particular concern for aging road users, drivers and pedestrians alike.

Knoblauch et al. (1995) found that both drivers younger than the age of 65 and drivers

age 65 and older failed to understand that they could turn right on a circular red after 

stopping in the right lane. Although the survey indicated that older drivers were more 

likely to stop and remain stopped (45 percent) than younger drivers (36 percent), the 

differences were not significant.

Staplin, et al. (1997) conducted a controlled field study to measure differences in drivers’ 

RTOR behavior as a function of driver age and right-turn lane channelization. In this 

study, 100 subjects divided across three age groups were observed as they drove their 

own vehicles around test routes using the local street network in Arlington, Virginia. 

The three age groups were young/middle-aged (ages 25–45), young-old (ages 65–74), 

and old-old (age 75+). The percentage of drivers who made RTOR maneuvers at the four 

intersections was included as a measure of mobility.

Staplin et al. (1997) found that significantly fewer drivers in the old-old driver group 

attempted to make an RTOR (16 percent), compared with young/middle-aged drivers 

(83 percent) and young-old drivers (45 percent). Similarly, young/middle-aged drivers 

made an RTOR nearly 80 percent of the time when they had the chance to do so, 

compared with nearly 36 percent for the young-old drivers and 15 percent for the old-old 

drivers. Drivers made significantly fewer RTORs at the skewed channelized intersection 

than at the other three locations. Analysis of the percentage of drivers who made an 

RTOR without a complete stop showed that age, right-turn lane geometry, gender, 

and the age-by-geometry interaction were significant. Young/middle-aged drivers 

made an RTOR without a complete stop nearly 35 percent of the time, compared with 

nearly 25 percent for the young-old and 3 percent for the old-old drivers. Channelized 

intersections, with or without exclusive acceleration lanes, encouraged making an RTOR 

without a complete stop. The unchannelized and the skewed locations showed the lowest 

percentage of RTORs without a complete stop, and were not significantly different from 

each other. The three age groups showed significantly different performance. Old-old 

drivers almost always stopped before making an RTOR regardless of the right-turn 

lane geometry. In only 1 of 26 turns did an aging driver not stop before making an 

RTOR; this occurred at the channelized right-turn lane with an acceleration lane. At 

the unchannelized intersection (which was controlled by a STOP sign), 22 percent of the 

young/middle-aged drivers, 5 percent of the young-old drivers, and none of the old-old 

drivers performed an RTOR without a stop. Where an acceleration lane was available, 

65 percent of the young/middle-aged drivers continued through without a complete stop, 
Handbook for Designing Roadways for the Aging Population 151

CHAPTER 7—INTERSECTIONS

compared with 55 percent of the young-old drivers and 11 percent of the old-old drivers. 

The increased mobility exhibited by the younger drivers at the channelized right-turn 

lane locations (controlled by YIELD signs) was not exhibited by old-old drivers, who 

stopped in 19 of the 20 turns executed at the channelized locations. In summary, with 

increases in driver age, the likelihood of RTOR decreases to a very low level for the 

present cohort of old-old drivers, but when these individuals do engage in this behavior, 

they are virtually certain to come to a complete stop before initiating the maneuver. 

Therefore, the emphasis is to ensure adequate sight distance for the aging turning driver, 

to provide sign and signal indications that are most easily understood by this group, and 

to prompt these motorists to devote adequate attention to pedestrians who may be in 

conflict with their turning maneuver.

Zegeer and Cynecki (1986) found that offsetting the stop line—moving the stop line 

of adjacent stopped vehicles back from the intersection by 6 to 10 ft—was effective in 

providing better sight distance to the left for RTOR motorists. It also reduced the RTOR 

conflicts with other traffic and resulted in more RTOR vehicles making a full stop 

behind the stop line. The offset stop line was recommended as a countermeasure for 

consideration at RTOR-allowed sites that have two or more lanes on an approach and 

heavy truck or bus traffic, or unusual geometrics. 

Zegeer and Cynecki (1986) also found that a novel sign (circular red symbol with NO 

TURN ON RED, shown in Figure 79) was more effective than the standard blackand-white NO TURN ON RED (R10-11a) sign, especially when implemented near the 

signal. This countermeasure resulted in an overall reduction in RTOR violations and 

pedestrian conflicts. They offered that the circular red symbol on the sign helps draw 

drivers’ attention to it, particularly as intersections are associated with a preponderance 

of signs and information, and recommended that it should be added to the MUTCD as an 

alternate or approved as a replacement to the current R10-11a design. Increasing the size 

of the standard NO TURN ON RED sign from its present size of 24 x 30 in to 30 x 36 in 

reduced the proportion of violations at most of the test sites. Finally, Zegeer and Cynecki 

(1986) found that an electronic NO TURN ON RED blank-out sign was found to be 

slightly better than the standard MUTCD sign in terms of reducing violations, and it was 

effective in increasing RTOR maneuvers when RTOR was appropriate, thereby reducing 

vehicle delay. Although the sign is more expensive than standard signs and pavement 

markings, the authors concluded it may be justified in situations where pedestrian 

protection is critical during certain periods (i.e., school zones) or during a portion of the 

signal cycle when a separate, opposing left-turn phase may conflict with an unsuspecting 

RTOR motorist.

Figure 79. Novel 

Sign Tested as a 

Countermeasure 

to Reduce RTOR 

Violations and 

Pedestrian Conflicts 

(Zegeer and 

Cynecki, 1986)
152 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

10 Street Name Signs

The MUTCD (2009) specifies that the lettering on street name signs should be at least 6 

in for upper-case letters and 4.5 in for lower-case letters, and that larger letters should 

be used for street name signs that are mounted overhead. It provides an option for 

using 4-in upper-case lettering and 3-in lower-case lettering on street name signs that 

are posted on local roads with speed limits 25 mph or less. Burnham (1992) noted 

that the selection of letter size for any sign must evaluate the needs of the user, which 

are continuously changing as a function of changes in automotive technology, the 

roadway system, and the population itself. For example, Phoenix, Arizona, a city with 

a large aging driver population, has been using “jumbo” street name signs at signalized 

intersections since 1973. These signs are 16 in high and use 8 in capital letters (Rural 

and Urban Roads, 1973). It is estimated that by the year 2020, 17 percent or more of the 

population will be older than 65 years of age, and by the year 2030, 1 in 5 Americans will 

be older than age 65 (U.S. Bureau of the Census, 1996). The ability to read street signs is 

dependent on visual acuity as well as divided attention capabilities, both of which decline 

significantly with advancing age.

Aging drivers participating in focus groups and completing questionnaires for traffic 

safety researchers over the past two decades have consistently stated that larger street 

signs with bigger lettering and standardization of sign placement overhead would make 

driving an easier task (Yee, 1985; Gutman and Milstein, 1988; Cooper, 1990; Staplin,

Lococo, and Sim, 1990; Benekohal, et al., 1992; Knoblauch, et al., 1995). Problems

with placement included signs that were either obstructed by trees, telephone poles, 

billboards, or large trucks, or placed too close to or across the intersection rather than 

on the near side. Aging drivers stated that they needed more advance notice regarding 

upcoming cross streets and larger street-name signs placed overhead, to give them 

more time to make decisions about where to turn. Also noted were difficulties reading 

traffic signs with too much information in too small an area, and/or with too small a 

typeface, which results in the need to slow down or stop to read and respond to the sign’s 

message. May (1992) noted that providing sufficient time to allow motorists to make 

appropriate turning movements when approaching cross streets can improve safety and 

reduce congestion, and that consistent street signing across political jurisdictions can be 

helpful in this regard, as well as presenting an orderly, predictable picture of the region to 

tourists, business people, and residents. 

A decade later, Eck and Winn (2002) conducted a survey of 172 individuals between the 

age of 50 and 91 (mean age of 73.3). The overall objective was to assess the understanding 

Table 22. Cross-References Of Related Entries For Street-Name Signs.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500–

Volume 9

(2004)

Sect. 1A.14, Abbreviations

Sects. 2A.07, 2A.08, 2A.11, 2A.14, 2A.17, 2D.01 

through 2D.06, 2D.43 & 2E.29

Pg. 2-39, Para. 3

Pg. 3-176, Paras. 1-2

Pgs. V-8-V-16, Sects. on Strategy 3.1 

B1 through Strategy 3.1 B3
Handbook for Designing Roadways for the Aging Population 153

CHAPTER 7—INTERSECTIONS

by West Virginia’s aging drivers of traffic control devices and roadway design features 

associated with unsignalized at-grade intersections on high speed divided roadways. A 

survey was administered in 15 senior centers in counties with high-speed roads within 

their boundaries. One of the survey items asked participants to pick from a list the 

factor that presented the greatest difficulty for them in trying to find a side road when 

traveling on a divided highway. Just over 20 percent indicated that finding a side road 

was not a problem for them. The most frequent factor was “fast moving traffic on my rear 

bumper,” by 24 percent of the respondents, followed by “road sign name that is too small 

to read” by just over 20 percent of the participants. This finding underscores the need for 

larger lettering on street name signs, the use of overhead street name signs, and advance 

placement of street name signs.

Taoka (1991) discussed “spare glance” duration in terms of how drivers allocate their 

visual search time among different tasks/stimuli. The tasks ranged from side/rearview 

mirror glances during turning to reading roadway name signs. Although specific results 

were not differentiated by age, Taoka asserted that 85th percentile glance times at signs 

(about 2.4 s) were likely too long, as 2.0 s is the maximum that a driver should divert 

from the basic driving task. Since aging drivers are more apt to be those drivers taking 

longest to read signs, these results imply that they will commonly have problems dividing 

attention between searching for/reading signs and the basic driving task. Malfetti and 

Winter (1987) observed that aging drivers exhibited excessive vehicle-braking behavior 

whenever a signal or road sign was sighted. This was categorized as an unsafe behavior, 

because it is confusing and disruptive to following traffic when the lead vehicle brakes for 

no apparent reason. These researchers obtained many descriptions of aging drivers who 

stopped suddenly at unexpected times and in unexpected places, frequently either within 

the intersection or 40 ft before the intersection to read street signs. 

The visibility of retroreflective signs must be considered with regard to their dual 

requirements of detection and legibility. The sign components affecting detection are sign 

size, color, shape, brightness, and message or content design. External factors affecting 

sign detection include its placement (e.g., left, right, or overhead), the visual complexity 

of the area, and the contrast of the sign with its background. The component parts of 

retroreflective signs that determine legibility fall into two major classes of variables: 

character and message. Character variables include the variables related to brightness—

i.e., contrast, luminance, color, and contrast orientation—as well as font, letter height, 

letter width, case, and stroke width. Message variables address the visibility issues of 

spacing and include interletter, interword, interline, and copy-to-border distances. 

Most studies of sign legibility report legibility distance and the letter height of the 

stimulus; dividing the former measure by the latter defines the “legibility index” (LI), 

which can serve as a common denominator upon which to compare different studies. 

Forbes and Holmes (1939) used the LI to describe the relative legibility of different letter 

styles. Under daytime conditions, series B, C, and D were reported to have indexes of 

(33 ft/in, 42.5 ft/in, and 50 ft/in), respectively. Forbes, Moskowitz, and Morgan (1950) 

found the wider, Series E letters to have an index of 55 ft/in. Over time the value of 50 ft/

in of letter height became the nominal, though arbitrary and disputed, standard. The LI 

is important to the size requirement determination for a sign in a specific application. 

Based on the physical attributes of the aging driver population, the then-standard of 
154 Handbook for Designing Roadways for the Aging Population

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50 ft of legibility for every 1 in of letter height (corresponding to a visual acuity of 20/25) 

exceeded the visual ability of approximately 40 percent of the drivers between ages 65 and 

74. The MUTCD (2009) section 2A.13, which provides guidance for determining sign 

letter heights, indicates that sign letter heights should be determined based on 1 inch of 

letter height per 30 ft of legibility distance; this shift is certainly desirable considering the 

human factors issues addressed in this chapter. 

Mace (1988), in his work on minimum required visibility distance (MRVD) for highway 

signs, noted the following relationships:

Required letter size = MRVD / LI or Required LI = MRVD / letter size

Either the letter size or the LI may be manipulated to satisfy the MRVD requirement, 

which specifies the minimum distance at which a sign should be read for proper driver 

reaction. 

Olson and Bernstein (1979) suggested that aging drivers should not be expected to 

achieve a LI of 50 ft/in under most nighttime circumstances. The data provided by this 

report gives some expectation that 40 ft/in is a reasonable goal under most conditions. 

A 40 ft/in standard can generally be effective for aging drivers, given contrast ratios 

greater than 5:1 (slightly higher for guide signs) and luminance greater than 10 cd/m2

 for 

partially reflectorized signs. With regard to the effect of driver age on legibility, Olson, 

Sivak, and Egan (1983) concluded that older drivers require more contrast between the 

message and the sign’s background than younger drivers to achieve the same level of 

comprehension. They also noted that legibility losses with age are greater at low levels 

of background luminance. A reduction in legibility distance of 10 to 20 percent should 

be assumed when signs are not fully reflectorized. (It should be noted that the MUTCD

(2009) includes text in section 2A.07 that states that regulatory, warning, and guide signs 

shall be retroreflective or illuminated to show the same shape and color by both day and 

night, unless specifically stated otherwise in the MUTCD text discussion of a particular 

sign or group of signs. Section 2D.03 further states that all messages, borders, and legends 

on guide signs shall be retroreflective, and all backgrounds shall be retroreflective or 

illuminated.) Also, higher surround luminance improved the legibility of signs more 

for aging drivers and reduced the negative effects of excessive contrast. In general, the 

LI for aging drivers is 70 to 77 percent of the LI for younger drivers. The average LI for 

aging drivers is clearly below the nominal value of 50 ft/in of letter height. The means 

for aging drivers are generally between 40 ft/in and 50 ft/in; however, the 85th percentile 

values reported are between 30 ft/in and 40 ft/in (Sivak, Olson, and Pastalan, 1981; 

Kuemmel, 1992; Mace, Garvey, and Heckard, 1994). Mace (1988) concluded that a most

conservative standard would provide drivers with 2 minutes of arc, which corresponds to 

20/40 vision and a 30 ft/in LI. 

In a laboratory simulation study, Staplin et al. (1990) found that older drivers (ages 

65–80) demonstrated a need for larger letter sizes to discern a message on a guide sign, 

compared with a group of younger drivers (ages 19–49). To read a one-word sign, older 

drivers required a mean letter size corresponding to 2.5 minutes of visual angle (or a 

Snellen acuity of 20/50), compared with the mean size required by younger drivers of 

1.8 minutes of visual angle (or Snellen acuity of 20/35). Character size requirements 

increased for both age groups when the message contained four words, to 3.78 minutes 
Handbook for Designing Roadways for the Aging Population 155

CHAPTER 7—INTERSECTIONS

of visual angle (acuity equivalent of 20/75) for the older drivers, and to 2.7 minutes of 

visual angle (acuity equivalent of 20/54) for the younger drivers. The main effect of age 

for the word and message legibility measure was highly significant. Staplin et al. (1990) 

concluded that for standard highway signing, an increase in character size in the range 

of 30 percent appears necessary to accommodate age-related acuity differences across the 

driving population.

Tranchida, Arthur, and Stackhouse (1996) conducted a field study using aging drivers 

who drove the research laboratory’s vehicle at nighttime, to determine the legibility 

distances of street-name signs as a function of sheeting type. The subjects included 

nine males ages 68 to 74, and nine females ages 62 to 83. The four sheeting types were: 

Type IX, Type VII, Type III, and Type I (American Society for Testing and Materials, 

2001). Intersections of three levels of complexity were used: high complexity/ high traffic 

activity (e.g., large intersection in downtown business area); intermediate complexity/

intermediate traffic activity (e.g., small intersection area in suburban small business/

apartment area); and low complexity/low traffic activity (e.g., residential area of singlefamily homes). All intersections were lighted. Street-name signs with invented names 

(Strike, Strong, Stress, Straw, Story, and Storm) were created using Series C letters, with 

a 6-in uppercase “S”, followed by 4.5-in lowercase letters. There were no borders on the 

street name signs. The signs were placed on the far side of the intersection, either on the 

right or the left side, and the drivers’ task was to read aloud the street name as soon as it 

was legible to them, as they approached at a speed of 20 mph. The vehicle was a two-door 

sedan with automatic transmission, power steering, and power brakes.

The mean legibility distances across the three intersections and two street sides were as 

follows for the four sheeting types: Type VII=170 ft; Type IX=172 ft; Type III=142 ft; and 

Type I=130 ft. Legibility distances were always longer for signs placed on the right side 

of the street than for those placed on the left. The mean legibility distances for the signs 

mounted on the right side of the road and corresponding luminances of the sheeting at 

the legibility distances are as follows: Type VII=205 ft) and 4.392 cd/m2

; Type IX=201 ft 

and 7.369 cd/m2

; Type III=177 ft and 1.1314 cd/m2; and Type I=174 ft and 0.9671 cd/m2. 

Sheeting Types VII and IX performed similarly, and produced significantly longer 

legibility distances than both Type III and Type I sheeting. However, Types VII and Type 

IX provided significantly longer legibility distances only for the intersections with high 

complexity viewing conditions. There was no significant benefit in legibility distance 

for Type VII and Type IX sheeting at the two streets making up the low complexity 

intersection and on one street that was less traveled and less visually complex than the 

other in the intermediate complexity intersection.

These results suggest that at visually complex intersections with exaggerated demands 

for divided attention, the use of retroreflective sheeting that provides increased legibility 

distance would be of clear benefit to aging drivers. Sheeting that provides for high 

retroreflectance overall, and particularly at wide observation angles typical when viewing 

street-name signs, would best meet this need. The anticipated benefit is that fewer 

glances will need to be directed toward the sign to determine the legend, and more effort 

can be devoted to vehicle control and visual search for traffic and pedestrian conflicts.

The use of mixed-case letters on overhead street name signs was studied by Garvey,

Gates, and Pietrucha (1997). Based on this research, it was recommended that for any
156 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

approach with a 35 mph or lower speed limit, an overhead street name sign should 

have 8-in uppercase and 6-in lowercase letters. For approaches with a speed limit above 

35 mph, an overhead street name sign should contain 10-in uppercase and 8-in lowercase 

letters. This recommendation is based on the need for street name signs to be legible for 

5.5-s before the intersection, which allows for a 1.5-s alerted perception-reaction time 

to read a sign and initiate a response (Johannson and Rumar, 1971), plus a 4.0-s interval 

to complete a combined speed reduction and tracking task (McGee, et al., 1979). Street

name signs should therefore be readable at 300 ft at speeds of 35 mph, and at 450 ft at 

55 mph.

In an earlier study, Garvey, Meeker, and Pietrucha (1996) found a 12 to 15 percent

increase in recognition distance for mixed-case text over all upper case legends under 

both daytime and nighttime conditions. However, this result was for recognition of 

words that drivers already knew would appear on the signs. Because the reading of street 

name signs is often a recognition task, rather than a pure legibility task, the reading 

distance of street name signs will be higher than would be predicted on driver visual 

acuity alone. At the same time, street name legends provide useful information only 

when they can be read and understood by motorists. This fact underscores the focus on 

manipulations of those characteristics of sign legends that can increase reading distance. 

The rationale for mixed-case letters is reported above; the case for enhancements of street 

name letter fonts follows. Another obvious manipulation, of course, is simply the size of 

the letters themselves.

Garvey, Pietrucha, and Meeker (1997) investigated an experimental font in two controlled

field studies, using drivers ages 65 to 83. To accurately describe this research, it is 

necessary to use a trademarked name; however, this does not imply an endorsement of 

this product by the U.S. Government. Also, until this font undergoes the procedures

required for MUTCD approval (rule making process), a recommendation cannot be made 

to use a non-standard font on standard highway signs. Garvey at al. (1997) compared

the recognition distances and legibility distance of words displayed in mixed-case 

Clearview® font with those displayed in Standard Highway Series D uppercase font, and 

mixed-case Standard Highway Series E(M) font. The Clearview® font was developed to 

have open, wider spaces within a letter, to eliminate the effects of irradiation/halation 

that is caused by bright, bold stroke widths that “bleed” into a character’s open spaces, 

rendering it illegible. Since each Clearview® character has more openness than the 

Standard Highway font, the intercharacter spacing is smaller. Clearview® spacing results 

in words that take up 10.8 percent less space than Standard Highway fonts, such that a 

12 percent increase in Clearview® character height results in words equal in sign space to 

words presented in the Standard fonts. The Clearview® font was produced in a regular 

version, with visual proportions similar to the Standard FHWA Series E(M) font, as 

well as in a condensed version, with visual proportions similar to the Standard FHWA 

Series D font. Two sizes of the Clearview® font were displayed: Clearview® 100 (fonts 

matched to Standard Highway font height) and Clearview® 112 (fonts 112 percent of 

Standard Highway font letter height, but equal in overall sign size to Standard Highway 

font). The fonts tested are described in Table 23. The Clearview® fonts will be referred 

to as Clear Condensed 100, Clear Condensed 112, Clear 100, and Clear 112 throughout 

the remainder of this section. White words were created with either encapsulated lens 

(ASTM Type III: RA=250 cd/lux/m2

) material or microprismatic sheeting designed for 
Handbook for Designing Roadways for the Aging Population 157

CHAPTER 7—INTERSECTIONS

short-distance brightness (RA=430 cd/lux/m2), and were displayed on a green sign panel 

measuring 4 ft2

. Each sign contained three place names, each containing six letters (from 

the same font). The study was conducted using one subject at a time, who was seated in 

the front passenger’s seat of a vehicle driven by the experimenter. For each test run, the 

vehicle was started at a point 1,000 ft from the sign.

For the word recognition study, the experimenter read aloud the place name that 

the subject was to look for on a sign. As the experimenter drove toward the sign at 

approximately 5 to 10 mph, the subject’s task was to tell the experimenter when he or she 

could determine where the place name was located on the sign: top, middle, or bottom. 

The distance from the sign at which the subject answered correctly was recorded as the 

recognition distance. Twelve aging drivers (mean age = 70.9 years) completed the word 

recognition study during the day, and another 12 aging drivers (mean age = 74.8 years) 

completed the study at nighttime.

A new set of 24 subjects was recruited for the legibility study, with half completing 

the study during daytime (mean age = 71.3 years) and half at nighttime (mean age = 

73.9 years).

For the word legibility study, subjects were presented with only one word on a sign, and 

were required to read the word. Legibility distance was recorded at the point where 

subjects correctly read the word. 

Results of the word recognition study indicated that during the daytime, there were no 

significant differences between either the Clear 100 or Clear 112 and the Series E(M) 

fonts. However, when comparing the Clear Condensed 100 and Clear Condensed 112 

to the Series D font, the mixed-case fonts produced significantly longer recognition 

distances (14 percent greater) than the all uppercase Standard Highway font. At 

nighttime, the Clear 100 font did not produce recognition distances significantly 

different from those obtained with the Standard E(M) font, however, the Clear 112 

font produced significantly greater recognition distances (16 percent greater) than the 

Standard E(M) font. The Clear 112 and Clear Condensed 112 fonts produced significantly 

longer recognition distances than the all-uppercase Series D font. Under both daytime 

and nighttime, there were no significant effects of material brightness, for the word 

Table 23. Fonts Tested by Garvey, Pietrucha, and Meeker (1997).

Font Name Case Letter Height

Clear Condensed 100 mixed case Upper Case: 5 in 

Lower Case: 3.9 in loop height

Clear Condensed 112 mixed case Upper Case: 5.6 in 

Lower Case: 4.4 in

Standard Highway Series D Uppercase 5 in 

Standard Highway Series E(M) mixed case Upper Case: 5 in 

Lower Case: 3.9 in loop height

Clear 100 mixed case Upper Case: 5 in 

Lower Case: 3.9 in loop height

Clear 112 mixed case Upper Case: 5.6 in 

Lower Case: 4.4 in
158 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

recognition study. The mean daytime and nighttime recognition distances for the six 

fonts are displayed in Table 24.

Table 24. Daytime and Nighttime Recognition Distances for Fonts Studied by Garvey, 

Pietrucha, and Meeker (1997).

Font Name

Daytime Recognition Distance

(ft)

Nighttime Recognition 

Distance

(ft)

Clear Condensed 100 394 282

Clear Condensed 112 440 344

Standard Highway Series D 384 282

Clear 100 433 338

Clear 112 472 387

Standard Highway Series E(M) 449 331

The results of the word legibility study conducted during the daytime indicated that 

the microprismatic sheeting produced a 4 percent improvement in legibility distance, 

compared to the encapsulated lens sheeting. There was no significant interaction between 

font and material, however. Looking at the effects of font on legibility distance, there 

was no significant difference in the daytime legibility distances obtained with the Series 

E(M) font and the Clear 100 and Clear 112 fonts. There was also no significant difference 

in legibility distance between the Series D font and the Clear 112 and Clear Condensed 

112 fonts. However, the all uppercase Series D font showed significantly longer legibility 

distances than the Clear Condensed 100 font. 

At nighttime, there was a significant interaction effect between font and sheeting 

material, such that the Clear 112 font produced significantly longer legibility distances 

(22 percent longer) than the Series E(M) font, using the encapsulated lens sheeting. The 

microprismatic sheeting showed the same trend (although not significant), with the Clear 

112 font producing 11 percent longer legibility distances than the Series E(M). There 

were no differences between the all uppercase Series D font and the same-size, mixedcase Clear fonts (i.e., Clear 112 and Clear Condensed 112). However, the Series D font 

produced significantly longer legibility distances than the Clear Condensed 100 font 

at night. The legibility distances obtained for the six fonts studied under daytime and 

nighttime are shown in Table 25.

Table 25. Daytime and Nighttime Legibility Distances for Fonts Studied by Garvey, Pietrucha, 

and Meeker (1997).

Font Name

Daytime Legibility Distance

(ft)

Nighttime Legibility 

Distance

(ft)

Clear Condensed 100 187 148

Clear Condensed 112 220 194

Standard Highway Series D 223 207

Clear 100 220 197

Clear 112 230 246

Standard Highway Series E(M) 223 ft 197 ft
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CHAPTER 7—INTERSECTIONS

Garvey, Pietrucha, and Meeker (1997) state that guide signs are read using both legibility

and recognition criteria, depending on the familiarity of a traveler with the location 

words used on the signs. A driver who is looking for a particular word on a sign will be 

able to read it at a farther distance that a driver who has no idea of what might be on the 

sign. In the legibility task, the larger letters used with the all-uppercase Series D font 

produced greater legibility distances than the smaller mixed case Clear 100 Condensed 

font. But when the mixed-case font was increased to take up the same sign area as the 

Series D font (Clear Condensed 112), the legibility distances for the mixed-case and 

uppercase fonts were the same. In the recognition task, for which Garvey, Pietrucha, and

Meeker (1998) state more closely represents real-world behavior, the same-size, mixedcase fonts performed significantly better than the all uppercase Series D font. And, even 

the mixed-case font that took up less sign space performed as well as the all-uppercase, 

Series D font, in terms of word recognition. The authors explain that uppercase words 

look like blurry rectangles when viewed from a distance. Mixed-case font, on the other 

hand, produces words with a recognizable overall shape, due to the ascending and 

descending elements in each letter. The data from this study indicate that if the size of 

mixed-case words on a sign is matched to the size of words presented in all uppercase 

font, the mixed-case font provides equal legibility distance and superior recognition 

distance.

Next, the MUTCD states that street-name signs should be placed at least on diagonally 

opposite corners so that they will be on the far right-hand side of the intersection for 

traffic on the major street. Burnham (1992) noted that signs located over the highway 

are more likely to be seen before those located on either side of the highway. In this 

regard, Zwahlen (1989) examined detection distances of objects in the peripheral field 

versus line-of-sight detection and found that average detection distances decrease 

considerably as the peripheral visual detection angle increases. Placement of street-name 

signs overhead places the sign in the driver’s forward line of sight, eliminating the need 

for the driver to take his/her eyes away from the driving scene, and reduces the visual 

complexity of the sign’s surround, but under some sky conditions (e.g., backlit by the 

sun at dawn and dusk) the sign may be unreadable. Thus, overhead street-name signing 

should be a supplement to standard roadside signing. 

The use of an advance street name plaque (W16-8) with an advance warning crossroad, 

side road, or T-intersection sign (W2-1, W2-2, W2-3, and W2-4) provides the benefit 

of additional decision and maneuver time prior to reaching the intersection. Section 

2C.46 of the MUTCD (2009) indicates the use of such supplemental street-name signs 

on intersection warning signs as an option (e.g., an advance street name plaque may be 

installed above or below an Intersection Warning Sign). The use of advance street name 

plaques on advance warning signs has been successful in Phoenix, AZ (Rural and Urban 

Roads, 1973); the size of the lettering on these signs is 8 in (200 mm). Midblock streetname signs provide the same benefit, and are described as an option in section 2D.36 of 

the MUTCD. 

Finally, noting Mace’s (1988) conclusions supporting a legibility index as conservative 

as 30 ft/in to accommodate aging drivers, and the practical limitations of increasing 

sign panel size, a justification emerges for eliminating the border on street name signs 

to permit the use of larger characters. The MUTCD (2009) section 2A.14 states that, 
160 Handbook for Designing Roadways for the Aging Population

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11 Stop and Yield Signs

“Unless otherwise provided, each sign illustrated in this Manual shall have a border of 

the same color as the legend, at or just inside the edge.” In section 2D.43 (Street Name 

Signs), the MUTCD states that, “Regardless of whether green, blue, or brown is used as 

the background color for Street Name (D3-1 or D3-1a) signs, the legend (and border, 

if used) shall be white. For Street Name signs that use a white background, the legend 

(and border, if used) shall be black.” The border on street name signs is presumed to 

enhance the conspicuity of the sign panel at intersections, where visual complexity and 

driving task demands may be relatively high. However, the aspect of conspicuity at issue 

here is “search conspicuity” rather than “attention conspicuity;” as demonstrated by 

Cole and Hughes (1984), a sign is noticed at significantly greater distance when a driver 

expects its presence and knows where to look for it. This is the case with street name 

signs at intersections. Detecting the presence of street name signs isn’t the problem—

reading them is. Thus, a strong argument can be made that any marginal reduction in 

conspicuity that may result from eliminating sign borders will be more than offset by the 

resultant gains in legibility produced by larger characters in the sign legend. 

Drivers approaching an unsignalized intersection must be able to detect the presence of 

the intersection and then detect, recognize, and respond to the intersection traffic control 

devices present at the intersection. Next, drivers must detect potential conflict vehicles, 

pedestrian crosswalk locations, and pedestrians at or near the intersection. Proper 

allocation of attention has become more difficult, as drivers are overloaded with more 

traffic, more signs, and more complex roadway configurations and traffic patterns, as well 

as more complex displays and controls in newer vehicles (Dewar, 1992). The presence of 

large commercial signs near intersections has been associated with a significant increase 

in crashes at stop-controlled intersections (Holahan, 1977). 

Age-related deficits in vision and attention are key to developing recommendations for 

improved stop control and yield control at intersections. Researchers examining the 

State crash records of 53 aging drivers found that those with restrictions in their “useful 

field of view,” a measure of selective attention and speed of visual processing, had 15 

times more intersection crashes than those with normal visual attention (Owsley, et al., 

1991). A follow-up study with a sample of 300 drivers demonstrated that visual attention 

deficits could account for up to 30 percent of the variance in intersection crash experience 

(Ball, et al., 1993). Additional relevant findings may be cited from a simulator study 

of peripheral visual field loss and driving impairment which also examined the actual 

driving records of the study participants (Szlyk, Severing, and Fishman, 1991). It was 

found that visual function factors, including acuity as well as visual field measures, could 

account for 26 percent of the variance in real-world crashes. Also, greater visual field loss 

was associated in the simulator data with greater distance traveled (“reaction distance”) 

before responding to a peripheral stimulus (e.g., a STOP sign).

A considerable body of evidence exists documenting the difficulties of aging driver 

populations in negotiating stop-controlled intersections. Specifically, analyses of crash 

and violation types at these sites highlight the aging driver’s difficulty in detecting, 
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CHAPTER 7—INTERSECTIONS

Table 26. Cross-References Of Related Entries For Stop And Yield Signs.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 –

Volume 9

(2004)

NCHRP 279 

Intersection 

Channelization

Design Guide 

(1985)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, regulatory sign

Tables 2B-1 & 2C-4 

Sects. 2B.03 through 2B.12, 

3B.16 & 2C.36

Pgs. 3-2 through 3-6, 

Sect. 3.2.2 Stopping Sight 

Distance

Pg. 9-30, Fig.9-15

Pgs. 9-36 through 

9-50, Sects. on Case 

B-Intersections with Stop 

Control on the Minor Road & 

Case C—Intersections with 

Yield Control on the Minor 

Road

Pg. 9-180, Para. 2

Pg. 10-90, Sect. on At-grade 

terminals

Pg. 10-105, Para. 1 

Pgs. V-8-V-11, Sect. on 

Strategy 3.1 B1: Provide 

Advance Warning Signs (T)

Pg. 9, Figs. 2-5 & 2-7

Pg. 10, Table 2-4, 4th bullet

Pg. 21, Fig. 3-1

Pgs. 357, Sects. on 

Regulatory Signs

Pg. 381, Sect. on Stop and 

Yield Lines

Pgs. 629-630, Sects. on 

Yield Control and Stop 

Control

Pgs. 110-111, Sect. on 

Traffic Characteristics at 

Unsignalized Intersections

Pg. 391-392, Sect. on Older 

Drivers and Pedestrians

comprehending, and responding to signs within an appropriate timeframe for the safe 

completion of intersection maneuvers.

Statistics on Iowa fatal crashes show that during 1986–1990, running STOP signs was a 

contributing circumstance in 297 fatal crashes which killed 352 people; drivers age 65 

and older accounted for 28 percent of the fatal crashes, and drivers younger than age 25 

were involved in 27 percent of the fatal crashes (Iowa Department of Transportation, 

1991). Stamatiadis, Taylor, and McKelvey (1991) found that at stop-controlled urban

intersections, the percentage of drivers age 75 and older involved in right-angle crashes 

was more than double that of urban signalized intersections. Malfetti and Winter (1987), 

reporting on the unsafe driving performance of drivers age 55 and older, noted that 

aging drivers frequently failed to respond properly or respond at all to road signs and 

signals; descriptions of their behavior included running red lights or STOP signs and 

rolling through STOP signs. Some aging persons’ behavior at STOP signs and signals 

seemed to indicate that they did not understand why they needed to wait when no other 

traffic was coming. Brainan (1980) used in-car observation to gain firsthand knowledge 

and insight into aging people’s driving behavior. Drivers in the 70 and older age group 

showed difficulty at two of the STOP signs on the test route; their errors were in failing to 

make complete stops, poor vehicle positioning at STOP signs, and jerky and abrupt stops. 

Campbell, Wolfe, Blower, Waller, Massie, and Ridella (1990), looking at police reports of 

crossing crashes at unsignalized intersections, found that aging drivers often stopped and 

then pulled out in front of oncoming traffic, whereas younger drivers more often failed to 

stop at all. Further evidence of unsafe behaviors by aging drivers was provided in a study 

by McKnight and Urquijo (1993). Their data consisted of 1,000 police referral forms from

the motor vehicle departments of California, Maryland, Massachusetts, Michigan, and 

Oregon; the forms included observations of incompetent behavior exhibited by aging 
162 Handbook for Designing Roadways for the Aging Population

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drivers who were stopped for a violation by law enforcement personnel or were involved 

in a crash. The specific behaviors contributing to the contact between the aging driver 

and the police officer included failing to yield right-of-way or come to a complete stop at 

a STOP sign, and failing to stop or yield to other traffic; taken together, these behaviors 

contributed to significant numbers of crashes (74) and violations (114).

Data from 124,000 two-vehicle crashes (54,000 crashes at signalized intersections and 

70,000 crashes at unsignalized intersections) showed that drivers younger than age 

25 and older than age 65 were overinvolved in crashes at both types of intersections 

(Stamatiadis et al. 1991). However, the overinvolvement of aging drivers in unsignalized 

intersection crashes was more pronounced than it was for signalized intersection crashes. 

Although the total number of crashes was reduced at unsignalized intersections that 

contained signs when compared with unsigned intersections, the crash involvement 

ratios of aging drivers were higher at signed intersections than at unsigned intersections. 

At unsignalized intersections, the highest percentage of fatalities resulted from rightangle collisions (25 percent). In terms of the frequency of injury at unsignalized 

intersections, rear-end crashes were the most frequent cause (35 percent), followed by 

right-angle crashes (18 percent), other-angle crashes (10 percent), and head-on/leftturn crashes (8 percent). The leading violation types for all aging drivers in descending 

order were failure to yield right-of-way, following too closely, improper lane usage, and 

improper turning. At unsignalized intersections, aging drivers showed the highest crash 

frequency on major streets with two lanes in both directions (a condition most frequently 

associated with high-speed, low-volume rural roads), followed by roads with four lanes, 

and those with five lanes in both directions. These configurations were most often 

associated with low-speed, high-volume urban locations, where intersection negotiation 

involves more complex decisions involving more conflict vehicles and more visually 

distracting conditions. 

Cooper (1990) utilized a database of all 1986 police-attended crashes in British Columbia, 

in an effort to compare the crash characteristics of aging drivers with those of their 

younger counterparts. While 66.5 percent of crashes involving drivers ages 36–50 

occurred at intersections, the percentage increased to 69.2 percent, 70.7 percent, and 

76.0 percent for drivers ages 55–64, 65–74, and 75 and older, respectively. Overall, the 

two oldest groups identified in this analysis were significantly more crash involved at 

STOP/YIELD sign locations and less involved at either uncontrolled or signal-regulated 

locations. In follow-on questionnaires administered to a sample of drivers in each age 

group studied, intersection negotiation was mentioned by the aging drivers as second in 

difficulty to problems changing lanes. About 20 percent of the aging drivers mentioned 

not stopping properly at STOP signs. Vehicle maneuvering prior to the crash was a key 

variable for drivers over age 65, and in particular, for left turns at uncontrolled or STOP/

YIELD sign-controlled intersections. Drivers ages 36–50 experienced only 10.9 percent 

of their crashes while turning left at this type of intersection, compared with 13.0, 15.4, 

and 19.5 percent of drivers ages 55–64, 65–74, and 75 and older, respectively.

Council and Zegeer (1992) conducted an analysis of intersection crashes occurring 

in Minnesota and Illinois for the time period of 1985–1987 to highlight crash types, 
Handbook for Designing Roadways for the Aging Population 163

CHAPTER 7—INTERSECTIONS

situations, and causes of crashes, in an effort to increase the knowledge of how aging 

drivers react at intersections. For all the analyses, comparisons were made between a 

“young-old” group (ages 65–74), an “old-old” group (age 75 or older), and a “middleaged” comparison group (ages 30–50). Their findings regarding driver age differences in 

collision types, pre-crash maneuvers, and contributing factors are described below.

With respect to collision type at stop-controlled intersections, analysis of the data showed 

little difference in the proportion of crashes involving left-turning vehicles at either urban 

or rural locations when the older groups were compared with the middle-aged group. 

There was, however, a significant over-involvement for both groups of older drivers in 

right-angle collisions, both in urban and in rural locations. At urban intersections, 

right-angle collisions accounted for 56.1 percent of the middle-aged driver crashes, 

compared with 64.7 percent of the young-old, and 68.3 percent of the old-old driver 

crashes. These percentages increase for all groups at rural intersections—61.3, 68.6, and 

71.2 percent, respectively for middle-aged drivers, young-old drivers, and old-old drivers. 

Data for yield-controlled intersections showed older drivers over-contributing to left-turn 

collisions in urban areas and to angle collisions in both urban and rural areas. 

Regarding pre-crash maneuvers at stop-controlled intersections, for both rural and 

urban locations, right-angle collisions were the most frequent collisions, and middleaged drivers were more likely to be traveling straight or slowing/stopping than the two 

older groups. The older drivers were more likely to be turning left or starting from a 

stop than their younger counterparts. The pattern is similar for left-turning crashes. 

For rear-end collisions, the old-old drivers were more likely to be going straight (thus 

being the striking vehicle), and the middle-aged and young-old drivers were more likely 

to be stopped or slowing. For the few right-turning collisions at urban stop-controlled 

intersections, the middle-aged drivers were going straight and the old-old drivers were 

more likely to be turning left or right or starting from a stop. Rural stop-controlled 

locations showed the same patterns of pre-crash maneuvers among the three age groups.

Finally, breakdowns of contributing factors for the urban and rural stop-controlled 

intersections showed that the middle-aged drivers exhibited a higher proportion of no 

improper driving behavior, while the young-old and old-old drivers were more often cited 

for failure-to-yield, disregarding the STOP sign, and driver inattention. When starting 

from a stop, however, the old-old drivers had a lower probability of being cited for 

improper driving. When cited, the old-old group was more likely to have disregarded the 

STOP sign than the other two driver groups. The young-old drivers as well as the old-old 

drivers more frequently failed to yield than the middle-aged drivers.

For left turns, the middle-aged drivers again were more frequently found to have 

exhibited “no improper driving.” The two older driver groups were most frequently 

cited with failure-to-yield. There was no difference in the number of drivers in each age 

group who disregarded the STOP sign. For going-straight situations, the middle-aged 

driver was found to have exhibited no improper driving behavior twice as often as the 

young-old driver and almost three times as often as the old-old driver. Failing to yield, 

disregarding the STOP sign, and inattention were most often cited as the contributing 

factor for the two older groups.
164 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Signing countermeasures to improve safe operation by aging drivers at stop- and yieldcontrolled intersections follow.

Greene, et al. (1996) noted that the MUTCD provides for the possibility of enlarging 

STOP signs where greater emphasis or visibility is required. They proposed an 

enlargement from 30 x 30 in to 36 x 36 in at well-traveled intersections or at intersections 

of small country lanes with State highways. This would also be appropriate at 

intersections where there is a high incidence of STOP-sign running. Further, Swanson, 

Dewar, and Kline (1994) reported that aging drivers participating in focus group

discussions in Calgary, Alberta, Canada; Boise, Idaho; and San Antonio, Texas indicated 

a need for bigger and brighter STOP signs.

Mace and Pollack (1983) noted that conspicuity is not an observable characteristic of a 

sign but a construct which relates measures of perceptual performance with measures 

of background, motivation, and driver uncertainty. In this regard, conspicuity may be 

aided by multiple treatments or advance signing as well as changes in size, contrast, and 

placement. They noted that STOP signs following a STOP AHEAD (W3-1a) sign are 

more conspicuous not only to aging drivers but to everyone, because expectancy has been 

increased.

The need for appropriate levels of brightness to ensure conspicuity and timely detection 

by drivers of highway signs, including STOP and YIELD signs, was addressed in 

FHWA-sponsored research to establish minimum retroreflectivity requirements for 

these devices (minimum maintained levels, as opposed to new or in-service levels). 

Mace developed a model to derive the retroreflectivity levels necessary for adequate 

visibility distance, taking into account driver age and visual performance level, as 

well as the driver’s response requirements (action versus no action) to the information 

presented on a given sign when encountered in a given situation (city, highway) with an 

assumed operating speed (ranging from 10 mph to 65 mph), for signs of varying size 

and placement (shoulder, overhead). This work is reported by Ziskind, et al. (1991), who 

conducted laboratory and controlled field studies using 200 younger and older drivers 

(ages 16 to 70+) to determine the minimum visibility requirements for traffic control 

devices. Taking speed and sign application into account, the recommended (minimum 

maintained, below which the sign should be replaced) retroreflectivity for STOP signs 

resulting from this research ranged between 10 cd/lux/ m2 up to 24 cd/lux/ m2 for 

the sign background (red) area, with significantly higher values for the sign legend. 

For the YIELD sign, the recommended minimum maintained levels ranged between 

24 and 39 cd/lux/ m2. These units, in cd/lux/m2, or coefficient of retroreflection (RA) 

express the efficiency with which the material is able to return incident light at a given 

geometry between the sign, the vehicle, and the driver. A retroreflectometer is used to 

obtain these data in the field; reflectivity of a material is measured at specific angles. The 

observation angle is the angle between the headlamps, the sign, and the driver’s eye. 

The RA measurements provided by FHWA are all measured at a 0.2 degree observation 

angle, which corresponds roughly to a viewing distance of 700 ft, for a right shouldermounted sign on a straight road viewed from a passenger sedan. This is important, 

because in general, as a vehicle approaches a sign, the observation angle becomes larger, 

reaching 1.0 degrees at 300 ft, which is roughly legibility distance. Knowing the RA of a 

material at 0.2 degrees does not automatically predict its reflectivity at a closer distance 
Handbook for Designing Roadways for the Aging Population 165

CHAPTER 7—INTERSECTIONS

(larger observational angle). Because both the STOP and YIELD signs are so extensively 

overlearned by drivers, their comprehension is believed to be associated with the icon, 

i.e., their unique shape and coloration. Thus, the brightness of the sign’s background 

area is most critical, because these devices will typically be recognized and understood 

as soon as they are detected (the conspicuity distance), rather than closer in (legibility 

distance).

Mercier, et al. (1995) conducted a laboratory study using younger and older drivers to 

measure the minimum luminance thresholds for traffic sign legibility, to accommodate 

varying percentages of the driving population. The purpose of the study was to evaluate 

the proposed minimum retroreflectivity values derived using CARTS (Computer 

Analysis of the Retroreflectance of Traffic Signs) that uses a mathematical model to study 

the relationships between driver variables, vehicle variables, sign variables, and roadway 

variables (Paniati and Mace, 1993). This model uses MRVD (Minimum Required 

Visibility Distance), which is the shortest distance at which a sign must be visible to 

enable a driver to respond safely and appropriately, and includes the distance required 

for a driver to detect the sign, recognize the message, decide on a proper action, and 

make the appropriate maneuver before the sign moves out of the driver’s view. Paniati 

and Mace’s minimum in-service values (below which sign replacement is indicated) were 

reported to accommodate an unknown level between 75 to 85 percent of all drivers (see 

Table 27).

The subjects in the Mercier et al. (1995) study included 10 drivers ages 16 to 34; 10 drivers 

ages 35 to 44; 10 drivers ages 45 to 54; 10 drivers ages 55 to 64; 13 drivers ages 65 to 74; 

and 10 drivers age 75 or older. All subjects had a visual acuity of at least 20/40. Subjects 

viewed 25 scaled signs at two distances to simulate minimum required visibility 

distances (MRVD) traveling at 30 mph and 55 mph. Among the signs tested were whiteon-red regulatory signs. Illumination levels were manipulated using 20 neutral density 

filters ranging from 0.02 to 3.0. Type I engineering grade sheeting was used for all signs. 

Retroreflectance values were calculated based on the luminance levels needed to 

accommodate 67, 85, and 95 percent of the population of U.S. drivers. Mercier et al. 

Table 27. Minimum (Maintained) Retroreflectivity Guidelines for White on Red Signs Specified 

by Paniati and Mace (1993) to Accommodate 75 to 85 Percent of all Drivers.

Sign Size 

(in)

Speed

(mph)

Minimum Retroreflectivity

(cd/lux/m2

)

30 ≥45 70 (white) 

14 (red)

30 ≤40 40 (white) 

8 (red)

36 ≥45 60 (white) 

12 (red)

36 ≤40 35 (white) 

7 (red)

48 ≥45 50 (white) 

10 (red)

48 ≤40 30 (white) 

6 (red)
166 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

(1995) concluded that the values recommended by Paniati and Mace (1993), reproduced 

in Table 27 for the white on red signs, are sufficient to accommodate a high percentage 

of drivers, with the exception of a few signs, which includes the YIELD sign. The 95th 

percentile driver could not be accommodated by the minimum retroreflectivity suggested 

for the YIELD sign measuring 30 in, for MRVD at both 30 and 55 mph. The authors point 

out that increasing brightness for this sign does not increase legibility for aging drivers; 

instead, a redesign of the sign or an enlargement would be needed to enable aging drivers 

to resolve the level of detail required for recognition.

Next, there has been increasing interest in the use of durable fluorescent sheeting for 

highway signs, because of its increased conspicuity over standard highway sign sheeting, 

under daytime conditions. Highway signs with fluorescent sheeting have been found 

to be more conspicuous and can be detected at a further distance than signs with 

standard sheeting of the same color. In addition, the color of fluorescent signs is more 

frequently recognized correctly at farther distances than standard sheeting of the same 

color (Jenssen, et al., 1996; Burns and Pavelka, 1995). Of particular interest, however, 

are findings reported by Burns and Pavelka (1995) for a field study conducted at dusk 

(15 min after sunset), without the use of vehicle headlights. In this study, 14 drivers 

ages 19 to 57 (median age = 40 years) viewed signs with fluorescent red sheeting and 

signs with standard red sheeting at a distance of 98 ft. The signs with fluorescent red 

sheeting were detected by 90 percent of the participants; only 23 percent were able to 

detect the standard red signs. In terms of correct color recognition, 49 percent were 

able to correctly recognize the color of the fluorescent red signs at dusk from a distance 

of 90 ft, compared to 12 percent who correctly identified the standard red signs as 

red. Luminance measurements of the targets and the background were taken for these 

north-facing signs at dusk, so that luminance contrast ratios could be calculated. The 

luminance contrast ratio (Lt-Lb/Lb, or the luminance of the target minus the luminance 

of the background, divided by the luminance of the background) for the fluorescent red 

signs was 0.7, and the luminance contrast ratio for the standard red signs was 0.3. The 

results of this study suggest that the use of fluorescent red sheeting on STOP signs would 

serve to increase their conspicuity both under daytime and low luminance conditions, 

and would be of particular benefit to aging drivers, who suffer from decreases in contrast 

sensitivity and have greater difficulty quickly isolating and attending to the most 

relevant targets in a cluttered visual background. When additional studies quantify 

the performance gains for aging road users, recommendations for relatively widespread 

use of fluorescent sheeting keyed to specific characteristics of stop- and yield-controlled 

intersections are likely to emerge. Present recommendations for applications of 

fluorescent sheeting are limited to the special cases of controlling prohibited movements 

on freeway ramps (see Chapter 3) and for passive control systems at highway-rail grade 

crossings (see Chapter 6).

A two-way stop requires a driver to cross traffic streams from either direction; this 

poses a potential risk, because cross traffic may be proceeding rapidly and drivers may 

be less prepared to accommodate to errors made by crossing or turning drivers. Most 

critically, drivers proceeding straight through the intersection must be aware of the 

fact that the cross-street traffic does not stop, and that they must yield to cross-street 

vehicles from each direction before proceeding through the intersection. Aging drivers 
Handbook for Designing Roadways for the Aging Population 167

CHAPTER 7—INTERSECTIONS

are disproportionately penalized by the late realization of this operating condition, due 

to the various sources of response slowing noted earlier. Studies of cross-traffic signing 

to address this problem have shown qualified but promising results in a number of 

jurisdictions (Gattis, 1996). Although findings indicate that conversion of two-way to

four-way stop operations may be more effective in reducing intersection crashes than the 

use of cross-traffic signing, there are obvious tradeoffs for capacity from this strategy. 

However, data from crash analyses in Arkansas, Oregon, and Florida reported by Gattis

(1996) showed significant reductions in right-angle crashes after cross-traffic signing was 

installed at problem intersections. Until fairly recently, there was no standard sign design 

to convey this message; Ligon, Carter, and McGee (1985) identified a number of alternate

wordings used in different States. In addition, a warrant for use of a cross-traffic sign 

applied in the State of Illinois may be reviewed in the Gattis (1996) article. The MUTCD

(2009) indicates in section 2C.59 that a CROSS TRAFFIC DOES NOT STOP plaque (W4-

4p) may be used in combination with a STOP sign when engineering judgment indicates 

that conditions are present that are causing or could cause drivers to misinterpret the 

intersection as an all-way stop. 

Picha, et al. (1996) conducted a survey of 2,129 drivers in five States (California, 

Minnesota, Mississippi, Pennsylvania, and Texas) to evaluate driver understanding of 

right-of-way conditions and preference for supplemental signs at two-way, stop-controlled 

intersections. The majority of the respondents (59 percent) were between ages 25 and 54; 

however, 22 percent were age 65 or older. The mail survey presented nine supplemental 

sign designs (three word messages, three symbol messages, and three word-plus-symbol 

messages), and respondents were asked to choose the preferred sign in each category that 

best conveyed the right of way conditions at a two-way, stop-controlled intersection, and 

then to choose the most preferred design of the three. The sign most often preferred (by 

84 percent of the sample) was the CROSS TRAFFIC DOES NOT STOP word message 

with a horizontal double-headed arrow symbol. When asked whether a supplemental 

sign was needed at all two-way, stop-controlled intersections to tell drivers who has 

the right-of-way (a diagram was provided with the question), 44 percent of the drivers 

responded “yes,” 50 percent “no,” and 6 percent “not sure.” Picha et al. (1996) provided 

a list of conditions that may lead a driver to misinterpret an intersection to be all-way 

stop controlled, which would justify a supplemental sign treatment. In addition to 

intersections converted from four-way to two-way stop control, these include:

•	 The intersection of two single-jurisdictional roadways (e.g., two state-maintained

roadways) in a rural or isolated area.

•	 Intersections with similar average daily traffic (ADT) volumes on all approaches,

but less than the minimum volumes that would warrant the installation of a 

traffic signal. Typical volumes ranging from 5,000 to 10,000 ADT will not likely 

meet signal warrants, but could justify a supplemental treatment.

•	 Intersections with a high conflict frequency and rate, i.e., 20 to 25 conflicts per

day (all conflicts combined) or a rate of at least 4 conflicts per 1,000 entering 

vehicles.

•	 Intersections with a right-angle crash frequency in the range of three to five

(or more) per year. Such a condition may not necessarily meet traffic signal 

warrants.
168 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

•	 A system of roadway intersections (at-grade) that is not consistent with respect

to traffic control schemes.

•	 Intersections with similar high speeds (i.e., greater than 50 mph on all

approaches.

•	 Intersections with similar cross-sectional elements (number and width of lanes,

shoulders, grades, drainage) on all approaches.

The issue of driver expectancy, a key predictor of performance for aging motorists, was 

addressed in a study by Agent (1979) to determine what treatments would make drivers 

more aware of a stop-ahead situation. Agent concluded that at rural sites, transverse 

pavement striping should be applied approximately 1,200 ft in advance of the STOP sign 

to significantly reduce approach speeds. Later research (Agent, 1988) recommended 

the following operational improvements at intersections controlled by STOP signs: (1) 

installing additional advance warning signs; (2) modifying warning signs to provide 

additional notice; (3) adding stop lines to inform motorists of the proper location to stop, 

to obtain the maximum available sight distance; (4) installing rumble strips, transverse 

stripes, or post delineators on the stop approach to warn drivers that they would be 

required to stop; and (5) installing beacons. Although Agent emphasized that beacons do 

not eliminate the problem of drivers who disregard the STOP sign, flashing beacons used 

in conjunction with STOP signs at isolated intersections or intersections with restricted 

sight distance have been consistently shown to be effective in decreasing crashes by 

increasing driver awareness and decreasing approach speeds (California Department of 

Public Works, 1967; Cribbins and Walton, 1970; Goldblatt, 1977; King, et al., 1978; Lyles,

1980). 

With regard to the crash reduction effectiveness of rumble strips placed on intersection 

approaches, Harwood (1993) reported that rumble strips can provide a reduction of at 

least 50 percent in the types of crashes most susceptible to correction, including crashes 

involving running through a STOP sign. They can also be expected to reduce vehicle 

speed on intersection approaches and to increase driver compliance with STOP signs. In 

an evaluation conducted by the Virginia Department of Highways and Transportation 

(1981a) where rumble strips were installed at stop-controlled intersections, the total crash 

frequency was reduced by 37 percent, fatal crashes were reduced by 93 percent, injury 

crashes were reduced by 37 percent, and property-damage-only crashes were reduced 

by 25 percent. In this study, 39 of the 141 crashes in the before period were classified as 

being types susceptible to correction by rumble strip installation, particularly rear-end 

crashes and ran-STOP-sign crashes. The crash rate for these crash types was reduced 

by 89 percent. Carstens and Woo (1982) found that primary highway intersections 

where rumble strips were installed experienced a statistically significant reduction in 

the crash rate in the first year or two following their installation, both at four-way and 

T-intersections. The crash rate at the 21 study intersections decreased by 51 percent for 

total crashes and by 38 percent for ran-STOP-sign crashes. Carstens and Woo found 

no statistically significant change in crash rate at 88 intersections on secondary roads 

where rumble strips were installed. They concluded that rumble strips are more effective 

at primary highway intersections than secondary road intersections for the following 

reasons: (1) primary highways serve a higher proportion of drivers who are unfamiliar 
Handbook for Designing Roadways for the Aging Population 169

CHAPTER 7—INTERSECTIONS

with the highway; (2) trips tend to be longer on primary highways so that fatigue and the 

monotony of driving may play a more important role than on secondary roads; (3) traffic 

volumes are higher on primary highways, so the number of potential conflicts is greater; 

and (4) the geometric layout of primary highway intersections is often more complex than 

that of secondary road intersections. These researchers also found that rumble strips may 

be more effective in reducing nighttime crashes at unlighted intersections than at lighted 

intersections. Harwood (1993) reported that several highway agencies commented that it 

was important to avoid the temptation to use rumble strips where they are not needed; if 

every intersection had rumble strips on its approach, rumble strips would soon lose their 

ability to focus the attention of the motorist on an unexpected hazard. 

Before concluding this discussion, certain aspects of YIELD sign operations deserve 

mention. A YIELD sign facilitates traffic flow by preventing unnecessary stops and 

allowing drivers to enter the traffic flow with minimum disruption of through traffic. 

Most YIELD signs are posted where right-turning drivers can approach the cross street at 

an oblique angle. Such configurations benefit elderly drivers in carrying out the turning 

maneuver by avoiding the tight radii that characterize right-angle turns. However, in 

several respects, intersections regulated by YIELD signs place greater demands upon 

drivers than those employing other controls, in terms of gap selection, difficulty with 

head turning, lane-keeping, and maintaining or adjusting vehicle speed. The angle of 

approach to the street or highway being entered ranges from the near perpendicular 

to the near parallel. The closer the angle is to the parallel, the further the driver must 

turn his/her head to detect and to judge the speed and distance of vehicles on the road 

to be entered. Many elderly drivers are unable to turn their heads far enough to get a 

good look at approaching traffic, while the need to share attention with the road ahead 

necessarily limits the gap search to 1 or 2 s. Some drivers are reduced to attempting to 

judge distance and gaps by means of the outside mirror. The inability to judge gaps in 

this manner often results in the driver reaching the end of the access lane without having 

identified an appropriate gap. The driver in this situation comes to a complete stop and 

then must enter the cross street by accelerating from a stopped position. The difficulty in 

judging gaps may lead to aborted attempts to enter the roadway, leaving the aging driver 

vulnerable to following drivers who direct their attention upstream and fail to notice 

that a vehicle has stopped in front of them. The need to share attention between two 

widely separated points results in eyes being off the intended path for lengthy periods. 

The diversion of attention, along with movement of the upper torso, hampers the aging 

driver’s ability to maintain directional control.

McGee and Blankenship (1989) reported that intersections converted from stop to yield

control are likely to experience an increase in crashes, especially at higher traffic volumes, 

at the rate of one additional crash every 2 years. In addition, converted yield-controlled 

intersections have a higher crash rate than established yield-controlled intersections. 

They note that while yield control has been found to be as safe as stop control at very low 

volumes, the safety impacts are not well established for higher volume levels. Agent and 

Deen (1975) reported that rural road crash types at yield-controlled intersections are 

different from those at stop-controlled intersections. At YIELD signs, more than half of 

the crashes were rear-end collisions, while more than half of the crashes at STOP signs 

were angle collisions. 
170 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

12 Lane Assignment on 

Intersection Approach

As a driver approaches an intersection with the intention of traveling straight through, or 

turning onto an intersecting roadway, he/she must first determine whether the currently 

traveled lane is the proper one for executing the intended maneuver. This understanding 

of the downstream intersection geometry is accomplished by the driver’s visual search 

and successful detection, recognition, and comprehension of pavement markings 

(including stripes, symbols, and word markings); regulatory and/or advisory signs 

mounted overhead, in the median, and/or on the shoulder in advance of the intersection; 

and other geometric feature cues such as curb and pavement edge lines, pavement 

width transitions, and surface texture differences connoting shoulder or median 

areas. Uncertainty about downstream lane assignment produces hesitancy during the 

intersection approach; this in turn decreases available maneuver time and diminishes the 

driver’s attentional resources available for effective response to potential traffic conflicts 

at and near intersections.

Aging drivers’ decreased contrast sensitivity, reduced useful field of view, increased 

visual search and decision times—particularly in response to unexpected events—and 

slower vehicle control during movement execution combine to put these highway users at 

greater crash risk when approaching and negotiating intersections. Contrast sensitivity 

and visual acuity are the visual/perceptual requirements necessary to detect pavement 

markings and symbols and to read lane control signs and word and symbol pavement 

markings. The early detection of lane control devices, by cueing the driver in advance 

that designated lanes exist for turning and through maneuvers, promotes safer and more 

confident performance of any required lane changes. This is because the traffic density 

is lighter, there are more available gaps, and there are fewer potential conflicts with 

other vehicles and pedestrians the farther away from the intersection the maneuver is 

performed. Of course, even the brightest delineation and pavement markings will not be 

visible to an operator unless an adequate sight distance (determined by horizontal and 

vertical alignment) is available. 

In an effort to analyze the needs and concerns of aging drivers, the Illinois Department of 

Transportation sponsored a statewide survey of 664 drivers, followed up by focus group 

meetings held in rural and urban areas (Benekohal, et al. 1992). Within this sample, the 

following four age categories were used for statistical analyses: ages 66–68, ages 69–72, 

ages 73–76, and age 77 and older. Comparisons of responses from drivers ages 66–68 

and age 77 and older showed that the older group had more difficulty following pavement 

markings, finding the beginning of the left-turn lane, driving across intersections, and 

driving during daytime. Similarly, the level of difficulty for reading street signs and 

making left turns at intersections increased with increasing driver age. Turning left 

at intersections was perceived as a complex driving task, made more difficult when 

channelization providing visual cues was absent and only pavement markings designated 

which lane ahead was a through lane and which was a turning lane. The processes of 

lane location, detection, and selection must be made upstream at a distance where a lane 

change can be performed safely. Late detection by aging drivers will result in erratic 

maneuvers such as lane weaving close to the intersection (McKnight and Stewart, 1990).
Handbook for Designing Roadways for the Aging Population 171

CHAPTER 7—INTERSECTIONS

More than half of 81 aging drivers participating in another set of focus group discussions 

stated that quite often they suddenly find themselves in the wrong lane, because (1) 

they have certain expectations about lane use derived from intersections encountered 

earlier on the same roadway, (2) the advance signing is inadequate or lacking, or (3) the 

pavement markings are covered by cars at the intersection (Staplin, et al., 1997). The 

biggest problem with turn-only lanes reported by group participants was that there is not 

enough warning for this feature. The appropriate amount of advance notice, as specified 

by these drivers, ranged from 5 car lengths to 1 mi. Sixty-four percent of the participants 

said that multiple warning signs are necessary when the right lane becomes a turnonly lane, with the need for an initial sign 20 to 30 s away, and a second sign 10 s away 

from the turn location. The remaining participants said that these distances should be 

increased.

Table 28. Cross-References of Related Entries for Lane Assignment on Intersection Approach.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 279 Intersection 

Channelization

Design Guide 

(1985)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, approach

Table 2B-1

Sects. 2B.19 through 2B.27, 2B.42 

through 2B.48,Sects. 2B.51 

through 2B.55, 

Fig. 2B-4

Sects. 3A.01, 3A.02, 3A.06, & 

3B.05

Figs. 3B-13 

Sect. 3B.20

Figs. 3B-18, 3B-23, 3B-24, & 3B-27

Pgs. 5-13 through 5-14, Sects. on 

Width of Traveled Way & Parking 

Lanes

Pg. 6-13, Para. 5

Pg. 7-31, Para. 6

Pgs. 9-10 through 9-19, Sects. 9.3.1 

and 9.3.2 Three-Leg Intersections & 

Four-Leg Intersections

Pg. 9-131 through 9-133, sect. on 

Guidelines for Design of Left-Turn 

Lanes 

Pgs. 9-11 and 9-13, Figs. 9-4 and 

9-5

Pgs. 9-124 through 9-125, Sect. 

9.7.1 General Design Considerations

Pgs. 9-124 through 9-40, Sect. 9.7 

Auxiliary Lanes Pgs. 9-176 through 

9-179, Sect. 9.11.1 Intersection 

Design Elements with Frontage 

Roads 

Pgs. 9-180 through 9-181, Sect. 

9.11.3 Bicycles

Pgs. 9-182 through 9-183, Sect. 

9.11.7 Midblock Left Turns on Streets 

with Flush Medians 

Pg. 1, Item 2, 3rd bullet

Pg. 19, Middle fig.

Pg. 21, 2nd col., item 1

Pg. 24, Para. 1 & top fig.

Pg. 32, Bottom fig.

Pg. 34, Para. 1 & two figs.

Pg. 35, Top right fig.

Pg. 36, Para. 1 & top & bottom figs.

Pg. 37, Para. 2 & top two figs.

Pgs. 47-48, Sect. on Warrants/

Guide-lines For Use of Left-Turn 

Lanes

Pg. 51, Fig. 4-12

Pg. 57, Sects. on Double Left-Turn 

Lanes—Guidelines for Use & 

Guidelines for Implementation of 

COTWLTL

Pg. 59, Fig. 4-20

Pgs. 61-63, Sect. on Exclusive RightTurn Lanes

Pgs. 92-97, Intersct. Nos. 2 & 4

Pgs. 99-119, Intersct. Nos. 6-16

Pgs. 132-139, Intersct. Nos. 22-24 

& 29

Pgs. 142-144, Intersct. Nos. 31-33

Pgs. 146-153, Intersct. Nos. 34-37

Pg. 243, 2nd & 7th Principles

Pg. 391-392, Sect. on Older Drivers 

and Pedestrians
172 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Even greater consensus was shown in this study regarding sign location for lane 

assignment. Seventy-nine percent of the group reported that overhead lane-use signs 

are far more effective than roadside-mounted signs for this type of warning. Several 

participants suggested that a combination of roadside and overhead signs, in addition 

to roadway markings, would be beneficial. Although roadway markings were deemed 

helpful, 84 percent of all participants stated that they are useless in isolation from signs, 

because they are usually at the intersection and are obscured by traffic, and they are 

frequently worn and faded. The result is that drivers end up in the wrong lane and must 

go in a direction they had not planned for, or they try to change lanes at a point where it 

is not safe to do so. Thus, a general conclusion from this study is that overhead signing 

posted in advance of, as well as at, an intersection provides the most useful information 

to drivers about movement regulations which may be difficult to obtain from pavement 

marking arrows when traffic density is high or when pavement markings are obscured by 

snow or become faded, or where sight distance is limited. 

In an early study conducted by Hoffman (1969), the installation of overhead lane-use 

control signs in advance of six intersections in Michigan contributed to a reduction 

in the total number of crashes by 44 percent in a 1-year period, and a reduction in the 

incidence of crashes caused by turning from the wrong lane by 58 percent. Later, older 

drivers (as well as their younger counterparts) were shown to benefit from redundant 

signing (Staplin and Fisk, 1991). In addition to redundant information about right-ofway movements at intersections, drivers should be forewarned about lane drops, shifts, 

and merges through advance warning signs, and ideally these conditions should not 

occur close to an intersection. Advance route or street signing as well as reassurance 

(confirmatory) signing/route marker assemblies across the intersection will aid drivers of 

all ages in deciding which lane will lead them to their destination, prior to reaching the 

intersection. 

The 2009 MUTCD specifies in section 2B.19 that Intersection Lane Control signs should 

be mounted overhead, except where the number of through lanes for an approach is two 

or less, where the Intersection Lane Control signs (R3-5 through R3-8) may be overhead 

or ground mounted. The Mandatory Movement Lane Control signs (R3-5, R3-5a, R3-

7, and R3-20) are required to be located where the regulation applies. The Optional 

Movement Lane Control Sign (R3-6) is required to be located in advance of and/or at the 

intersection where the regulation applies. The section on Advance Intersection Lane 

Control signs (sign series R3-8, section 2B.22), states that when used, these signs should 

be placed at an adequate distance in advance of the intersection so that road users can 

select the appropriate lane (e.g., in advance of the tapers or at the beginning of the turn 

lane). Where three or more approach lanes are available to traffic, Advance Intersection 

Lane Control signs, if used, shall be post-mounted in advance of the intersection and 

shall not be mounted overhead. Section 3B.20 indicates that where through lanes become 

mandatory turn lanes, lane-use arrow markings shall be used and shall be accompanied 

by standard signs.

Although pavement markings have obvious limitations (e.g., limited durability when 

installed in areas exposed to heavy traffic, poor visibility on wet roads, and obscuration 

by snow in some regions), they have the advantage of presenting information to drivers 

without distracting their attention from the roadway.
Handbook for Designing Roadways for the Aging Population 173

CHAPTER 7—INTERSECTIONS

13 Traffic Signals

Finally, the Institute of Transportation Engineers identified several features to enhance 

the operation of urban arterial trap lanes (through lanes that terminate in an unshadowed 

mandatory left- or right-turn regulation): (1) signing that gives prominent advance 

notice of the unexpected mandatory turn regulation, followed by a regulatory sign at the 

point where the mandatory turn regulation takes effect, followed by a third sign at the 

intersection itself if there are intervening driveways from which motorists might enter the 

lane; (2) supplemental pavement markings which consist of a double-width broken lane 

line beginning at the advance warning sign and extending to the first regulatory sign; (3) a 

pavement legend in the trap lane; and (4) overhead signing. Candidates for these remedial 

treatments include left-turn trap lanes on roadways with high volumes, high speeds, poor 

approach visibility, and complex geometrics (Foxen, 1986).

Traffic signals are power-operated signal displays used to regulate or warn traffic. They 

include displays for intersection control, flashing beacons, lane-directional signals, 

ramp-metering signals, pedestrian signals, railroad-crossing signals, and similar devices. 

Warrants for traffic signals are thoroughly described in the MUTCD. The decision to 

install a traffic signal is based on an investigation of physical and traffic flow conditions 

and data, including traffic volume, approach travel speeds, physical condition diagrams, 

crash history, and gap and delay information (Wilshire, 1992). The MUTCD incorporates 

the intensity, light distribution, and chromaticity standards from the following Institute 

of Transportation Engineers (TEH) standards for traffic signals: Vehicle Traffic Control 

Signal Heads, TEH Standard No ST-008B (TEH, 1985b); Pedestrian Traffic Control 

Signal Indications, TEH Standard No. ST-011B (TEH, 1985a); Traffic Signal Lamps, 

TEH Standard No. ST-010 (TEH, 1986); Lane-Use Traffic Control Signal Heads (TEH, 

Table 29. Cross-References of Related Entries for Traffic Signals.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, flashing & traffic control 

signal (traffic signal)

Sects. 4A.02, 4D.01, 4D.04, through 

4D.31, 4E.03 through 4E.13, 4I.02, 

4J.02, 4M.03, & 4L.01

MUTCD references to TEH standards 

ST-008B, ST-011B, ST-010 & LaneUse Traffic Control Signal Heads

Pg. 2-62, Para. 2

Pgs. 3-76, Paras. 2-4

Pg. 6-19, Sect. on Traffic Control 

Devices

Pgs. 7-43 through 7-44, Sect. on 

Traffic Control Devices

Pg. 9-19, Paras. 2 & 3 & Fig. 9-9 on 

pg. 9-18

Pg. 9-51, Sect. on Case 

D-Intersections with Traffic Signal 

Control

Pg. 9-180, Paras. 3 & 4

Pg. 10-38, Para. 1

Pg. 10-105, Para. 1

Pgs. V-17-V-18, Sect. on Strategy 

3.1 B4: Provide All-Red Clearance 

Interval at Signalized Intersection (T)

Chapter 12
174 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

1980); Vehicle Traffic Control Signal Heads: Light Emitting Diode (LED) Circular Signal 

Supplement, TEH Standard No. ST-052 (TEH, 2005); and Vehicle Traffic Control Signal 

Heads: Light Emitting Diode Vehicle Arrow Traffic Signal Supplement, TEH Standard No. 

ST-054 (TEH, 2008). Standards for traffic signals are important because it is imperative 

that they attract the attention of every driver, including aging drivers and those with 

impaired vision who meet legal requirements, as well as those who are fatigued or 

distracted, or who are not expecting to encounter a signal at a particular location. It 

is also necessary for traffic signals to meet motorists’ needs under a wide range of 

conditions including bright sunlight, nighttime, in adverse weather, and in visually 

cluttered surroundings.

To date, studies of traffic signal performance have not typically included observer age as 

an independent variable. Available evidence suggests, however, that aging individuals 

have reduced levels of sensitivity to intensity and contrast, but not to color. Fisher (1969) 

reported that as a person ages, the ocular media yellows and has the effect of enhancing 

the contrast between a red signal and a sky background. However, this effect is more 

than offset by increasing light scatter within the eye, which diminishes contrast. Aging 

drivers need increased levels of signal luminance and contrast in certain situations to 

perceive traffic signals as efficiently as 20- to 25-year-old drivers; however, higher signal 

intensities may cause disability glare. Fisher and Cole (1974), using data from Blackwell 

(1970), suggested that aging drivers may require 1.5 times the intensity at 50 years of 

age and 3 times the intensity at 70 years of age, and protanopes (individuals with a 

color-vision deficiency resulting in partial or full insensitivity to red light) may require 

a fourfold increase. They noted that while increased intensity will ensure that aging 

observers see the signal, the reaction time of aging drivers will be longer than for younger 

drivers. To compensate for this, it would appear necessary to assume a longer required 

visibility distance, which would result in an increase in the signal intensity required. 

However, Fisher (1969) also suggested that no increase in signal intensity is likely to 

compensate for increasing reaction time with age. It therefore deserves emphasis that the 

goal of increased response times for aging drivers, requiring longer visibility distances, 

can also be provided by ensuring that the available signal strength (peak intensity) 

is maintained through a wide, versus a narrow, viewing angle. This makes signal 

information more accessible over longer intervals.

It is generally agreed that the visibility issues associated with circular signals relate to 

the following factors: minimum daytime intensity, intensity distribution, size, nighttime 

intensity, color of signals, backplates, depreciation (light loss due to lamp wear and dirt 

on lenses), and phantom (apparent illumination of a signal in a facing sun). To place 

this discussion in context, it should also be noted that traffic signal recommendations 

for different sizes, colors, and in-service requirements have, in large part, been derived 

analytically from one research study conducted by Cole and Brown (1966).

In establishing minimum daytime intensity levels for (circular) traffic signals, the two 

driver characteristics that are considered with regard to the need to adjust peak intensity 

requirements are color anomalies and driver age. Cole and Brown (1968) determined 

that the optimum red signal intensity is 200 cd for a sky luminance of 10,000 cd/m2

, and 

an adequate signal intensity for this condition would be 100 cd. Cole and Brown (1966, 

1968) defined “optimum” as “a signal intensity that provides a very high probability 
Handbook for Designing Roadways for the Aging Population 175

CHAPTER 7—INTERSECTIONS

of recognition and which also evokes the shortest response times from the observer.” 

In their research, very high probability was defined as 95 to 100 percent probability 

of detection. An “adequate signal,” although not likely to be missed, results in driver 

reaction time that is slower than for a signal of “optimum” intensity.

The number of foreign and domestic highway organizations that specify a minimum 

standard for peak daytime traffic signal intensity is larger than the number of research 

studies upon which those standards are based. In fact, all of the standards including 

those for 8-in (200-mm) and 12-in (300-mm) signals, those for red, yellow, and 

green signals, and those for new and in-service applications are derived from a single 

requirement for a red traffic signal, established from the work of Cole and Brown (1966). 

The conclusion of this laboratory study was that a red signal with an intensity of 200 

cd should invoke a “certain and rapid response” from an observer viewing the signal at 

distances up to 328 ft even under extremely bright ambient conditions. This conclusion 

was based on experiments in which the background luminance was 5,142 cd/m2

. The 

results were linearly extrapolated to a background luminance of 10,000 cd/m2

 which 

yielded the 200-cd recommendation. Janoff (1990) concluded that a value of 200 cd 

minimum intensity for a red signal will suffice for observation distances up to 328 ft 

and vehicle speeds up to 50 mph, based on analytic, laboratory, and controlled field 

experiments performed by Adrian (1963); Boisson and Pages (1964); Rutley, Christie, and 

Fisher (1965); Jainski and Schmidt-Clausen (1967); Cole and Brown (1968); Fisher (1969); 

and Fisher and Cole (1974). Fisher and Cole (1974) cautioned against using a value less 

than 200 cd, to ensure that aging drivers and drivers with abnormal color vision will see 

the signal with certainty and with “reasonable speed.”

For green signals, Fisher and Cole (1974) indicated that the ratio of green to red intensity 

should be 1.33:1, based on laboratory and controlled field research by Adrian (1963), 

Rutley et al. (1965), Jainski and Schmidt-Clausen (1967), and Fisher (1969), and the ratio 

of yellow to red should be 3:1, based on research performed by Rutley et al. (1965) and 

Jainski and Schmidt-Clausen (1967). Janoff (1990) noted that the evidence to support 

these ratios is somewhat variable, and support of these recommendations is mixed. 

Table 30, from Janoff (1990), presents the peak intensity requirements of red, green, and 

yellow traffic signals for 200-mm (8-in) signals for normal-speed roads and for 12-in 

signals for high-speed roads; the values presented exclude the use of backplates and 

ignore depreciation. A normal-speed road, in this context, includes speeds up to 50 mph, 

distances up to 328 ft, and sky luminances up to 10,000 cd/m2

. A high-speed road is 

defined as one with speeds up to 62 mph, distances up to 787 ft, and sky luminances up to 

10,000 cd/m2

. Janoff also noted that although signal size is included, research performed 

by Cole and Brown (1968) indicated that signal size is not important because traffic 

Table 30. Peak (Minimum) Daytime Intensity Requirement (CD) For Maintained Signals with no 

Backplate (Janoff, 1990).

Signal Size Signal Color

Red Green Yellow

8 in (200 mm) 200 265 600

12 in (300 mm) 895 1,190 2,685
176 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

signals are point sources rather than area sources and only intensity affects visibility. 

Thus, the required intensity can be obtained by methods other than increasing signal size 

(i.e., by using higher intensity sources in 8-in signals).

The specification of standard values for peak intensity is important because the 

distribution of light intensity falls off with increasing horizontal and vertical eccentricity 

in the viewing angle. Janoff (1990) summarized the peak intensity standards of TEH, 

Commission Internationale de l’Éclairage (CIE), the British Standards Organization, and 

standards organizations of Australia, Japan, and South Africa. The U.S. (TEH) standard 

provides different recommendations for each of the three colors for each signal size. The 

recommendations are as follows: for red, 157 cd for 8-in signals and 399 cd for 12-in 

signals; for green, 314 cd for 8-in signals and 798 cd for 12-in signals; and for yellow, 

726 cd for 8-in signals and 1,848 cd for 12-in signals. Australia recommends the same 

peak intensity for red and green (200 cd for 8-in signals and 600 cd for 12-in signals), 

and a yellow intensity equal to three times the red intensity. The CIE recommends the 

same peak intensity for all three colors (200 cd for 8-in signals and 600 cd for 12-in 

signals), but acknowledges that actual intensity differences between colors result due to 

the differential transmittance of the colored lenses (1:1.3 for red to green and 1:3 for red 

to yellow). Japan recommends 240 cd for all three colors. Great Britain recommends a

peak intensity of 475 cd for 8-in red and green signals, and 800 cd for 12-in red and green 

signals. The range for red signals among all of these standards is from 157 cd (TEH) to 

475 cd (British Standards Organization). The 157 cd is from research by Cole and Brown. 

The modal value of 200 cd, specified by Australia, South Africa, and the CIE, is based 

upon a depreciation factor of 33 percent.

Only two research reports provide intensity requirements for green and/or yellow signals 

based upon empirical data. Adrian (1963) used a subjective scale and threshold detection 

criteria in a study that tested red and green signals at different background luminances. 

He concluded that the intensity requirements for green were 1.0 and 1.2 times that of 

red for the subjective and threshold studies, respectively. Jainski and Schmidt-Clausen 

(1967) tested the ability of observers to detect the presence of a red, amber, or green spot, 

which was either 2 minutes or 1 degree, against varying background luminances. Their 

results found that green required 1.0 and 2.5 times that of red, and yellow required 2.5 

and 3.0 times that of red, for 1 degree and 2 minutes, respectively. Using these results, 

most standards set requirements for green and yellow to be 1.3 and 3.0 times that of red, 

respectively. The CIE standard discusses the fact that the ratios of 1.3 and 3.0 for green 

and yellow appear to reflect the differences in the transmissivity of the varying color 

lenses.

Information on signal intensity requirements that will accommodate road users with 

age-related vision deficiencies is provided by NCHRP Project 5-15, Visibility Performance 

Requirements for Vehicular Traffic Signals. This investigation includes a series of 

laboratory and field studies to determine performance-based signal requirements 

for traffic signal intensity, intensity distribution, and related photometric parameters 

using a subject population that oversamples aging drivers (Freedman, Flicker, Janoff, 

Schwab, and Staplin, 1997). What NCHRP 5-15 makes clear is that the 200 cd intensity 

requirement for red 200 mm (8-in) signals that appears most prominently in the 

literature cited above (e.g., Janoff, 1990) is the maintained, in-service performance 
Handbook for Designing Roadways for the Aging Population 177

CHAPTER 7—INTERSECTIONS

level for signals in visually simple to moderately complex environments. For more 

highly complex visual environments, the intensity recommendation for the red signal 

is approximately doubled. The NCHRP 5-15 recommendation for maintained intensity 

levels also establishes a need for in-service intensity performance measurement. 

Holowachuk, Leung, and Lakowski (1993) conducted a laboratory study to evaluate the 

effects of color vision deficiencies and age-related diminished visual capability on the 

visibility of traffic signals. Subjects ranged in age from 18 to 80 and older, and included 

64 individuals with normal color vision and 51 subjects who were color-vision deficient. 

A laboratory simulation apparatus was used to present photographs taken of seven signal 

head assemblies at intersections at distances of 164 and 328 ft. The photographs were 

taken at intersections in the Vancouver area within simple and complex environments. 

Each subject viewed 48 photographs shot during daylight conditions and 38 photographs 

shot at nighttime. Subjects’ reaction times to recognize the color of the “on” signal 

were measured, as was the accuracy of response. The basic highway signal head used by 

the Ministry of Transportation and Highways in British Columbia consists of a 12-in 

red light, a 8-in amber light, and a 8-in green light arranged vertically with a yellow 

backplate. This “standard highway” signal plus six other off-the-shelf signal-head designs 

were used in the study (see Table 31).

Results indicated that color-vision-deficient drivers had significantly longer reaction 

times than drivers with normal color vision, and aging drivers had longer reaction times 

compared to younger drivers. Of particular importance is that the reaction times of 

the normal color vision drivers over age 50 (n=15) compared closely to those of colorvision-deficient drivers (n=50). Regarding signal design, for daytime conditions, the no 

backplate assembly produced the longest reaction times for both the normal color vision 

and the color-vision deficient drivers. Reaction times for the larger and brighter lenses 

(shape coded and 12 RYG) were the shortest, for both groups of subjects. For nighttime

conditions, the signal assemblies showed few differences in reaction time for subjects 

with normal color vision. Reaction times were shortest for the shape coded and 12 RYG

assemblies; however the baseline assembly and the No Backplate assemblies produced the 

longest reaction times. For the color-vision-deficient group, the reaction times for the 

shape-coded, 12 RYG, and the Modified Backplate assemblies were distinctly shorter than

Table 31. Signal Head Designs Evaluated by Holowachuk et al. (1993, 1994).

Name Abbreviation Lens Size (in)* Backplate Other Features

No Backplate NO BP Red 8, Amber 8, Green 8 No N/A

Base Line Baseline Red 8, Amber 8, Green 8 Yes N/A

Modified Backplate Mod BP Red 8, Amber 8, Green 8 Yes Backplate with 2-in reflective border

Standard Highway Std Hwy Red 12, Amber 8, Green 8 Yes N/A

12-in LED LED Red 12 (LED), Amber 8, Green 8 Yes 12-in red LED signal

12-in Red, Green, 

Amber

12 RYG Red 12, Amber 12, Green 12 Yes N/A

12-in Shape Coded Shape Coded Red 12, Amber 12, Green 12 Yes Red Square 

Amber Diamond 

Red Circle

*Note: 12-in lens uses 150-Watt bulb; 8-in lens uses 69-Watt bulb. 
178 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

those for the Baseline and No Backplate assemblies. Nighttime reaction times were much 

longer than daytime reaction times for the subjects with color vision deficiencies. Signal 

light colors were identified more incorrectly for night conditions than for day conditions. 

This difference was greatest for the aging color-vision-deficient drivers (n=22).

Overall, findings indicated that the reaction times for all subjects were the shortest for 

signal designs with larger 12- in lenses and higher luminances (150-W bulbs). There was 

no significant difference in reaction times between the shape-coded and the 300 RYG, for

the normal subjects or for the color-vision deficient subjects. The next-best performing 

signal design was the Modified Backplate. The signal assembly with no backplate 

produced the longest reaction times. Based on these findings, a before and after safety 

evaluation was conducted with the larger signal head, consisting of a 12-in red light, a 

12-in amber light, and a 12-in green light, all with 150-W lamps and a yellow backboard 

with an additional 2-in reflective border (Sayed, Abdelwahab, and Nepomuceno, 1998). 

The signal head design was tested at 10 urban intersections in British Columbia, that 

were originally equipped with the standard signal head design consisting of a 12-in 

150-W red light, an 8-in 69-W amber light, and an 8-in 69-W green light, with a yellow 

backboard. Crash frequency and severity were analyzed at the treatment sites 1 year 

before the treatment and 2 years after the treatment. Another 10 sites similar to the 

treatment sites were selected as comparison sites, to adjust for time trend effect. An 

empirical Bayes before and after safety analysis indicated that the improved signal head 

design had a significant effect in reducing the overall frequency and severity of crashes 

at the treatment sites. Crashes were reduced by approximately 24 percent, and injury 

and fatal crashes were reduced by approximately 16 percent. These results indicated that 

increasing traffic signal visibility through the improvement of signal head design is an 

effective countermeasure in reducing both the frequency and severity of traffic crashes at 

signalized intersections.

Some research has indicated that the dimming of signals at night may have advantages, 

while also reducing power consumption. Freedman, Davit, Staplin, and Breton (1985) 

conducted a laboratory study and controlled and observational field studies to determine 

the operational, safety, and economic impact of dimming traffic signals at night. Results 

indicated that drivers behaved safely and efficiently when signals were dimmed to as low 

as 30 percent of TEH recommendations. Previously, however, Lunenfeld (1977) cited 

the considerable range of night background luminances that may occur in concluding 

that in some brightly lit urban conditions, or where there is considerable visual noise, 

daytime signal brightness is needed to maintain an acceptable contrast ratio. The TEH 

standard does not differentiate between day and night intensity requirements. The CIE 

has recommended that intensities greater than 200 cd or less than 25 cd be avoided at 

night and advises a range of 50 to 100 cd for night, except for high-speed roads where the 

daytime values are preferred. While the option for dimming on a location-by-location 

basis should not be excluded, from the standpoint of aging driver needs, there is no 

compelling reason to recommend widespread reduction of traffic signal intensity during 

nighttime operations.

It is common practice to try to enhance the visibility of signals by placing a large, 

black backplate around the signals. The backplate, rather than the sky, becomes the 

background of the signals, enhancing the contrast. Regarding backplate size, no 
Handbook for Designing Roadways for the Aging Population 179

CHAPTER 7—INTERSECTIONS

recommendation is contained in the TEH standard. The CIE (1988), however, recommends 

that all signals use backplates of a size (width) of three times the diameter of the signal. 

Researchers have postulated further safety gains by adding a 1-inch to 3-inch yellow 

retroreflective strip around the perimeter to “frame” the backplate. In theory, by drawing 

drivers’ attention to the backplate, their attention to the signal will be similarly enhanced. 

In other words, this represents an attempt to heighten signal conspicuity, while the 

backplate itself improves signal visibility. Sayed, de Leur, and Pump (2005) conducted a 

before-after study of crash experience at 17 signalized intersections in British Columbia, 

Canada, using auto insurance claims data. An empirical Bayes analysis, which included a 

comparison group to control for trend effects and a reference group to adjust for regression 

to the mean, indicated a nearly 15% drop in the number of crash claims following 

introduction of the enhanced-conspicuity backplates. The types of collisions (either 

before or after the backplate treatment was introduced) were not revealed in this report 

(i.e. it is unknown whether rear end crashes or more injurious angle crashes figured more 

prominently in these data). In addition, there is no discussion of driver age in the study 

results. Thus, while this practice has gained adherents in a number of jurisdictions, reliable 

evidence of its benefit for aging road users is still pending. However, FHWA has named 

backplates with retroreflective borders as a Proven Safety Countermeasure to reduce 

red-light-running crashes for all drivers (Office of Safety, 2012). Retroreflective backplate 

borders are included as an option in the 2009 MUTCD and have been implemented 

statewide in Ohio and Nebraska.

As a practical matter, the use of a backplate also serves to compensate, in part, for the 

effects of depreciation, since a backplate reduces the required intensity by roughly 25 

percent (Cole and Brown, 1966) while depreciation increases the requirement by the same 

amount. Guidelines published by the CIE (1988) include an allowance of 25-percent

transmissivity for depreciation due to dirt and aging (a 33-percent increase in intensity for 

new installations). The 200-cd requirement for red signals, as noted earlier, must be met 

after the depreciation factor has been taken into account.

Regarding signal size, section 4D.07 of the MUTCD specifies that the two nominal 

diameter sizes for vehicular signal lenses are 8 in and 12 in, and requires that 12-in 

lenses be used at all new signal locations with only a few exceptions. Existing 8-inch 

circular signal indications may be retained for the remainder of their useful service life. 

Researchers at the Texas Transportation Institute proposed that the larger 12-in lens should 

be used to improve the attention-getting value of signals for aging drivers (Greene, et al.,

1996). Use of the large lens also provides motorists with more time to determine the signal 

color and to make the correct response. 

A final issue with respect to signal performance and aging drivers is the change intervals 

between phases, and the assumptions about perception-reaction time (PRT) on which 

these calculations are based. At present, a value of 1.0 s is assumed to compute change 

intervals for traffic signals, a value which, according to Tarawneh (1991), dates back to 

a 1934 Massachusetts Institute of Technology study on brake-reaction time. Tarawneh 

examined findings published by proponents of both “parallel” and “sequential” (serial) 

models of driver information processing, seeking to determine the best estimator for 

aging individuals of a PRT encompassing six different component processing operations: 
180 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

(1) latency time (onset of stimulus to beginning of eye movement toward signal); (2) eye/

head movement time to fixate on the signal; (3) fixation time to get enough information 

to identify the stimulus; (4) recognition time (interpret signal display in terms of possible 

courses of action); (5) decision time to select the best response in the situation; and 

(6) limb movement time to accomplish the appropriate steering and brake/accelerator 

movements.

Tarawneh’s (1991) review produced several conclusions. First, the situation of a signal 

change at an intersection is among the most extreme, in terms of both the informationprocessing demand and subjective feelings of stress that will be experienced by many 

aging drivers. Second, the most reasonable interpretation of research to date indicates 

that the best “mental model” to describe and predict how drivers respond in this 

context includes a mix of concurrent and serial-and-contingent information-processing 

operations. In this approach, the most valid PRT estimator will fall between the bounds 

of values derived from the competing models thus far, also taking into account agerelated response slowing for recognition, decision-making, and limb movement. After a 

tabular summary of the specific component values upon which he based his calculations, 

Tarawneh (1991) called for an increase in the current PRT value used to calculate the 

length of the yellow interval (derived from tests of much younger subjects) from 1.0 s to 

1.5 s to accommodate aging drivers.

A contrasting set of results was obtained in a FHWA-sponsored study of traffic operations 

control for older drivers (Knoblauch, et al., 1995). This study compared the decision/

response times and deceleration characteristics of older drivers (ages 60–71 and older) 

with those of younger drivers (younger than age 60) at the onset of the amber signal phase. 

Testing was conducted using a controlled field test facility, where subjects drove their own 

vehicles. Subjects were asked to maintain speeds of 30 mph and 20 mph for certain test 

circuits. The duration of the yellow signal was 3.0 s before turning to red. On half of the 

trials, the signal changed from green to yellow when the subject was 3.0 to 3.9 s from the 

signal, and on the remaining trials, when the subject was 4.0 to 4.9 s away from the signal. 

For three of the circuits, subjects were asked to brake as they normally would and to stop 

before reaching the intersection, if they chose to do so. During a fourth circuit, they were 

asked to brake to a stop, if they possibly could, if the light changed from green to yellow. 

Response times were measured for the drivers who stopped, from the onset of the yellow 

phase to the time the brake was applied. 

Results of the Knoblauch et al. (1995) study showed no significant differences in 85th

percentile decision/response times between younger and older drivers when subjects 

were close to the signal at either approach speed. The 85th percentile decision time of 

younger subjects was 0.39 s at 20 mph and 0.45 s at 30 mph. For older drivers, these 

times were 0.51 and 0.53 s, for 20 mph and 30 mph, respectively. When subjects were 

further from the signal at amber onset, older drivers had significantly longer decision/

response times (1.38 s at 20 mph and 0.88 s at 30 mph) than the younger drivers (0.50 s 

at 20 mph and 0.46 s at 30 mph). The authors suggested that the significant differences 

between older and younger drivers occurred when the subjects were relatively far from the 

signal, and that some older subjects will take longer to react and respond when additional 

time is available for them to do so. Thus, they concluded that the older drivers were not 

necessarily reacting inappropriately to the signal. In terms of deceleration rates, there 
Handbook for Designing Roadways for the Aging Population 181

CHAPTER 7—INTERSECTIONS

14 Intersection Lighting

were no significant differences, either in the mean or 15th percentile values, between the 

older and younger subjects. Together, these findings led the authors to conclude that no 

changes in amber signal phase timing are required to accommodate aging drivers.

Taking the review and study findings of Tarawneh (1991) and Knoblauch et al. (1995) into

consideration, an approach that retains the 1.0-s PRT value as a minimum for calculating 

the yellow change interval seems appropriate; but, to acknowledge the significant body 

of work documenting age-related increases in PRT, the use of a 1.5-s PRT is well justified 

when engineering judgment determines a special need to take aging drivers’ diminished 

capabilities into account. A treatment for an all-red clearance interval logically follows, 

with length determined according to the TEH (1992).

One of the main purposes of lighting a roadway at night is to increase the visibility of 

the roadway and its immediate environment, thereby permitting the driver to maneuver 

more safely and efficiently. The visibility of an object is that property which makes it 

discernible from its surroundings. This property depends on a combination of factors; 

principally, these factors include the differences in luminance, hue, and saturation 

between the object and its immediate background (contrast); the angular size of the 

object at the eye of the observer; the luminance of the background against which it is 

seen; and the duration of observation.

Of all the highway safety improvement projects evaluated by FHWA (1996), using data 

Table 32. Cross-References of Related Entries for Intersection Lighting.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 – 

Volume 9

(2004)

Roadway Lighting Handbook

(1978)

Sect. 1A.13, sign illumination

Sects. 2A.07, 2D. 03, 2E.06, & 3I.04

Sect. 4B.04

Sects. 6D.01 & 6D.03

Sect. 6F.81 and 6F. 82

Sect. 6G.14 and 6G. 19

Table 6H-2

Figs. 6H-12, 6H-40, 6H-41

Sects. 8A.06

Pgs. 3-172 through 3-173, 

Sect. 3.6.3 Lighting

Pg. 3-176, Para. 3

Pgs. 5-22, Sect. 5.3.8 Street 

and Roadway Lighting

Pg. 6-19, Sect. 6.3.8 on 

Roadway Lighting

Pg. 7-52, Sect. 7.3.17 Lighting

Pg. 9-181, Sect. 9.11.5 Lighting 

at Intersections

Pgs. V-21-V-22, Sect. on

Strategy 3.1 B7:Improve 

Lighting at Intersections, 

Horizontal Curves, and 

Railroad Grade Crossings (T)

Pgs. 16-27, Sects. on Analytical Approach to 

Illumination Warrants, Informational Needs 

Approach to Warrants, & Warrants for Rural 

Intersection Lighting

Pgs. 29-30 Sect. on Adverse Geometry and 

Environment Warrant

Pgs. 42-45, Sect. on Summary of Light Sources

Pgs. 53-56, Sect. on Classification of Luminaire 

Light Distributions

Pg. 71, 5th bullet

Pg. 94, Sect. on Coordination of the Arterial 

Lighting System and Traffic Controls

Pg. 96, Sect. on Intersection Lighting

Pgs. 98-99, Sect. on Rural Intersection Lighting

Pgs. 120-129, Sect. on Illumination Design 

Procedure

Pgs.187-200, Sect. on Maintaining the System
182 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

from 1974 to 1995 where before- and after-exposure data were available, intersection 

illumination was associated with the highest benefit-cost ratio (26.8) in reducing fatal and 

injury crashes. The link between reduced visibility and highway safety is conceptually 

straightforward. Low luminance contributes to a reduction in visual capabilities such 

as acuity, distance judgment, speed of seeing, color discrimination, and glare tolerance, 

which are already diminished capabilities in aging drivers. 

A recent NCHRP report shows that intersection lighting can reduce total nighttime 

crashes by 21 percent and nighttime injury crashes by 27 percent. On the basis of daynight crash distributions, this translates into a 4 percent reduction in total crashes at 

an intersection where lighting is added and a 5 percent reduction in all injury crashes. 

(Harkey et al., 2008) These results are based on a meta-analysis of 38 studies, including 

14 conducted in the U.S. (Elvik and Vaa, 2004) and review by an expert panel as part of 

the referenced NCHRP study. 

The Commission Internationale de l’Éclairage (1990) reports that road crashes at night 

are disproportionately higher in number and severity compared with crashes during 

the daytime. Data from 13 Organization for Economic Cooperation and Development 

countries showed that the proportion of fatal nighttime crashes ranged between 25 and 

59 percent (average value of 48.5 percent). In this evaluation of 62 lighting and crash 

studies, 85 percent of the results showed lighting to be beneficial, with approximately 

one-third of the results statistically significant.

In 1990, drivers (without regard to age) in the United States experienced 10.37 fatal 

involvements per 100 million mi at night and 2.25 fatal involvements per 100 million mi 

during the day (Massie and Campbell, 1993). In their analysis, the difference between 

daytime and nighttime fatal rates was found to be more pronounced among younger age 

groups than among older ones, with drivers ages 20–24 showing a nighttime rate that was 

6.1 times the daytime rate, and drivers age 75 and older showing a nighttime rate only 

1.1 times the daytime rate. The lower percentage of nighttime crashes of aging drivers 

may be due to a number of factors, including reduced exposure—aging drivers as a group 

drive less at night—and a self-regulation process whereby those who do drive at night 

are the most fit and capable to perform all functional requirements of the driving task 

(National Highway Traffic Safety Administration, 1987).

A specific driving error with high potential for crash involvement is wrong-way 

movements. Analyses of wrong-way movements at intersections frequently associate 

these driving errors with low visibility and restricted sight distance (Vaswani, 1974, 1977; 

Scifres and Loutzenheiser, 1975) and note that designs that increase the visibility of access 

points to divided highways and treatments that improve drivers’ understanding of proper 

movements at these locations have been found to reduce the potential for crashes.

Inadequate night visibility, where the vehicle’s headlights are the driver’s primary light 

source, was reported by Vaswani (1977) as a factor that makes it more difficult for drivers 

to determine the correct routing at intersections with divided highways. Similarly, 

Woods, Rowan, and Johnson (1970) reported that locations where highway structures, 

land use, natural growth, or poor lighting conditions reduce the principal sources of 

information concerning the geometry and pavement markings are associated with 

higher occurrences of wrong-way maneuvers. Crowley and Seguin (1986) reported that 
Handbook for Designing Roadways for the Aging Population 183

CHAPTER 7—INTERSECTIONS

drivers over the age of 60 are excessively involved in wrong-way movements on a per-mile 

basis. Suggested countermeasures include increased use of fixed lighting installations. 

Lighting provides a particular benefit to aging drivers by increasing expectancy of 

needed vehicle control actions, at longer preview distances. It has been documented 

extensively in this Handbook that an aging driver’s ability to safely execute a planned 

action is not significantly worse than that of a younger driver. The importance of fixed 

lighting at intersections for aging drivers can therefore be understood in terms of both 

the diminished visual capabilities of this group and their special needs to prepare farther 

in advance for unusual or unexpected aspects of intersection operations or geometry. 

Targets that are especially critical in this regard include shifting lane alignments; 

changing lane assignments (e.g., when a through lane changes to turn-only operation); 

a pavement width transition, particularly a reduction across the intersection; and, of 

course, pedestrians.

Detectability of a pedestrian is generally influenced by contrast, motion, color, and size 

(Robertson, Berger, and Pain, 1977). If a pedestrian is walking at night and does not 

have good contrast, color contrast, or size relative to other road objects, an increase 

in contrast will significantly improve his/her detectability. This is one effect of street 

lighting. Extreme contrasts as well as dark spots are reduced, giving the driver and the 

pedestrian a more “even” visual field. The effectiveness of fixed lighting in improving the 

detectability of pedestrians has been reported by Pegrum (1972); Freedman, et al. (1975); 

Polus and Katz (1978); and Zegeer (1991).

While age-related changes in glare susceptibility and contrast threshold are currently 

accounted for in lighting design criteria, there are other visual effects of aging that 

are currently excluded from visibility criteria. Solid documentation exists of agerelated declines in ocular transmittance (the total amount of light reaching the retina), 

particularly for the shorter wavelengths (cf. Ruddock, 1965); this suggests a potential 

benefit to aging drivers of the “yellow tint” of high-pressure sodium highway lighting 

installations. The aging eye experiences exaggerated intraocular scatter of light—all 

light, independent of wavelength (Wooten and Geri, 1987)—making these drivers more

susceptible to glare. Diminished capability for visual accommodation makes it harder 

for aging observers to focus on objects at different distances. Pupil size is reduced among 

aging individuals through senile miosis (Owsley, 1987), which is most detrimental at 

night because the reduction in light entering the eye compounds the problem of light lost 

via the ocular media, as described above.

The loss of static and dynamic acuity—the ability to detect fine detail in stationary 

and moving targets—with advancing age is widely understood. Although there are 

pronounced individual differences in the amount of age-related reduction in static visual 

acuity, Owsley (1987) indicated that a loss of about 70 percent in this capability by age 85 

is normal. Among other things, declines in acuity can be used to predict the distance at 

which text of varying size can be read on highway signs (Kline and Fuchs, 1993), under a

given set of viewing conditions. 

There are a number of other aspects of vision and visual attention that relate to driving. 

In particular, saccadic fixation, useful field of view, detection of motion in depth, 

and detection of angular movement have been shown to be correlated with driving 
184 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

performance (see Bailey and Sheedy, 1988, for a review). As a group, however, these 

visual functions do not appear to have strong implications for highway lighting practice, 

with the possible exception of the “useful field of view.” It could be argued that it would 

be advantageous to provide wider angle lighting coverage to increase the total field of 

view of aging drivers. High-mast lighting systems can increase the field of view from 

30 degrees to about 105 degrees (Hans, 1993). Such wide angles of coverage might have 

advantages for aging drivers in terms of peripheral object detection. However, because 

high-mast lighting systems tend to sacrifice target contrast for increased field of view, 

opinion is divided about their application at intersections. Traditionally, field of view has 

not been considered as a parameter that needs to be optimized in lighting system design 

for intersection applications.

Rockwell, Hungerford, and Balasubramanian (1976) studied the performance of drivers 

approaching four intersection treatments, differentiated in terms of special reflectorized 

delineators and signs versus illumination. A significant finding from observing 168 

test approaches was that the use of roadway lighting significantly improved driving 

performance and earlier detection of the intersection, compared with the other 

treatments (e.g., signing, delineation, and new pavement markings), which showed 

smaller improvements in performance. 

Finally, it must be emphasized that the effectiveness of intersection lighting depends 

upon a continuing program of monitoring and maintenance by the local authority. 

Guidelines published by AASHTO (1984) identify depreciation due to dirt on the

luminaires and reduced lumen output from the in-service aging of lamps as factors that 

combine to decrease lighting system performance below design values. Maintained values 

in the range of 60 to 80 percent of initial design values are cited as common practice 

in this publication. With a particular focus on the needs of aging drivers for increased 

illumination relative to younger motorists, to accommodate the age-related sensory 

deficits documented earlier in this discussion, a recommendation logically follows that 

lighting systems be maintained to provide service at the 80 percent level—i.e., the upper 

end of the practical range—with respect to their initial design values.
Handbook for Designing Roadways for the Aging Population 185

CHAPTER 7—INTERSECTIONS

15 Pedestrian Crossings

A nationwide review of fatalities during the year 1985, and injuries during the period 

of 1983–1985, showed that 39 percent of all pedestrian fatalities and 9 percent of all 

pedestrian injuries involved persons age 64 and older (Hauer, 1988). While the number of 

injuries is close to the population distribution (approximately 12 percent), the number of 

fatalities far exceeds the proportion of aging pedestrians. The percentages of pedestrian 

fatalities and injuries occurring at intersections were 33 percent and 51 percent, 

respectively (Hauer, 1988). People age 70 and older have the highest pedestrian death 

rate – 2.7 per 100,000 people vs. 1.5 per 100,000 people for those younger than 70 (IIHS, 

Table 33. Cross-References Of Related Entries For Pedestrian Crossings.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Roadway Lighting 

Handbook

(1978)

NCHRP 279

Intersection

Channelization

Design Guide (1985)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, crosswalk, 

crosswalk lines, & pedestrian

Tables 2A-1 & 2C-2 through 

2C-3

Sects. 1A.15, 2B.51 through 

2B.54, 2C.50, 3B.15 & 3B.18

Figs. 3B-17, 3B-19, 3B-20, 

Sect. 3B.20

Sect. 3G.01

Sect. 4A.02

Sects. 4C.05 & 4D.03

Sect. 4D.07 through 4D.11

Sects. 4E.01 through 4E.13

Fig. 4E-1

Sect. 7A.03

Fig. 7A-1

Table 7B-1

Sects. 7B.11 & 7B.12

Fig. 7B-1

Sects. 7C.02, 7D.01 through 

7D.05

Pgs. 2-78 through 2-81, 

Sect. 2.6 The Pedestrian Pg. 

4-49, Para. 2

Pg. 5-15, Sect. on Bicycle/

Pedestrian Facilities

Pg. 6-16, Sect. on Bicycle/

Pedestrian Facilities

Pgs. 7-41 through 7-42, 

Sect. 7.3.9 Bicycle and 

Pedestrian Facilities

Pgs. 9-83 through 9-92, 

Sects. on Effect of Curb Radii 

on Turning Paths and Effect 

of Curb Radii on Pedestrians

Pg. 9-98, Sect. on Refuge 

Islands

Pg. 9-181, Sect. 9.11.4 

Pedestrians

Pg. 2, 2nd col., Para. 1

Pg. 9, Sect. on Contrast

Pg. 18, Form 2

Pgs. 21-22, Tables 1-2

Pgs. 27-30, Sect. on 

Warrants for Application 

of Specialized Crosswalk 

Illumination

Pg. 45, Para. 3

Pg. 71, 3rd bullet

Pgs. 94-9, Sects. on 

Coordination of the Arterial 

Lighting System and Traffic 

Controls & Pedestrian 

Lighting on Arterials

Pg. 1, Item 3, 2nd bullet

Pg. 6, Table 2-2

Pg. 9, Fig. 2-4

Pg. 11, Bottom left photo

Pg. 21, Item 9 & Fig. 3-1

Pg. 27, Bottom left fig.

Pg. 33, Bottom right fig.

Pg. 38, Para. 1 & top two 

figs.

Pg. 39, Entire pg.

Pg. 40, Fig. 4-1

Pg. 42, 2nd col., item 3

Pg. 61, 2nd col, Paras. 2-3 

& item 2

Pg. 66, Paras. 1 & 4 & 

item 4

Pg. 67, 2nd col, Paras. 1-2

Pg. 68, Fig. 4-26

Pg. 69, 2nd col., Para. 4

Pgs. 70-72, Figs. 4-27 & 

4-28

Pg. 75, Paras. 4-5, Table 

4-10, & 2nd col, Para. 1

Pg. 76, Item 4 & Table 4-11

Pgs. 96-97, Intersct. No. 4

Pgs. 104-105, Intersct. No. 9

Pgs. 150-151, Intersct. 

No. 36

Pgs. 18-23, Sect. on 

Pedestrians

P. 29, Para. 5

Pgs. 252-254, Sect. on 

Pedestrian Facilities

Pg. 404, Para. 1

Pgs. 369-370, Sect. on 

Crossing Warning Signs

Pg. 153, Sect. on NonMotorist Safety

Pgs. 381-382, Sect. on 

Crosswalks

Pgs. 421-422, Sect. on 

Pedestrian Signal Heads

Pg. 450, Sect. on Pedestrian 

Countdown Signals
186 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

2007). Crash types that predominantly involve aging pedestrians at intersections are as 

follows (Blomberg and Edwards, 1990):

•	 Vehicle turn/merge—The vehicle turns left or right and strikes the pedestrian.

•	 Intersection dash—A pedestrian appears suddenly in the street in front of an 

oncoming vehicle at an intersection.

•	 Multiple threat—One or more vehicles stop in the through lane, usually at a 

crosswalk at an unsignalized intersection. The pedestrian steps in front of the 

stopped vehicle(s) and into the path of a through vehicle in the adjacent lane.

•	 Bus-stop related—The pedestrian steps out from in front of a stopped bus and is 

struck by a vehicle moving in the same direction as the bus.

•	 Pedestrian trapped—At a signalized intersection, a pedestrian is hit when 

a traffic signal turns red (for the pedestrian) and cross-traffic vehicles start 

moving.

•	 Nighttime—A pedestrian is struck at night when crossing at an intersection.

Earlier analyses of over 5,300 pedestrian crashes occurring at urban intersections 

indicated that a significantly greater proportion of pedestrians age 65 and older were hit 

at signalized intersections than any other group (Robertson, Berger, and Pain, 1977).

Age-related diminished capabilities, which may make it more difficult for aging 

pedestrians to negotiate intersections, include decreased contrast sensitivity and visual 

acuity, reduced peripheral vision and “useful field of view,” decreased ability to judge 

safe gaps, slowed walking speed, and physical limitations resulting from arthritis and 

other health problems. Aging pedestrian problem behaviors include a greater likelihood 

to delay before crossing, to spend more time at the curb, to take longer to cross the road, 

and to make more head movements before and during crossing (Wilson and Grayson,

1980).

Older and Grayson (1972) reported that although aging pedestrians involved in crashes 

looked more often than the middle-aged group studied, over 70 percent of the adults 

struck by a vehicle reported not seeing it before impact. Job, et al. (1992) found that 

pedestrians over age 65 looked less often during their crossings than did younger 

pedestrians. In a survey of aging pedestrians (average age of 75) involved in crashes, 63 

percent reported that they failed to see the vehicle that hit them, or to see it in time to 

take evasive action (Sheppard and Pattinson, 1986). Knoblauch, et al. (1995) noted that

difficulty seeing a vehicle against a (complex) street background may occur with vehicles 

of certain colors, causing them to blend in with their background. This is especially 

problematic for aging persons with reduced contrast sensitivity, who require a higher 

contrast for detection of the same targets than younger individuals, and who also have 

greater difficulty dividing attention between multiple sources and selectively attending 

to the most relevant targets. In addition, the loss of peripheral vision increases an aging 

pedestrian’s chances of not detecting approaching and turning vehicles from the side. 

Reductions in visual acuity make it more difficult for aging pedestrians to read the 

crossing signal. In a survey of aging pedestrians in the Orlando, Florida area, 25 percent 

of the participants reported difficulty seeing the crosswalk signal from the opposite 
Handbook for Designing Roadways for the Aging Population 187

CHAPTER 7—INTERSECTIONS

side of the street (Bailey, et al., 1992). Aging pedestrians wait for longer gaps between 

vehicles before attempting to cross the road. In one study, approximately 85 percent of 

the pedestrians age 60 and older required a minimum gap of 9 s before crossing the road, 

while only 63 percent of all pedestrians required this minimum gap size duration (Tobey, 

Shungman, and Knoblauch, 1983). The decline in depth perception may contribute to

aging persons’ reduced ability to judge gaps in oncoming traffic. It may be concluded from 

these studies that aging pedestrians do not process information (presence, speed, and 

distance of other vehicles) as efficiently as younger pedestrians, and therefore require more 

time to reach a decision. Other researchers have observed that aging pedestrians do not 

plan their traffic behavior, are too trusting about traffic rules, fail to check for oncoming 

traffic before crossing at intersections, underestimate the speed of approaching vehicles, 

and follow other pedestrians without first checking for conflicts before crossing (Jonah 

and Engel, 1983; Mathey, 1983). 

With increasing age, there is a concurrent loss of physical strength, joint flexibility, 

agility, balance, coordination and motor skills, and stamina. These losses contribute to 

slower walking speeds and difficulty negotiating curbs. In addition, aging persons often 

fall as a result of undetected surface irregularities in the pavement and misestimation of 

curb heights. This results from a decline in contrast sensitivity and depth perception. 

In an assessment of 81 aging residents (ages 70–97) to examine susceptibility to falling, 

58 percent experienced a fall in the year following clinical assessment (Clark, Lord, and 

Webster, 1993). Impaired cognition, abnormal reaction to any push or pressure, history of 

palpitations, and abnormal stepping were each associated with falling. Knoblauch, et al.

(1995) reported that locating the curb accurately and placing the foot is a matter of some 

care, particularly for the elderly, the very young, and those with physical disabilities. 

The studies discussed below define the types of crashes in which aging pedestrians are 

most likely to be involved, and under what conditions the crashes most frequently occur. 

In addition, the specific geometric characteristics, traffic control devices (including 

signs, signals, and markings), and pedestrian signals that seem to contribute to aging 

pedestrians’ difficulties at intersections are discussed. Zegeer and Zegeer (1988) stressed 

the importance of “tailoring” the most appropriate traffic control measures to suit the 

conditions at a given site. The effect of any traffic control measure is highly dependent 

on specific locational characteristics, such as traffic conditions (e.g., volumes, speeds, 

turning movements), pedestrian volumes and pedestrian mix (e.g., young children, college 

students, aging adults, persons with physical disabilities), street width, existing traffic 

controls, area type (e.g., rural, urban, suburban), site distance, crash patterns, presence of 

enforcement, and numerous other factors.

Harrell (1990) used distance stood from the curb as a measure of pedestrian risk for 

intersection crossing. Observations of 696 pedestrians divided among three age groups 

(age 30 and under, ages 31–50, and age 51 and older) showed that the oldest group stood 

the farthest from the curb, that they stood even farther back under nighttime conditions, 

and that aging females stood the farthest distance from the curb. The author used these 

data to dispel the findings in the literature that aging pedestrians are not cognizant of 

the risks of exposure to injury from passing vehicles. Similarly, it may be argued that 

this behavior keeps them from detecting potential conflict vehicles and makes speed 
188 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

and distance judgments more difficult for them, while limiting their conspicuity to 

approaching drivers who might otherwise slow down if pedestrians were detected standing 

at the curbside at a crosswalk. 

A study of pedestrian crashes conducted at 31 high-pedestrian crash sections in Maryland 

between 1974 and 1976 showed that pedestrians age 60 and older were involved in 53 (9.6 

percent) of the crashes, and children younger than age 12 showed the same proportions. 

The pedestrians age 60 and older accounted for 25.6 percent of the fatal crashes. 

Compliance with traffic control devices was found to be poor for all pedestrians at all study 

locations; it was also found that most pedestrians keyed on the moving vehicle rather than 

on the traffic and pedestrian control devices. Only when the traffic volumes were so high 

that it was impossible to cross did pedestrians rely on traffic control devices (Bush, 1986). 

Garber and Srinivasan (1991) conducted a study of 2,550 crashes involving pedestrians

that occurred in the rural and urban areas of Virginia to identify intersection geometric 

characteristics and intersection traffic control devices that were predominant in crashes 

involving aging pedestrians. Crash frequency by location and age for the crashes within 

the cities showed that while the highest percentage of crashes involving pedestrians age 59 

and younger occurred within 150 ft from the intersection stop line, the highest percentage 

of crashes for pedestrians age 60 years and older (51.8 percent) occurred within the 

intersection.

Knoblauch, et al. (1995) reported that, compared with younger pedestrians, aging adults

are overinvolved in crashes while crossing streets at intersections. In their earlier analysis 

of the national Fatal Analysis Reporting System (FARS) data for the period 1980–1989, 32.2 

and 35.3 percent of the deaths for pedestrian ages 65–74 and age 75 and older, respectively, 

occurred at intersections (Reinfurt, et al., 1992). This compared with 22 percent or less 

for the younger age groups. Analysis of the North Carolina motor vehicle crash file for 

1980–1990 displayed somewhat smaller percentages, but showed the trend of increasing 

pedestrian crashes at intersections as age increased. Further analysis of the North Carolina 

database showed that pedestrians age 65 and older as well as those ages 45–64 experienced 

37 percent of their crashes on roadways with four or more lanes. This compares with 23.7 

percent for pedestrians ages 10–44 and 13.6 percent for those age 9 and younger. The 

highest number of pedestrian-vehicle crashes occurred when the vehicle was going straight 

(59.7 percent), followed by a vehicle turning left (17.2 percent), and a vehicle turning right 

(13.3 percent). Right-turn crashes accounted for 18.9 percent of crashes with pedestrians 

ages 65–74, compared with 14.2 percent for pedestrians age 75 and older. The oldest 

pedestrian group was the most likely to be struck by a left-turning vehicle; they accounted 

for 23.9 percent of the crashes, compared with 18.1 percent of those ages 65–74 and 15.8 

percent of those ages 45–64.

Knoblauch, et al. (1995) conducted a study to determine if pedestrian comprehension of

and compliance with pedestrian signals could be improved by installing a placard that 

explained the three phases of pedestrian signals. They used findings from: (1) a focus 

group and workshop conducted in Baltimore, Maryland, with 13 participants ages 19–62 

and (2) questionnaires administered to 225 individuals ages 19–80 and older at four 

Virginia Department of Motor Vehicles offices to determine the most effective message 

content and format for a pedestrian signal education placard. The newly developed placard 
Handbook for Designing Roadways for the Aging Population 189

CHAPTER 7—INTERSECTIONS

was installed at six intersections in Virginia, 

Maryland, and New York. Observational studies 

of more than 4,300 pedestrians during 600 signal 

cycles found no change in pedestrian signal 

compliance. However, results from questionnaires 

administered to 92 subjects at Departments 

of Motor Vehicles in Virginia, Maryland, and 

New York indicated a significant increase in 

understanding of the phases of the pedestrian 

signal. The authors concluded that although 

pedestrian crossing behavior is more influenced by 

the presence or absence of traffic than the signal 

indication, the wording on the placard was based 

on quantitative procedures using a relatively large 

number of subjects and should be used where signal educational placards are installed. 

The wording of the educational placard recommended by Knoblauch, et al. (1995) for

one-stage and two-stage crossings is shown in Figure 80. The MUTCD has adopted 

similar wording, which is shown as part of Recommendation C of Design Element 16. 

Zegeer and Cynecki (1986) tested a LOOK FOR TURNING VEHICLES pavement

marking in a crosswalk, as a low-cost countermeasure to remind pedestrians to be alert 

for turning vehicles, including right-turn-on-red (RTOR) vehicles. Results showed an 

overall reduction in conflicts and interactions for RTOR vehicles and also for the total 

number of turning vehicles. Even with an RTOR prohibition, approximately 20 percent 

of motorists committed an RTOR violation when given the opportunity (Zegeer and 

Cynecki, 1986). Of those violations, about 23.4 percent resulted in conflicts with 

pedestrians or vehicles on the side street.

Zegeer, Opiela, and Cynecki (1982) conducted a crash analysis to determine whether 

pedestrian crashes are significantly affected by the presence of pedestrian signals and 

by different signal timing strategies. They found no significant differences in pedestrian 

crashes between intersections that had standard-timed (concurrent walk) pedestrian 

signals compared with intersections that had no pedestrian signals. Concurrent or 

standard timing provides for pedestrians to walk concurrently (parallel) with traffic 

flow on the WALK signal. Vehicles are generally permitted to turn right (or left) on a

green light while pedestrians are crossing on the WALK interval. Other timing strategies

include early release timing, late release timing, and exclusive timing. In early release 

timing—also termed a “leading pedestrian interval”—the pedestrian WALK indication

is given before the parallel traffic is given a green light, allowing pedestrians to get a head 

start into the crosswalk before vehicles are permitted to turn. In late release timing, 

the pedestrians are held until a portion of the parallel traffic has turned. Exclusive 

timing is a countermeasure where traffic signals are used to stop motor vehicle traffic 

in all directions simultaneously for a phase each cycle, while pedestrians are allowed 

to cross the street. “Barnes Dance” or “scramble” timing is a type of exclusive timing 

where pedestrians may also cross diagonally in addition to crossing the street. Exclusive 

timing is intended to virtually eliminate turning traffic or other movements that 

conflict with pedestrians while they cross the street. In the Zegeer et al. (1982) analysis, 

exclusive-timed locations were associated with a 50 percent decrease in pedestrian 

Figure 80. 

Recommended 

Wording For 

Educational Placards 

For One-Stage And 

Two-Stage Crossings 

(Knoblauch et al., 

1995)
190 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

crashes for intersections with moderate to high pedestrian volumes when compared 

with both standard-timed intersections and intersections that had no pedestrian signals. 

However, this timing strategy causes excessive delays to both motorists and pedestrians. 

Aging road users (age 65 and older) recommended the following pedestrian-related 

countermeasures for pedestrian signs and signals, during focus group sessions held as 

a part of the research conducted by Knoblauch, et al. (1995): (1) reevaluate the length of

pedestrian walk signals due to increasingly wider highways, (2) implement more Barnes 

Dance signals at major intersections, and (3) provide more YIELD TO PEDESTRIANS 

signs in the vicinity of heavy pedestrian traffic.

Several studies have been conducted to determine whether regulatory signing aimed 

at turning motorists could reduce conflicts with pedestrians. Zegeer, Opiela, and 

Cynecki (1983) found that the regulatory sign YIELD TO PEDESTRIANS WHEN 

TURNING was effective in reducing conflicts between turning vehicles and pedestrians. 

They recommended that this sign be added to the MUTCD as an option for use at 

locations with a high number of pedestrian crashes involving turning vehicles. Zegeer 

and Cynecki (1986) found that the standard NO TURN ON RED sign with the 

supplementary WHEN PEDESTRIANS ARE PRESENT message was effective at several 

sites with low to moderate right-turn vehicle volumes. However, it was less effective when 

RTOR volumes were high. It was therefore recommended that the supplemental message 

WHEN PEDESTRIANS ARE PRESENT be added to the MUTCD as an accepted message 

that may be used with an NTOR sign when right-turn volume is light to moderate and 

pedestrian volumes are light or occur primarily during intermittent periods, such as in 

school zones. The supplemental message when added to the NTOR sign with the circular 

red symbol reduced total pedestrian conflicts at one site and increased RTOR usage (as 

desired, from 5.7 percent to 17.4 percent), compared with full-RTOR prohibitions. It was 

recommended that the supplemental message be added to the MUTCD for the NTOR 

sign with the circular red symbol, under low to moderate right-turn vehicle volumes and 

light or intermittent pedestrian volumes.

In the late 1990s, Abdulsattar, Tarawneh, and McCoy (1996) found that the TURNING

TRAFFIC MUST YIELD TO PEDESTRIANS sign was effective in significantly reducing 

pedestrian-vehicle conflicts during right turns. The sign was installed at six marked 

crosswalks in Nebraska, where right-turn vehicle-pedestrian conflict data were collected 

before and after its installation in an observational field study. For the six study 

crosswalks combined, a conflict occurred in 51 percent of the observations in the before 

period, but in only 38 percent of the observations during the after period. The reductions 

in pedestrian-vehicle conflicts across the observation sites ranged from 15 to 30 percent, 

and were statistically significant.

The type of markings used to define a crosswalk can also make a difference in driver 

compliance. Fitzpatrick, et al (2010) investigated the relative daytime and nighttime 

visibility of three crosswalk marking patterns: transverse lines, continental, and bar 

pairs. The conclusions from their study were as follows:

•	 The detection distances to continental and bar pairs are statistically similar. The

detection distances to continental and bar pairs are statistically different from 

transverse markings.
Handbook for Designing Roadways for the Aging Population 191

CHAPTER 7—INTERSECTIONS

•	 For the existing midblock locations, a general observation is that the continental

marking was detected at about twice the distance upstream as the transverse 

marking during daytime conditions. This increase in distance reflects 8 s of 

increased awareness of the crossing for a 30-mph operating speed.

•	 The results of the appearance ratings of the markings on a scale of A to F

mirrored the findings from the detection distance evaluation. Participants 

preferred the continental and bar pairs markings over the transverse markings.

•	 Participants gave the continental and bar pairs markings similar ratings during

both the day and night. However, the transverse marking ratings differed 

based on the light level. The participants gave slightly better ratings, although 

still worse than continental or bar pairs markings, for transverse markings 

during the nighttime as compared to the daytime. The lower ratings during 

daylight conditions could be due to sun glare or shadow issues mentioned by the 

participants.

Considering pedestrian walking times, section 4E.06 of the MUTCD (2009) indicates that 

a pedestrian change interval consisting of a flashing UPRAISED HAND (symbolizing 

DONT WALK) signal indication shall begin immediately following the WALKING

PERSON (symbolizing WALK) signal indication. The pedestrian clearance time should

be sufficient to allow a pedestrian crossing in the crosswalk who left the curb or shoulder 

at the end of the WALKING PERSON (symbolizing WALK) signal indication to travel

at a walking speed of 3.5 feet per second to at least the far side of the traveled way or to 

a median of sufficient width for pedestrians to wait. The MUTCD further states that, 

“where pedestrians who walk slower than 3.5 ft per second, or pedestrians who use 

wheelchairs, routinely use the crosswalk, a walking speed of less than 3.5 ft per second 

should be considered in determining the pedestrian clearance time.” 

Aging pedestrian walking speed has been studied by numerous researchers. TEH (1999) 

reports walking speeds obtained by Perry (1992) for physically impaired pedestrians. 

Average walking speeds for pedestrians using a cane or crutch were 2.62 ft/s; for 

pedestrians using a walker, 2.07 ft/s; for pedestrians with hip arthritis, 2.24 to 3.66 

ft/s; and for pedestrians with rheumatoid arthritis of the knee, 2.46 ft/s. Sleight (1972) 

determined that there would be safety justification for use of walking speeds between 

3.0 to 3.25 ft/s, based on the results of a study by Sjostedt (1967). In this study, average 

adults and the elderly had walking speeds of 4.5 ft/s; however, 20 percent of the aging 

pedestrians crossed at speeds slower than 4.0 ft/s. The 85th percentile aging pedestrian 

walking speed in that study was 3.4 ft/s. A 1982 study by the Minnesota Department 

of Transportation found that the average walking speed of aging pedestrians was 3.0 

ft/s. In a study conducted in Florida, it was found that a walking speed of 2.5 ft/s would 

accommodate 87 percent of the aging pedestrians observed (TEH, undated). Weiner 

(1968) found an average rate for all individuals of 4.22 ft/s, and of 3.7 ft/s for women only. 

A Swedish study by Dahlstedt (undated), using pedestrians age 70 and older, found that 

the 85th percentile comfortable crossing speed was 2.2 ft/s.

Interviews and assessments were conducted with 1,249 persons age 72 and older from 

the New Haven, CT community of Established Populations for Epidemiologic Studies 

of the Elderly, to determine walking speeds and self-reported difficulty with crossing 

the street as pedestrians (Langlois, et al., 1997). The study population excludes persons 
192 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

in nursing homes or hospitals. In a telephone interview, 11.4 percent indicated that they 

had difficulty crossing the street. Reasons provided included insufficient time to cross 

and difficulty with right-turning vehicles. The mean walking speed for those reporting 

difficulty crossing the street was 1.25 ft/s, and for those reporting no difficulty was 1.94 

ft/s. Only 7.3 percent of the population had measured walking speeds 3 ft/s, and less than 

1 percent had walking speeds of 4.0 ft/s.

Hoxie and Rubenstein (1994) measured the crossing times of older and younger 

pedestrians at a 71.69-ft wide intersection in Los Angeles, CA, and found that aging 

pedestrians (age 65 and older) took significantly longer than younger pedestrians to cross 

the street. In this study, the average walking speed of the older pedestrians was 2.8 ft/s, 

with a standard deviation of 0.56 ft/s); the average speed of the younger pedestrians was 

4.2 ft/s, with a standard deviation of 0.56 ft/s). Of the 592 older pedestrians observed, 

27 percent were unable to reach the curb before the light changed to allow cross traffic 

to enter the intersection, and one-fourth of this group were stranded at least a full traffic 

lane away from safety. A study of crossing speeds by Coffin and Morrall (1995) limited 

to 15 pedestrians age 60 or older, at each of six crosswalk locations in Calgary, Canada, 

documented an 85th percentile walking speed of 3.28 ft/s for midblock crosswalks and 

4.0 ft/s for crosswalks at signalized intersections. The authors noted that the walking 

speed of aging pedestrians varies according to functional classification, gender, and 

intersection type, and stated that approximately 95 percent of pedestrians in this study 

would be accommodated using a design walking speed of 2.62 ft/s. 

Much more extensive observations of pedestrian crossing behavior were conducted at 

two crosswalk locations at two intersections in Sydney, Australia (a major 6-lane divided 

street, and a side street), where the design crossing speed was changed from 4.0 ft/s to 3.0 

ft/s (Job, et al., 1994). Observations were made during 3,242 crossings during a baseline 

period (4.0 ft/s design crossing speed) and 2 and 6 weeks after the flashing DONT WALK

interval was extended to allow for the slower crossing speed under study. This study was 

conducted to evaluate countermeasures to address the over-representation of pedestrians 

age 70 and older in crashes in the greater Sydney metropolitan area. At all crosswalk 

locations, the WALK phase remained a constant 6 s, and the clearance interval was

extended from 14 s to 20 s at one intersection 59.7 ft wide, and from 18 to 20 s at the other 

intersection measuring 79.4 ft wide. Observations were conducted for 2,377 pedestrians 

ages 20-59, 511 pedestrians ages 60-65, and 354 pedestrians age 66 and older. The 

number of males and females was approximately equal. For both intersections, a general 

trend showed that the older the pedestrian, the longer the crossing time. Also, females 

crossed more slowly than males in all age groups. At the wider intersection, mean 

crossing speeds were 4.9 ft/s for pedestrians ages 20-59; 4.27 ft/s for pedestrians ages 

60-65, and 3.6 ft/s for pedestrians age 66 and older. The mean walking speed for females 

age 66 and older was 3.28 ft/s. The authors note that the assumed walking speed of 

4.0 ft/s leaves almost 15 percent of the total population walking below the assumed speed. 

Extending the clearance interval resulted in a decrease in the percentage of pedestrianvehicle conflicts, from 4 percent in the baseline period to 1 percent in the experimental 

period at 2 weeks and also 1 percent at 6 weeks, at the wider intersection. This difference 

was significant at the p≤.001 level. Observed changes in pedestrian-vehicle conflicts 

at the smaller intersection were contaminated by an increase in the proportion of 

pedestrians (in the young and young/middle age groups only) who crossed illegally 
Handbook for Designing Roadways for the Aging Population 193

CHAPTER 7—INTERSECTIONS

(i.e., began to cross during the flashing DONT WALK phase); consequently, sustained

differences between the baseline and experimental phases were not demonstrated. At 

the conclusion of this research, the authors recommended a reduction in the design 

walking speed from 4.0 ft/s to 3.0 ft/s at locations where there is significant usage by aging 

pedestrians.

Knoblauch, et al. (1995) conducted a series of field studies to quantify the walking speed,

start-up time, and stride length of pedestrians younger than age 65 and pedestrians 65 

and older under varying environmental conditions. Analysis of the walking speeds of 

3,458 pedestrians younger than age 65 and 3,665 pedestrians age 65 and older crossing at 

intersections showed that the mean walking speed for younger pedestrians was 4.95 ft/s 

and 4.11 ft/s for older pedestrians. The 15th percentile speeds were 4.09 ft/s and 3.19 ft/s 

for younger and older pedestrians, respectively. These differences were statistically 

significant. Among the many additional findings with regard to walking speed were the 

following: 

•	 pedestrians who start on the WALK signal walk slower than those who cross on

either the flashing DONT WALK or steady DONT WALK;

•	 the slowest walking speeds were found on local streets while the faster walking

speeds were found on collector-distributors; 

•	 sites with symbolic pedestrian signals had slower speeds than sites with word

messages; 

•	 pedestrians walk faster where RTOR is not permitted, where there is a median,

and where there are curb cuts; 

•	 faster crossing speeds were found at sites with moderate traffic volumes than at

sites with low or high vehicle volumes. 

For design purposes, a separate analysis was conducted by Knoblauch, et al. (1995) for

pedestrians who complied with the signal, as they tended to walk more slowly than those 

who crossed illegally. The mean crossing speed for the young compliers was 4.79 ft/s and 

for the older compliers was 3.94 ft/s. The 15th percentile speed for the young compliers 

was and was 3.08 ft/s for the older compliers. Older female compliers showed the slowest 

walking speeds, with a mean speed of 3.74 ft/s and a 15th percentile of 2.97 ft/s. One of 

the slowest 15th percentile values (2.94 ft/s) was observed for older pedestrians crossing 

snow-covered roadways. It was concluded from this research that a mean design speed 

of 4.0 ft/s is appropriate, and where a 15th percentile is appropriate, a walking speed of 

3.0 ft/s is reasonable. It was also determined by Knoblauch, et al. (1995) that the slower

walking speed of older pedestrians is due largely to their shorter stride lengths. The 

stride lengths of all older pedestrians are approximately 86 percent of those of younger 

pedestrians.

Knoblauch, et al. (1995) also measured start-up times for younger and older pedestrians

who stopped at the curb and waited for the signal to change before starting to cross. 

The mean value for younger pedestrians was 1.93 s compared with 2.48 s for older 

pedestrians. The 85th percentile value of 3.06 s was obtained for younger pedestrians, 

compared with 3.76 s for older pedestrians. For design purposes, the authors concluded 

that a mean value of 2.5 s and an 85th percentile value of 3.75 s would be appropriate. 
194 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

These data specifically did not include pedestrians using a tripod cane, a walker, or two 

canes; people in wheelchairs; or people walking bikes or dogs. The MUTCD (2009) states 

that the walk interval should be at least 7 s long so that pedestrians will have adequate 

opportunity to leave the curb or shoulder before the pedestrian clearance time begins 

(where pedestrian volumes and characteristics do not require 7 s, walk intervals as short 

as 4 s may be used). Parsonson (1992) noted that the reason this much time is needed 

is because many pedestrians waiting at the curb watch the traffic, and not the signals. 

When they see conflicting traffic coming to a stop, they will then look at the signal to 

check that it has changed in their favor. If they are waiting at a right-hand curb, they 

will often take time to glance to their left rear to see if an entering vehicle is about to 

make a right turn across their path. Parsonson reported that a pedestrian reasonably 

close to the curb and alert to a normal degree can be observed to require up to 4 or 5 s 

for this reaction, timed from when the signal changes to indicate that it is safe to cross, 

to stepping off the curb. It may be remembered that aging pedestrians stand farther 

away from the curb, and may or may not be alert. In addition, there are many drivers 

who run the amber and red signals, and it is prudent for pedestrians to “double-check” 

that traffic has indeed obeyed the traffic signal, and that there are no vehicles turning 

right on red or (permissive) left on green before proceeding into the crosswalk. Because 

aging persons have difficulty dividing attention, this scanning and decision-making 

process requires more time than it would for a younger pedestrian. Parsonson (1992) 

reported that the State of Delaware has found that pedestrians do not react well to the 

short WALK and long flashing DON’T WALK timing pattern. They equate the flashing

with a vehicle yellow period. The Florida Department of Transportation and the city of 

Durham, Ontario, provide sufficient WALK time for the pedestrian to reach the middle

of the street, so that the pedestrian will not turn around when the flashing DONT WALK

begins.

Fitzpatrick, et al (2006) studied characteristics of walking speed associated with different 

roadway conditions and pedestrian characteristics. Data on pedestrian crossings were 

grouped into “young” (between the ages of 15 and 60) and “old” (older than 60). A total 

of 3,155 pedestrian crossings were recorded during the study. Of that, 81 percent (2,552 

pedestrians) were observed as “walking.” The remaining 19 percent of the pedestrians 

(603) were observed to be running, both walking and running during the crossing, 

or using some form of assistance (e.g., skates or bicycles). Those 603 data points were 

not included in the analyses, nor were 107 walking pedestrians whose ages could not 

be estimated and six pedestrians whose genders could not be determined. For the 

remaining crossings, they determined that the walking speed values for older pedestrians 

were lower than those for younger people. For young pedestrians, the 15th percentile 

walking speed was 3.77 ft/s (1.15 m/s). Older pedestrians had a slower walking speed 

with the 15th percentile being 3.03 ft/s (0.9 m/s). The average walking speed was 4.25 and 

4.74 ft/s (1.3 and 1.45 m/s) for old and young pedestrians, respectively. 

Most recently, TEH and AAA Foundation for Traffic Safety (Stollof, McGee, and Eccles,

2007) published a study on pedestrian walking rates of aging persons and the effects 

of slower rates on signal timing operations. The study included a review of past studies 

(many of which were previously discussed) and the collection of additional observational 

data in six cities throughout the U.S. The results showed the 15th percentile of aging 
Handbook for Designing Roadways for the Aging Population 195

CHAPTER 7—INTERSECTIONS

pedestrians to range between 3.4 and 3.8 ft/s. The study recommended a walking speed 

of 3.5 ft/s. However, additional guidance was provided to use a walking speed of 3.0 ft/s 

at locations where pedestrians are routinely crossing at a slower pace. Under those 

conditions, it is also recommended that the crossing distance used in the calculation 

of the WALK and pedestrian clearance interval be measured from 6 ft back of the edge

of curb (starting location assumption) to the far side of the travel way being crossed. 

Recommendation A of this Design Element 16 reflects the guidance for accommodating 

slower pedestrians.

One strategy that has appeared to offer promise in assisting pedestrians who are 

slower or more reluctant to cross when there is a perceived likelihood of conflict with 

turning vehicles is the leading pedestrian interval (LPI). A LPI is a brief, exclusive 

signal phase dedicated to pedestrian traffic. Van Houten, et al. (1997) investigated the 

effects of a 3-s LPI on pedestrian behavior and conflicts with turning vehicles at three 

urban intersections in St. Petersburg, FL. In the study, pedestrian-vehicle conflicts 

were observed during a baseline period, where the signal phasings at each intersection 

provided the onset of the pedestrian WALK signal and the onset of the green signal

for turning vehicles concurrently. During the experimental phase, a 3-s LPI was 

installed to release pedestrian traffic three seconds before turning vehicles. The LPI was 

implemented using a modified, solid-state plug-in signal load switch that had the capacity 

to delay the change of the traffic signal phase from red to green. Pedestrians estimated to 

be age 65 and older were scored separately from those estimated to be age 12 and older. 

A total of 1,195 seniors and 3,680 nonseniors were observed across all three sites during 

the baseline condition. During the LPI condition, 860 seniors and 4,288 nonseniors were 

observed.

Observers collected data between 8:30 a.m. and 5:00 p.m., and scored the number of 

pedestrians who left the curb within 2 s before the start of the WALK indication, within

3 s after onset of the WALK indication, during the remainder of the WALK cycle, and

during the flashing DON’T WALK indication. The number of conflicts was scored for

each of these intervals, defined as any situation where a driver engaged in abrupt braking 

or either the driver or pedestrian took sudden evasive action to avoid a collision. Conflicts 

were scored separately for right-tuning and left-turning vehicles. Other data of interest 

included the number of times that a pedestrian yielded to a turning vehicle by stopping 

or waving the vehicle through, and the distance covered by the pedestrian during the LPI 

condition. The intersection geometries included the following: (1) one-way traffic with 

four northbound lanes by two-way traffic with one lane in each direction and diagonal 

parking (north and west crosswalks were observed because both included left-on-green 

conflict potential); (2) one-way traffic with four southbound lanes by two-way traffic 

with one lane in each direction and diagonal parking (south and east crosswalks were 

observed because both included left-on-green conflict potential); and (3) two-way traffic 

with two lanes in each direction by two-way traffic with two lanes in each direction (all 

four crosswalks were observed).

The number of conflicts per 100 pedestrians who started crossing during a defined 5-s 

begin-walk period (which began 2 s before and ended 3 s after the onset of the WALK

indication) showed that during the baseline period, the number of conflicts averaged 

3.0, 2.1, and 3.3 for the three sites. After the introduction of the LPI, the number of 
196 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

conflicts averaged 0.1, 0.1, and 0.2 for the three sites. The likelihood of conflict was 

significantly lower during the LPI condition than during the baseline condition for both 

left- and right-turning vehicles; the odds of conflict for pedestrians leaving the curb 

during the begin-walk period were reduced by approximately 95 percent. The reduction 

in odds conflict for seniors as a function of an LPI phase (89 percent reduction) was not 

significantly different from that of their younger counterparts (97 percent reduction). 

There was no significant effect of LPI on the odds of conflict for pedestrians leaving the 

curb after the begin-walk period, indicating that an LPI does not move conflicts to a later 

phase in the WALK interval. 

The LPI also had the effect of significantly reducing the number of pedestrians yielding 

to turning vehicles; the odds of a pedestrian yielding to a turning vehicle were reduced by 

approximately 60 percent. Van Houten et al. (1997) indicate that once pedestrians were 

in the crosswalk, drivers acknowledged their presence and were more likely to yield the 

right of way. Also, they state that pedestrians occupying the crosswalk were more visible 

to drivers who were waiting for the light to change than they would have been had the 

drivers and pedestrians been released concurrently. The final measure of interest was the 

mean distance traveled by the lead pedestrian during the LPI condition, which averaged 

8.5 ft. The authors state that this distance (which is greater than one-half of a lane width) 

appears sufficient for pedestrians to assert their right of way ahead of turning vehicles, 

and reduces conflicts that may result when pedestrians and vehicles begin to move at the 

same time.

In terms of research on the countdown pedestrian signal, only one formal study was 

found which attempted to quantify the effects on pedestrian crashes after converting 

standard WALK/DONT WALK signals to the countdown signals. A study by Markowitz,

et al. (2006) involved installing countdown signals at about 700 of the 1,100 signalized 

intersections in San Francisco. An initial pilot evaluation was performed at nine sites, 

which found that pedestrian injury crashes dropped from 27 to 13 after countdown signal 

installation, a 52% reduction, with a slight decline in pedestrian crashes for the primary 

untreated comparison group. The authors cited regression-to-the-mean as a factor in this 

crash reduction, but noted that the decline in pedestrian injury crashes was consistently 

greater with the countdown sites than the non-countdown sites. The authors further 

concluded that “...although the 53% reduction in collisions overstates the impact of the 

countdown, a real reduction did occur.”

As a part of that Markowitz article, the authors also conducted a behavioral evaluation 

of the countdown signals at eight intersections and found that after installing the 

countdown signals, there was a significant reduction in the percentage of pedestrians still 

in the crosswalk when the signal turned to red. There was also a significant reduction 

in the percentage of pedestrians who were running or had an aborted crossing after 

the countdown signal installation. There was a small increase in the percentage of 

pedestrians who left early (i.e., on the flashing hand or solid hand) but that increase was 

not statistically significant.

A follow-up crash-based analysis by the authors was performed which involved a sample 

of 579 intersections which involved converting traditional pedestrian signal heads with 

countdown pedestrian heads and the use of 204 untreated control sites. Based on an 
Handbook for Designing Roadways for the Aging Population 197

CHAPTER 7—INTERSECTIONS

16 Roundabouts

average of pedestrian crashes in a one-year before period (average for years 2001 and 

2002) and a one-year after period (2003), pedestrian crashes dropped by 25% at the 

“treated” sites, compared to an increase of 16% at the “Untreated” sites. The authors 

add that: “This provides some statistical support to popular claims that the addition of 

countdown devices has improved safety.”

Numerous other studies have been conducted in recent years to evaluate the effects of 

countdown signals on pedestrian and motorist behavior, conflicts between pedestrians 

and motorists, and/or surveys which ask pedestrians their opinions about countdown 

signals. For example, Eccles, Tao, and Mangum (2003) evaluated countdown pedestrian 

signals at 5 intersections in Montgomery County, Maryland. The results found that of the 

20 intersection approaches, the proportion of pedestrians entering the street during the 

flashing or steady hand decreased at 13 of the approaches (6 decreases were significant) 

with a significant increase at 2 approaches. Of the 4 approaches where pedestrian/vehicle 

conflicts were recorded, pedestrian-vehicle conflicts decreased at all four intersections 

after installation of the countdown signals (significant at the 0.05 level). 

A study by Rousseau and Davis (2003) compared 6 display-timing strategies with the 

standard MUTCD pedestrian signal to gain information on pedestrian understanding. 

A total of 134 participants were tested in three age groups: 18 to 29, 30 to 59, and 60 

and above. A higher percentage of aging pedestrians (compared to other age groups) 

were found to have difficulties in understanding the conventional pedestrian signal 

displays. The countdown signal display resulted in a substantial improvement in the 

understanding of the pedestrian signal display by aging adults. 

Countermeasures that have been suggested to reduce the occurrence of aging driver 

crashes at intersections have included changes to intersection operations (e.g., protected 

left-turn phases, elimination of RTOR, redundant signing, etc.) and geometric design 

(e.g., full positive offset of opposite left-turn lanes, increases in turning radius for right 

turns, etc.). One proposed solution to reduce not only the frequency but also the severity 

of crashes at intersections is the installation of a modern roundabout (Harkey, 1995; 

Jacquemart, 1998). Modern roundabouts are an intersection design that has been in 

use in Europe and Australia for decades, but have more recently come into their own 

in the United States. Over a 10-15 year period beginning in the late 1990s interest 

in roundabouts has increased exponentially in this country, and more jurisdictions 

have installed them as their benefits have become better known. FHWA released two 

Roundabout Guides (Robinson, et al. 2000; Rodegerdts, et al. 2010) during that period of

time, and a number of other research projects have explored the various operational and 

safety benefits of roundabouts. In addition, FHWA considers roundabouts to be a Proven 

Safety Countermeasure (FHWA Office of Safety 2012).

There are treatments currently within the Handbook that discuss features at roundabout 

intersections that can benefit aging drivers; however, roundabouts themselves can 

be a beneficial treatment over a traditional stop- or signal-controlled intersection if 

properly designed to meet the needs of that location. A great deal of existing research on 

roundabouts has not been conducted specifically from the perspective of the aging road 
198 Handbook for Designing Roadways for the Aging Population

CHAPTER 7 CHAPTER 7—INTERSE INTERSECTIONS

Table 34. Cross-References of Related Entries for Roundabouts.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Highway Capacity 

Manual

(2010)

Roundabouts: An Informational Guide, Second Edition

(2010)

Sect. 2B.43 through 

2B.45, 3B.16 Chapt. 

3C

Pgs. 9-167 through 9-176, 

Sect. 9-10 Roundabout 

Design

Chapter 21 Pg. 1-7, Exhibit 1-5, Items c & d 

Pg. 1-11, Exhibit 1-8, Items g and h

Pg. 1-11, Exhibit 1-8, Item f

Pg. 1-12, Exhibit 1-9

Pg. 1-13, Sect. 1.3.2

Pgs. 2-3 through 2-4, Sect. 2.2.1

Pgs. 2-15 through 2-17, Sect. 2.3.2

Pgs. 2-18 through 2-19, Sect. 2.3.4

Pg. 3-5, Exhibit 3-1 (Determine 

Preliminary Lane Numbers, and 

Determine the Space Requirements)

Pg. 3-8, first two bullets on pg.

Pgs. 3-21 through 3-24, Sect. 3.5.1

Pg. 3-30, third bullet

Pg. 3-26, Sect. 3.5.3 and Pg. 3-27, 

Exhibit 3-17

Pgs. 4-4 and 4-5, Sect. 4.2.1

Pgs. 4-10 through 4-19, Sects. 4.4 

through 4.6 

Pg. 5-4, 1st Bullet

Pgs. 5-6 through 5-7, Sect. 5.2.1

Pgs. 5-10 through 5-12, Sect. 5.2.3

Pg. 5-15, Exhibit 5-9

Pg. 5-19, Para. 1

Pg. 5-21, last paragraph 

Pgs. 5-22 through 5-24, Sect. 5.4.1

Pg. 6-9, Exhibit 6-2 (Entry Width, 

Circulatory Roadway Width, & Inscribed 

Circle Diameter)

Pgs. 6-11 through 6-13, Sect. 6.2.3

Pgs. 6-17 through 6-18, Sect. 6.3.1

Pgs. 6-24 through 6-25, Sects. 6.4.2 

and 6.4.3 

Pg. 6-25, Sect. 6.4.4 

Pgs. 6-22 through 6-24, Sect. 6.4.1

Pgs. 6-67 through 6-71, Sect. 6.8.1

Pgs. 6-76 through 6-77, Sects. 6.8.5.2 

and 6.8.5.3

Pgs. 6-46 through 6-47, Sect. 6.6.1

Glossary: Central Island, Circulatory 

Roadway Width, Entry Width, Inscribed 

Circle Diameter, Pedestrian Refuge, & 

Splitter Island

user, but the benefits apply to drivers and pedestrians of any age. It may be necessary to 

provide focused educational efforts to aging drivers when roundabouts are introduced 

into a community, so that unfamiliarities with that design can be at least somewhat 

mitigated. Indeed, FHWA’s Roundabout Outreach and Education Toolbox (FHWA Office 

of Safety 2013) provides a search feature that includes “older drivers” as a searchable 

target audience. 

This countermeasure, it has been suggested, addresses problems that aging drivers 

experience in judging speeds and gaps, understanding operational rules at complex 

intersections, and maneuvering through turns. Specifically, the following advantages of 

roundabouts for aging road users have been postulated:

•	 Reductions in the speed of vehicles entering the intersection/circle— this

makes it easier to choose an acceptable gap to merge into, removes the need to 

accelerate quickly which occurs after a conventional right turn, and results in 

lower severity crashes with less serious injuries.

•	 The left turn is completely eliminated.

•	 The larger curb radius improves maneuverability.
Handbook for Designing Roadways for the Aging Population 199

CHAPTER 7—INTERSECTIONS

•	 Simplified decision process results from one-way operation, yield-at-entry, and a

reduced number of conflict points compared to a conventional intersection.

•	 A potential for improved pedestrian safety results from shorter crossing

distances, fewer possibilities for conflicts with vehicles, and lower vehicle 

speeds—but, there are many unresolved issues surrounding the use of these 

facilities by (elderly and visually impaired) pedestrians at this time.

At the same time, there are significant human factors concerns about special driving task 

demands associated with the geometric and operational characteristics of roundabouts, 

and their novelty in this country. First, the driver approaching a roundabout must 

comprehend the prescribed movements, and in particular the yield-on-entry operation, 

as conveyed by upstream signing. For some years to come, these TCD’s will be novel to 

motorists; and aging persons are at a disadvantage in responding to novel, unexpected 

stimuli. Upon closer approach, the appropriate speed and heading changes to conform to 

the splitter island’s controlling channelization must be performed; and where increased 

crash experience has been documented following roundabout installation, as discussed 

below, excessive entry speeds have been the prevalent contributing factor. Again, vehicle 

control for smooth entry may be more challenging for aging than for younger drivers. At 

the point of entry, depending upon the deflection angle of the splitter island, there are 

critical seconds where confirmation that no conflict exists with a vehicle already in the 

roundabout requires a glance orientation that well exceeds 90°. The increased difficulty 

for aging drivers for visual search at skewed intersections has been underscored elsewhere 

in this Handbook (see page 41).

During negotiation of a roundabout, the ability to share attention between path guidance; 

gap (headway) maintenance; and visual detection, recognition, comprehension, and 

decision making associated with exit location cues is a near-continuous requirement, 

even for single-lane facilities. With multiple lanes, the avoidance of conflicts with 

adjacent vehicles places an exaggerated demand on motorists’ attention-sharing abilities; 

and of course, the increased traffic volumes and speeds associated with these highercapacity installations pose still greater demands. In the absence of controlled studies 

in the use of roundabouts by aging drivers, it can only be stated qualitatively that 

information processing capacity will be exceeded sooner for older than younger persons, 

and that accommodation by some seniors—probably by reducing their speed while in the 

roundabout—is likely. This will detract from the operational benefits roundabouts are 

designed to produce, and may impact safety as well.

A better understanding of the operational and safety issues surrounding the use of 

roundabouts by aging drivers and pedestrians depends upon crash data analyses from 

the limited number of existing facilities, and controlled and observational research in 

this area. This will require time, and more and more of these facilities are expected 

to come into operation in the immediate future. Thus, recommendations about when 

and why to use roundabouts to accommodate aging road users remain premature, but 

an understanding of roundabout task demands that pose special difficulty for seniors 

allow for certain recommendations regarding preferred practices when a jurisdiction has 

decided to install a roundabout. The recommendations presented for this design element 

attempt to balance the human factors considerations above with the accumulating body 

of information supporting roundabout usage, discussed below.
200 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

AASHTO (2011) presents the principles for modern roundabouts and discusses the need 

to accommodate all modes; the Green Book provides some degree of specific design 

guidance in Section 9.10, but it refers the reader to NCHRP Report 672, which is the 

second edition of FHWA’s Roundabouts: An Informational Guide (FHWA, 2010) and 

provides more detail on specific design parameters. The Highway Capacity Manual 

(2010) includes methodology for estimating capacity and level of service at roundabouts. 

Presently, several States have design guidelines for roundabouts (Florida, 1996 and 

Maryland, 1995) based largely on Australian guidelines. Both Florida and Maryland 

used SIDRA software (Australian methodology) in those guidelines to conduct an 

analysis of the capacity of a planned roundabout, which is available through McTrans at 

the University of Florida at Gainesville. A guide written for the California Department

of Transportation by Ourston and Doctors (1995) is based on British standards; 

according to Jacquemart (1998), Caltrans decided not to publish it. However, California 

DOT has distributed a Design Information Bulletin (No. 80) to provide general guidance 

to project engineers on appropriate applications, site requirements, geometric elements, 

and traffic analysis. New York State is developing an Engineering Instruction (EI) on 

roundabouts that will base design guidance on British Guides and software (RODEL).

The EI notes that other software programs are permitted (e.g., Highway Capacity, SIDRA, 

ARCADY), provided that a RODEL analysis is performed for comparison purposes. This 

EI is to provide interim guidance for current projects, and will be incorporated into the 

NY State Highway Design Manual. 

Flannery and Datta (1996) indicate that roundabouts are commonly used in Australia, 

Great Britain, France, Germany, Denmark, Ireland, Norway, Portugal, Spain, South

Africa, Sweden, Switzerland, and the Netherlands. Sarkar, Burden, and Wallwork 

(1999) state that modern roundabouts are gaining in popularity in cities across the U.S. 

(in Arizona, California, Colorado, Florida, Kansas, Maryland, Massachusetts, Nevada,

Oregon, Texas, and Wisconsin) because of their success in reducing speeds and the 

number of collisions. Because speeds are reduced, crashes are less severe. Because 

perpendicular left and right turns are eliminated, a roundabout with one-lane entries 

has fewer potential conflict points than a conventional intersection (8 vehicle-to-vehicle 

conflicts and 8 vehicle-to-pedestrian conflicts for a roundabout with 4, 1-lane entries, 

compared to 32 vehicle-to-vehicle conflicts and 24 vehicle-to-pedestrian conflicts for a 

conventional four-leg intersection). Jacquemart (1998) reports that as of the middle of 

1997, there were fewer than 50 modern roundabouts in the U.S., compared to more than 

35,000 in the rest of the world, with France owning the leading number of roundabouts 

(15,000 modern roundabouts currently, and growing at a rate of 1,000 per year).

Flannery and Datta (1996) highlight the fact that modern roundabouts are different 

than earlier rotaries and traffic circles common in the early 1900's. First, the modern 

roundabout requires drivers who are entering the circle to yield to traffic already in the 

circle (known as “offside priority”). Early roundabout operations gave priority to drivers 

entering the circle (“nearside priority”), which caused circulating traffic to come to a 

complete stop resulting in grid-lock. As a result of nearside priority, Flannery and Datta 

state that the operational performance of traffic circles declined rapidly with the increase 

in traffic beginning in the 1950's. Because traffic engineers believed that the problem was 

increased volume as opposed to nearside priority, traffic circles were generally abandoned 
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CHAPTER 7—INTERSECTIONS

in the U.S. Studies conducted in the Netherlands, Victoria Australia, and Western 

Australia have found significant reductions in crashes and casualty rates (from 60 to 

90 percent fewer) at roundabouts converted from the old priority to the yield-on-entry 

priority.

Two other improvements in modern roundabout design are deflection, which helps to 

slow entering vehicles, resulting in safer merges with the circulating traffic stream, and 

flared approaches, which helps to increase capacity by increasing the number of lanes 

on the approach (Flannery and Datta, 1996). Jacquemart (1998) describes deflection 

as: “No tangential entries are permitted and no traffic stream gets a straight movement 

through the intersection. Entering traffic points toward the central island, which deflects 

vehicles to the right, thus causing low entry speeds.” The splitter island is the geometric 

feature that physically separates entering traffic from exiting traffic, and defines the entry 

angle, which deflects and slows entering traffic. Looking at flared approaches from the 

viewpoint of accommodating aging driver needs for simplicity, one-lane approaches 

are likely to be easier to negotiate. In the NCHRP Synthesis of Roundabout Practice in 

the United States, Jacquemart (1998) notes that safety benefits of roundabouts (from 

studies in Australia and Europe) seem to be greatest for single-lane roundabouts in rural 

conditions. Generally, safety benefits are related to the reduced speed in the roundabouts,

the simplification of conflict points, and the “increased responsibility caused by the 

slower motion and the need to concentrate and yield, as compared to driver behavior in 

signalized intersections” (Jacquemart, 1998).

As noted earlier, studies performed to date to evaluate the safety performance of 

roundabouts have not included driver age as a variable. Flannery and Datta (1996) 

conducted a safety analysis of six sites in Florida, Maryland, and Nevada that were 

converted from conventional intersections with traditional control (1-way stop, 2-way 

stop, or signalized) to roundabouts. All six sites had one-lane entrances and only one 

lane of circulating traffic. Five roundabouts had a posted speed of 35 mph and one 

had a posted speed of 45 mph. Four of the sites had four approaches and two sites had 

three approach legs. Crash data were collected for a period of 1 to 3 years before and 

after retrofitting the sites (depending on location). Results of chi-squared and normal 

approximation statistical tests indicated that crash frequencies were significantly 

reduced in the period after the sites were retrofitted as modern roundabouts. The sites 

were not stratified by ADT or previous type of traffic control, as the sample size was 

small; therefore particular crash reduction factors were not identified. However, quick 

inspection of the crash frequencies provided by site indicate that only the roundabout 

retrofitted from a signalized intersection showed an increase in crashes in the after 

period; the other five sites (1-way and 2-way stop controlled) showed decreases in crash 

frequency in the after period (in the range of 60 to 70 percent). Analyses could only be 

performed on crash frequencies by group (as opposed to site), because traffic volumes 

before and after were not characterized, and the six retrofitted roundabouts varied in 

ADT from 4,069 to 17,825 vehicles. 

Rahman (1995) and Jacquemart (1998) provided before and after crash data for the 

roundabout established in Lisbon, MD in 1993. In the six years prior to the roundabout, 

there were 45 reported intersection crashes with an average of eight crashes per year. 
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From 1993 to 1995 (after roundabout installation), there were only two reported crashes. 

Before the roundabout, the crashes were almost all angle crashes, and after the roundabout 

was installed, one of the crashes was a single-vehicle crash against a fixed object, and 

the other crash was a rear-end crash. Injury crashes decreased from 4.3 per year to 0.3. 

Total delays decreased by 45 percent, from 1.2 vehicle hours to 0.34 vehicle hours in the 

morning peak hour and from 1.09 vehicle hours to 0.92 vehicle hours in the afternoon 

peak. This roundabout has four approach legs; it was retrofitted from a 2-way stopcontrolled (flashing red beacon) intersection. The ADT was 8,500 vehicles (in March of 

1995). The inscribed diameter is 100 ft, there are one-lane entries measuring 18 ft, there is 

one lane of circulating traffic that is 18-ft wide, and in 1995 the peak hour total approach 

volume was 630 (Jacquemart, 1998). Rahman (1995) stated that, “the performance of this 

first experimental roundabout in Maryland demonstrates the safety of roundabouts when 

properly designed.”

Jacquemart (1998) examined the before and after crash data of 11 roundabouts in the U.S. 

Results are described for large roundabouts with three-lane entries (one in Long Beach, 

CA and two in Vail, CO) and smaller roundabouts with one- or two-lane entries and 

inscribed circle diameters of 37 m (121 ft) or less (Santa Barbara, CA; Lisbon, Cearfoss, 

Lothian, and Leeds, MD; Tampa, FL; Montpelier, VT; and Hilton Head, SC). He states 

that the small- to moderate- size roundabouts showed significant reductions in total 

crashes (from an average annual crash frequency 4.8 to 2.4, or 51 percent) and injury 

crashes (from an average annual crash frequency of 2.0 to 0.5, or 73 percent). There 

were no statistically significant differences in property-damage-only (PDO) crashes at 

the smaller roundabouts, although there was a reduction from 2.4 to 1.6 average annual 

crashes, or 32 percent. Although there was a trend toward crash reduction for the larger 

roundabouts, there were no statistically significant reductions in total crashes, injury 

crashes, or PDO crashes. Each roundabout experienced a reduction in injury crashes 

ranging from 20 to 100 percent. PDO crashes increased at a roundabout in Vail, CO from 

15 to 18 per year, and at Leeds, MD from 1.5 to 5.3 per year. At the other 9 roundabouts, 

however, PDO crashes decreased from 6 to 1 per year. Although PDO crashes at the 

Leeds, MD site showed an increase, injury crashes decreased from 2.2 to 0.0 per year. The 

PDO crashes at this site were all single-vehicle crashes that occurred because the vehicles 

entered the roundabout too fast. Jacquemart (1998) reports findings by Niederhauser, 

Collins, and Myers (1997) who showed that the average cost per crash decreased by 30 

percent across the 5 conventional intersections in Maryland that were retrofitted to 

roundabouts, from $120,000 before the roundabout to $84,000 after the roundabout.

Niederhauser, Collins, and Myers (1997) reported 

the before and after average annual crash history 

for the five intersections in Maryland that 

were converted to roundabouts. All sites are 

single-lane approach and single-lane circulating 

roundabouts. Overall, the average crash rate was 

reduced from an average of 5.0 crashes per year 

to an average of 2.4 crashes per year, which is a 

reduction of greater than 50 percent. Data for 

each roundabout is reported in Table 35. 

Table 35. Before and After Average Annual Crash History For 

The Five Intersections In Maryland That Were Converted To 

Roundabouts (Niederhauser, Collins, And Myers, 1997).

Site Average Annual Crashes

Before After

Lisbon 6.0 2.0

Cearfoss 2.7 0.0

Leeds 3.3 4.9

Lothian 7.7 5.1

Taneytown 5.3 0.0
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CHAPTER 7—INTERSECTIONS

Persuad, et al. (2000) evaluated the change in crashes following conversion of 24 

intersections in urban, suburban, and rural environments in 8 States (California, 

Colorado, Florida, Kansas, Maine, Maryland, South Carolina, and Vermont) from

stop-sign or signal control to modern roundabouts. The Bayes procedure was used 

to account for regression to the mean and to normalize differences in traffic volume 

between the before and after periods. The number of months of crash data available in 

the before period ranged from 21 to 66, and the number of months of crash data available 

in the after period ranged from 15 to 68. Across all sites and crash severities, crashes 

were reduced by 39 percent in the after-conversion period. A 76-percent reduction was 

estimated in the after period for injury crashes. For the 20 sites where injury data were 

available, there were 3 fatal crashes in the before period, and none in the after period. 

There were 27 incapacitating injury crashes in the before period, and 3 in the after period. 

Thus, the estimated reduction in fatal and incapacitating injury crashes is 89 percent. 

Persuad et al. (2000) looked at the crash reduction rates as a function of operating 

environment and before-conversion control. For the nine urban single-lane roundabouts 

converted from stop control, a 61-percent reduction was estimated for all crash severities 

combined, and a reduction of 77 percent was estimated for injury crashes. For the five 

rural single-lane roundabouts converted from stop control, a 58-percent reduction was 

estimated for all crash severities combined, and a reduction of 82 percent was estimated 

for injury crashes. For the seven urban multilane roundabouts, a 15 percent reduction 

in crashes of all severities was estimated. Injury data were not available for four these 

sites in the before-conversion period. For the three roundabouts converted from traffic 

signal control, all crashes were reduced by 32 percent, and injury crashes by 68 percent. 

The authors noted that the smaller safety effects for the group of urban multilane 

roundabouts suggests that there may be differences in safety performance for single-lane 

designs compared to multi-lane designs. However, they caution that all seven of these 

roundabouts were located in one State (Colorado) where three of the four in the city of 

Vail were part of a freeway interchange that also included nearby intersections that were 

previously four-way stop-controlled. Finally in this research, pedestrian and bicycle 

crash samples were too small to be meaningful; however, there were three reported 

pedestrian crashes during the before period and one with minimal injuries in the after 

period. Four bicyclists were injured in the before period and three during the after 

period.

Wallwork (1993) notes that crashes do occur at roundabouts, and consist of rear-end 

or merge-type crashes. Both crash types are low speed and low impact, and result in 

few – if any – injuries. He stated that with a roundabout, “no one can ‘run the red,’ and 

cause a right-angle collision, nor can drivers make a mistake in selecting a gap in the 

approaching through traffic when making a left turn. The only decision an entering 

driver needs to make is whether or not the gap in the approaching/circulating traffic is 

large enough to enter safely.” Lower speeds (less than 25 mph) result in shorter braking 

distances and longer decision making times. Even if a driver makes a mistake and 

chooses a gap that is too short, a collision is easier to avoid. Thus, the reduction in task 

difficulty coupled with the low speed environment, results in an overall reduction in the 

number of crashes, and a reduction in the severity of the crashes that do occur, which 

should be especially beneficial to aging persons.
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The delays before and after eight intersections (seven of which were two-way, or multiway stop-controlled, and one was signalized) were converted to roundabouts were also 

described by Jacquemart (1998). The total delay (stopped delay plus move-up time in 

queue) for eight U.S. roundabouts before retrofit was 13.7 s for morning peak time and 

14.5 s for afternoon peak time. This compares to 3.1 s for morning and 3.5 s for afternoon 

peak times after conversion to roundabouts. Delays were thus reduced by 78 percent in 

morning peak periods, and by 76 percent in afternoon peak periods, after intersections 

were converted to roundabouts.

Jacquemart (1998) received information about the design of 38 roundabouts in the U.S., 

and presented data for four major geometric features: (1) inscribed circle diameter; 

(2) circulatory roadway width; (3) central island; and (4) entry widths. The inscribed 

circle diameter is defined as the circle that can be inscribed within the outer curbline 

of the circulatory roadway. Twenty-eight of the 31 roundabouts for which data were 

provided on this element have an inscribed circle diameter in the range of 98 to 200 ft, 

with the majority of these (11) ranging from 98 to 108 ft. Regarding circulatory roadway 

width, 43 percent of the cases are 15- to 18- ft wide; 21 percent are 20 to 23-ft wide; 

25 percent are 24 to 30-ft; and 11 percent are 35 to 36-ft wide. Thus, 36 percent are at 

least 2 lanes wide. The central island can be raised or flush, or it can be raised with a 

sloping curb or drivable apron surrounding it. The truck apron is generally included 

in the central island diameter. Jacquemart reports that approximately 66 percent of 

the roundabouts for which data were provided have central islands greater than 30 ft 

diameter. Regarding entry widths, 59 percent of the reported cases have single-lane 

entries, 30 percent have two-lane entries, and 11 percent have three or more lane 

entry legs. Studies in other countries help to shed some light on the optimum design 

characteristics of modern roundabouts. 

In the Jacquemart (1998) synthesis, a study by Brilon (1996) of 34 modern roundabouts in 

Germany concluded that 98 ft seemed to be the ideal inscribed diameter for a single-lane

roundabout. Brilon states that smaller diameters result in larger circulatory roadways, 

which reduces the deflection. Additionally, truck aprons with a rougher pavement are 

recommended, so that the circulatory roadway remains 13 to 15-ft wide. In a study of 

83 roundabouts in France (Centre D’Etudes Techniques de L’Equipment de l’Ouest, 1986) 

in Jacquemart (1998), it is also concluded that roundabouts with smaller diameters have 

fewer crashes than larger roundabouts or those with oval circles (see Table 36). 

Splitter islands are another geometric feature of modern roundabouts. These are 

generally raised islands that are 

placed within a leg of a roundabout to 

separate entering and exiting traffic, 

and to deflect entering traffic. They also 

serve as a safety zone for pedestrians. 

Only one of the 38 roundabouts has 

painted (marked) splitter islands. 

The study conducted in Germany

(Brilon, 1996, in Jacquemart, 1998) 

concluded that splitter islands are 

important to the safety of pedestrians, 

Table 36. Roundabout crashes compared to diameter (Jacquemart, 1998)

Number of 

Roundabouts

Inscribed Diameter 

(ft)

Crashes per 

Roundabout

13 <98 0.69

11 98 to 164 1.54

26 164 to 230 1.58

16 230 to 295 1.81

8 >295 3.80

9 Oval 4.40
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CHAPTER 7—INTERSECTIONS

and should be 5- to 8-ft wide, with pedestrian crossings located 13 to 16 ft back from 

the circulating roadway. A study conducted in Switzerland by Simon and Rutz, 1988 

(in Jacquemart, 1998) also concluded that the distance between the pedestrian crossing 

and the inscribed circle should be 16 ft as greater distances do not increase pedestrian 

safety. They recommended the use of splitter islands with safety zones for pedestrians 

for crossings of more than 300 vehicles per hour. Wallwork (1999) states that a feature 

of roundabouts that makes them safer for pedestrian than conventional intersections is 

that pedestrians walk behind the cars. He recommends moving the crosswalk back one 

car length from the yield line for each lane of entry (i.e., one car length for a one-lane 

entry, two car lengths for a two-lane entry, or three car lengths for a three-lane entry). 

Brilon (1996) recommended Zebra-striped crossings only when there were more than 100 

pedestrians crossing during the peak hour. Maryland (DOT/SHA, 1995) normally places 

pedestrian crossings 20 to 25 ft from the yield line. Crosswalk striping is not used, to 

avoid driver confusion of crosswalk limit lines with yield lines. Special consideration is 

given in providing priority crossings for pedestrians where pedestrian volumes are high, 

where there is a high proportion of younger or older pedestrians, or where pedestrians 

experience particular difficulty in crossing, and are being delayed excessively. The agency 

believes that it is desirable to place these crossings at least 75 ft downstream of the exit 

from the roundabout and possibly augment the crossing with a signal. This will reduce 

the possibility that vehicles delayed at the pedestrian crossing will queue back into the 

roundabout, and gridlock the whole intersection.

In the survey conducted by Jacquemart (1998) detailing 38 U.S. roundabouts, 56 percent 

of the sites were reported to have no or very few pedestrians, 22 percent have between 20 

and 60 pedestrians during the peak hour, and 22 percent have more than 60 pedestrians 

per hour. Of particular interest is the Montpelier, Vermont roundabout, which is located 

next to a senior housing project and is also close to a middle school (400 students), and 

carries in excess of 260 pedestrians during each rush-hour (morning and afternoon) 

period on school days (Gamble, 1996; Redington, 1997). This roundabout has 3 legs, an

inscribed diameter of 34 m, one-lane entries for each lane and one lane of circulating 

traffic. The AADT is approximately 11,000 (7,300 AADT for each leg) and carries 

approximately 40 tractor trailers (WB-62) each day (Redington, 1997). The peak hour 

total approach volume is 1,000 vehicles (Jacquemart, 1998). Prior traffic control was a 

one-way stop at a Y-intersection.

Jacquemart (1998) lists criteria to assist visually impaired pedestrians that include: 

(1) keeping the crossing away from the circle (e.g., 5 to 6 m from the outer circle) lets 

the blind person distinguish the exiting traffic from the circulating traffic; and (2) the 

splitter island provides a refuge where the pedestrian can shift his or her attention from 

one traffic stream to another. Different pavement texture for the walkways will assist 

the visually impaired pedestrian in locating the crosswalks. Drivers approaching a 

roundabout approach at speeds slower than they would for an approach to a conventional 

intersection; thus, they are more likely to stop for pedestrians, and may be more likely to 

notice a pedestrian on an approach to a roundabout because they are not concentrating 

on finding a gap in the opposing traffic stream to turn left.

Harkey and Carter (2006) evaluated pedestrian and bicyclist behaviors at single-lane and 

multilane roundabouts in eight states. The results of the study showed vehicles exiting 
206 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

a roundabout to be less likely to yield (38% non-yield rate) to crossing pedestrians than 

vehicles approaching a roundabout (23% non-yield rate). There was also less yielding to 

crossing pedestrians on multilane approaches (43% non-yield rate) compared to singlelane approaches (17% non-yield rates). The authors concluded that roundabouts need 

to be designed to ensure adequate sight lines and slow vehicle speeds on the exit legs. 

Multilane roundabouts may also require additional measures to minimize the risk of 

multiple-threat collisions and create a safe crossing environment.

Jacquemart (1998) also provided a summary of the current lighting, signing, and 

pavement marking practices at the 38 U.S. roundabouts for which questionnaire data 

were provided. First, all existing roundabouts were reported to have nighttime lighting. 

Next, all roundabouts were reported to have the standard YIELD sign, although 

often it was supplemented by an additional plate with specific instructions, such as 

“TO TRAFFIC ON LEFT;” “TO TRAFFIC IN ROUNDABOUT;” or “ TO TRAFFIC 

IN CIRCLE;” or with the international roundabout symbol, which is three arrows in 

a circular pattern. In addition, 90 percent of the roundabouts contain 

an advance YIELD AHEAD symbol sign and 7 percent use the YIELD 

AHEAD legend sign. Twenty-four percent included a supplemental plate 

on the advance YIELD sign that said “AT ROUNDABOUT,” presented the 

roundabout symbol, or displayed a speed limit sign. All roundabouts had 

either a one-way sign (R6-1 or R6-2) or a large arrow warning sign (W1-

6) in the central island. Chevron signs often accompanied the one-way 

signs at the sites studied (see Figure 81). Regarding pavement markings, 

approximately 20 percent of the roundabouts supplemented the yield line 

at the roundabout entrance with the pavement marking legend “YIELD” 

or “YIELD AHEAD.” For multilane roundabouts, only in the case of the 

Hilton Head, SC, roundabout were lane lines present. Jacquemart (1998) 

reported that the authorities responsible for the roundabout believe that 

the large number of senior drivers in the area would be more comfortable 

with lane markings in the circle. Simon and Rutz, 1988 (in Jacquemart, 

1998) recommended that for main roads or national highways, advance directional signs 

with the roundabout symbol should supplement the roundabout yield sign at the entry, 

but that other special warning signs—such as roundabout ahead or priority to the left—

are not recommended. Wallwork (1999) does not recommend the widespread use of 

supplemental signs (e.g., posting “TO TRAFFIC IN CROSSWALK” on the YIELD sign),

because it constitutes visual clutter. Instead, he recommends their use only as a local 

measure to educate road users for a short time period after roundabout installation.

Molino, Inman, Katz, and Emo (2007) conducted a driving simulator study using

90 participants equally distributed into three age groups: young (ages 18 to 25), middleaged (26 to 64) and older (age 65 and older). Participants “drove” through double-lane 

roundabouts marked with five signing and pavement marking schemes: 

1. traditional arrow signs and markings; 

2. fishhook arrow signs and markings; 

3. traditional arrow signs and markings with clarifying words (e.g., “all” and 

“only”);

Figure 81. One Way and Chevron 

Sign Combination Used in Central 

Island of Roundabout (Jacquemart 

1998)
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CHAPTER 7—INTERSECTIONS

4. fishhook arrow signs and markings with clarifying words; and 

5. destination lane restriction sign with no lane restriction markings. 

A sixth condition with no lane restriction signs or markings, served as the control. 

Except for the destination lane restriction sign condition, all roundabouts had redundant 

indications of proper lane approach. Participants chose the correct entry lane between 89 

and 91 percent of the time, and the percentages did not vary significantly among marking 

schemes. The overall compliance score across schemes was 89.2 percent; all 5 schemes 

resulted in successful compliance performance, if the criterion is set to 85 percent. 

However, the fact that in 11 percent of the scenarios, drivers continued to make left turns 

from the right lane, even when the signs and markings clearly showed that the right lane 

must turn right is both an operational and safety concern. The 11 percent compliance 

failure occurred regardless of the fact that signs/markings were redundantly presented on 

each approach. Molino et al. (2007) report that in field conditions, where there may be 

less redundancy in signs and markings, and where traffic may cause drivers to miss some 

lane restriction indications, overall compliance may be less than 89 percent.

In terms of driver comprehension, participants correctly understood the left and right 

lane options approximately 90 percent of the time across schemes, but often did not 

understand markings allowing them to use “either” entry lane to reach their destination. 

Comprehension for “either” lane entry options was only 44 percent, and was not 

significantly different across the 5 schemes. Comprehension for the marking schemes 

ranged from 70 to 78 percent when participants were required to report which, among 

three lane choices was correct (left, right, or either). Overall comprehension, collapsed 

across the 5 schemes was 74.9 percent; none of the signing and marking schemes resulted 

in successful comprehension performance. Poor comprehension that entry from 

either lane was allowable could interfere with roundabout capacity design calculations. 

Although comprehension across all schemes was poor, there were no attempts to drive 

through the roundabout in the wrong direction with any of the schemes.

In terms of age and gender effects, Molino et al. (2007) found that although younger 

participants had higher percentages of correct responses for both compliance and 

comprehension than middle-aged participants, who in turn had higher percentages 

of correct responses than older participants, the differences were not statistically 

significant. Males had higher percentages of correct responses for both compliance and 

comprehension than females; however, the difference was significant only for compliance.

Molino et al. (2007) concluded that, based on the simulation results, conventional arrow 

signs and markings, fishhook signs and markings, or lane restrictions included on 

diagrammatic navigation signs would be equally effective, however, additional steps may 

be needed to achieve a higher rate of compliance where lane restriction compliance is 

deemed important for either operations or safety. The simulation results did not point to 

what steps would be effective.

Lord, et al. (2007) conducted a laboratory study with aging drivers to evaluate 

countermeasures that may have the potential to improve the perceived comfort, 

confidence, and/or safety of aging persons using roundabouts. Structured interviews 

were conducted in Texas and Arizona with 31 licensed drivers ages 65 and older, in 

addition to animated video presentations simulating an approach to and traversal of a 
208 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

roundabout. Five design elements were evaluated: (1) advance warning signs; (2) lane 

control signs; (3) directional signs; (4) yield treatments; and (5) exit sign treatments. For 

each design element, a base condition (representing existing standards of engineering and 

design practice as per the 2003 MUTCD) was presented along with two countermeasures. 

The countermeasures were developed using input from focus groups conducted with 

aging drivers in an earlier phase of the study. Still images were photographed of a 

roundabout unfamiliar to all participants (in Washington State), every 10 ft during an 

approach to and going around the roundabout, for a total of 64 images. The images 

were manipulated with photo-editing software to reflect each of the three alternatives, 

described in Table 37.

The evaluation was carried out using paired comparisons between the base condition 

and alternative 1; followed by comparisons between the base condition and alternative 

2. Subjects were asked to rate the perceived change in terms of safety, comfort, and 

confidence. A 7-point Likert scale was used for the ratings, with the endpoints being 

significantly lower or higher (e.g., 1 = the alternative drive was significantly lower than 

the baseline, 7= the alternative drive was significantly higher than the baseline) and the 

midpoint of the scale (4) meaning no change. Study findings are described below for each 

of the design elements evaluated.

Advance Warning Sign

Based on the ratings of comfort, confidence, and safety, there was no significant 

difference between Countermeasures 1 and 2, but both were superior to the baseline. 

Participants’ comment suggested that Countermeasure 2 would best meet their needs. 

Based on these findings, Lord et al. (2007) recommended the use of the roundabout 

Table 37. Description of Countermeasures Studied for Roundabout Traffic Control Devices (Lord et al. 2007).

Traffic Control Device Baseline Countermeasure 1 Countermeasure 2

Advance Warning Signs W-2-6 Advance roundabout 

warning sign

Baseline sign with solid 

black circle added to center 

and supplemental plaque 

“Roundabout”

Countermeasure 1 sign with 

supplemental plaque (30 mph), 

but no “Roundabout” plaque

Lane Control Signs Modeled after R3-8 advance 

intersection lane control signs, 

where solid lines displayed the 

2 possible routes for traveling 

through the roundabout (one for 

each entering lane).

A solid black circle representing 

the central island was added to 

the left lane’s route.

The text “Left Lane” and “Right 

Lane” were added under the 

corresponding routes, on the 

sign used in Countermeasure 1.

Directional Signs A central island without 

any guide signs or special 

pavement marking guiding 

traffic circulating around the 

roundabout, as per MUTCD

(2003) guidelines.

One Way (R-6-1) placed on 

central island, facing centerline 

of approaching roadway.

One Way (R-6-1) placed on 

central island, in front of driver’s 

entry point (closer to driver’s line 

of sight.

Yield Treatment Standard R1-2 Yield sign 

placed on both sides of road 

at roundabout entrance, per 

MUTCD.

A Yield line consisting of solid 

white isosceles triangles was 

added to the base condition.

Yield line from countermeasure 

1 plus supplemental signs 

below Yield sign “TO TRAFFIC IN 

CIRCLE.”

Exit Treatment Street Name exit sign placed 

between two intersecting 

streets, prior to the exit.

Same street name exit sign in 

Baseline, but placed onto splitter 

island of intended street exit.

Arrow added to street name 

exit sign and placed as in 

Countermeasure 1
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CHAPTER 7—INTERSECTIONS

advance warning sign, augmented with a 

symbol representing the center island, as 

shown in Figure 82.

Lane Control Signs: Both countermeasures 

received higher ratings than the base, but 

Countermeasure #2 received significantly 

higher ratings. Based on the study findings, 

Lord et al. (2007) recommended the use of 

lane control signs designating the intended 

destinations for each lane (for multilane 

roundabouts), augmented with a black solid 

circle for the left lane’s route representing the 

central island, augmented by text under each 

route, indicating “LEFT LANE” and “RIGHT

LANE,” as shown in Figure 83.

Directional Signs

The use of a ONE WAY sign on the center 

island was associated with increased 

ratings over the baseline (no signs); there were no significant differences between 

the countermeasures, however, comments provided by study participants indicated 

placement to maximize the visibility of a driver just about to enter the roundabout 

is beneficial. Lord et al. (2007) recommended the use of a ONE WAY sign, shown in 

Figure 84, placed on the center island in direct view of a driver’s entry point, rather than 

at the centerline of the approaching roadway.

Yield Treatment

Countermeasure 1 (inverted isosceles triangle pavement markings) did not improve 

participants’ understanding of the yield treatment at the entrance of the roundabout; 

and some participants thought they were traveling in the wrong direction, given that 

the triangles were pointed toward the drivers entering. Countermeasure 2 (Yield sign 

Figure 82. Roundabout 

Advance Warning Sign 

Recommended by Lord et al. 

(2007)

Figure 83. Lane Control Sign 

Recommended by Lord et al. 

(2007)

Figure 84. Roundabout Sign Recommended by Lord et al. (2007)
210 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

with supplemental plaque “To Traffic in Circle”) received significantly higher comfort 

ratings than the baseline condition. Based on their study findings, Lord et al. (2007) 

recommended that the supplemental panel bearing the legend “TO TRAFFIC IN 

CIRCLE” be placed immediately below the R1-2 Yield signs on both sides of the road at 

the entrance to a roundabout, as shown in Figure 85.

Exit Treatment

Countermeasure 1 did not significantly improve the perceived comfort, confidence, or 

safety relative to the baseline. The addition of the arrow on the street name sign pointing 

toward the exit leg showed significantly improved comfort, confidence, and safety over 

the baseline. Based on their study findings, Lord et al. (2007) recommended that the 

name of each intersecting leg on a roundabout be labeled with a sign panel placed on the 

splitter island for that intersection, facing toward approaching traffic in the roundabout, 

and that a directional arrow pointing toward the exit leg accompany the street name on 

the panel, as shown in Figure 86.

As noted by Lord et al., (2007) the findings from the laboratory study should be 

confirmed through naturalistic field study observations prior to their adoption in Federal 

Figure 85. Yield Sign Treatment Recommended by Lord et al. (2007)

Figure 86. Exit Treatment Recommended by Lord et al. (2007)
Handbook for Designing Roadways for the Aging Population 211

CHAPTER 7—INTERSECTIONS

and State design manuals. This is particularly important for the lane use control signs 

and the exit signs evaluated, because misunderstandings about proper lane use, and 

placement of exit signs at the exit location may result in last-minute, erratic lane-change 

maneuvers, and crashes. For multilane approaches to roundabouts, signs should be 

designed to assure that drivers choose the proper lane for their destination before reaching 

the roundabout, and once in that lane, they should be able to circumnavigate the central 

roadway of the roundabout and exit to their destination without having to change lanes 

while in the circular roadway of the roundabout. To ensure that the signs recommended 

in the laboratory perform as intended, they should be tested in the field, and therefore, 

no recommendation for their implementation is made for this Handbook, and the study 

findings should be considered as preliminary.

At the same time, providing drivers with more detailed information about what to expect 

when they reach the roundabout should enhance the operational safety of roundabouts 

for aging drivers in particular, as well as the general population of drivers, without any 

unintended consequences. The advanced roundabout sign with the center island symbol 

advises drivers that traffic flows counterclockwise around an island. The educational plaque 

on the Yield sign “TO TRAFFIC IN CIRCLE” provides more detail about the right-of-way 

rules, advising entering drivers that they are the ones who must yield because circulating 

traffic has the right of way. The ONE WAY sign is a familiar regulatory sign and indicates 

that the required movement of entering traffic is to the right. Understanding these 

roundabout operational rules is paramount to avoiding wrong-way maneuvers (and their 

consequent head-on crashes), panic stops by circulating traffic trying to avoid crashing into 

a driver who does not yield at entry (resulting in rear-end crashes by following circulating 

drivers), and angle crashes between entering and circulating drivers when an entering 

driver fails to yield and an approaching driver does not take evasive action. 

The enhanced advanced roundabout warning sign used by Lord et al. (2007) is a novel 

design, and care must be taken in determining the size of the center island symbol to 

ensure legibility of the sign. The visual task detail size of the central island symbol should 

be large enough for detection at a preview distance of at least 5 s, but not so large that it 

interferes with recognition of the circular intersection arrows. A dimension that satisfies 

these objectives may be analytically determined; though of course, field validation is 

desirable. Using principles evidenced in Standard Highway Signs (FHWA, 2004), to avoid 

legibility problems while affording detection for aging drivers at meaningful preview 

distances, the center island symbol should be centered on the sign and its diameter should 

range from 2.0 to 2.5 times the stroke width of the arrows. 

Jacquemart (1998) lists several location types where it is appropriate to install 

roundabouts, based on a review of guidelines from abroad and those existing guidelines in 

the U.S. (e.g., Maryland and Florida). These locations include: 

•	 High crash locations, particularly with high crash rates related to cross

movements or left-turn or right-turn movements.

•	 Locations with high delays.

•	 Four-way stop intersections.

•	 Intersections with more than four legs.
212 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

•	 Intersections with unusual geometry (Y or acute angle).

•	 Intersections with high left-turn flows.

•	 Intersections with changing traffic patterns.

•	 Intersections where U-turns are frequent or desirable along commercial

corridors.

•	 At locations where storage capacities for signalized intersections are restricted,

or where the queues created by signalized intersections cause operational or 

safety problems.

•	 Intersections where the character or speed of the road changes, such as at entry

points to a community or at junctions where a bypass road connects to an 

arterial.

Ourston and Bared (1995) cited the work of Guichet (1992) who investigated 202 crashes

at 179 urban roundabouts in France. The crash causes and relative frequencies are 

presented in Table 38. 

Table 38. Causes of Crashes at Urban Roundabouts in France (Ourston and Bared, 1995). 

Cause of Crash Percent of 

Crashes

Entering traffic failing to yield to circulating traffic 36.6

Loss of control inside the circulatory roadway 16.3

Loss of control at entries 10.0

Rear-end crashes at entries 7.4

Sideswipe, mostly at two-lane exits with cyclists (2 of 3 instances) 5.9

Running over pedestrians at marked crosswalks, mostly at two-lane entries 5.9

Pedestrians on the circulatory roadway 3.5

Loss of control at exits 2.5

Head-on collision at exits 2.5

Weaving inside the circulatory roadway 2.5

Guichet (1992) listed the major design recommendations, based on the findings of the

crash investigation:

•	 Ensure that motorists recognize the approach to the roundabout.

•	 Avoid entries and exits with two or more lanes, except for capacity requirements.

•	 Separate the exit and entry by a splitter island.

•	 Avoid perpendicular entries or very large radii.

•	 Avoid very tight exit radii.

•	 Avoid oval-shaped roundabouts.

Wallwork (1999) recommends that in areas where there is a high concentration of aging 

drivers, it is desirable to use the lower end of the speed range that he has determined 

for roundabouts in a particular roadway class. He states that a roundabout meets 

drivers’ requirements for simple decision making, and low speed is paramount for safe 
Handbook for Designing Roadways for the Aging Population 213

CHAPTER 7—INTERSECTIONS

roundabout operation. His design-speed recommendations 

by roadway class are presented in Table 39.

He states that the best way to control driver behavior is 

through the use of concrete: the roundabout has a concrete 

circle in the center, which defines a path to control speed, 

and a roundabout uses concrete islands to deter wrong-way 

movements and to control entry speeds. Roundabouts that 

are not designed for slow speeds result in high crash rates; 

there are at least two in the U.S. (Boulder, Colorado and 

Daytona Beach, Florida) that are being removed, because of 

poor design (e.g., no bulbouts for deflection on the entries 

allowing for 40-mph speeds). 

Regarding public opinion about roundabout implementation, Taekratok (1998) indicates 

that people do not make a clear distinction between modern roundabouts and traffic 

circles, and therefore public responses to roundabout proposals are negative. Jacquemart 

(1998) presents copies of media coverage (Howard County Sun Newspaper) about the 

Lisbon, Maryland roundabout installed in Howard County as an experimental solution 

to an intersection with a high crash rate. One year before the roundabout opened, 

most of the Lisbon residents objected to the idea of a roundabout. Four months after 

the roundabout opened, a local citizen’s committee voted overwhelmingly to make the 

roundabout permanent. Taekratok (1998) reports that the strategies taken by Florida, 

Maryland, and Vermont have been successful in improving public perception, and 

include public education through the use of brochures, videotapes, and mass media 

to provide information during the development stage. This will help the public to 

understand the differences between circles and roundabouts, and will gradually reduce 

opposition. 

Redington (1997) notes that roundabouts are small (e.g., 91.8 to 180 ft) compared to the 

old time traffic circles found in New England and New Jersey (e.g., 249 ft or greater), and 

that drivers strongly dislike traffic circles with their typical operating speeds of 31 to 

41 mph. While the Montpelier, VT, Keck Circle Roundabout was under construction,

the Roundabout Demonstration Committee prepared educational materials that 

included a brochure providing safety rules for drivers and pedestrians, as well as news 

releases and public service announcements in response to negative public reaction 

during construction, and negative commentary from local morning radio personalities 

(Redington, 1997). This Committee also conducted a survey of 111 citizens working 

or living near the roundabout one year after its opening to measure public opinion. 

Of the 111 respondents, 104 had driven the roundabout, 89 had walked, and 19 had 

bicycled. “Very favorable” or “favorable” responses were obtained from 57.6 percent 

of the respondents, 27.9 percent of the responses were “neutral” and 14.4 percent were 

“unfavorable” or “very unfavorable.” The survey contained two open-ended questions 

to allow respondents to contribute “likes,” dislikes,” and comments about “what they 

miss about the old intersection.” The 111 respondents contributed 214 comments. The 

majority of the 65 “like” comments pertained specifically to smoother and better traffic 

movement. Fifty-six comments were obtained from respondents who “dislike” the 

Table 39. Design-Speed Recommendations For 

Modern Roundabouts By Roadway Class (Wallwork, 

1999). 

Roadway 

Classification

Roundabout 

Design Speed 

(mph)

Local Road 12-15

Collector Road 15-18

Secondary Arterial 18-21

Major Arterial 21-23

Rural Roadway Maximum 25
214 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

roundabout. The majority of these were directed toward poor driver behavior such as 

drivers failing to yield, failing to follow the rules, and failure to use turn signals.

Finally, Sarkar, Burden, and Wallwork (1999) reviewed driver’s manuals for 32 States 

and the District of Columbia, and concluded that the information on traffic circle and 

roundabout use was inadequate. Only 10 of the States provided some instruction in their 

manuals about how to use the circles (i.e., entering drivers should yield to drivers who 

are already in the circle) and none provided information about how to use roundabouts. 

Information about types of signs placed near roundabouts and circles was not present, 

nor was there any explanation about the differences between circles and roundabouts. 

Only one State had an illustration of a circle, but in the authors’ opinion, it was not clear 

or easy to understand. They recommend that State driver manuals be revised to include 

information about correct use of traffic circles and roundabouts, as roundabouts are 

becoming increasingly popular in the U.S.
Handbook for Designing Roadways for the Aging Population 215

CHAPTER 7—INTERSECTIONS

PROMISING PRACTICES

17 Right-Turn Channelization Design

Description of Practice: This practice reflects improved design of the corner island, 

turning lane width, and turning radii for channelized right turns to discourage high-speed 

turns while still accommodating large trucks and buses, and also facilitating pedestrians 

crossing the intersection. Specifically, the triangular corner island should have the "tail" 

pointing to approaching traffic. This will make the total pedestrian crossing distance of 

the intersection shorter, as the channelized right-turn is closer to the through lanes. In 

addition, the crossing of the channelized right-turn lane itself is shorter as pedestrians 

can cross at a right angle. This design has the additional advantage of the crosswalk being 

located in an area where the driver is still looking ahead; older designs place the crosswalk 

in a location where the driver is already looking left for a break in the traffic. The improved 

channelized right-turn lane design will place a sharper curve at the downstream end of 

the lane, which will force drivers to negotiate the lane more slowly; and by having the slip 

lane intersect the destination street at a larger angle, a driver will have better sight lines 

of approaching traffic on the destination street. Known implementations of this design

include an intersection in Charlotte, NC, and several intersections in Florida and Texas.

Anticipated Benefits to Aging Road Users: Aging drivers, who as a group experience 

reduced head/neck mobility, should have a longer time in which to search for conflicts with 

through traffic before entering the destination street as the result of these design changes. 

They should also benefit from carrying out this search without dividing their attention to 

potential conflicts with pedestrians crossing to the corner island. Aging pedestrians, who 

as a group walk more slowly, should benefit from the shorter crossing distances afforded 

by this design. The safety of aging pedestrians—and all pedestrians—should also be 

enhanced to the extent that this design compels turning drivers to enter the turn lane at 

a lower speed, while permitting them to direct attention to the search for conflicts with 

pedestrians and conflicts with traffic in separate phases of the turning maneuver.

18 Combination Lane-Use/Destination 

Overhead Guide Signs 

Description of Practice: Lane use signs indicate the turning movements that can be 

made from each approach lane of an intersection. This practice is now included in the 

2009 MUTCD (the D15-1 sign). A green guide sign is placed over the lane with a street 

name, route shield, or destination in the top half, and a lane-use regulatory sign in the 

bottom half. The State of Iowa currently utilizes some examples of overhead lane use 

signs, though different than the D15-1 series sign found in the 2009 MUTCD. The Iowa 

signs are on a white background with a route shield and a down arrow pointing to the 

appropriate approach lane. New York State DOT utilizes examples similar to the 2009 

MUTCD D15-1 series sign.
216 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Anticipated Benefits to Aging Road Users: The benefits of advance street name 

signs described above may be amplified by this treatment, which not only provides 

identification of the receiving leg routes at an intersection but also path guidance for the 

approaching driver. A driver who is properly positioned for a downstream maneuver will 

experience reduced demands for divided attention as s/he nears the intersection. Posting 

the advance signing described in this treatment overhead increases the conspicuity of this 

guidance information; this is likely to have the greatest benefit for aging drivers who, as 

a group, do not execute visual search as efficiently as younger persons when concurrent 

task demands are high.

19 Signal Head Visibilty

Description of Practice: Traffic signal heads are placed overhead, using one signal head 

per lane. Several states and municipalities have adopted this signal head placement as 

policy, including Iowa, Minnesota, Virginia, and the cities of Las Vegas, Nevada and 

Grand Rapids, Michigan routinely place signal heads centered over each lane. In Kansas

City, Missouri, pedestal pole signals were converted to overhead mast arm installations. 

Anticipated Benefits to Aging Road Users: Increasing the conspicuity of traffic control 

devices at intersections and reducing any ambiguity about the information they convey 

may be expected to have the greatest benefits for those with (age-related) visual and 

cognitive deficits. Physically separating the target stimulus from potentially distracting 

stimuli in the roadside environment should result in faster and more reliable visual 

detection, and this performance advantage for an overhead signal (especially with a 

backplate) compared to a pedestal mount should be disproportionately greater for aging 

drivers with a reduced ability to “screen out” irrelevant stimuli (selective attention). 

Similarly, the reduction in decision time that should be realized from centering the signal 

over the approach lane will be of greatest benefit to aging drivers with reduced speed 

of processing who face the highest demand for “executive control” when negotiating an 

intersection.

Reductions in the overall number of crashes and right-angle crashes among drivers 

65 and over have been observed in jurisdictions where overhead signals, centered over 

the approach lane have been introduced (in conjunction with the addition of an all-red 

clearance interval and/or increasing signal size from 8 to 12 inches).

20 High-Visibility Crosswalks

Description of Practice: Crosswalk markings provide guidance for pedestrians crossing 

roadways by defining and delineating paths on approaches. These markings are used in 

conjunction with signs and other measures to alert road users to a designated pedestrian 

crossing point. Section 3B.18 of the 2009 MUTCD contains basic information about 

crosswalk markings; however, some States adopt their own supplement or manual 

on traffic control devices and some develop policies and practices for subjects not 

discussed in the MUTCD, so differences in markings occur among States, cities, and 

other jurisdictions. Some crosswalk markings are more effective than others at drawing 
Handbook for Designing Roadways for the Aging Population 217

CHAPTER 7—INTERSECTIONS

attention to the crosswalk and the pedestrians who use it. The traditional set of 

transverse parallel lines define the boundaries of a crosswalk for the pedestrian, 

but they are not particularly visible to approaching drivers, especially in dark and/

or wet conditions, compared to other marking patterns. More recent crosswalk 

marking patterns such as continental and bar pairs (see Figures 87 and 88) have 

shown better recognition among approaching drivers (Fitzpatrick, et al, 2010). 

Markings commonly called "ladder" crosswalks (see Figure 36) combine the 

transverse and continental to also increase visibility to approaching drivers. 

Anticipated Benefits to Aging Road Users: Crosswalk markings not only define 

a path for the pedestrian to cross the street, but they also call attention to the 

presence of the crosswalk for approaching drivers. High-visibility crosswalks 

are beneficial to all drivers, but as eyesight diminishes with age, the increased 

recognition quality of high-visibility crosswalks becomes even more useful for 

aging drivers to see and prepare for crossing pedestrians as they approach marked 

crosswalks.

21 Supplemental Pavement Markings 

for Stop and Yield Signs

Description of Practice: Pavement messages in advance of an intersection may 

be used to supplement critical warning sign messages, such as the stop ahead and 

yield ahead signs. Such markings are currently in use in many locations in the 

country, including Irvine, California and Williamston, Michigan. The use of these 

markings is permitted according to Section 3B.20 of the 2009 MUTCD. 

Anticipated Benefits to Aging Road Users: As the result of normal aging, drivers 

may be at higher risk of failing to detect advance stop and yield warning signs 

posted at the side of the road due to loss of visual sensitivity in the periphery; a 

narrowing of the attentional (or “useful”) field of view; or a reduced ability to 

engage in a search of the visual periphery when, for example, road or weather 

Figure 87. Example of continental crosswalk markings Figure 88. Example of bar pairs crosswalk markings
218 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Figure 90. Diagram 

of Restricted 

Crossing U-Turn 

Intersection. (Image 

Credit: Debbie 

Murillo, Texas A&M 

Transportation 

Institute)

Figure 89. Diagram 

of Median U-Turn 

Intersection. (Image 

Credit: Debbie 

Murillo, Texas A&M 

Transportation 

Institute)

Crossing

Merging

Diverging

Vehicle Paths

Crossing

Merging

Diverging

Vehicle Paths

conditions increase demands for path guidance information. To the extent that 

aging drivers experience any of these limitations, they should derive an extra 

benefit from advance warning messages presented as pavement markings—if 

these markings are applied and maintained at contrast levels sufficient to ensure 

legibility to an “aging design driver.” 

22 Reduced Left-Turn Conflict 

Intersections

Description of Practice: Within the last five years, interest in a set of intersection 

designs collectively called “innovative” or “alternative” has grown rapidly. These 

intersection designs use a combination of geometric design features and traffic 

control devices to mitigate congestion problems at at-grade intersections as an 

alternative to traditional signalized intersections or grade-separated interchanges. 

One of the common characteristics of these alternative designs is that they typically 

accommodate left-turns in unique ways, with the end result that left-turns at the 

intersection are greatly reduced, if not eliminated. Designs such as the displaced 

left-turn (DLT) intersection, median U-turn intersection (see Figure 89), and 

restricted-crossing U-turn (RCUT) intersection (see Figure 90) all have features 

that minimize the operational delay and potential for crashes due to left turns. 

More information on the specific design features and traffic control devices used at 

these intersections can be found in FHWA’s Alternative Intersections/Interchanges: 

Informational Report (Hughes, et al. 2010).
Handbook for Designing Roadways for the Aging Population 219

CHAPTER 7—INTERSECTIONS

Anticipated Benefits to Aging Road Users: While modern roundabouts can 

be found in many parts of the country, these alternative intersections are more 

isolated and can present some challenges to drivers who have not seen them 

before, particularly aging drivers. These designs are the subject of a great deal of 

research at the current time, with studies investigating operational efficiencies and 

geometric design requirements. Specific benefits for aging drivers are a subject 

worthy of further exploration, but indications are that they can improve operations 

and safety for aging drivers as with the driving population as a whole.

As with roundabouts, alternative intersections may require additional outreach 

and educational efforts to help aging drivers understand what to expect when 

approaching them, as the geometric patterns of these alternative forms may appear 

to be complex designs; however, evaluation and observation show that users do 

find them easy to navigate. FHWA’s Every Day Counts 2 initiative has listed 

“Intersections with Displaced Left-turns or Variations on U-turns” among the 

treatments for Intersection and Interchange Geometrics that state departments of

transportation should consider to reduce conflicts and improve safety. Additional 

information on these designs and their respective features and benefits can be 

found at the Alternative Intersections website (www.alternativeintersections.org).

23 Accessible Pedestrian Signal 

(APS) Treatments 

A. Pushbutton-Activated Extended Pedestrian Crossing Phase

Description of Practice: A broad range of technologies can be classified as 

Accessible Pedestrian Signal (APS) treatments (Harkey, et al. 2009). One 

particular technology is that in which a controller can be programmed to 

provide extended pedestrian phase timing in response to an extended button 

press. In most advanced APS devices, these special features are actuated by 

pressing and holding the pedestrian pushbutton for an additional length of 

time (Noyce and Bentzen 2005).

Paragraph 2 of MUTCD Section 4E.13 states that if an extended pushbutton 

press is used to provide any additional feature(s), a pushbutton press of less 

than one second shall actuate only the pedestrian timing and any associated 

accessible walk indication, and a pushbutton press of one second or more shall 

actuate the pedestrian timing, any associated accessible walk indication, and 

any additional feature(s).

Paragraph 3 of Section 4E.13 states that if additional crossing time is 

provided by means of an extended pushbutton press, a PUSH BUTTON FOR 

2 SECONDS FOR EXTRA CROSSING TIME (R10-32P) plaque (see Figure 91)

shall be mounted adjacent to or integral with the pedestrian pushbutton.

Figure 91. 

Supplemental Plaque 

Used with Extended 

Crossing Time Feature 

for APS. (MUTCD R10-

32P)
220 Handbook for Designing Roadways for the Aging Population

CHAPTER 7—INTERSECTIONS

Anticipated Benefits to Aging Road Users: With such a feature, the controller 

can regularly provide pedestrian timing that is the minimum permissible, 

while allotting additional crossing time when it is needed by pedestrians who 

move or react slowly or who do not use visible cues and thus wait to confirm 

audible or vibrotactile cues before starting a crossing. 

B. Passive Pedestrian Detection

Description of Practice: Another APS treatment is passive detection. Most 

commonly, this is used in the vicinity of the curb ramp to enable the WALK

signal to be requested without the pedestrian needing to use a pushbutton. 

This feature is particularly useful where site constraints make it difficult for 

pedestrians with disabilities to approach the pushbutton. However, passive 

detection also can be used to detect pedestrians within the crosswalk that may 

need more time to complete their crossing maneuver. According to Harkey, et 

al. (2010), they were not aware of installations of passive detection in the United 

States that include audible signals as well as visual signals, but the combination 

of passive pedestrian detection and audible signals is being used in the United 

Kingdom, Australia, New Zealand, and the Netherlands. An example of

passive pedestrian detection technology is the “Pedestrian User-Friendly 

Intelligent” (PUFFIN) crossing in use in England (Department of Transport, 

2006). PUFFIN crossings employ pedestrian detectors for both the pedestrian 

waiting area and the crosswalk. Crosswalk detectors at PUFFIN facilities 

are used to vary the pedestrian clearance times between defined minimum 

and maximum times; when there are large numbers of pedestrians or if slowmoving pedestrians are crossing, the clearance time is extended to provide 

ample time for them to complete their crossing. Crosswalk detectors can be 

infrared or microwave detectors mounted on the signal pole or video cameras 

serving remote sensor software.

Anticipated Benefits to Aging Road Users: Like pushbutton-activated 

extensions, passive pedestrian detection treatments can help aging pedestrians 

register their call for a pedestrian phase and receive additional time to cross as 

needed.

24 Flashing Yellow Arrow

Description of Practice: Research has been conducted over the previous decade 

to identify more effective means of indicating permissive (i.e., not protected) leftturn phases at signalized intersections, replacing the traditional circular green (i.e., 

“green ball”) indication. One treatment that has shown promising results is the 

flashing yellow arrow (FYA). Brehmer, et al (2003) studied a variety of displays 

for protected/permissive left-turn control, and they found that drivers over the 

age of 65 had extremely low correct response rates with the permissive circular 

green indications, as many aging drivers assume right-of-way with circular green 

permissive left-turn indications. When the permissive circular green indication 
Handbook for Designing Roadways for the Aging Population 221

CHAPTER 7—INTERSECTIONS

and the circular red through-movement indication were shown, less than 29 

percent of aging drivers correctly responded. Meanwhile, drivers over the age of 

65 had a higher correct response rate with flashing circular red indication and 

flashing yellow permissive indications than all other age groups. Overall, their 

research indicated an improved response rate for the flashing yellow arrow among 

users of all ages, as compared to the circular green. Noyce, Bergh, and Chapman 

(2007) similarly found that the installation of the FYA indication for permissive 

left-turns provided a safety improvement when added to existing protected/

permissive left-turn signal phasing operations. The average annual frequency of 

total crashes was reduced at 12 of 13 study sites after implementation of the FYA 

indication, and the average annual frequency of left-turn crashes was reduced at all 

13 study sites.

Anticipated Benefits to Aging Road Users: The improved recognition and 

understanding of the flashing yellow arrow increases the likelihood that all drivers, 

but particularly aging drivers, will wait for an appropriate gap in oncoming 

traffic before beginning a permissive left-turn maneuver, rather than incorrectly 

assuming that they have the right-of-way. This, in turn, results in a decrease in 

the likelihood of right-angle and other crashes (and associated injuries) that are 

particularly common among aging drivers making unprotected left turns.
222 Handbook for Designing Roadways for the Aging Population
Handbook for Designing Roadways for the Aging Population 223

CHAPTER 8

Interchanges

The following discussion presents the rationale and supporting evidence for Handbook

recommendations pertaining to these eight proven and promising practices.

Proven Practices

25. Exit Signs and Markings

26. Freeway Entrance Traffic Control Devices

27. Delineation

28. Acceleration/Deceleration Lane Design

29. Interchange Lighting

30. Restricted or Prohibited Movements 

Promising Practices

31. Route Shield Markings at Major Freeway Junctions

32. Wrong-Way Driving Countermeasures
224 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

25 Exit Signs and Markings

A motorist’s ability to use highway information from signing and delineation is governed 

by information acquisition, or how well the source can be seen. It is also governed by 

information processing, or the speed and accuracy with which the message content can be 

understood. When either of these key aspects of driver performance is compromised, the 

result is delayed decision making, erratic behavior, and maneuver errors.

Taylor and McGee (1973) investigated driver behavior at exit gore areas to determine the

causes and characteristics of erratic maneuvers. Interviews were also conducted with 

many drivers whose actions at the gore area were indicative of route choice difficulties. 

Analyses of the patterns of erratic maneuvers (e.g., cross gore markings, cross gore area, 

stop in gore, back up, sudden slowing, lane change, swerve, stop on shoulder) and onsite driver interviews were used to determine causative factors of these maneuvers. The 

most frequent erratic maneuver was crossing the gore marking, which had a 69 percent 

relative frequency of occurrence for drivers exiting, and a 61 percent relative frequency 

of occurrence for drivers traveling through the interchange. Most of the motorists who 

made erratic maneuvers (77 percent) were unfamiliar with the route on which they were 

traveling. Interviews with exiting motorists who made erratic maneuvers indicated 

Table 40. Cross-references of Related Entries for Exit Signs.

Applications in Standard Reference Manuals

MUTCD (2009)

AASHTO

Green Book

(2011)

NCHRP 500- Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Sects. 2A.11, 2A.13, 2A.17, Sects. 

2B.03, 2B.37 through 2B.41 

Tables 2B-1 & 2C-4

Sects. 2C.14, 2C.15, 2D.05, 2D.06, 

Sects. 2E.10 through 2E.12 & 2E.14

Tables 2E-2 through 2E-5

Sects. 2E.19 through 2E.24

Figs. 2E-3 through 2E-16

Figs. 2E-22, 2E-26 & 2E-27, 2E-28, 

2E-30, 2E-34 through 2E-40

Sect. 2E.27

Sects. 2E.31 & 2E.33 through 2E.37

Sects. 2E-40 through 2E-53

Sect. 3B.05

Figs. 3B-8, 3B-10, 3B-12, & 3B-23

Sects. 3C.01, 3C.03, 3D.01, 3D.02

Figs.6H-42 & 6H-43 plus 

accompanying notes

Pg. 3-146, Final Paragraph

Pg. 10-71, Sect. on Signing and 

Marking

Pgs. 10-96 through 10-101, Sect. 

on Gores

Pg. 10-103, Final Paragraph

Pg. 10-113, Para. 3

Pgs. V-15-V-17 Sect. on Strategy 3.1 

B3: Increase Size and Letter Height of 

Roadway Signs (T)

Pgs. V-22-V-23 Sect. on Strategy 3.1 

B8: Improve Roadway Delineation 

(T)

Pgs. 372-373, Sect. on Sign Sizes

Pg. 391-392, Sect. on Older Drivers 

and Pedestrians

PROVEN PRACTICES
Handbook for Designing Roadways for the Aging Population 225

CHAPTER 8—INTERCHANGES

that more than half of the drivers were not adequately prepared for the exit. These 

drivers indicated that the signs lacked needed information or that the information 

was misleading. Interviews with drivers who made erratic maneuvers and continued 

through, indicated that approximately one-half had difficulty identifying their direction. 

Approximately 35 percent stated the signing was not clear, 21 percent responded that they 

could not clearly distinguish the location of the exit ramp, and 34 percent thought the 

road markings were inadequate.

The following discussion of exit signing issues focuses on the legibility of text, the 

understandability of diagrammatic guide signs, and the placement of devices to provide 

needed message redundancy while avoiding information overload.

Prior to the Millennium edition of the MUTCD, legibility standards assumed that 

a 1-in tall letter was legible at 50 ft, which roughly corresponds to a visual acuity of 

20/25; as documented in the Transportation Research Board’s Special Report 218 (1988), 

this “legibility index” value of 50 ft/in exceeds the visual ability of 30 to 40 percent of 

drivers who are 65 to 74 years of age, even under favorable contrast conditions. The 

MUTCD (2003) section 2A.14 provided guidance for determining sign letter heights, 

which indicated that sign letter heights should be determined based on 1 inch of letter 

height per 40 ft of legibility distance. A 40 ft/in standard for signs can accommodate 

the majority of aging drivers if contrast ratios (between the legend and background) are 

greater than 5:1 (slightly higher for guide signs) and luminance is greater than 10 cd/

m2

 (candelas per square meter) for partially reflectorized signs. However, a more conservative standard corresponding to 20/40 vision (i.e., a legibility index of 30 ft/in) would 

accommodate a greater proportion of aging drivers under a wider range of viewing 

conditions. The 2009 MUTCD (Section 2A.13) has updated the recommendation for letter 

heights accordingly, stating that a minimum specific ratio of 1 inch of letter height per 

30 feet of legibility distance should be used.

Nighttime legibility requirements were addressed by Staplin, Lococo, and Sim (1990), 

who conducted a laboratory simulation using 28 young/middle-aged subjects (ages 

19–49) and 30 older subjects (ages 65–80) to measure age-related differences in drivers’ 

ability to read unique word combinations (of four letters) on green-and-white guide signs. 

As expected, older drivers required significantly larger letter sizes to read the (unfamiliar) 

words than younger drivers. Translating the 20-ft subject-to-stimulus distance in the 

laboratory to a requirement of 600 ft to read a freeway sign, the data showed that older 

subjects would require a letter height of 24 in, corresponding to an acuity of 20/46. This 

corresponds to a legibility index of 25 ft/in for positive contrast (lighter characters on 

darker background) highway guide signs.

In a review of State practices, McGee (1991) reported that Oregon reduced the size of

letters on their freeway signs from 13.33 in uppercase and 10 in lowercase to 8 in and 6 

in, respectively. They received numerous complaints that the signs were difficult to read 

at highway speeds and they therefore returned the letter sizes to their original heights 

(George, 1987). By contrast, North Carolina, in consideration of aging driver needs,

increased the Interstate shield size from 36 in to 48 in, the uppercase letter size from 

16 in to 20 in, and the lowercase letter size from 12 in to 15 in on guide signs at freewayto-freeway interchanges (McGee, 1991). No evaluation was planned to determine the

effectiveness of this countermeasure.
226 Handbook for Designing Roadways for the Aging Population

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Garvey, Pietrucha, and Meeker (1997, 1998) conducted daytime and nighttime controlled

field studies with aging drivers, to compare word legibility and word recognition 

distances obtained with the Standard Series E(M) font, and a new font with the 

proprietary name Clearview®, which was designed to reduce the effects of a phenomenon 

referred to as “irradiation,” “halation,” or “overglow.” This phenomenon occurs when 

bright bold strokes bleed into a character’s open spaces under headlight illumination, 

causing the lettering to appear blurry, rendering the text illegible. The study details 

are presented on page 152 in Chapter 7, Design Element 10 (Street Name Signs). Two 

versions of this experimental font were employed: one version matched Series E(M) in 

letter width and height, but because of its smaller intercharacter spacing, it resulted in a 

smaller word area (referred to in this Handbook as Clear 100); and one version contained 

letters that were increased in size to 112 percent of the standard font, so that the words 

created with the experimental font (referred to in this Handbook as Clear 112) were the 

same size as the standard font words. The signs were erected with a lateral offset of 12 ft 

from the center of the observation vehicle (or 6 ft) outside of the right edge line, and were 

raised to a height of 6 ft above the ground. Study results indicated that during the day, 

the Series E(M) fonts and both of the experimental fonts produced approximately equal 

reading distances. At night, using low-beam headlights and bright signing materials, the 

Clear 112 font (occupying as much sign space as the standard font) produced significantly 

longer legibility distances (22 percent longer) and recognition distances (16 percent 

increase) than the Series E(M) font. With highway-size signs on 55-mph roadways, 

this increased legibility could add up to two full seconds, or an additional 160 ft to the 

interval in which drivers must read and respond to a sign.

Hawkins,et al. (1999) conducted a study of the legibility of three sign alphabets with 

lowercase letters: the standard U.S.DOT/FHWA Series E(M); Transport Medium (the 

alphabet used in Great Britain for overhead guide signs with positive contrast); and

Clearview®. The British Transport letters were designed in the 1950’s to eliminate 

irradiation when viewed at nighttime using headlights (Hawkins et al., 1999), and 

consequently a narrower stroke width is used for positive contrast signs (white legends 

on a blue or green background) than is used for negative contrast signs (black legends 

on white, yellow, or orange backgrounds). Also, the letters are designed to fit on tiles, 

which are placed side-by-side to create words, eliminating the need to measure distances 

between words as is done in the U.S. Hawkins et al. indicate that the Clearview® font 

retains the visual proportions of the standard FHWA alphabets, but it also incorporates 

desirable attributes from foreign and domestic typefaces, particularly British Transport 

Medium. However, the Clearview® letter is typically wider than the same letter in 

Transport Medium. 

Hawkins et al. (1999) employed 54 individuals to participate in the controlled field study 

as follows: 7 “young” drivers, age 35 or younger; 18 “young-old” drivers, ages 55 to 64; 

and 29 “old-old” drivers age 65 and older. Word legibility and word recognition data were 

recorded as an experimenter drove three subjects at a time toward the test signs, during 

daytime and nighttime. Each test sign was created using three, six-letter words arranged 

vertically on the sign, all in the same font, using high intensity white letters on green 

high intensity sheeting. Signs measured 12 by 9 ft and were either ground mounted or 

mounted overhead. The ground-mounted signs were erected at a height of 7 ft from the 

ground to the bottom of the sign, and were placed 30 ft from the right edge of the travel 
Handbook for Designing Roadways for the Aging Population 227

CHAPTER 8—INTERCHANGES

lane. The overhead signs were erected 20 ft above the traveled lane. Each word used a 16-

in initial uppercase letter, followed by 5 lowercase letters. The lowercase letter size varied 

somewhat according to the alphabet type, but was generally 75 percent of the uppercase 

letter size (12 in).

Results indicated that the Clearview® font was more legible at both the mean and 85th 

percentile levels than the Series E(M) font for signs placed overhead, both under daytime 

and nighttime conditions. The 85th percentile daytime legibility index for the young-old 

drivers was 40, and for the old-old drivers it was 30 ft/in for the Series E(M) font. The 

extent of the improvement was in the range of two percent, however, some driver groups 

experienced improvements in legibility distance for the Clearview® font that were over 

nine percent greater than those experienced with the Series E(M) font. Hawkins et al. 

state that the improvement was greatest for drivers with poor vision (worse than 20/40). 

For the ground-mounted signs, Clearview® was less legible under daytime conditions 

than Series E(M), and only slightly (less than 2 percent) more legible at night. The 

Transport Medium font did not show improvements in legibility distance over the Series 

E(M) font.

In terms of recognition distance, for the overhead signs, the Clearview® font produced 

larger recognition distances than the Series E(M) font, in both daytime and nighttime 

conditions, except for the drivers with minimum (20/40) vision at night. The extent of the 

improvement in recognition distance was up to 8.7 percent—considerably higher than the 

improvements found in legibility distance, and translates to an increase in recognition 

distance of up to 50 ft. For ground-mounted signs, Clearview® produced a small 

improvement at night among worst-case drivers, but showed no improvement under 

daytime conditions. The 85th percentile recognition distance for drivers age 65 and older 

for ground-mounted signs at night with Clearview® font was 8.6 percent greater than 

that obtained with the Series E(M) font. Under a few conditions (85th percentile daytime 

distance for ground-mounted signs for all subjects, and for those age 65+), the Transport 

Medium font produced recognition distances that were, on average 3 percent greater 

than those obtained with the E(M) font. At nighttime, the 85th percentile recognition 

distance for drivers age 65 and older was 12.2 percent higher for Transport Medium 

font on the ground-mounted signs than for the Series E(M)font. The authors note that 

the recognition data showed significant variability from one condition to the next, and 

caution readers to take care in applying the results. 

Overall, Hawkins et al. (1999), state that the results of their study indicate that the 

Clearview® font was more effective than the Series E(M) font in the overhead position, 

in both daytime and at night, with the greatest improvement achieved for the worst-case 

drivers. They further indicate that while the Clearview® font may be more appropriate 

than the E(M) font for overhead signs, ground-mounted signs should continue to use 

only the Series E(M) alphabet. Hawkins et al. suggest using different design parameters 

for overhead and ground-mounted signs to account for the differences in performance 

characteristics of each. They also note that the Clearview® font is an evolving font, and 

that there are differences in the font used in the Garvey et al. (1997) study and in the

current research. 

In Knoblauch, Nitzburg, and Seifert’s (1997) focus group discussions with aging drivers,

participants indicated that they prefer overhead signs to those mounted on the side of 
228 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

the road, stating a need for redundant (overhead) signs to provide advance notice of 

upcoming exits, including the distances to each, and indicating whether the exit is on the 

right or left side of the highway. This report, coupled with findings that the Clearview® 

font provides greater recognition and legibility distance over the standard Series E(M) 

font when used on overhead signs under both daytime and nighttime conditions, 

identifies highway destination signs (D1-D3) placed over the highway and fabricated 

using the Clearview® font as the preferred practice to accommodate aging drivers. 

A more recent project was conducted to compare the nighttime legibility distance of the 

Clearview® font (Clearview® Regular Express) to that of the standard series E(Modified) 

font on overhead and right shoulder-mounted freeway guide signs, fabricated with 

either the standard ASTM Type III sheeting or with microprismatic sheeting (Carlson, 

2001; Carlson and Brinkmeyer, 2002; and Carlson and Hawkins, 2003). Two types 

of microprismatic sheeting were evaluated: ASTM Type VIII and ASTM Type IX. 

Participants in this closed-course field study consisted of 20 young drivers (ages 18-34), 

20 middle-aged drivers (ages 35-54), and 20 older drivers (age 55+), with 10 males and 

10 females in each group. Each had a valid driver’s license, and their acuity ranged from 

20/10 to 20/50. Test vehicles included a 2001 Chevy Suburban with tungsten-halogen 

replacement bulb headlights and a 1989 Ford Crown Victoria, LTD with sealed-beam 

headlamps. Signs were made using 16-in uppercase letters with 12-in lowercase letter 

heights. All words were presented on a sign background 12-ft wide by 9-ft tall. Sign 

legends and backgrounds were made with the same type of retroreflective sheeting. 

The bottom of each overhead sign was 18 ft above the road surface. The bottom of each 

shoulder-mounted sign was 9 ft above the road surface with an offset of 24 ft from the 

edge of the right travel lane to the left of the sign background. Study was conducted 

on a closed-course facility in a dark rural area with no ambient lighting. Test subjects 

drove each vehicle type on a runway at night under dry conditions, beginning at a 

distance where the signs were not legible. They accelerated to 35 mph, set the cruise 

control, and concentrated on reading the test word on a sign. When the subject read 

the word correctly, a researcher in the vehicle recorded the distance. Each subject read 

56 randomly selected test words equally distributed between the Clearview® Series and 

the Series E(M) alphabets. Of the 56 words, 40 were located in the shoulder-mounted 

position and 16 were in the overhead distance. Study findings overall indicated that the 

combined benefit of microprismatic sheeting and Clearview® font resulted in an increased 

legibility distance of approximately 75 ft, and were greatest for drivers age 55 and older. 

Detailed results by sign location are provided below.

For shoulder-mounted signs, the overall mean legibility distance associated with 

Clearview® was 32 ft greater (a 5.2% improvement) than for Series E(M). Improvements in 

mean legibility distances ranged from 18 to 58 ft, with the largest differences occurring 

with the sealed beam headlamps and the Type IX sheeting. Assuming a 70 mph roadway, 

the improvements would result in added time to read a sign between 0.2 and 0.6 sec; 

for a 55 mph roadway, improvements would range from 0.2 to 0.7 sec. The increased 

legibility distances associated with the Clearview® alphabet were statistically significant. 

The largest difference between the Clearview® and the Series E(M) alphabets were 

associated with aging drivers, where legibility differences were 6.0 percent longer with 

the Clearview® than the Series E(M). This difference equates to an additional 0.45 sec of 

reading time for aging drivers. Legibility differences were 5.8 percent and 4.6 percent 
Handbook for Designing Roadways for the Aging Population 229

CHAPTER 8—INTERCHANGES

greater for the Clearview® than the Series E(M) font, for young and middle-aged drivers 

respectively. The effect of age was significant, as were the main effects of alphabet and 

sheeting. The interaction between age and alphabet was not significant, however.

For overhead guide signs, overall mean legibility distances were 53 ft greater for the Type 

IX sheeting than for the Type III sheeting (a 9.5% improvement). Type VIII sheeting 

was not tested on overhead signs, but would be expected to provide longer legibility 

distances than Type IX sheeting. The effect of sheeting type was significantly significant, 

with legibility distances significantly greater with Type IX sheeting than for Type III 

sheeting. Luminance values and legibility distances were significantly greater for the 

sealed beam headlights than for the tungsten-halogen bulbs. For Type IX sheeting, the 

overall mean legibility distance for the Clearview® alphabet was 40 ft greater than for the 

Series E(M) alphabet (a 6.7% improvement). The main effect of age was significant, as was 

the interaction between age and alphabet. As age increased, the benefits of Clearview® 

were more pronounced. For the aging drivers, Clearview® provided an increase in 

legibility distance of 33 feet, or 6.8% (compared to increases of 2.3% and 3.5% for young 

and middle-aged drivers). The increased legibility distance results in an additional 0.33 

seconds of reading time, assuming a 70 mph) highway.

A legibility analysis using the data collected in the field within the ERGO program

showed the sequential and overall benefits in legibility distance expected by switching 

from Type III sheeting to microprismatic sheeting and by switching from Series E(M) 

alphabet to Clearview® alphabet. For overhead signs, switching from Type III sheeting 

with Series E(M) to microprismatic sheeting with E(M) increases mean legibility 

distance by 44 ft. Switching from microprismatic sheeting with E(M) to microprismatic 

sheeting with Clearview® adds another 30 ft. Together, switching from Type III with 

Series E(M) to microprismatic with Clearview® would increase legibility distance by 

70 ft, an 11.9 percent improvement. Assuming a 70 mph highway, the overall legibility 

improvement provides drivers with an extra 0.68 s to read an overhead guide sign (and 

for 55 mph it is an extra 0.86 s). Assuming a last look distance equal to 3 s before passing 

the sign, these time improvements equate to a 24.4 percent increase in time to read 

an overall guide sign at 70 mph and an increase in 21.2 percent on a 55 mph highway. 

For shoulder-mounted guide signs, switching from Type III sheeting with Series E(M) 

to microprismatic sheeting with E(M) increases mean legibility distance by 41 ft. 

Switching from microprismatic sheeting with E(M) to microprismatic sheeting with 

Clearview® adds another 33 ft. Together, switching from Type III with Series E(M) to 

microprismatic with Clearview® would increase legibility distance by 74 ft, a 12 percent 

improvement. Assuming a 70-mph highway, the overall legibility improvement provides 

drivers with an extra 0.72 s to read an overhead guide sign (and for 55 mph it is an extra 

0.92 s). Assuming a last look distance equal to 3 s before passing the sign, these time 

improvements equate to a 24.1 percent increase in time to read an overall guide sign at 70 

mph) and an increase in 19.8 percent on a 55 mph highway.

FHWA issued an Interim Approval for the optional use of the Clearview® font for 

positive contrast legends on guide signs on September 2, 2004. The conditions of Interim 

Approval are specified at http://mutcd.fhwa.dot.gov/res-ia_clearview_font.htm.

Carlson and Holick (2005) conducted a controlled field study to determine how the 

legibility of full-scale unlit guide signs could be maximized with combinations of font 
230 Handbook for Designing Roadways for the Aging Population

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and retroreflective sheeting. A total of 30 subjects participated, distributed equally across 

three age groups (ages 18 to 34; 35 to 54; and 55+), with equal numbers of males and 

females in each age group. Two fonts were studied: Series E (Modified) and Clearview® 

5WR, where “R” stands for “reduced,” designed to produce the same word lengths on a 

sign as Series E (Modified). Clearview® 5WR has letter spacings reduced by 6.4 percent 

from the standard Clearview® 5W. Five combinations of retroreflective sheeting were 

studied:

•	 Type III legends on Type III backgrounds, where Type III was 3M high-intensity

encapsulated-lens glass-bead material.

•	 Type VIII legends on Type III backgrounds, where Type VIII was Avery Dennison

T-7500 sheeting, a super-high-intensity microprismatic material.

•	 Type IX legends on Type III backgrounds, where Type IX was 3M Visual Impact

Performance sheeting, a very high-intensity microprismatic material.

•	 Type VIII legends on Type IX backgrounds

•	 Type IX legends on Type IX backgrounds.

Two luminance levels were studied: low-beam headlamps at full power and lowbeam 

headlamps at 27 percent power, to simulate the possible ranges in sign luminance that 

could result from different conditions such as sign position (over-head or shoulder 

mounted), signs viewed from heavy trucks, and vehicles with poorly maintained or 

misaimed headlights. These levels corresponded to 13.0 and 3.6 cd/m2

 for the white Type 

III materials at 640 ft, based on research showing a 50th percentile minimum required 

luminance of 3.4 cd/m2

 for a legibility index of 12.2 m per 40 ft/in of letter height. 

All guide signs used in the Carlson and Holick (2005) study had white 16-in uppercase 

letters on a green background. The lowercase letters were the appropriate size, depending 

on the font used. Half of the signs were constructed with Series E(Modified) font and half 

with Clearview® 5WR font. The signs were posted to follow current signing practices as 

closely as possible (9 ft above the road surface and 30 ft from the edge of the travel lane). 

The study was conducted on a closed-course facility in a dark rural area with no ambient 

lighting. Subjects drove a 2000 Ford Taurus sedan, with an experimenter in the front 

passenger seat who (unaware to the subjects) controlled the headlamp illumination level 

(to produce two levels of sign luminance throughout the study). Subjects were told to read 

the word on the guide sign as soon as they could correctly identify it, and that there was 

no penalty for being wrong.

The effect of font on legibility distance was significant, with the average legibility distance 

for Clearview® 5WR 593 ft compared to 570 ft for Series E(Modified). In a smaller 

and independent study conducted within this study, Clearview® 5W was compared to 

Clearview® 5WR, and the two fonts produced statistically equivalent results, with the 

legibility of Clearview® 5W equal to 593 ft and the legibility of Clearview® 5WR equal to 

590 ft compared with Series E(Modified), which produced an average legibility distance of 

539 ft.

For each age group studied by Carlson and Holick (2005), all combinations of sheeting 

produced higher legibility distances compared to Type III on Type III. Sign brightness was 

statistically significant and was most evident for the aging subjects. The mean decrease in 
Handbook for Designing Roadways for the Aging Population 231

CHAPTER 8—INTERCHANGES

sign legibility from the full headlight to the reduced headlight condition was 8.5 percent 

for the young group, 3.3 percent for the middle group, and 16.7 percent for the older 

group. 

All signs with microprismatic legends performed significantly better than signs with 

Type III legends. There were no significant differences in legibility distance between 

signs made with microprismatic legends. Signs made with microprismatic backgrounds 

performed statistically similarly to signs made with high-intensity backgrounds.

The longest legibility distances were achieved with a microprismatic legend on a 

microprismatic background, but the legibility distances were not statistically different 

from those achieved with microprismatic legends on Type III backgrounds. The 

study authors state that this is important because of the cost of the microprismatic 

materials ($3.00 to $4.00 per sq/ft) compared to the cost of Type III materials ($1.00 to 

$1.50 per sq/ft.) 

Collapsing data across subject age and luminance level, and using only Clearview® font 

(based on its significantly longer legibility distances), the legibility distances are shown 

in Table 41 for the retroreflective sheeting types. Combinations within the two groupings 

(* or x) had statistically similar legibility means.

Table 41. Legibility distance on the basis of legend and background sheeting type

Legend 

Sheeting Type

Background 

Sheeting Type

Legibility 

Distance

Significance Grouping

(legibility means with the same symbol are 

not significantly different from each other)

VIII IX 626.4 ft *

IX III 602.4 ft *

IX IX 595.4 ft * X

VIII III 591.5 ft * X

III III 549.9 ft X

Caution must be taken with the finding by Carlson and Holick (2005) that legibility 

distance was not affected by background sign material, considering the small sample 

size within each group. Although the study authors recommend the use of Type II 

backgrounds over microprismatic backgrounds as a cost-saving measure, earlier findings 

by Carlson and Hawkins (2003) provide a rationale to first recommend the use of 

microprismatic materials for both the legend and the background, and then allow for 

the use of Type III materials for the background if cost is an issue. Carlson and Hawkins 

(2003) recommended that microprismatic sheeting be used on overhead signs in place of 

encapsulated sheeting, as a countermeasure for the increasing number of SUVs on the 

road with reduced headlight illumination on signs. In that study, the legibility distances 

were smaller for drivers in the Subaru (with larger observation angles, tungsten-halogen 

bulbs, and reduced light directed toward the sign) than the LTD (a passenger car with 

smaller observation angles, sealed-beam headlamps, and increased light directed toward 

the sign).

Moving from a consideration of legibility issues to the broader question of how well a 

motorist can actually use highway sign information, reading time and ease of recall for 

sign messages deserve attention. Reading time is the time it actually takes a driver to read 
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a sign message, contrasted with exposure time or available viewing time, which is the 

length of time a driver is within the legibility distance of the message. As drivers travel, 

they must look away from the highway to read signs posted overhead or at the side of 

the road, and then back to the roadway. During each glance, the maximum amount of 

text that can be read is three to four familiar words or abbreviations. A motorist’s rapid 

understanding and integration of message components in memory will greatly assist 

his/her recall of the message while deciding upon a response. Two errors in message 

presentation must be avoided: (1) providing too much information in too short a time 

and (2) providing ambiguous information that leaves either the intent of the message or 

the desired driver response uncertain. 

Mace, Hostetter, and Seguin (1967) conducted laboratory, controlled field, and 

observational field studies to evaluate how information presentation time (the amount of 

time that a sign is readable to a driver) and information lead distance (the distance from 

an exit that the advance sign is placed) affect exiting behavior at freeway interchanges. 

They found that 0.25 mi is inadequate for information lead distance and, because there 

were few differences in driver exiting behavior with information lead distances of 0.5 

mi and 1.0 mi, that 0.5 mi is optimal. In addition, a viewing time of 5 s was adequate for 

signs containing one to four pieces of information. Lunenfeld (1993) noted that a driver’s 

short-term memory span is between 0.5 and 2 min, and that drivers may forget advance 

interchange information messages if the time span between the advance notification 

and the exit ramp exceeds the memory limit. He advocates the use of repetition for 

interchange information treatments (multiple/successive signs), which will also aid in 

situations where a sign is blocked by foliage or trucks.

The effect of diagrammatic signing on driver performance at freeway interchanges was 

studied by numerous researchers in the early 1970’s. Bergen (1970) found that graphic 

guide signs permitted significantly better route guidance performance than conventional 

signs on certain interchanges, such as collector-distributor with lane drop and multiple 

split ramps. In pilot studies conducted in New Jersey, Roberts (1972) found that 

diagrammatic signs that included lane lines were more effective (resulted in a significant 

reduction in erratic maneuvers) than conventional signs at the interchange of I-287 

and U.S. 22, a complex interchange with both left- and right-side exits. Flener (1972) 

commented on the difficulty in evaluating the effectiveness of traffic control devices in 

reducing erratic maneuvers at exit gore areas using before and after designs, due to the 

“novelty effect.” Although Roberts (1972) noted that the change could be attributed to 

the greater attention-getting value of novel signs, it was demonstrated that diagrammatic 

guide signs provide advance information that is readable at a farther distance than that 

provided by conventional sign text, as well as information about the number of lanes 

available for any one movement. 

Roberts, Reilly, and Jagannath (1974) studied the effectiveness of diagrammatic versus 

conventional guide signs in a field study at 10 sites. The results were mixed. Several sites 

showed a reduction in stopping, backing, or weaving erratic maneuvers after installation 

of the diagrammatic signs. Some sites showed a reduction in stopping and backing 

maneuvers but an increase in weaving maneuvers (or vice versa). Still other sites showed 

no change as a function of sign type. Stopping and backing erratic maneuvers were 

reduced, however, at 9 of the 10 sites. 
Handbook for Designing Roadways for the Aging Population 233

CHAPTER 8—INTERCHANGES

Taylor and McGee (1973) noted that the main advantage of diagrammatic signing lies

in the ability to provide information regarding the interchange layout prior to the exit 

area. Sign format, however, remains an issue. Conflicting evidence on the effectiveness 

of diagrammatic signs was reported by Gordon (1972), who found that conventional

signs produced fewer lane-placement errors and errors on exit lanes and were more 

quickly responded to than experimental diagrammatic signs tested at six interchanges 

in a laboratory study. At the same time, an analysis of particular diagrammatic designs 

showed that when a diagrammatic sign provided a single arrow or a forked arrow, 

reaction time was faster and there were fewer errors compared with the conventional 

sign. Zajkowski and Nees (1976) studied subject response time and correctness of lane 

choice as a function of sign type, in the laboratory. They found that response times were 

consistently longer for diagrammatic signs than for conventional signs; however, the 

difference may have been attributable to an increase in information on diagrammatic 

signs. There were more correct lane-choice responses for conventional signs, and subjects 

reported more confidence in their lane-choice decisions and a preference for conventional 

signs. Mast, Chernisky, and Hooper (1972) found that some drivers may require more 

time to read and interpret information on diagrammatic signs in comparison with 

conventional signs, and driver information interpretation time may increase as the 

graphic component of the sign becomes more complex. 

Aging drivers participating in focus group discussions have indicated that they prefer 

large, lighted overhead signs with arrows that indicate the lanes for specific destinations, 

especially if they are approaching a fork in the road (Knoblauch, Nitzburg, and Seifert,

1997). These aging drivers stated that the arrows on the overhead signs do not always 

point to the correct lane, causing drivers to change lanes needlessly; they also stated a 

desire to see signs that indicate when two travel lanes bear to the same destination.

Brackett, et al. (1992) conducted a survey of 662 drivers in three age groups (younger 

than age 25, ages 25-54, and 55 and older) comparing alternative methods of providing 

lane assignment information on freeway guide signs. The findings of several comparisons 

in the research are reported, although no analyses using age as an independent variable 

were performed. First, when two common routes were displayed side by side on an exit 

guide sign, approximately one-half of the drivers believed that the destinations referred to 

different routes to be accessed by different lanes (i.e., drivers spatially cluster information 

with each arrow, assuming that information located on the left side of a sign is associated 

with an arrow also on the left side, and information on the right side is associated with 

EXIT ONLY or EXIT ONLY with an arrow). When destinations were arrayed one below 

another, 85 percent of the drivers understood that they were a common route. Second, 

white downward arrows used in a side-by-side format with an EXIT ONLY (E11-1) panel 

to indicate that two lanes could exit, were misunderstood by 80 percent of the subjects. 

Third, 56 percent of drivers misinterpreted the phrase NEXT RIGHT on conventional

signs as an indication of a mandatory exit, and 30 percent misinterpreted the phrase 

NEXT LEFT in the same manner, when these signs were placed over the right and 

left lanes, respectively. Fourth, when conventional MUTCD diagrammatic signs were 

compared with modified diagrammatic signs that provided separate arrows for each lane, 

the modified diagrammatic signs resulted in a 13 to 17 percent greater understanding 

of when a lane must exit and when an adjacent lane may exit or continue through (twolane exit with optional lane). When the number of arrow shafts exceeded the number 
234 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

of lanes (for example, when there is an auxiliary exit lane downstream of the overhead 

sign), less than 30 percent of the respondents understood that there would be an added 

exit lane downstream on the right. With one arrow per lane, comprehension increased 

by 28 percent over when there were more arrows than lanes (optional use or added lanes). 

Figure 92 display an example of a conventional diagrammatic sign (from Section 2E.20 of 

the 2003 MUTCD) and a modified diagrammatic sign for this exit situation. The sign in 

Figure 92b resembles the recommended sign shown in Figure 2E-3 of the 2009 MUTCD; 

Figure 92a is similar to the sign shown in Figure 2E-7 of the 2009 MUTCD.

The benefit of using one (upward-pointing) arrow per lane to show the number and 

direction of lanes for a given highway geometry on freeway guide signs was demonstrated 

by Golembiewski and Katz (2008). Twenty-four younger (mean age = 33) and 24 older

(mean age = 79) drivers viewed five alternative diagrammatic sign designs at the Highway 

Sign Design and Research Facility at the FHWA Turner-Fairbank Highway Research 

Center. As the signs were presented to participants, they indicated by a button press when 

they were sure of which lane(s) could be used to get to their destination. The distance to 

each sign when the choice was made (decision sight distance) and the correctness of each 

decision were recorded.

The five designs evaluated in this study included 1) Standard, which followed the 2003 

MUTCD guidance for freeway guides signs at lane splits; 2) Modified, which followed the 

same guidance but included Exit Only placards where appropriate; 3) Enhanced, which 

followed the MUTCD guidance but had wider dashed lines and wider arrowheads; 4) 

Enhanced Modified, which was similar to Enhanced, but included Exit Only placards 

when appropriate; and 5) Arrow Per Lane, which used upward pointing arrows centered 

over each lane to indicate movements appropriate for that lane. All study participants 

viewed all sign designs in a repeated-measures design, counterbalancing the order of 

presentation across subjects.

Signs using the Arrow Per Lane design yielded significantly better performance for 

aging drivers than the other types. While the performance of younger participants was 

significantly better than that of the older participants they, too, benefited from this 

design. These findings indicate that the Arrow Per Lane sign type is appropriate for all 

drivers and is especially beneficial for aging drivers. Golembiewski and Katz (2008)

conclude that, because signs in this experiment were presented without the surrounding 

roadway context, the present study may even underestimate the benefit of this design 

relative to the others evaluated.

Figure 92. 

Example of MUTCD

diagrammatic sign 

(a) and modified 

diagrammatic 

sign (b) used in 

comprehension 

evaluation (Brackett, 

Huchingson, Trout, 

and Womack (1992))

a b
Handbook for Designing Roadways for the Aging Population 235

CHAPTER 8—INTERCHANGES

26 Freeway Entrance Traffic Control Devices

Violations of driver expectancy, use of alcohol, and reductions in the ability to integrate 

information from multiple sources to make navigation decisions while concurrently 

controlling the vehicle may all result in driver confusion at critical decision points, 

resulting in wrong-way maneuvers. Tamburri and Theobald (1965) found that many 

aging drivers and drinking drivers did not know where their wrong-way movement 

began (i.e., they could identify neither where the decision point was nor the location of 

the wrong-way maneuver). The information provided for this design element focuses on 

positive signing and ramp design for freeway entrances, as well as the use of advanced 

diagrammatic guide signs on urban multilane arterials leading to freeways, while design 

element 30 focuses on wrong-way signing and pavement markings at interchanges.

Age-related diminished capabilities contributing to wrong-way movements include 

the cognitive capabilities of selective attention and divided attention, and the sensory/

perceptual capabilities of visual acuity and contrast sensitivity. Selective attention refers 

to the ability to identify and allocate attention to the most relevant targets in the driving 

scenario on an instant-to-instant basis, while divided attention refers to the ability to 

perform multiple tasks simultaneously. Individuals less capable of switching attention, 

or who switch too slowly, may increase their chances of choosing the wrong response or 

choosing the correct response too slowly. Treat, et al. (1977) reported that 41 percent of 

crashes in which aging adults were involved were caused by a failure to recognize hazards 

and problems, and that 18 to 23 percent of their crashes were due to problems with visual 

search. The selective attention literature generally suggests that for adults of all ages, 

but particularly for aging drivers, the most relevant information must be signaled in a 

dramatic manner to ensure that it receives a high priority for processing in situations 

where there is a great deal of complexity at the level of information to be processed.

In their study of highway information systems, Woods, Rowan, and Johnson (1970) found 

that motorists frequently experience difficulty in locating entrance ramps to freeways, 

and drivers were often confused when there were several side roadways intersecting in 

close proximity to the interchange area. These researchers suggested that more efficient 

use could be made of “positive” signing techniques in guiding motorists to the freeway 

entrance ramps and discouraging drivers from possible wrong-way maneuvers. 

Table 42. Cross-references of related entries for freeway entrance traffic control devices. 

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Sects. 2A.23, 2B.37, & 2B.38

Tables 2B-1 & 2C-1

Sects 2D.45, 2E.52, 2B.41, 2E.53, 

3B.20, 3D.01

Figs. 3B-24, 2B-18, 2B-19, 

Figs. 2D-11 through 2D-16

Pgs. 10-83 through 10-87, Sect. on 

Wrong-Way Entry

Pg. 23, Paras. 1-2 Pgs. 372-373, Sect. on Sign Sizes

Pg. 391-392, Sect. on Older Drivers 

and Pedestrians
236 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

Woods et al. (1970) indicated that positive signing which indicates the correct path or 

turning maneuver to the motorist rather than a restriction may help most to minimize 

driver confusion at freeway interchanges. Examples include route markers, trailblazers, 

and a FREEWAY ENTRANCE sign that positively designates an entrance to the freeway. 

The California Standard specifies that large FREEWAY ENTRANCE signs (48 in x 30 in) 

be placed on on-ramps, but the location of the sign package (FREEWAY ENTRANCE 

sign, plus route shield, cardinal direction sign, and down diagonal arrows) should not 

be controlled by the use of the larger signs; smaller signs (36 in x 21 in) may be used for 

proper placement, if necessary.

Advance guide signs on multilane highway approaches to an 

interchange provide drivers with information about which lane they 

should use to enter the freeway in the desired direction of travel. 

Interchanges may require right turns from the multilane arterial 

for both available directions of travel on the freeway (cloverleaf 

interchanges), a left turn to travel left and a right turn to travel 

right (diamond interchange), or other combinations of right and 

left turns. This lack of consistency coupled with late recognition 

of the required entrance ramp lane may result in last-second lanechange maneuvers that increase the potential for crashes. Advance 

information is important for preventing erratic, risky lane change 

maneuvers during the approach to the interchange. Although it 

is desirable to present this information on overhead guide signs, it 

is costly and not always feasible. Zwahlen, et al. (2003) evaluated 

the effectiveness of ground-mounted diagrammatic guide signs on 

urban multilane arterials leading to freeways as a lower-cost alternative to overhead 

span-type sign bridges. In this field study conducted in actual traffic, 40 drivers (20 

males and 20 females) who were unfamiliar with the test city area (Columbus, OH) 

drove an instrumented vehicle and were accompanied by an experimenter who provided 

instructions. The average age of the participants was 20 years old, and acuity was 

described by the researchers as “good.” Ground-mounted diagrammatic signs were

placed 0.5 mi and 0.25 mi along urban multilane arterials in advance of 6 highway 

interchanges before the last point of the gore (see Figure 93). The letter height for the 

destination letters was 6 in for uppercase letters and 4.5 in for lowercase letters. The letter 

height for the cardinal directions was 6 in (152 mm). The FHWA standard alphabet was 

used. The arrows were 8 in wide by 90 to 104 in long. All signs were fabricated with 

microprismatic Stimsonite 6200 traffic signing material (meeting ASTMD 4956 Type III 

and IV. These signs supplemented existing trailblazer assemblies on entrance ramps.

Subjects in the Zwahlen et al. study began in a parking lot and were asked to start driving 

and to merge with traffic on a multilane arterial approximately 3 mi in advance of the 

test interchange. The experimenter told subjects to find their way to a specific freeway 

entrance ramp (i.e., I-270 Northbound); subjects were always started out in the wrong 

lane for accessing the freeway in the direction given by the experimenter. The measure of 

effectiveness was the distance from the point at which the subject realized he or she was 

in the wrong lane and a lane change was required, to the interchange gore. The study was 

performed at night to avoid the daytime delays associated with the freeway interchanges. 

Twenty-one subjects participated before the advanced diagrammatic signs were installed, 

Figure 93. 

Ground-Mounted 

Diagrammatic 

Guide Sign for 

Urban Multilane 

Arterial, Used by 

Zwahlen et al. 

(2003)
Handbook for Designing Roadways for the Aging Population 237

CHAPTER 8—INTERCHANGES

and 19 drivers participated after installation of the signs. Subjects who participated 

in the “before” condition did not participate in the “after” condition. Overall, the 

“after” condition (diagrammatic guide signs present) was associated with a substantial, 

statistically and operationally highly significant improvement in lane change distance. 

Combining all six sites, the 50th percentile lane change distance in the “before” condition 

was 1,237 ft and in the “after” condition 2,686 ft. The 85th percentile lane change 

distance in the “before” condition was 666 ft and in the “after” condition 1,971 ft. These 

distances represent an increase in lane change distance by a factor of 2.2 and 3.0 between 

the before and after conditions. With ground-mounted diagrammatic guide signs, the 

test subjects (who were unfamiliar to the area) were able to initiate a lane change from 

the incorrect lane much earlier (4 to 5 times earlier at some interchanges) than in the 

period before the signs were installed. Although aging drivers were not represented in 

the sample, it is logical that they would benefit from upstream, redundant signing using 

positive guidance principles. 

Aside from difficulties in the use of signs, problems for aging drivers at interchanges most 

likely to result from (age-related) deficits in spatial vision relate to the timely detection 

and recognition of pavement markings and delineation. Data from a study by Blackwell 

and Blackwell (1971) show that between age 20 and age 70, aging directly reduces contrast 

sensitivity by a factor of about 3.0. Mace (1988) stated that age differences in glare 

sensitivity and restricted peripheral vision coupled with the process of selective attention 

may cause higher conspicuity thresholds for aging drivers. Overall, these deficits point to 

the need for more effective and more conspicuous signing and delineation.

Vaswani (1974) identified specific sources of wrong-way movements where alcohol was 

believed not to be a factor. In this study, exit ramps on partial interchanges generated 

wrong-way maneuvers because, unlike the ramps on full interchanges that converge with 

right-hand traffic, the ramps meet the crossroad at about 90 degrees to accommodate 

both left and right turns. Therefore the wrong-way entries consist of left turns off of 

the exit ramp into wrong-way traffic on a two-way divided highway, right turns from 

the divided highway into traffic exiting the ramp, and left turns from the crossroad into 

the exit ramp. At intersections with four-lane divided highways (divided arterial and 

primary highways), 45 percent of the wrong-way entries were at their intersections with 

exit ramps or secondary roads. The wrong-way entries were due to left-turning vehicles 

making an early left turn rather than turning around the nose of the median. Almost all 

these crashes involved sober drivers. 

Some ramp designs are more problematic than others. In Tamburri and Theobald’s 

1965 analysis of 400 wrong-way incidents where entry was made to the freeway via an 

off-ramp, the trumpet interchange category had the highest wrong-way entry rate, with 

14.19 incidents per 100 ramp-years, and the full cloverleaf interchanges had the lowest 

wrong-way entry rate, with 2.00 incidents per 100 ramp-years. Parsonson and Marks 

(1979) also determined that several ramp types were particularly susceptible to wrongway movements, as follows: half-diamond (3.9 per month), partial cloverleaf (“parclo”) 

loop ramp (11.0 per month) and parclo AB loop ramp (6.7 per month). The parclo loop 

ramp and the parclo AB loop ramp share the same problem, which is an entrance and 

exit ramp in close proximity. The half-diamond is susceptible because it is an incomplete 

interchange, and drivers may make intentional wrong-way entries. A “problem” ramp 
238 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

27 Delineation

Table 43. Cross-references of related entries for delineation. 

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Sects. 2C.09 & 3F.03 Pg. 8-17, Paras. 1-2

Pgs. 10-89 through 10-101, Sect. on General Ramp Design Considerations 

has been defined as one that experiences more than five wrong-way movements per 

month; a corrected ramp has less than two per month (Rinde, 1978). 

Vaswani (1974) found that on almost all the interchanges on which wrong-way entries 

had been made into the exit ramp or from the exit ramp onto the crossroad, the corner 

of the exit ramp flared into the right pavement edge of the crossroad. He suggested 

that such a flare provides for a very easy but incorrect right-hand turn, and may help 

to induce a driver to make a wrong-way entry from the crossroad into the exit lane. A 

countermeasure consisting of a sharp right-hand junction would require a driver to 

reduce speed and almost come to a stop before maneuvering into the left lane, and would 

also reduce the chances that a driver exiting the ramp would turn left into wrong-way 

traffic on the crossroad. Site inspections showed that where the flare was not provided 

and the left lane of the exit ramp and the passage through the median were channelized, 

no wrong-way entry to or egress from the exit ramps was reported. Additionally, 

Vaswani (1974) reported that generous widths of an exit ramp with its junction with the 

crossroad make wrong-way entry or egress from the exit ramp easy. Narrow pavement 

widths will discourage such entries. A serious impediment to turning maneuvers by 

heavy vehicles could also result from this strategy, however.

Vaswani (1974) also indicated that too large a set-back of the median noses from the exit 

ramp increases the width of the crossover and makes the intersection harder to “read.” 

Vaswani suggests that if the width cannot be reduced, then pavement nose markings 

in the form of a striped median should be applied, for improved visibility of this design 

element. See also the discussion on page 122 of this Handbook for design element 5, 

about extending delineation treatments from a set-back median nose to the intersecting 

roadway. 

The following discussion of exit ramp gore delineation focuses on studies conducted 

to determine which treatments are necessary to ensure rapid and accurate detection of 

the gore location and ramp heading, particularly under nighttime or reduced visibility 

conditions.

Taylor and McGee (1973) reported that the location of the gore is usually perceived easily

during daylight hours, because a driver can rely on a direct view of the geometry, as 

well as signing and delineation. However, this task becomes considerably more difficult 

during darkness, because the driver can no longer rely on a direct view of the geometry, 

and exit gore signing may be misleading because of the inconsistency in the distance 
Handbook for Designing Roadways for the Aging Population 239

CHAPTER 8—INTERCHANGES

at which it is placed from the nose of the gore area from location to location. At night, 

delineation is probably the most beneficial information source to the exiting motorist, 

because it outlines and therefore pinpoints the location of the gore.

Taylor and McGee (1973) measured the effects of the presence of gore area delineation

on driver performance at night, to determine which of various delineation devices 

(pavement markings, post delineators, raised pavement markers (RPMs), and a 

combination of treatments) were most effective. Measures of effectiveness included the 

point of entry into the deceleration lane, the exiting speed, and any erratic maneuvers. 

Two right-hand exits, one with a parallel-lane type of deceleration lane and one with a 

direct-taper type, were selected as test sites. Specifically, the treatment conditions were: 

(1) post delineator treatment—yellow post delineators placed along the ramp edge of the 

gore area, plus white delineators positioned along the through side; (2) RPM treatment—

yellow RPM’s placed on the ramp side of the gore (paint) markings, plus white RPM’s on 

the through side; and (3) combination treatment—the post delineator treatment and the 

RPM treatment installed in combination. 

The baseline condition for this study was moderately worn painted diagonal gore 

markings and edge lines, with no other delineation devices. All three delineation 

treatments produced earlier points of entry into the deceleration lane than under 

the baseline condition. The RPMs were more effective than the post delineators 

and produced earlier exiting points. The earliest exiting points were found with the 

combination of RPM’s and post delineators. Gore area delineation reduced the frequency

of erratic maneuvers at night at both sites. The RPM technique and combination 

treatment produced significantly lower exiting speeds than did the use of post delineators 

at one site, and all three treatments produced lower exiting speeds compared with the 

baseline condition. 

The work by Taylor and McGee (1973) also included a comprehensive review of several

case studies. As a result of their state-of-the-art summary, coupled with the results 

of their field observations in the study outlined above, a set of recommendations 

was developed for pavement marking delineation, post delineators, and RPMs; these 

recommendations, which have since been widely implemented, are described below. 

For pavement marking delineation:

•	 8- to 12-in wide white lines should be used to outline the exit gore, and

where additional emphasis is necessary, diagonal or chevron markings are 

recommended.

•	 An 8-in wide line with a 5-ft mark and 15-ft gap should be used as an extension of

the mainline right edge line (or median edge line for left exits) and should replace 

the lane line for at least 1,000 ft upstream from the gore nose at an exit lane drop.

For post delineators: 

•	 Post delineators should be placed in the gore area to enhance nighttime visibility.

White delineators are recommended for the through roadway side, and yellow 

delineators should be used on the exit side. A spacing of 10 to 20 ft, depending on 

ramp divergence angle, is recommended. 
240 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

•	 Yellow delineators should be placed along the right edge of the deceleration lane at

a spacing of 100 ft. Beyond the beginning of the gore, the spacing is dependent on 

the degree of curvature.

•	 White delineators should be placed on the inside shoulder of the through roadway,

at a spacing of 100 ft, to help strengthen the through-way delineation in the exit 

area.

For RPM’s:

•	 Raised pavement markers are recommended as a supplement to standard gore

pavement markings and should be placed inside the “V” formed by the pavement 

marking lines.

•	 Raised pavement markers should be supplemented with post delineators where the

view of the roadway is limited, such as at vertical sections.

Other researchers have also evaluated the effects of RPM’s at exit gore locations. RPM’s 

have been shown to reduce erratic maneuvers through (painted) gores at exits and 

bifurcations.

Hostetter, et al. (1989) conducted a controlled field study using 15 subjects ages 18 to 

60+, to determine the effect of lighting, weather, and improved delineation on driver 

performance. Data were obtained on two exits in dry and wet weather under full lighting 

with baseline delineation (see diagram in Recommendation 20 (A1)). The baseline system 

is similar to the delineation used at many of the partially lighted interchanges cataloged 

by the study authors during site selection, and in the opinion of an expert panel convened 

during the research, constituted a minimum system for partially lighted interchanges. 

Data were then obtained under partial lighting, with baseline and three improved 

delineation systems.

Upgrade 1 investigated by Hostetter et al. (1989) differed from the baseline in the use of 

RPM’s along the left ramp stripe, and the substitution of fully retroreflective posts (46-in 

strip of 3-in wide sheeting) for partially retroreflective posts (18-in strip of 3-in wide 

sheeting) in the physical gore. Upgrade 2 differed from the baseline in the deployment of 

additional posts along the left ramp shoulder to create a spacing of 50 ft rather than 100 ft 

and in the installation of wide RPM’s (“traffic diverters”) on the gore strips to replace the 

4-in RPM’s placed adjacent to the gore stripes in the baseline system. Upgrade 3 replaced 

all baseline system partially retroreflective posts with fully retroreflective posts except in 

the gore, used RPM’s along the left ramp stripe, and used beaded profiled tape containing 

a raised-diamond pattern for gore striping. The tape was used because it would project 

above a film of water during rain. The test sites were a half-diamond interchange and 

a full diamond, which contained very little ramp curvature. The exit ramps were 14 ft 

wide, with a single lane widening to two lanes near the intersection with the crossing 

roadways. Measures of effectiveness included ramp and spot/trap vehicle speeds, overall 

travel time, deceleration estimates, and lane placement, as well as selected types of erratic 

maneuvers and brake and high-beam headlight activations.

Analysis of delineation effects on ramp and spot speeds, and on speed distributions 

showed few differences under dry conditions. Under rainy conditions, effects were 

stronger but were neither large enough nor consistent enough to recommend improved 
Handbook for Designing Roadways for the Aging Population 241

CHAPTER 8—INTERCHANGES

delineation over the baseline system. Although Upgrade 3 produced fewer edge line 

encroachments under both dry and wet conditions, from the standpoint of operations, 

safety benefit, or cost-effectiveness, the upgrade did not demonstrate enough advantage 

to merit a recommendation for use on diamond interchanges with little ramp curvature. 

Lerner, et al. (1997) conducted a series of laboratory and field studies to identify 

conspicuity and comprehensibility problems with current object markers across various 

hazardous situations, for young-middle/aged drivers (ages 20 to 40); young-old drivers 

(ages 65 to 69) and old-old drivers (age 70 and older). In addition, novel object markers 

and pavement markings were evaluated to determine whether they improved conspicuity 

or understanding over the current Types 1, 2, and 3 object markers. With regard to 

object markers used at gore areas, the MUTCD (Section 2C.65) states that in some 

cases “there might not be a physical object involved [that needs to be marked], but other 

roadside conditions exist, such as narrow shoulders, drop-offs, gores, small islands, and 

abrupt changes in the roadway alignment, that might make it undesirable for a road user 

to leave the roadway, and therefore would create a need for a marker.” 

In the laboratory experiment conducted by Lerner et al., 64 subjects viewed color 

photographic illustrations of an object marker situated within a roadway scene. Six 

stimuli were used to mark gore areas: (1) a Type-1 object marker; (2) a Type-3 object 

marker; (3) yellow cones; (4) green cones; (5) modified French gore signs (signs used in 

France, consisting of two, white isosceles triangles pointing left and right on a green 

background, were modified to show black triangles with a cut-out base pointing left and 

right on a yellow background); and (6) a novel treatment displaying double modified 

chevron arrows (directional arrows pointing left and right, derived from the chevron 

alignment sign, consisting of black arrows on a yellow background). The dependent 

measure was the correctness of response (e.g., the subject correctly identified the hazard 

or described the correct driving action). Percent-correct ratings for each marker 

presented in a gore situation across age were as follows: Type-1 (80%); Type-3 (75%); 

yellow cones (46.7%); green cones (73.3%); French gore markers (56.3%); and double 

modified chevrons (87.5%). For drivers over age 70, the percent correct ratings were as 

follows: Type-1 (83.3%), Type-3 (76.8), and double modified chevron (100%). One finding 

of interest that should be highlighted here, is the lack of understanding of directional 

information presented by a solitary Type-3 object marker. In a study conducted during 

the problem identification stage of this research, participants were correct 39 percent 

of the time about the direction the marker conveyed (i.e., drive in the direction of the 

downward pointing stripes). 

Next, the object markers were viewed on a test track by different groups of subjects in 

the same three age ranges to determine daytime and nighttime detection distances. 

Each trial began at 1,000 ft. An experimenter drove along a test track toward the object 

marker, with the subject seated in the passenger seat. When a subject was just able to 

discriminate some feature of the marking, the experimenter was told to stop, and this 

detection distance was recorded. The experimenter then continued to drive toward the 

marking, stopping every 50 ft, at which point the subject described the salient features 

of the marking. In addition to the markers described above, the following pavement 

markings were also evaluated: a double edge line pavement marking, and diagonal 

hash mark pavement markings. The first finding of interest was that the threshold 
242 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

distances were significantly greater for the post-mounted marker types than for the 

pavement marking types. There were no main effects of age group or marker type for the 

pavement markings and no interactions between these variables. The mean nighttime 

detection distance for the hash marks was 224 ft and for the double edge line 226 ft. 

By comparison, all of the subjects detected all of the other post-mounted markers at 

1,000 ft at night under low-beam headlight illumination. This finding underscores the 

importance of including post-mounted markings at gore areas, to supplement pavement 

markings applied in these areas. There was no age group effect or interaction between 

age group and post-mounted marker type for detection distance. 

In terms of nighttime symbol recognition distance, the Type-1 and Type-3 object 

markers had the highest mean recognition distances 790 ft and 910 ft, respectively). 

While Type 3 was the single best performer, both had significantly higher mean symbol 

shape recognition distances than all other markers. Next in terms of nighttime symbol 

recognition distance were the Type-2 object marker, the double modified chevrons, and 

the French gore signs, which were not significantly different from each other. Significant 

main effects of age group and marker type were found but there was no significant 

interaction between the two. 

The only marker that resulted in a significant change in daytime detection distance was 

the small Type-2 marker, for which detection distance was significantly reduced for 

the age 70 and older group versus the young/middle-aged subjects. The mean detection 

distance of the Type-2 object marker was 919 ft by the young-old drivers and 803 ft by the 

old-old drivers, compared to 1,000 ft for the young/middle-aged drivers. In fact, all of the 

subjects in the age 65 to 69 age group saw all other post-mounted markers at 1,000 ft, and 

the drivers over age 70 saw all other post-mounted markers at distances ranging from 

973 to 1,000 ft. The Type-2 marker also resulted in significantly shorter daytime color 

recognition distances than any other post-mounted marker type.

Finally, a limited validation study conducted by Lerner et al. on actual roads in Calvert 

County, Maryland, compared the Type-1 object marker and the double modified chevron 

post mounted markers at a gore situation. The Type-1 object marker produced a correct 

response rate of 50 percent, compared to 82.4 percent for the two modified chevron 

design, across driver age groups. However, the double modified chevron marker was 

better understood than the Type-1 marker at a gore location, only during the daytime. 

Thus, based on the findings of the laboratory and controlled field studies conducted by 

Lerner et al. (1996), undelineated gores (i.e., without any object marker) were identified 

only 1.5 percent of the time by drivers age 75 and older, highlighting the importance of 

using object markers at such locations. Another finding of importance is that the Type2 object marker is a poor choice for marking gore areas, particularly for aging drivers. 

The novel double modified chevron marker may be the best candidate for marking gore 

locations; however, more research would be required to enable a recommendation to be 

made for its use, based on its poorer nighttime performance compared to the Type-1 

marker. Currently, the MUTCD only allows for the use of a Type-2 or a Type-3 marker 

for objects adjacent to the roadway (such as a gore). Based on the poor performance 

demonstrated by the Type-2 marker in the Lerner et al. research, a recommendation 

to use the Type-3 marker at freeway gore locations is made in this Handbook. It is 
Handbook for Designing Roadways for the Aging Population 243

CHAPTER 8—INTERCHANGES

28 Acceleration/Deceleration 

Lane Design

also noted that, based on the comprehension data, a Type-1 marker may be a better 

candidate—for use as an experimental device—when other treatments have not proven 

successful.

To meet the needs of aging drivers, the point of controlling curvature on an exit ramp, 

as well as the curve speed advisory, must be highly conspicuous to create an appropriate 

expectancy of the required vehicle control actions. With this expectancy, aging drivers 

should be able to negotiate deceleration lane geometries meeting AASHTO or NCHRP 

guidelines competently. Raised curve delineation treatments are recommended in this 

regard; post-mounted delineators or chevrons are particularly effective at improving 

driver performance on sharp horizontal curves, as noted by Johnston, 1983; Jennings, 

1984; Good and Baxter, 1986; Zador, Stein, Wright, and Hall, 1986, and Pietrucha,

Hostetter, Staplin, and Obermeyer, 1996. 

Studies dating back to the 1960’s have addressed the effects of ramp design on driving 

performance; however, Koepke (1993) reported that the basic design criteria, and

therefore design standards, used by governmental agencies to design exit and entrance 

ramp terminals have not changed in more than 30 years. Recommendations for 

selected design features for interchange ramps may be justified by both the changing 

characteristics of the driving population and the operating characteristics of the highway 

system. Age-related functional decreases in visual acuity, motion judgment, and 

information-processing capabilities cause increased difficulty for aging drivers entering 

and exiting highways. At the same time, traffic density has increased dramatically, 

resulting in more complex decision-making and divided-attention requirements at these 

Table 44. Cross-references of related entries for acceleration/deceleration lane design.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Traffic Engineering Handbook

(2009)

Sect 3B.05

Fig 3B-8 through 10

Pgs. 3-6 through 3-8, Sect. 3.2.3 Decision Sight 

Distance

Pg. 8-17, Paras. 1-2

Pgs. 10-76 through 10-79, Sect. on Auxiliary 

Lanes

Pg. 10-92, Para. 4

Pgs. 10-103 through 10-105, Sects. on Left-side 

entrances and exits & Traffic Control

Pgs. 10-107 through 10-127, Sects. on Speedchange lanes, Single-Lane Free-Flow Terminals, 

Entrances, and Single-Lane Free-Flow Terminals, 

Exits 

Pgs. 251-252, Sect. on Ramp Design

Pgs. 225-226, Sect. on Decision Sight Distance 

(DSD)

Pgs. 65-70, Sect. on Vehicle Performance
244 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

sites. In a survey of 664 drivers age 65 and older, one-half of those surveyed (49 percent) 

reported that the length of freeway entry lanes was a highway feature that was more 

important to them now compared with 10 years ago (Benekohal, et al., 1992).

The difficulties aging drivers are likely to experience on freeway ramps, particularly 

acceleration lanes, are a function of changes in gap judgment ability resulting from a 

diminished capability to accurately and reliably integrate speed and perceived distance 

information for moving targets; reduced neck/trunk flexibility; and age-related deficits 

in attention-sharing capabilities. First, the requirement to yield to approaching traffic 

on the mainline requires a merging driver to assess the adequacy of gaps in traffic by 

turning his/her head to look over the shoulder and/or by using the sideview mirrors. 

In a survey of 297 adults ranging in age from 22 to 92, which was conducted to gain a 

greater understanding of the visual difficulties they encounter while driving, the aging 

participants reported greater difficulty judging both the speed of their vehicle and the 

speed of other vehicles, and expressed a concern over other vehicles “moving too quickly” 

(Kline,et al., 1992). 

It has been shown that aging persons require up to twice the rate of movement to perceive 

that an object is approaching, and require significantly longer to perceive that a vehicle 

is moving closer at a constant speed, compared with younger individuals (Hills, 1975). 

Darzentas, McDowell, and Cooper (1980) used Hills’ data in a simulation model to 

estimate conflict involvement for each class of subject as a function of main-road flow 

and speed. In the model, a conflict occurs when a poor gap acceptance decision is made 

by a driver, causing an oncoming vehicle to decelerate to avoid collision. The model 

indicated that aging drivers were involved in more conflicts than younger drivers of the 

same gender, and male drivers were involved in more conflicts than females in the same 

age class at all flows. 

Other findings describing age differences in driver behavior on acceleration ramps are 

reported in a National Highway Traffic Safety Administration (NHTSA) study of driver 

age and mirror use. In this study, which measured the time required to make a “safe/

unsafe” maneuver decision in a freeway lane-change situation, old-old drivers (age 75 

and older) consistently required longer response times to make a lane-change decision 

than a group of drivers ages 65–74, who in turn demonstrated exaggerated response 

times compared with a younger control group (Staplin, et al., 1996). This was a simulator 

study, using large screens showing dynamic videos of overtaking vehicles, in correct 

perspective, as the test stimuli; also, all drivers were forced to rely on their mirror 

information alone to make the maneuver decision in this research. The mean response 

time for a lane-change decision for the oldest (75 and older) driver group in this study, 

across a large number of trials in which the relative speed of the overtaking vehicle was 

varied between 10 and 25 mph (i.e., faster than the subject’s own vehicle was traveling 

when the video was shot), changed with changes in the target distance (separation of 

overtaking vehicle from driver). At close separation distances (100 to 200 ft), where 

virtually all aging drivers quickly decided that a lane-change maneuver was unsafe, 

decision latency averaged approximately 2.1 s. At a 200-ft separation distance, some 

drivers were more willing to merge, and required longer to reach a maneuver decision, 

producing a mean latency of 2.5 s. At a 300-ft separation distance and above (between 

the overtaking vehicle and the driver wishing to change lanes), maneuver decision 
Handbook for Designing Roadways for the Aging Population 245

CHAPTER 8—INTERCHANGES

latency reached an asymptote at 2.95 s, as increasing percentages of subjects accepted the 

available gap ahead of the overtaking vehicle. 

Findings from reviews of crash rates and ramp characteristics are also relevant. Lundy 

(1967) found that off-ramp crash rates were consistently higher than on-ramp crash 

rates. However, Oppenlander and Dawson (1970) reported that at urban interchanges, 

68 percent of the interchange ramp crashes occurred at entrance ramps, while 32 percent 

occurred at exit ramps; for rural interchanges, these percentages were reversed. Similarly, 

Mullins and Keese (1961) reported that in urban areas, 82 percent of the interchange

crashes occurred at on-ramps and 18 percent at exit ramps. Further, Lundy’s (1967) study 

of 722 freeway ramps in California found that the crash rate was reduced for off-ramps 

when deceleration ramps were at least 900 ft (274 m) long (not including the length of the 

taper), for on-ramps when acceleration lanes were at least 800 ft) long, and for weaving 

sections that were at least 800 ft long. Oppenlander and Dawson (1970) also concluded 

that safety was improved for on-ramps, off-ramps, and weaving areas 800 ft in length or 

greater. Cirillo (1970) found that increasing the length of weaving areas reduced crash 

rates, and increasing the length of acceleration lanes reduced crash rates if merging 

vehicles constituted more than 6 percent of the mainline volume. Reduced crash rates 

from lengthening of deceleration lanes also appears to be related to the percentage 

of diverging traffic, with significant safety benefits beginning when 6 percent of the 

mainline traffic diverges (Cirillo, 1970).

The most comprehensive work to develop guidelines for freeway speed-change lanes 

(SCLs) was conducted in NCHRP project 3-35 by Reilly, et al. (1989), who collected data 

on the entry and exit processes by videotaping 35 sites in three States. An entrance 

model was developed, based on gap acceptance and acceleration characteristics of 

drivers as determined by the controlling geometry. An exit model was developed, based 

on the driver’s behavioral response to design geometrics. The purpose of the research 

was to develop new criteria that would offer greater flexibility than the (then) current 

AASHTO (1984) guidelines, which “do not provide the designer with the ability to reflect 

important geometric and traffic conditions” (Reilly et al., 1989). In this research, it was 

reported that the AASHTO (1984) SCL design criteria were based on the acceleration 

and deceleration characteristics of early-model vehicles, with little regard to traffic flow 

characteristics or driver behavior. The design values produced by the NCHRP project 

entry model for SCL length were slightly lower at low freeway speeds and significantly 

higher at moderate to high freeway speeds when compared with the 1984 AASHTO 

values. The exit model values for length were significantly higher than 1984 AASHTO 

values for all freeway and ramp speeds. The findings of the study suggest that for certain 

traffic conditions, the current SCL design criteria do not provide sufficient length for 

proper execution of the merge or diverge process. This is of particular importance with 

regard to the age-related diminished capabilities documented above.

Potts, Harwood, and Pietrucha (2001) compared the design values produced by NCHRP 

Project 3-35 and the AASHTO values for acceleration lane length during the conduct 

of NCHRP Project 20-7. They concluded that there were only limited cases where 

NCHRP 3-35 values exceed the AASHTO values, and voiced concern with determining 

acceleration lane lengths based on NCHRP Project 3-35 because the design criteria are 

volume dependent. For these reasons, they recommended against changing Green Book
246 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

policy on acceleration lane lengths, stating, “traditionally, AASHTO has been reluctant 

to adopt volume-dependent design criteria because a project designed in anticipation of 

one volume level might not meet the criteria for the volume level that actually occurs at 

some future time.” Bared, Giering, and Warren (1999) also compared the acceleration

lane length values from NCHRP Project 3-35 to AASHTO’s values, presenting models 

to predict the safety performance of different acceleration lengths and a procedure 

to determine economic benefits of lengthening acceleration lanes. Bared et al. (1999) 

concluded that from a safety and economic perspective, minimum lengths of acceleration 

lanes are comparable to the minimum lengths recommended by AASHTO rather than 

the longer lengths recommended by NCHRP 3-35. They also concluded that higher 

benefit-cost ratios are possible by extending deceleration lanes compared to acceleration 

lanes, due to the higher crash occurrence on deceleration lanes, and that regardless of 

the original speed-change lane length, the benefit-cost ratio reaches a maximum for 

additions of 500 ft. 

Another issue addressed by NCHRP 3-35 was acceleration lane geometry. Koepke

(1993) reported that 34 of the 45 States responding to a survey conducted as a part of 

NCHRP 3-35 on SCL’s use a parallel design for entrance ramps. Thirty of the agencies 

interviewed use a taper design for exit ramps and a parallel design for entrance ramps. 

The parallel design requires a reverse-curve maneuver when merging or diverging, but 

provides the driver with the ability to obtain a full view of following traffic using the side 

and rearview mirrors (Koepke, 1993). Although the taper design reduces the amount of

driver steering control and fits the direct path preferred by most drivers on exit ramps, 

the taper design used on entrance ramps requires multitask performance, as the driver 

shifts between accelerating, searching for an acceptable gap, and steering along the lane. 

Reilly et al. (1989) pointed out that the taper design for entrance lanes poses an inherent 

difficulty for the driver and is associated with more frequent forced merges than the 

parallel design. Forced merges were defined as any merge that resulted in the braking of 

lagging vehicles in Lane 1, or relatively quick lane changes by lagging vehicles from Lane 

1 to a lane to the left. The parallel design would thus appear to offer strong advantages 

in the accommodation of aging driver diminished capabilities. Indeed, aging drivers 

participating in focus groups voiced support for dedicated acceleration lanes (parallel 

entrance ramps) in place of tapered entrance ramps, and an analysis of on-ramp crashes 

involving aging drivers showed a decline of 1 percent in the period following replacement 

of tapered acceleration lanes with dedicated acceleration lanes with ramp meters (Kihl,

2005; Kihl, et al., 2004). Because the treatment in the “after” period included two

countermeasures (ramp geometry plus ramp meters), it was not possible to determine 

singular effects of geometry and operations on crash rate reduction.

Finally, Keller (1993) provided a review of interchange design principles in need of

reconsideration to accommodate aging drivers with diminished capabilities. According 

to this review, the factors that influence ramp alignment and superelevation design 

include design consistency and simplicity, the roadway user, design speed, and (stopping 

and decision) sight distance. Because driver reaction time is slowed when elements 

of ramp geometry are different than expected, design should provide for long sight 

distances, careful coordination between horizontal and vertical alignment, generous 

curve radii, and smooth coordinated transitions, particularly when complex interchange 

designs are unavoidable. Increasing the sight distance and simplifying interchange layout 
Handbook for Designing Roadways for the Aging Population 247

CHAPTER 8—INTERCHANGES

can reduce some of the effects of decreasing visual acuity, short-term memory decline, 

reduced decision making ability, reduced ability to judge vehicle speed, decreased muscle 

flexibility and pain associated with arthritis, and early fatigue and slower reaction times 

associated with increasing driver age. With regard to design speed, Keller (1993) stated

that the ramp proper should be viewed as a transition area with a design speed equal 

to the speed of the higher speed terminal wherever feasible, and that few diagonal or 

loop ramps are long enough to accommodate more than two design speeds. Thus, the 

terminals and the ramp proper should be evaluated to determine the appropriate speed 

for design.

In terms of stopping sight distance (SSD) requirements, Keller (1993) noted that designers

can reduce drivers’ stress at interchanges by providing sight distances greater than the 

minimum SSD’s. Although a brake reaction time of 2.5 s is representative of 90 percent of 

the drivers used in a 1971 study by Johansson and Rumar, and was used in the AASHTO 

SSD formula, it has been suggested that a 3.5-s perception and braking time should be 

used to accommodate the elderly with diminished visual, cognitive, and psychomotor 

capabilities (Gordon, McGee, and Hooper, 1984). Another assumption in the 1984

AASHTO calculations for SSD is a driver eye height of 3.5 ft; the eye height of aging 

drivers is often less. Finally, alignment affects braking distance, such that curves impose 

greater demands on tire friction than tangents, resulting in increased braking distance 

when the friction requirements of curves and braking are combined (Glennon, Neuman,

and Leisch, 1985).

Keller (1993) noted that locations where SSD values do not provide the time necessary to

process information and react properly highlight the importance of the use of decision 

sight distance (DSD). Examples of locations at interchange ramps where DSD is desirable 

include ramp terminals at the main road, especially at an exit terminal beyond the grade 

separation and at left exits; ramp terminals at the cross road; lane drops; and abrupt or 

unusual alignment changes. AASHTO guidelines (2004) note that sight distance along 

a ramp should be at least as great as the safe stopping distance. The sight distance on 

a freeway preceding the approach nose of an exit ramp should exceed the minimum 

stopping distance for the through traffic speed, desirably by 25 percent or more, although 

the desirable goal remains DSD.

DSD values—which include detection, recognition, decision, and response initiation 

and maneuver times—are provided in AASHTO (2011) Table 3-3 by design speed and 

type of avoidance maneuver required. Lerner, et al. (1995) measured DSD for three 

driver age groups (ages 20–40, ages 65–69, and age 70 and older) at six freeway lane drop 

locations. While perception-reaction time values measured by Lerner et al. (1995) were 

actually somewhat lower than the values assumed by AASHTO, they nevertheless found 

that the 85th percentile total time required by each age group for detection, decision 

and maneuvering exceeded the recommended AASHTO value of 14.5 s. The freeway 

total times averaged 16.5 s, 17.6 s, and 18.8 s, for the three groups (from youngest to 

oldest), respectively. The researchers explained that the original AASHTO work assumed 

free-flow traffic conditions, in which drivers were not required to wait for a gap in 

traffic to change lanes. The Lerner et al. (1995) study, by comparison, was conducted on 

heavily traveled urban freeways, and subjects often had to wait for gaps in traffic before 

maneuvering. This led to significantly higher maneuver times than were assumed by 
248 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

29 Interchange Lighting

Table 45. Cross-references of related entries for interchange lighting.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 –

Volume 9

(2004)

Roadway Lighting

Handbook

(1978)

Sect. 1A.13, Sign 

Illumination

Sects. 2E.06 & 3I.04

Sect. 4B.04, Item I

Sect. 6G.14

Pg. 3-172, Para. 4 Pgs. V-21-V-22 Sect. on 

Strategy 3.1 B7: Improve 

Lighting at Intersections, 

Horizontal Curves, and 

Railroad Grade Crossings 

(T)

Pgs.14-15, Sects. on Complete 

Interchange Lighting & Partial 

Interchange Lighting

Pgs. 16-26, Sects. on Analytical 

Approach to Illumination Warrants 

& Informational Needs Approach to 

Warrants

Pgs. 42-45, Sect. on Summary of Light 

Sources

Pg. 71, 4th bullet

Pgs. 84-89, Sect. on Interchange 

Lighting

Pgs. 120-129, Sect. on Illumination 

Design Procedure

AASHTO. No modifications to the existing DSD standards were deemed necessary. 

Keller (1993), reporting on the results of a 1991 survey about distances used when

locating ramp exits beyond a crest vertical curve, indicated that 15 (38 percent) of State 

design agencies use the safe SSD, 9 (23 percent) use the safe SSD plus 25 percent, and 12 

(31 percent) use DSD.

Research has documented that: (1) freeway interchanges experience a higher crash rate 

than the mainline (Cirillo, 1968); and (2) urban freeway lighting has beneficial safety 

effects (Box, 1972). Cirillo (1968) also found a reduction in the number of interchange 

crashes as lighting intensity increased. Gramza, Hall, and Sampson (1980) evaluated the

interchanges in the Interstate Accident Research (ISAR-2) database at which lighting had 

been introduced during the 10-year study period. During the daytime, there were 83 

crashes before lighting and 80 crashes after lighting. At nighttime, by comparison, there 

were 76 crashes before lighting and 43 crashes after lighting. Taylor and McGee (1973)

found a reduction in erratic maneuvers at exit lane drop sites in a before after study, when 

the exit area was illuminated during the “after” period of data collection. 

Although nighttime driving is associated with a higher crash risk for drivers of all 

ages, the effects of aging on the visual system are further compounded by the effects of 

darkness. The aging process causes gradual declines in a variety of visual functions, 

including acuity, contrast sensitivity, glare recovery, and peripheral vision, making night 

driving especially difficult for aging drivers. Of particular difficulty is the ability to 

notice and recognize objects at night and in low-light conditions such as dawn and dusk, 

rain, fog, haze, and snow. Between age 20 and age 70, aging directly reduces contrast 
Handbook for Designing Roadways for the Aging Population 249

CHAPTER 8—INTERCHANGES

sensitivity by a factor of about 3.0 (Blackwell and Blackwell, 1971); aging drivers are thus 

at a greater relative disadvantage at lower luminance levels than younger drivers. 

The impact for the aging driver of lost sensitivity under nighttime conditions should 

be assessed against the nature of the night driving task. Even at night, most visual 

information is processed by the cone or daylight system in the foveal region of the 

retina where fine detail is resolved. Artificial lighting raises the illumination level of the 

roadway environment to the photopic range so that reading and tracking functions can 

occur. The peripheral rod system participates primarily by alerting the driver to a weaker 

signal away from the foveal line of sight, which may then be oriented to by the driver 

with a foveal fixation. The implication of a loss in rod sensitivity is that a much brighter 

peripheral signal will be needed to elicit proper visual attention from the driver, and that 

signals now falling below threshold will be ignored. In fact, the signal may need to be 

10 to as much as 100 times brighter, depending on age and object color (Staplin, Lococo, 

and Sim, 1990). Since both rod and cone thresholds increase with age, it is also true that 

more light will be needed to bring important tasks such as reading and tracking (path 

maintenance) above the cone limit. In a survey of 1,392 drivers ages 50 to 97, 70 percent 

indicated that more highway lighting is needed on freeways. These respondents identified 

the following areas where more lighting is needed: interchanges, construction zones, and 

toll plazas (Knoblauch, Nitzburg, and Seifert, 1997).

There are a number of other aspects of vision and visual attention that relate to driving. 

In particular, saccadic fixation, useful field of view, detection of motion in depth, 

and detection of angular movement have been shown to be correlated with driving 

performance (see Bailey and Sheedy, 1988, for a review). While these visual functions 

do not appear to have strong implications for highway lighting practice, it could be 

advantageous to provide wider angle lighting coverage to increase the total field of view 

of aging drivers. High-mast lighting systems can increase the field of view from 30 

degrees (provided by conventional fixtures) to about 105 degrees (Hans, 1993). Such 

wide angles of coverage provided by high-mast lighting might have advantages for aging 

drivers in terms of peripheral object detection, thus easing the task of identifying ramp 

geometry, traffic control devices, and traffic patterns. However, while effective high-mast 

systems have been demonstrated (Ketvirtis and Moonah, 1995), such installations also

tend to sacrifice target contrast for the increased field of view they provide. 

Hans (1993) defines “high mast” as any lighting structure that rises at least 60 ft above 

road level. Some designs extend up to 150 ft (46 m) and higher above the ground. One 

pole, anchored 50 to 70 ft from the edge of the roadway, may be used to support a cluster 

of 3 to 12 luminaires. As a comparison, conventional cobra-head poles mounted on the 

shoulder support 1 or 2 luminaires, at a height of 26 to 50 ft above the road. For example, 

the New Jersey Roadway Design Manual defines their high-mast lighting system as one 

that utilizes a mounting height of 100 ft with a cluster of a maximum of eight, 400-

watt, high-pressure sodium luminaires, and their conventional lighting system as one 

that utilizes mounting heights of 26 ft with 150-watt, high-pressure sodium luminaires 

for ramp application. The NJ Manual states that tower lighting (high mast) shall be 

considered first (over conventional lighting) for full interchange lighting, preferably using 

400-watt cutoff-type luminaires; however, non-cutoff luminaires may be employed if the 

designer can justify their use.
250 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

The following paragraphs summarize studies that: (1) evaluated the effects of lighting on 

crash experience at interchanges; and (2) evaluated specific aspects of driver performance 

as a function of number and type of luminaires at an interchange. 

Gramza et al. (1980) conducted a crash analysis of 400 nighttime crashes that occurred

at 116 interchanges during the period of 1971–1976, in five States (Maine, Maryland, 

Minnesota, Texas, and Utah). In an analysis of the presence of high-mast lighting at 

interchanges, versus no lighting or other kinds of interchange lighting, the presence 

of high-mast lighting was found to significantly reduce total crash rates, total crashes 

involving fatalities and injuries, and crashes involving fatalities and injuries other than 

the vehicle-to-vehicle and vehicle-to-fixed-object categories (e.g., crashes caused by 

striking pedestrians). Table 46, taken from Gramza et al. (1980), shows the predicted

effect of high-mast lighting on annual number of crashes. 

Gramza et al. (1980) also found that although the number of lights at an interchange

and the level of illumination had no significant effect on the total number of nighttime 

crashes, significant decreases in a variety of distinct crash types were found with 

increases in illumination. Increases in the illumination level—measured in lux or 

horizontal foot-candles (hfc)—at interchanges were associated with significant reductions 

in two types of crashes: vehicle-to-fixed-object crashes involving property damage, 

and vehicle-to-vehicle crashes involving fatalities and injuries. In addition, increases 

in the number of lights active at an interchange were found to significantly influence 

(reduce) the following two crash types: vehicle-to-fixed-object crashes involving fatalities 

and other injuries, and other property damage crashes. The number of lights at an 

interchange ranged from 0 to 114, with an average of 16 active lights and a median of 

10. Thirty-two percent of the interchanges were unlit. As lighting levels increased, crash 

rates decreased. Illumination ranged from 0.0 lux to 10.76 lux (0.0 hfc to 1.0 hfc), with an 

average of 5.49 lux (0.51 hfc) for the lighted sections. These four crash types accounted 

for 61 percent of the crashes observed in the sample. 

Since there were relatively few crashes per interchange per year, Gramza et al. (1980)

employed a model to predict the number of each crash type per year, assuming three 

levels of traffic volume (average nighttime traffic of 5,000, 7,500, and 10,000 vehicles) 

at partial cloverleaf and other types of interchanges, and allowing varying levels of 

illumination or varying numbers of lights. The predicted relationships between traffic 

volume, lighting, and crash frequency showed that reductions in number of lights and 

in level of illumination (hfc) resulted in higher frequencies of vehicle-to-fixed-object and 

other property damage crashes, for all traffic volumes. Vehicle-to-vehicle crashes were 

Table 46. Relative annual effect of lighting type on total nighttime crashes (n=400) at urban and nonurban 

interchanges (Gramza, Hall, and Sampson, 1980).

Night Traffic 

Volume

Urban Nonurban

NonHigh-Mast High-Mast % Decrease NonHigh-Mast High-Mast % Decrease

5,000 2.0 0.0 100 3.6 0.4 89

7,500 3.8 0.6 84 5.4 2.2 59

10,000 5.7 2.5 56 7.3 4.1 44
Handbook for Designing Roadways for the Aging Population 251

CHAPTER 8—INTERCHANGES

also shown to increase in frequency as illumination was reduced, for all interchange 

types.

In addition, the findings at the level of one interchange were translated to estimate, 

as an overall annual impact for the five-State sample, the relative influence of the 

lighting variables on numbers of crashes at interchanges through three levels of night 

traffic volume. A level of 7.53 lux (0.7 hfc) was used to represent the allowable base of 

average maintained illumination. Overall, the model predicted that reductions in levels 

of illumination appear to cause greater increases in the number of crashes than do 

reductions in numbers of lights (Gramza et al., 1980).

Although the work of Gramza et al. (1980) is noteworthy in its attempt to quantify the

complex relationships between interchange lighting and safety, it is critical to remember 

that their model was applied to data derived to fit 1975 conditions—including, by 

implication, both the then-current number of aging drivers and their exposure to this 

highway feature during nighttime operations. By contrast, present and anticipated future 

driving patterns of aging drivers—whose actual numbers, as well as their percentage of 

all drivers, will increase dramatically—show much higher use rates for freeways (Lerner 

and Ratté, 1991). This trend should sharply accentuate the safety impacts cited by Gramza

et al.

Janoff, Freedman, and Decina (1982) conducted a study to determine the effectiveness 

of partial lighting of interchanges, where partial interchange lighting (PIL) was defined 

as lighting that consists of a few luminaires located in the general areas where entrance 

and exit ramps connect with the through traffic lanes of the freeway (between the 

gore and the end of the acceleration ramp/beginning of the deceleration ramp). A 

complete interchange lighting (CIL) system includes lighting on both the acceleration 

and deceleration areas plus the ramps through the terminus. In their survey of 

approximately 50 agencies which supplied information on over 14,000 interchanges and 

over 7,500 interchange lighting systems, it was found that 37 percent of the interchange 

lighting was CIL and 63 percent was PIL. An observational field study was conducted 

to determine the effects of lighting level (various levels of PIL, CIL, no lighting, and 

daylight), geometry of the interchange (straight versus curved ramps), and presence of 

weaving area versus no weaving area on driver behavior and traffic operations. PIL was 

stratified by the number of lights at each ramp, and included three levels: PIL 1 (one 

light), PIL 2 (two lights), and PIL 4 (four lights). CIL test sites included a full cloverleaf 

in suburban Baltimore, Maryland, and a three-leg interchange in suburban Philadelphia, 

Pennsylvania, with luminaire mounting heights of 40 and 31 ft, respectively. The 

dependent measures included speed and acceleration of individual vehicles traversing the 

interchanges; merge and diverge points of individual vehicles entering the main road or 

leaving it; and erratic maneuvers such as brake activations, use of high beams, and gore 

or shoulder encroachments. 

Both field studies indicated that CIL provided a better traffic operating environment than 

did PIL and that any interchange lighting performed better than no lighting (although 

the differences were not always as great as between CIL and PIL). In particular, to the 

extent that traffic flow and safety are important issues, the Janoff et al. study concluded 

that existing CIL systems should not be reduced to PIL systems. When installing new 
252 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

30 Restricted or Prohibited Movements

lighting and economics are not an overriding issue, a CIL system is preferred over a 

PIL system. However, a PIL system with one or two luminaires per ramp will normally 

perform better than no lighting at far lower cost than a CIL system. PIL systems with 

fewer luminaires (one or two) frequently performed better than PIL systems with greater 

numbers of luminaires (four). This was explained by the fact that drivers may experience 

transitional visibility problems under the PIL conditions when they are forced to drive 

from dark to light to dark areas and at the same time perform complex maneuvers such 

as diverging, merging, and tracking a 90-degree curve.

Hostetter, Crowley, Dauber, and Seguin (1989) noted that when luminaires are not placed 

downstream of the physical gore of a partially lighted exit ramp, a driver proceeds from 

a lighted area to a nonlighted area. Citing evidence from various researchers (Boynton 

and Miller, 1963; Boynton, 1967; Boynton, Rinalducci, and Sternheim, 1969; Boynton, 

Corwin, and Sternheim, 1970; Rinalducci and Beare, 1974; and Fredericksen and Rotne, 

1978), they reported that the effect of going from higher to lower levels of luminance 

results in a reduction in visual sensitivity, which would help explain the findings of Janoff 

et al. (1982) that performance under partial lighting was better with fewer luminaires.

On a final note, Bjørnskau and Fosser (1996) conducted a before-after study on a section 

of roadway in Norway to record driver behavior as a function of roadway lighting. One 

interesting finding was that the percentage of aging drivers and female drivers increased 

after the introduction of roadway lighting. Thus, a secondary benefit of roadway lighting 

(beyond its capability to reduce crashes) is increased mobility and access to goods and 

services for aging drivers.

It has been reported that out of 100 wrong-way crashes, 62.7 result in an injury or fatality, 

versus 44.2 out of 100 for all freeway or expressway crashes (Tamburri and Theobald, 

1965). These data highlight the fact that wrong-way crashes are more severe than most 

other types. The most frequent origin of wrong-way incidents, as reported by these 

authors, was entering the freeway via an off-ramp.

Results of investigations of the wrong-way problem in California indicate that fatal 

wrong-way crashes as a percentage of all fatal crashes on freeways have decreased 

Table 47. Cross-references of related entries for traffic control devices for restricted or 

prohibited movements.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 –

Volume 9

(2004)

Roadway Lighting

Handbook

(1978)

Sects. 2A.23, 2B.37 

through 2B.41

Tables 2B-1 & 2C-1

Sects. 2E.53, 3B.20, 3D.01

Figs. 3B-24, 2B-18, 2B-19

Pgs. 10-83 through 10-87, 

Sect. on Wrong-Way Entry

Pg. 23, Paras. 1-2 Pgs. 373-374, Sect. on Mounting 

Height and Lateral Clearance
Handbook for Designing Roadways for the Aging Population 253

CHAPTER 8—INTERCHANGES

substantially in the last 20 years (Copelan, 1989). The actual number of wrong-way 

fatal crashes was the same in 1987 as it was in 1963 (about 35 per year), despite the 

fact that freeway travel has increased fivefold; the reduction appears to be related to 

the countermeasures employed by California Department of Transportation over the 

intervening years, including the implementation of guide and wrong-way signs and 

pavement markings providing better visual cues. Copelan (1989), while noting that half 

of the wrong-way driving on freeways was from deliberate, illegal U-turns, reported that 

additional improvements could still significantly reduce wrong-way crashes. 

Early studies found that the rate of wrong-way driving based on vehicle-miles of travel 

increased with driver age (Tamburri and Theobald, 1965). In their analysis of 1,214 

wrong-way driving incidents which occurred over two 9-month periods on California 

highways, they found a moderate increase in incidents for drivers ages 30–39 and those 

ages 40–49. Over age 60, the incidents rose rapidly; and over age 70, incidents occurred 

at rates approximately 10 times higher than for drivers ages 16–29. Lew (1971) reported 

on an analysis of 168 wrong-way crashes by civilians on California freeways in which the 

age of the wrong-way driver was recorded. While certain age groups (i.e., 30–39, 50–59, 

and 60–69) were represented to an extent corresponding closely to their proportion of 

the driving population, other groups such as those ages 16–19, 40–49, and 70–79 deviated 

markedly from expectation. Drivers ages 16–19 experienced approximately one-half 

of the wrong-way crashes expected for their age group; drivers ages 40–49 experienced 

three-quarters of the rate expected; and drivers ages 70–79 experienced over twice the 

number of freeway wrong-way crashes than would be expected.

Aging drivers’ use of signs designed to control wrong-way movements is affected by 

their visual performance capabilities. Letter acuity declines during adulthood (Pitts, 

1982) and aging adults’ loss in acuity is accentuated under conditions of low contrast, 

low luminance, and high visual complexity. A field investigation of the effect of driver’s 

age on nighttime legibility of highway signs indicated that aging subjects perform 

substantially worse than younger subjects on a nighttime legibility task using a wide 

range of sign materials (Sivak, Olson, and Pastalan, 1981). 

Preventative measures for reducing the frequency and severity of wrong-way maneuvers 

include modifications in ramp and roadway geometry, and signing and pavement 

markings, and the use of warning and detection devices and vehicle arresting systems. 

Traffic prohibition signing and marking are discussed in this section, while positive 

guidance signing for freeway entrances and ramp geometry and delineation were 

discussed under Design Element 26.

Campbell and Middlebrooks (1988), following the recommendation of Parsonson 

and Marks (1979) to widely separate the on- and off-ramps at partial cloverleaf 

interchanges, experimented with a design in which close exit and entrance ramps would 

be combined into one paved surface separated only by a double yellow line. Ten ramps 

in the Atlanta, Georgia, area were redesigned and evaluated using actual counts of

wrong-way movements. Two of the ramps were monitored before and after they were 

converted to combined ramps. At the first location, the wrong-way rate per month before 

construction was 86.7; after combining the ramps, the rate fell to 0.3 per month. At the 

second location, the wrong-way rate was 88.6 per month. After the installation of four 
254 Handbook for Designing Roadways for the Aging Population

CHAPTER 8 CHAPTER 8—INTERCH INTERCHANGES

countermeasures (trailblazers, lowered DO NOT ENTER and WRONG WAY signs,

18-in stop bar, and 8-in yellow ceramic buttons in the centerline of the crossroad), the 

rate dropped to 2.0 per month. Once the ramps were combined at this second location, 

the wrong-way rate jumped to 30.0 per month, even when ceramic buttons, permanent 

signing, and pavement markings and a dotted channelizing line (i.e., pavement markings 

that lead turning vehicles onto the ramp) were employed. 

The mixed results of the Campbell and Middlebrooks study (1988) led to the evaluation 

of 15 additional combined ramps in the same research project, 12 of which were partial 

cloverleaf, with the balance consisting of median entrance/exit ramps (designed for future 

access by high-occupancy vehicles to the median lanes, but during the study period were 

open to all traffic). The study periods ranged from 30 to 102 days. The results clearly 

indicated that the concept of combined exit and entrance ramps can work when signing 

and markings conform to MUTCD specifications. It was recommended that 8-in yellow 

ceramic buttons be installed along the cross street centerline if all other countermeasures 

do not work. 

With regard to signing, Friebele, Messer, and Dudek (1971) noted that the use of 

oversized signs and reflectorization may be needed in locations where motorists are apt 

to disregard wrong-way warnings, and Copelan (1989) suggested that the larger, highly 

retroreflective signs may be helpful for confused or elderly drivers.

Parsonson and Marks (1979) found that lowering the DO NOT ENTER and WRONG

WAY signs to 18 in above the pavement to place them in the path of the headlight 

beams at night and placing trailblazer signs on the on-ramp were effective, inexpensive 

countermeasures. Individually, these two countermeasures reduced the wrong-way 

incidence to about one-third to one-half of its original rate. This is consistent with 

California’s Standard Sign Package, which specifies that the DO NOT ENTER and 

FREEWAY ENTRANCE packages be mounted with the bottom of the lower sign 24 in 

above the edge of the pavement. It also specifies that ONE WAY arrows be mounted 18 in 

above the pavement. The Virginia Department of Highways and Transportation (1981b) 

noted concern regarding the 18 in mounting height of the ONE WAY signs, however, 

stating that the signs may become obscured by vegetation and by guardrails (when the 

sign is mounted behind a guardrail). Thus, mounting height was revised for this State to 

36 in, to alleviate these concerns. An additional concern with lowering the mounting 

height of these signs is the increased potential to impact a passenger vehicle windshield 

if struck by a motorist entering or exiting the freeway who strays off of the ramp and 

crashes into the sign support. However, wrong-way entries onto high-speed facilities 

can cause very serious head-on collisions in locations where there is a high incidence 

of wrong-way entry or a high likelihood of wrong-way entry due to geometrics. Since 

windshield penetration is less likely to occur at a location near the ramp terminus than at 

other locations because of lower travel speeds of drivers traveling in the correct direction 

along the ramp (who are slowing down for a stop or a signalized turn) and drivers 

making the wrong-way movement (who are accelerating from a turn), the anticipated 

benefit of increased sign conspicuity and prevention of wrong-way freeway entries is 

judged to significantly outweigh the risk of sign penetration. 
Handbook for Designing Roadways for the Aging Population 255

CHAPTER 8—INTERCHANGES

California uses the DO NOT ENTER and WRONG WAY signs together on a single

signpost, with the WRONG WAY sign mounted directly beneath the DO NOT ENTER

sign (the Do Not Enter Package). This sign package is placed on both sides of the ramp. 

For off-ramp signing, the Standard specifies the use of at least one Do Not Enter package 

(DO NOT ENTER and WRONG WAY signs), to be placed to fall within the area covered

by the car’s headlights and visible to the driver from the decision point on each likely 

approach; three or four packages may be required if the off-ramp is split by a traffic 

island. In addition, ONE WAY arrows should be placed as close to the crossing street as 

possible. As they are retrofitted and newly installed, the Do Not Enter sign packages in 

California have high intensity sheeting (Copelan, 1989).

Increases in conspicuity distance have been reported in the literature on fluorescent 

signing. As stated earlier in Chapter I for Design Element 12, Burns and Pavelka 

(1995) found that signs with fluorescent red sheeting were detected by 90 percent of the 

participants in a field study conducted at dusk. Only 23 percent of the subjects were 

able to detect the standard red signs, under the same lighting conditions. To improve 

the daytime conspicuity of DO NOT ENTER and WRONG WAY signs, as well as

conspicuity of these signs under low luminance conditions (dawn and dusk), fluorescent 

red sheeting is recommended. In addition, use of retroreflective sheeting that provides 

for high brightness at the wide observation angles typical of the sign placements and 

distances at which these signs are viewed (e.g., 1.0+ degrees), as well as lowering the 

sign heights for these signs will enhance their nighttime conspicuity under low-beam 

headlight illumination. 

Turning to a consideration of pavement markings, Tamburri (1969) found that a 

white pavement arrow placed at all off-ramps pointing in the direction of the rightway movement can be effective in reducing the number of wrong-way maneuvers. 

However, Parsonson and Marks (1979) found that at a parclo AB loop off-ramp that 

has its crossroad terminal adjacent to the on-ramp, standard pavement arrows, lowered 

DO NOT ENTER and WRONG WAY signs, trailblazer signs, and a 24-in (600-mm)

wide stop bar were not sufficient, as the ramp still showed 22.3 wrong-way movements 

per month. Large pavement arrows (24-ft long) and yellow ceramic buttons (with a 

diameter of 8 in) to form a median divider on the crossroad were required, in addition. 

It was specified that the ceramic buttons should touch each other to form a continuous, 

unbroken barrier, and should extend far enough toward the interchange structure (the 

freeway) to prevent a wrong-way driver from avoiding the buttons by turning early. The 

length required is typically 100 ft. The addition of the ceramic buttons reduced wrongway maneuvers from a rate of 88.6 per month to a rate of 2.0 per month. Campbell and 

Middlebrooks (1988) also found that installing yellow ceramic buttons to the extension 

of the centerline of the crossroad to aid in channelizing left-turning traffic entering the 

freeway, in combination with countermeasures employed by the Georgia Department

of Transportation as standard practice—trailblazer sign, 18-in wide stop line at the end 

of the off-ramp, 18-ft long arrow pavement marking, and lowered WRONG WAY and

DO NOT ENTER signs—reduced wrong-way maneuvers. It was also recommended in 

the Parsonson and Marks (1979) study that the two-piece, 24-ft long arrow pavement 

marking (part of the California standard) be adopted. This use of the wrong-way arrow 

is described in MUTCD section 3B.20 and shown in MUTCD Figure 3B-24.
256 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

Cooner, Cothron, and Ranft (2004) provided guidance for the application of wrong-way 

countermeasures and treatments for freeway exit ramps. In their survey of State DOTs, 

they found that some agencies use red retroreflective raised pavement markers as a 

supplement to wrong-way pavement arrows on freeway exit ramps. TxDOT’s standard 

wrong-way pavement arrow is comprised of raised pavement markers, arranged in a 

design that is slightly longer and wider than the national standard. Cooner et al. (2004) 

indicate that although these provide good visibility at night, they can be a maintenance 

concern because they are often run over, particularly on high-volume exit ramps in urban 

areas. This results in missing markers in wrong-way pavement arrows, or arrows that 

are worn in appearance. In addition to recommending the use of wrong-way pavement 

arrows on freeway exit ramps (comprised of retroreflective raised pavement markers 

in a revised design according to TxDOT’s standard), Cooner et al. (2004) recommend 

that deficient wrong-way pavement arrows be repaired and their maintenance be made 

a priority. No studies demonstrating safety or driver performance benefits for this 

treatment were described by Cooner et al. (2004).
Handbook for Designing Roadways for the Aging Population 257

CHAPTER 8—INTERCHANGES

31 Advance Pavement (Route Shield) 

Markings at Major Freeway Junctions

Description of Practice: Route shield markings on the pavement in advance of 

major freeway junctions are used to supplement diagrammatic or other guide signs, 

to provide additional confirmation to drivers that the lane leads to the desired 

destination. Such route shield markings are currently in use in many locations 

in the country including Orlando, Florida and Columbus, Ohio. Route shield 

markings are permitted as an option in Section 3B.20 of the 2009 MUTCD.

Anticipated Benefits to Aging Road Users: Guidance information acquired

from signs by drivers who are approaching a freeway junction at high speed must 

be remembered as they divide attention between concurrent demands—e.g., 

maintaining safe separation from other traffic while negotiating lane changes and/

or anticipating and reacting to other drivers changing lanes. A driver may have 

been exposed to route guidance information on upstream signing, but cannot 

recall it with confidence moments later when he/she is engaged in other tasks; 

and, safe operation of his/her own vehicle may preclude visual search. Under such 

conditions, drivers who experience age-related decline in divided attention ability 

and working memory should realize a disproportionate benefit with advance 

pavement markings that confirm which lanes lead to which destination routes, 

provided, as always, that these markings are applied and maintained at contrast 

levels sufficient to ensure legibility to an “aging design driver.” 

32 Wrong-Way Driving Countermeasures

Description of Practice: According to FHWA Office of Safety (2013), numerous 

studies of the contributing causes and issues surrounding wrong-way driving 

(WWD) crashes, conducted primarily by state departments of transportation since 

the 1960s, indicate that WWD crashes are much more likely to result in fatalities 

or severe injuries than other highway crash types and highlight several factors that 

must be acknowledged by any WWD-related road safety audit (RSA). The NTSB’s 

FARS analysis determined that drivers over the age of 70 are over-represented in 

fatal wrong-way crashes (NTSB, 2013). Categorically, there are significant human 

factors and environmental conditions generally associated with WWD crashes. 

Various research efforts have found the following correlations:

•	 A substantial percentage of wrong way drivers are impaired by alcohol.

•	 Over-representation of certain driver age groups, such as older drivers

(particularly those over the age of 70) and younger drivers (under the age of 25).

•	 The majority of WWD crashes that result in a fatality occur at night, when

visibility of roadway attributes and signs are diminished, and a disproportionate 

number occur on the weekend, which potentially coincides with elevated levels 

of alcohol consumption amongst the driving population.

PROMISING PRACTICES
258 Handbook for Designing Roadways for the Aging Population

CHAPTER 8—INTERCHANGES

Based on this information, RSA teams should carefully consider the conditions 

under which to conduct an RSA that includes review of WWD crashes. The RSA 

should consider the potential for various human factors, such as impaired driving, 

older drivers with diminished eyesight, and inexperienced drivers prone to driving 

mistakes, to affect WWD crash potential. In addition, ATSSA (2012) has published 

a document containing descriptions of selected WWD treatments and case studies 

on their installation; that document should also be consulted when considering the 

implementation of WWD countermeasures. 

Anticipated Benefits to Aging Road Users: Treatments such as improved lighting 

help drivers to better recognize the configuration of intersections and interchanges. 

Channelization helps to physically prohibit movements that lead to wrong-way 

driving where exit ramps intersect with surface streets. Signing and marking, 

particularly in advance of the intersection, provide the driver with important 

information on movements that are appropriate and reduce the likelihood of 

wrong-way driving.
Handbook for Designing Roadways for the Aging Population 259

CHAPTER 9

Roadway Segments

The following discussion presents the rationale and supporting evidence for Handbook 

treatments pertaining to these ten proven and promising practices.

Proven Practices

33. Horizontal Curves 

34. Vertical Curves

35. Passing Zones

36. Lane Control Devices 

Promising Practices

37. Lane Drop Markings

38. Contrast Markings on Concrete Pavement

39. Utilize Highly Retroreflective Marking Material 

40. Curve Warning Markings

41. Road Diets

42. High Friction Surface Treatments
260 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

33 Horizontal Curves

Pavement markings and delineation devices serve important path guidance functions 

on horizontal curves, particularly under adverse visibility conditions, at twilight, and 

at nighttime. They provide a preview of roadway features ahead and give the driver 

information about the vehicle’s lateral position on the roadway. Delineation must provide 

information that results in recognition of the boundaries of the traveled way both at 

“long” preview distances (5 to 8 s of travel time) and at more immediate proximities 

(within 1 s of travel time) where attention is directed toward instant-to-instant vehicle 

control responses. 

Surface pavement markings in current practice may vary along four dimensions: 

(1) brightness, (2) width, (3) thickness, and (4) the addition of structure to “thick” 

applications. Stripes of increased thickness have an advantage in wet weather because the 

material is more likely to protrude above the level of surface water and to provide a degree 

of retroreflectivity greater than that provided by thinner applications of paint. Also, 

the commercially available structured stripes (tapes) are brighter than other marking 

treatments, even under dry conditions. This is due to the ability of the raised element 

of the structure to reflect more light back to the driver than a horizontal surface. Even 

greater benefits are provided by raised retroreflectorized treatments, including raised

Table 48. Cross-references of related entries for horizontal curves.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, center line markings, 

delineator, edge line markings, 

object marker, raised pavement 

marker, & retroreflectivity

Sects. 3A.05 & 3A.06

Sect. 3B.01, Items A & B

Figs. 3B-4

Table 3B-1

Sect. 3B.04

Sect. 3B.06

Sect. 3B.11

Table 3D-1

Sects. 2C-63 & 2C-65

Fig. 3F-1

Sects. 3F.01 through 3F.04

Table 3F-1

Sect. 6F.77

Pg. 3-176, Paras. 1 & 3 

Pg. 5-32, Sect. on Signing and 

Marking

Pg. 7-43, Para. 5

Pgs. 3-91 through 3-97, Sect. 

3.3.10 Traveled Way Widening on 

Horizontal Curves

Pgs. V-22-V-23, Sect. on Strategy 

3.1 B8: Improve Roadway 

Delineation (T)

Pgs. 358-359, Sect. on Warning 

Signs

Pgs. 364-368, Sect. on Horizontal 

Alignment Warning Signs

Pgs. 382-385, Sect. on Centerline 

and Edge Line Markings

Pgs. 226-231, Sect. on Horizontal 

Alignment

PROVEN PRACTICES
Handbook for Designing Roadways for the Aging Population 261

CHAPTER 9—ROADWAY SEGMENTS

pavement markers (RPM’s), post-mounted delineators (PMD’s), and chevron signs, which 

may be used to improve the nighttime visibility of delineation and to indicate roadway 

alignment. 

A number of driver visual functions that have an impact on the use of pavement markings 

and delineation show significant age-related decrements: dynamic acuity, contrast 

sensitivity, dark adaptation, and glare recovery. Dynamic visual acuity (DVA) includes the 

ability to resolve the details of a high-contrast target that is moving relative to an observer. 

Activities that rely on dynamic acuity include making lateral lane changes and locating 

road boundaries when negotiating a turn. In these situations, greater speeds are associated 

with poorer DVA. Contrast sensitivity influences the response to both sharply defined, 

bright-versus-dark visual targets, and those with grayer, less distinct edges. In general, 

aging adults tend to have decreased contrast sensitivity (Owsley, Sekuler, and Siemsen, 

1983). This loss is more pronounced at lower light levels (Sloane, Owsley, and Alvarez, 

1988; Sloane, Owsley, and Jackson, 1988) and is associated with a heightened sensitivity to 

glare (Wolf, 1960; Fisher and Christie, 1965; Pulling, et al, 1980). The findings of Blackwell 

and Blackwell (1971) indicate that a 60-year-old observer needs approximately 2.5 times 

the contrast as a 23-year-old observer for the same level of visibility. 

Highway research studies that have varied one or more of the four dimensions of pavement 

markings are discussed below, along with studies on the effectiveness of RPM’s, PMD’s, 

chevron signs, and combinations of delineation treatments. Age differences are reported 

wherever data are available.

An early study of surface pavement markings, carried out with an interactive driving 

simulator plus field evaluations, concluded that driver performance—measured by the 

probability of exceeding lane limits—was optimized when the luminance (brightness) 

contrast between pavement markings and the roadway was 2.0 (Blackwell and Taylor, 

1969). A study by Allen, O’Hanlon, and McRuer (1977) also concluded that delineation 

contrast should be maintained above a value of 2.0 for adequate steering performance 

under clear night driving conditions. In other words, these studies have asserted that 

markings must appear to be at least three times as bright as the road surface, because 

contrast is defined as the difference between target and background luminance, divided 

by the background luminance alone. A difficulty with these studies, however, is that 

their data were not derived from—and thus are not representative of—normatively aged 

drivers. The ideal viewing conditions assumed by Allen et al. (1977) also disregard the 

effects of glare as well as adverse visibility, and both factors have a disproportionate impact 

on the performance of aging drivers. In Blackwell and Taylor’s work, a minimum preview 

time of 3 to 4 s was recommended for accurate maneuvering under adverse conditions. 

However, more conservative estimates of preview time to accommodate aging drivers (e.g., 

5 s) have frequently appeared in the literature.

Freedman, et al. (1988) showed significant performance decrements for 65-year-old 

drivers, as compared with 35-year-old drivers, in the visibility distance of 4-in pavement 

stripes on a simulated wet roadway. Staplin, Lococo, and Sim (1990) confirmed the 

need for higher levels of line brightness for aging drivers in a simulator study, where the 

contrast for a 4-in white edge line was continuously varied within a 40-step range in a 

method of limits. Under simulated opposing headlamp glare conditions, subjects ages 65–

80 required an increase in contrast of 20 to 30 percent over a younger sample to correctly 
262 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

discern downstream curve direction at criterion viewing distances. To accommodate less 

capable older drivers, this study’s results indicated that a 300-percent increase in stripe 

brightness versus that required by younger drivers may be warranted.

To describe the magnitude of the effects of age and visual ability on delineation detection/

recognition distance and retroreflective requirements for threshold detection of pavement 

markings, a series of analyses using the Ford Motor Company PC DETECT computer 

model (cf. Matle and Bhise, 1984) yielded the stripe contrast requirements shown earlier 

in this Handbook in Table 18 for Design Element 6 (Delineation of Edge Lines and Curbs) 

in the Rationale and Supporting Evidence section for Intersections. PC DETECT is 

a headlamp seeing-distance model that uses the Blackwell and Blackwell (1971, 1980) 

human contrast sensitivity formulations to calculate the distance at which various types 

of targets illuminated by headlamps first become visible to approaching drivers, with and 

without glare from opposing headlights. The top 5 percent (most capable) of 25-year-olds 

and bottom 5 percent (least capable) of 75-year-olds were compared in this analysis.

The more realistic operating conditions modeled as described above, together with the 

widely cited multiplier for aging observers advocated in the seminal work by Blackwell 

and Blackwell (1971), support the recommendation that an in-service pavement edge 

striping contrast value on horizontal curves maintained at or above 5.0 is appropriate 

to accommodate the needs of the large majority of aging drivers on highways and 

arterials without median separation between opposing directions of traffic. Where 

a median barrier (e.g., concrete safety shaped barrier) high enough to shield drivers 

from direct view of oncoming headlights is present, or where median width exceeds 

49 ft, a horizontal curve edge line contrast value of 3.75 or higher is recommended. It 

is important to note that these recommendations are not limited to standard striping 

width (4 in). Where wider pavement markings are implemented, either as general or spot 

treatments, the same contrast values apply. 

This leads logically to discussion of stripe width. This is one characteristic that has 

been advanced as a countermeasure to accommodate aging drivers, at least on roadways 

22 ft or more in width. The use of wider stripes has been advocated both as a general 

treatment and as a spot treatment on curves. A survey of State highway agencies by 

Wright (1983) found that engineers believe that treatments such as chevrons, delineators, 

and warning signs are more effective than surface markings for spot improvements at 

curves. Deacon (1988), who has concluded that 8-in edge lines should be used instead of 

standard 4-in edge lines on two-lane rural highways, states that “... while this finding is 

not based on benefits to older drivers, older drivers will share—probably proportionally 

more—the safety benefits with others who travel these highways during periods of 

impaired visibility.”

Relevant work in this area includes a report by Good and Baxter (1986) that 6-in

edge lines result in more favorable driver control than 3-in edge lines for “short range 

delineation,” which was defined as that which is useful to the driver for tracking the 

roadway at night under poor visibility conditions. In addition to the assumption that a 

wider stripe will provide greater visibility distances and be more conspicuous to aging 

drivers, there is evidence from a study by Hughes, et al. (1989) that 8-in edge lines offer 

the potential for cost-effective application. This conclusion is based on the finding that 

for 8-in edge lines to be a cost-effective replacement for 4-in edge lines, crashes need to be 
Handbook for Designing Roadways for the Aging Population 263

CHAPTER 9—ROADWAY SEGMENTS

reduced by only 0.7 percent when the daily traffic exceeds 1,000 vehicles.

However, while the use of a wide edge line is conceptually attractive for improving aging 

driver performance, the complete operational and safety benefits are not at all clear. For 

example, Hall (1987) reported that wide edge lines do not reduce the incidence of run-offthe-road (ROR) crashes, nor do they reduce the incidence of such crashes at night or on 

curves. A study by Cottrell (1988) also showed that the use of wide edge lines does not 

reduce the risk of crashes on curves or at night; still, he agrees that the use of wide edge 

lines only in the vicinity of curves, while retaining conventional edge lines on tangents, 

could be an effective spot improvement. Lum and Hughes (1990) have expressed concern 

over both the Cottrell and the Hall studies because the number of miles sampled was 

small. And finally, in a simulator study conducted to determine the most effective 

horizontal curve delineation treatments to accommodate aging drivers, Pietrucha, et al. 

(1996) found that although the recognition distance for a 8-in wide white edge line at inservice brightness level (ISBL) in combination with a standard yellow centerline produced 

longer recognition distance among the aging driver sample (mean recognition distance: 

217.5 ft compared to a 4-in wide white edge line at ISBL in combination with a standard 

yellow centerline (mean recognition distance: 179.4 ft), the difference was not significant.

Thus, wider edge lines deserve consideration wherever practical, particularly as spot 

treatments on horizontal curves, to accommodate the difficulties aging drivers have with 

visibility at nighttime. And it may be inferred from these various studies of stripe width 

that markings that are maintained at or above the recommended contrast levels and are 

wider than the conventional 4-in (100-mm) treatment will provide the greatest benefit to 

aging drivers. What is important to remember is that contrast remains the preeminent 

factor in stripe visibility, and increased width alone does not substitute for lower-thanrecommended contrast levels.

A current area of investigation which potentially could lead to the development of 

standards directly impacting stripe visibility is the measurement of the retroreflectivity 

of pavements and pavement markings. There is currently no pavement marking 

retroreflectivity requirement specified in design manuals, although the Roadway 

Delineation Practices Handbook (Migletz, Fish, and Graham, 1994) states that several

separate studies have concluded that the value of approximately 100 millicandelas per 

lux per square meter (mcd/lux/m2

) is the minimum value for the coefficient of reflected 

luminance (RL) for pavement markings. More common is the expression of delineation 

(pavement marking) retroreflectivity in millicandelas per square meter per lux, or the 

amount of reflected light per unit area of striping material, as a function of the incident 

illumination level. For present purposes, what is important is that, for a given amount 

of incident illumination (i.e., from a vehicle’s headlight beam distribution) the ratio of 

mcd/m2

/lux returned from the pavement marking to the mcd/m2/lux returned from the 

adjacent pavement surface generally describes the brightness of the treatment as viewed 

by an approaching motorist.

Graham, Harrold, and King (1996) conducted a field study at nighttime on public

roadways to determine the minimum pavement marking retroreflectivity requirements 

to accommodate aging drivers. Thirty-six drivers ages 60 to 80, with a mean age of 

71.3 years, and 29 drivers ages 20 to 59 rated the adequacy of 60-m long white and 

yellow stripes on tangent highway sections on clear, dry nights, under low-beam 
264 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

headlight illumination only. Using a 1980 model four-door sedan as the test vehicle, the 

retroreflectance values of the markings ranged from 28 to 301 mcd/m2

/lux. In 12 of the 

14 locations where the pavement markings measured 100 mcd/m2

/lux or higher, they 

were rated as adequate or above by at least 85 percent of the subjects age 60 and older. 

Markings with retroreflectivity levels of 142 mcd/m2

/lux or higher were rated as adequate 

or above by 95 percent or more of drivers age 60 and older. There was no significant effect 

of marking color, a result replicated by Schnell and Zwahlen (1996). 

Graham, Harrold, and King (1996) also documented the effects of a dirty windshield

and headlights on pavement marking visibility. They made measurements on a sample 

of in-service vehicles and found that for the 85th percentile vehicle, the light transmitted 

through a clean windshield was increased by 8 percent compared to an unclean 

windshield, and that cleaning the headlamps increases target luminance by 12 percent. 

Further, they note that vehicles in use from the mid-1990’s have headlamp systems that 

may provide less reflected light from pavement markings than the headlight system on 

the 1980 test vehicle.

Next, Garvey, Gates, and Pietrucha (1997) addressed delineation as an area where

engineering improvements could accommodate the needs of aging drivers. Their report 

indicates that the very best aging drivers will require 130 mcd/m2

/lux, whereas the 

majority of the aging driver population will require 300 mcd/m2

/lux. Jacobs, Hedblom, 

Bradshaw, Hodson, and Austin (1995) performed a field study of the visibility of a 4-inwide by 10-ft-long isolated centerline located 12 ft from the right edge of the road, with 

approximately one-third of their subject sample between the ages of 50 and 60. Results 

were interpreted in relation to the visibility distance needed for a 5-s preview of road 

heading at varying speeds. It was found that a pavement marking retroreflectivity level of 

100 mcd/m2

/lux was able to provide the required visibility distance only at a speed of 15 

mph. To achieve a 5-s preview distance (403.5 ft at 55 mph by the 50th percentile driver 

in this study—who was under 60 years old—required a stripe retroreflectance of 1,000 

mcd/m2

/lux. The vehicle used in the study was a 1993 model 4-door sedan. 

The development of retroreflectivity requirements for pavement markings is complicated 

by the geometric relationships that must be taken into account—including entrance and 

observation angle specifications which are sensitive to driver eye height, headlight type 

and height, the longitudinal separation from the target marking and the driver/headlight 

lateral position in the travel lane—as well as the lack of data regarding the retroreflectivity 

of different types of pavement surfaces under wet and dry conditions and different 

degrees of wear. Perhaps the most rigorous work in this area to date has been reported 

by Zwahlen and Schnell (1998), who conducted studies to define the performance levels 

of markings required to provide a 62-year-old design driver with a preview time of 

3.65 s. Finding no reliable data on the reflective properties of road surfaces under an 

automobile headlamp geometry (i.e., with observation angles less than 1 degree), the 

researchers conducted luminance and illuminance measurements for two bituminous/

asphalt (worn and relatively new) and two concrete (worn and relatively new) roadway 

surfaces in the field. The results of the measurements indicated that the new asphalt 

road surface (RL=20 mcd/m2

/lux) was substantially less reflective than the weathered, 

worn asphalt surface (RL=40 mcd/m2

/lux). In comparison, the worn concrete road 

surface (RL=28 mcd/m2

/lux) was considerably darker than the new concrete road surface 
Handbook for Designing Roadways for the Aging Population 265

CHAPTER 9—ROADWAY SEGMENTS

(RL=55 mcd/m2/lux). Their matrix of readings for each pavement type as a function 

of entrance angle and observation angle were included in a subsystem of the CARVE 

(Computer Aided Road Marking Visibility Evaluator) model that was a key product of 

their research. Zwahlen and Schnell (1998) subsequently selected old asphalt as the road 

surface for a controlled field study of pavement marking visibility. They also selected an 

entrance angle of 88.7 degrees and an observation angle of 1.05 degrees to represent the 

vehicle/observer geometry of an “average large car driven by an average size adult.”

The Zwahlen and Schnell (1998) controlled field study used younger and older drivers 

with near normal visual performance to quantify the visibility distance of pavement 

markings on fully marked two lane rural roads (white edge lines, dashed yellow 

centerline), to calibrate the CARVE computer model. The older driver group contained 

5 males and 5 females with an average age of 68.3 years, and the younger driver group 

contained 5 males and 5 females with an average age of 23.2 years. The authors note that 

their use of only subjects with healthy vision suggests that the visibility distances obtained 

in the study are likely to be longer than what would be obtained with a larger sample that 

represented the U.S. driver population, including individuals with diminished visual 

capabilities. The study measured detection distances for 4-in- (100-mm-) wide pavement 

markings under low- and high-beam headlight illumination. 

Based on the results of Zwahlen and Schnell (1998), the CARVE model was exercised to 

yield recommended retroreflectivity levels for white and yellow pavement markings under 

dry conditions, assuming a typical H6054 type vehicle headlamp. The 3.65-s preview 

time noted earlier was retained for roads with no raised treatments; when RPM’s are used 

in addition to pavement markings, the authors revised the preview time downward to 2.0 

s. The (white) edge line minimum required retroreflectivity (RL) values emerging from 

this effort are shown in Table 49.

The specification of RL values for pavement markings is likely to remain a difficult 

problem for some time, as indicated in the preceding discussion. It may also prove to be 

largely an academic issue. It is the effective contrast of a marking against the surrounding 

pavement area that a driver’s visual system responds to, and which determines both 

(detection) performance and subjective comfort with the information provided by such 

treatments. While this index can be arrived at through complicated calculations based 

on the retroreflectivity levels of pavements and markings, it can also be done through a 

Table 49. Minimum required RL (mcd/m2/lux) recommended by Zwahlen and Schnell (1998) for 

roads consisting of two white edge lines and a dashed yellow or white centerline.

Vehicle Speed 

(km/h)

Vehicle Speed 

(mph)

Minimum Required RL (mcd/m2/lux) for White Edge line

Without RPM’s

Preview Time = 3.65 s

With RPM’s 

Preview time = 2.0 s

0-40 0-25 30 30

41-56 26-35 50 30

57-72 36-45 85 30

73-88 46-55 170 35

89-104 56-65 340 50

105-120 66-75 620 70
266 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

simple, direct measurement of stripe and pavement luminance under the observation 

conditions of interest (e.g., nighttime, low beam headlights, dry pavement) at any site 

where the need for restriping must be determined. Based on luminance meter readings 

of stripe luminance and pavement luminance, obtained at any practical distance, 

the dimensionless number denoting contrast level for the pavement marking can be 

calculated as described in Appendix B of this Handbook.

What deserves emphasis—aside from the fact that when one measures contrast, one 

is measuring what drivers actually see—is just how straightforward it is to obtain this 

information. An engineer or technician, with a single hand-held piece of equipment 

(luminance meter) can quickly obtain the measures needed for the contrast calculation, 

under any operating condition of interest (see Appendix B).

This discussion now turns to raised and reflectorized treatments. Raised pavement 

markers have received widespread use because they provide better long-range delineation 

than conventional pavement markings, particularly under wet conditions. When used 

on a road edge, they also provide brighter peripheral cues, which could be advantageous 

to the aging driver for path guidance. Over time, however, RPM’s also are subject to loss 

of their initial retroreflectivity; in colder climates, RPM’s may be damaged by plowing 

operations.

Deacon (1988), in his review of research on delineation and marking treatments that 

he believed would be of particular benefit to the aging driver, found that highways with 

RPM-enhanced centerlines had lower crash rates than those with painted centerlines 

only. The average reduction in crash rates was approximately 0.5 crash per million 

vehicle-miles. Zador, et al. (1986) observed that after-modification vehicle paths were 

shifted away from the centerline on right and left curves with RPM’s mounted on both 

sides of the double yellow centerlines, and that placement changes were largest with 

RPM’s compared with PMD’s and chevrons. It has also been observed that RPM’s placed 

in the centerlines and edge lines at pavement width reductions at narrow bridges produce 

significant reductions in 85th percentile speeds and centerline encroachments (Niessner, 

1984). On two-lane rural curves, RPM’s in conjunction with the double yellow centerline 

have been recommended.

An RPM spacing study was conducted by Blaauw (1985), who tested several RPM 

patterns on 656-ft radii and 3,281-ft radii horizontal curves using a visual occlusion 

technique. White RPM’s were used for the tests, at spacing distances of approximately 

40 ft, 80 ft, and 120 ft. On 656-ft radius curves, the 80-ft and 120-ft spacing led to 

speed reductions and lane errors. Based on these results, it was recommended that on 

curves of this severity, the spacing of RPM’s be restricted to 40-ft spacing. In general, 

no differences between treatments were observed for the more gentle, 3,281-ft radius 

curves. Accordingly, this Handbook includes a recommendation for RPM installation, at 

standard (40-ft) spacing, on all horizontal curves with radii below 3,281 ft.

Roadside delineators and treatment combinations are also important to this discussion. 

Because of its increasing use throughout the United States, and because it accommodates 

different types of sheeting in varying amounts and different designs, the primary 

roadside delineation device of current interest is the flat, flexible post. The general crash 

data have shown that the installation of PMD’s is associated with lower crash rates for 
Handbook for Designing Roadways for the Aging Population 267

CHAPTER 9—ROADWAY SEGMENTS

highway sections with or without edge lines (Bali, et al., 1978; Schwab and Capelle, 1979). 

Deacon (1988) confirmed that installation of PMD’s lowered crash rates, for sections 

with or without edge lines. The reduction in crash rates resulting from the installation of 

these delineators averaged 1.0 crash per million vehicle-miles. Thus, especially for lower 

functional classification roadways where the use of enhanced (e.g., wider) edge lines may 

be limited (due to pavement width restrictions), existing data suggest that PMD’s can be 

an effective countermeasure.

In a driver performance study evaluating the effects of chevron signs, PMD’s, and 

RPM’s, both Johnston (1983) and Jennings (1984) found that driver performance on 

sharp curves was the most favorable when chevrons were used. With chevrons, drivers 

followed a better path around the curve (defined in terms of the ratio of the vehicle’s 

instantaneous radius to the actual curve radius). These studies also revealed that drivers 

use a corner-cutting strategy, and that chevron signs and PMD’s facilitated this strategy. 

On right curves with chevrons, drivers had an average midcurve placement closest to 

the centerline. On left curves with chevrons, vehicle placement was not significantly 

different. In the Good and Baxter (1986) study, chevron signs had a detrimental effect on

control behavior, but were rated favorably by drivers in reducing task difficulty. Zador 

et al. (1986) found that chevrons (as well as RPM’s) tend to shift vehicles away from the 

centerline on right and left curves, while PMD’s shift vehicles away from the centerline 

on right curves. A particular advantage for chevrons with high intensity retroreflective 

sheeting was demonstrated for drivers age 65 and older in a study by Pietrucha, et al. 

(1996), when used in combination with other treatments. 

The Pietrucha et al. (1996) study was specifically directed to the difficulties aging 

drivers have with horizontal curve delineation elements, and the possible benefits of 

brighter materials, larger target sizes, redundant and/or multidimensional cues using 

combinations of elements, and novel designs or configurations of elements. Twentyfive distinct delineation/pavement marking treatments (a baseline treatment and 24 

enhancements) were initially presented to subjects in 3 driver age groups (18–45, 65–74, 

and 75 and older). The baseline treatment was a 4-in (100-mm) yellow centerline at 

in-service brightness level (ISBL). The 24 treatments varied according to the presence/

absence of an edge line, edge line width, whether the edge line was enhanced with RPM’s, 

whether the centerline was enhanced with RPM’s, and the presence/absence of off-road 

elements and their characteristics (material, color, brightness, and/or spacing). Measures 

of effectiveness were downstream roadway feature recognition (subjects were required to 

report the direction in which the roadway curved) and recognition distance in a 35-mm 

simulation of nighttime driving. Treatments that included the addition of RPM’s to both 

the centerline and edge line, and all treatments that included delineating the roadway 

edge with high intensity chevrons or high intensity PMD’s, resulted in significantly 

longer mean recognition distances when compared with the baseline treatment, across 

all age groups. For the subjects age 65 and older, only a subset of the treatments with 

delineated roadway edges resulted in significantly longer mean recognition distances, 

due to the increased variance among older subjects’ data. Next, field evaluations were 

conducted with a subset of the most promising treatments. The treatment with the 

longest recognition distance for both age groups consisted of a 4-in wide yellow centerline 

at ISBL with yellow RPM’s at ISBL and standard spacing, a 4-in wide white edge line, 

and fully reflectorized T-post delineators with standard spacing. For the 500-ft radius of 
268 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

curvature used in this study, spacing for the PMD’s was 65 ft. This treatment included 

PMD’s that were fully retroreflectorized (i.e., retroreflective material extended from the 

top of the post to the ground and provided more retroreflective area than the standard 

posts most frequently used). 

Blaauw (1985) tested combinations of PMD’s and RPM’s, resulting in the following 

recommendations: (1) RPM’s exclusively at the center are favorable for lateral vehicle 

control inside the lane (short-range delineation) but are less adequate for preview 

information on the lane to be followed (long-range delineation); therefore, it is necessary 

to delineate both lane boundaries; (2) effective centerline delineation can be realized with 

RPM’s; (3) delineation at the outside of the traffic lane can be realized with RPM’s at the 

location of the lane boundary or with PMD’s spaced laterally at 5 ft—both configurations 

are equally efficient, but PMD’s at an approximate 12-ft spacing are less efficient; and 

(4) RPM’s at the location of the center and/or lane boundaries must be applied with a 

maximum spacing distance of 40 ft on a curve with 656-ft radius or less.

In a laboratory study of drivers’ responses to videotapes of four rural horizontal curves, 

six levels of delineation were studied by Nemeth, Rockwell, and Smith (1985). Seventyeight drivers ages 18 to 63 participated. The levels of delineation included: no delineation; 

centerline only; centerline plus edge line; centerline plus edge line plus PMD’s; centerline 

plus edge line plus RPM’s; and centerline plus edge line plus PMD’s plus RPM’s. Subjects 

were required to identify precisely the instant that they could detect the presence of a 

curve (left or right) and then express their level of confidence with their response. The 

largest increase in detection distance was associated with the addition of RPM’s and 

PMD’s to the centerline and edge line treatments, respectively. While the treatment 

condition that included all delineators (PMD’s and RPM’s, in addition to the centerline 

and edge line) produced the greatest detection distance (an increase in 148 percent over 

centerline and edge line delineation only), the most significant change occurred with the 

addition of the RPM’s to a road that initially had only the centerline and edge line (a 112 

percent increase in detection distance over centerline and edge line only). The addition of 

PMD’s to the centerline and edge line only condition resulted in an increase in detection 

distance of 58 percent.

While no specific roadside treatment on horizontal curves is advocated in this Handbook, 

a recommendation for roadside delineation devices at minimum spacing keyed to curve 

radius appears justified by the findings reported above. Using current practice as a guide, 

a spacing of 40 ft represents the median value in Table 3F-1 of the MUTCD, Approximate 

Spacing for Delineators on Horizontal Curves, for curves with radii from 50 to 500 ft. 

This value is also consistent with the 40-ft spacing requirement for RPM’s on curves with 

radii 656 ft noted above.

Finally, as noted by Puvanachandran (1995), vehicle speed upon curve entry is a 

function of vehicle speed at the approach to the curve, and is not necessarily related to 

the sharpness of the curve. This underscores the importance of efforts to reduce traffic 

speeds on the tangent sections preceding the points of curvature. In an IIHS-sponsored 

study, Retting and Farmer (1998) evaluated the effectiveness of an experimental 

pavement marking message in reducing excessive traffic speeds at rural and suburban 

two-lane roadway locations with sharp horizontal curvatures. The experimental text/

symbol message employed in this study consisted of the word “SLOW” in 8-ft high 
Handbook for Designing Roadways for the Aging Population 269

CHAPTER 9—ROADWAY SEGMENTS

white retroreflective letters, a 8-ft long white retroreflective left curve arrow, and a 18-

in wide white retroreflective line perpendicular to the centerline of the road at both 

the beginning and end of the message. This message was placed 220 ft in advance of a 

90-degree curve. Traffic speeds were measured at this site on the tangent section at two 

points: 650 ft and 90 ft prior to the point of curvature, both before and after application of 

the markings. Speeds were also measured at a control site located on the same roadway 

in the opposite direction of travel that contained a 45-degree left curve. Data were 

collected on Saturdays beginning at 10:30 a.m., and ending Sundays at 3:00 a.m., allowing 

for analysis of daytime (10:30 a.m. to 5:00 p.m.), evening (5:00 p.m. to midnight), and late 

night (midnight to 3:00 a.m.) traffic speeds. All measurement periods were free from 

precipitation. Data were analyzed for approximately 800 passenger cars at each location; 

driver age was not a variable in this study. 

The experimental message was associated with a significant decrease in mean speed 

under daytime, evening, and late-night conditions, and a significant decrease in the 

percentage of drivers exceeding 40 mph under the daytime and late-night conditions, 

compared to the upstream and control sites. During the daytime, the mean speeds at the 

experimental site dropped from 34.3 to 33.2 mph, while the speeds at the upstream site 

increased from 40.2 to 41.7 mph, and the speeds at the control site increased from 39.6 

mph to 41.1 mph. The percentage of drivers exceeding 64 decreased from 9.1 percent to 

3.5 percent at the experimental site, but increased from 54 to 66 percent at the upstream 

site, and from 47 to 62 percent at the control site. During the late-night period, the mean 

traffic speed decreased from 35.1 to 31.7 mph at the experimental site, and the percentage 

of drivers exceeding 40 mph decreased from 18.5 to 1.6 percent. This 10 percent decrease 

in speed was significantly different from the 3 percent decrease in speed measured at 

the upstream site. Retting and Farmer (1998) state that these average traffic speed 

reductions, and the reductions in the proportion of high traffic speeds associated with the 

experimental markings are highly significant; given the exponential relationship between 

fatality risk and change in velocity during collisions, even seemingly small reductions in 

mean traffic speeds are likely to result in significant safety benefits. The benefits of this 

experimental treatment to enhance the safety of aging drivers are unknown at this time, 

and therefore, no treatment has been included in this Handbook. However, based on 

the factors that contribute to run-of-the-road, head-on, and rollover collisions on curves 

(e.g., driver impairment, fatigue, attention, visual deficits, and excessive vehicle speed), it 

may be expected that such advance information would disproportionately benefit aging 

drivers with age-related diminished visual and attentional capabilities. 

Roadway alignment is a key factor in unsafe vehicular operation: i.e., increasing degrees 

of curvature cause more crashes (Haywood, 1980). The widening of lanes through 

horizontal curves, minimizing the use of controlling or maximum curvature for a given 

design speed, and the use of special transition curves for higher speed and sharper curve 

designs have all been suggested as countermeasures. Whereas in the past lane widening 

has been advocated to accommodate the tracking of large trucks through curves, the 

present focus is on the accommodation of aging drivers, whose diminished physical and 

perceptual abilities make curve negotiation more difficult. Lane widths on horizontal 

curves range from 9 ft to 13 ft, but are usually 11-ft or 12-ft wide. Neuman (1992) 

recommended that when less than 12-ft wide lanes are used, consideration should be 

given to widening the lane to this dimension through horizontal curves; and a further 
270 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

increase in width of 1–2 ft may be advised to provide for an additional margin of safety 

through the curve for heavy vehicles. This margin of safety could also be justified in terms 

of its benefit to aging drivers with diminished physical abilities.

Aging drivers, as a result of age-related declines in motor ability, have been found to be 

deficient in coordinating the control movements involved in lanekeeping, maintaining 

speed, and handling curves (Brainin, Bloom, Breedlove, and Edwards, 1977). McKnight and

Stewart (1990) also reported that aging drivers have difficulty in lanekeeping, which results 

in frequently exceeding lane boundaries, particularly on curves. Drivers who lack the 

required strength, including aging drivers and physically limited drivers, often swing too 

wide in order to lengthen the turning radius and minimize rotation of the steering wheel. 

Joint flexibility is an essential component of driving skill. Osteoarthritis, the most common 

musculoskeletal disability among aging individuals, affects more than 50 percent of 

the population age 65 and older (Roberts and Roberts, 1993). If upper extremity range 

of movement is impaired in the aging driver, mobility and coordination are seriously 

weakened. Aging drivers with some upper extremity dysfunction may not be able to steer 

effectively with both hands gripping the steering wheel rim. In a study of 83 people with 

arthritis, 7 percent used only the right hand to steer and 10 percent used only the left hand 

(Cornwell, 1987).

The general relationship between pavement width and safe driving operations has been well 

documented. Choueiri and Lamm (1987) reported the results of several early studies that 

found an association between decreasing crash frequency and increasing pavement widths. 

Krebs and Kloeckner (1977) reported that for every 3.3-ft increase in pavement width, a

decrease of 0.25 crash per million vehicle-kilometers could be expected. Hall, et al. (1976) 

examined the nature of single-vehicle crashes involving fixed objects along the roadside of 

non-freeway facilities. They found that the majority of these types of crashes were reported 

as non-intersection-related, and occurred most frequently on weekends, at night, under 

adverse pavement and weather conditions, and on horizontal curves (especially outside 

of curve). These crash types have high injury severity to drivers and passengers. Wright 

and Robertson (1979) reported that 40 and 31 percent of all fatal crashes in Pennsylvania 

and Maryland, respectively, resulted in a vehicle hitting a fixed object such as a tree, utility 

pole, or bridge abutment. In a study focused on 600 crash sites (and 600 comparison sites) 

involving fixed objects, crash locations were best discriminated from comparison locations 

by a combination of curvature greater than 9 degrees (radius: 637 ft) and downhill gradient 

steeper than 3 percent; and, for the fatal fixed-object crash population, the crash locations 

were best discriminated from comparison locations by a combination of curvature greater 

than 6 degrees (radius: 955 ft) and downhill gradient steeper than 2 percent. 

Glennon and Weaver (1971) evaluated the adequacy of geometric design standards for

highway curves by filming vehicles entering unspiraled highway curves with curvature 

ranging from 2 to 7 degrees (radius: 2,865 to 819 ft). While driver age was not analyzed, 

results of the study indicated that most vehicle paths, regardless of speed, exceed the 

degree of highway curve at some point on the curve. Glennon, Neuman, and Leisch (1985)

measured vehicle speed and lateral placement on horizontal curves and found that drivers 

tend to overshoot the curve radius, producing minimum vehicle path radii sharper than 

the highway curve, and that the tendency to overshoot is independent of speed. They 
Handbook for Designing Roadways for the Aging Population 271

CHAPTER 9—ROADWAY SEGMENTS

observed that the tangent alignment immediately in advance of the curve is the critical 

region of operations, because at about 200 ft before the beginning points of the curve 

(or approximately 3 s driving time), drivers begin to adjust both their speed and path. 

Such adjustments are particularly large on sharper curves. Thus, the margin of safety in 

current AASHTO design policy is much lower than anticipated. 

Zegeer, Stewart, Reinfurt, Council, Neuman, Hamilton, Miller, and Hunter (1990) 

conducted a study to determine the horizontal curve features that affect crash experience 

on two-lane rural roads and to evaluate geometric improvements for safety upgrading. 

An analysis of 104 fatal and 104 nonfatal crashes on rural curves in North Carolina 

showed that in more of the fatal crashes, the first maneuver was toward the outside 

of the curve (77 percent of the fatal crashes versus 64 percent of the nonfatal crashes). 

For approximately 28 percent of the fatal crashes (versus 8.8 percent of the nonfatal 

crashes), the vehicle ran off the road to the right and then returned to be involved in 

a crash. Further, an analysis on 10,900 horizontal curves in the State of Washington 

with corresponding crash, geometric, traffic, and roadway data variables showed that 

the percentages of severe nonfatal injuries and fatalities were greater on curves than on 

tangents with the same width, where total road width (lanes plus shoulders) was 30 ft.

Zegeer et al. (1990) concluded that widening lanes or shoulders on curves can reduce 

curve crashes by as much as 33 percent. Specifically, Table 50 shows the predicted percent 

reduction in crashes that would be expected on horizontal curves by widening the lanes 

and by widening paved and unpaved shoulders (Zegeer et al., 1990).

The evidence cited above from the engineering studies describing curve negotiation, 

pavement width, and crash reduction, together with the documented difficulties in lane 

keeping and diminished motor abilities of aging drivers, support the recommendation 

Table 50. Percent reduction in crashes on horizontal curves with 8 ft beginning lane width as 

a result of lane widening, paved shoulder widening, and unpaved shoulder widening. Source: 

Zegeer et al., 1990.

Total Amount of Lane or Shoulder 

Widening (ft) Percent Crash Reduction

Total Per Side Lane Widening* Paved Shoulder 

Widening

Unpaved 

Shoulder 

Widening

2 1 5 4 3

4 2 12 8 7

6 3 17 12 10

8 4 21 15 13

10 5 * 19 16

12 6 * 21 18

14 7 * 25 21

16 8 * 28 24

18 9 * 31 26

20 10 * 33 29

* Values of lane widening correspond to a maximum widening of 8 ft to 12 ft for a total of 4 ft per lane, or a total of 8 ft of 

widening.
272 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

34 Vertical Curves

From a human factors perspective, the accommodation of aging driver needs should 

be a high priority at sight-restricted locations because of the potential for violation of 

expectancy, even though the actual percentage of crashes occurring under conditions of 

limited (vertical) sight distance is quite small (Pline, 1996). Aging drivers, as a result of 

their length of experience, develop strong expectations about where and when they will 

encounter roadway hazards and “high-demand” situations with increased potential for 

conflict. At the same time, aging driver reaction time is slower in response to unexpected 

information, and aging drivers are slower to override an initial incorrect response 

with the correct response. Further, aging is associated with physical changes that may 

interfere with rapid vehicle control when an emergency maneuver is required. 

Of greatest importance during the approach to sight-restricted locations are the cognitive 

components of driving, most notably selective attention and response speed (complex 

reaction time). Selective attention refers to the ability to identify and allocate attention 

appropriately to the most relevant targets at any given time (Plude and Hoyer, 1985). One 

Table 51. Cross-references of related entries for vertical curves.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Tables 2C-1 through 2C-5

Sects. 2B.28, 2C.05, 2C.36, 2C.45, 

& 2C.55

Sect. 5C.04

Pg. 2-40, Paras. 1 & 2

Pgs. 3-1 through 3-8, Sects. 

3.2.1 through 3.2.3 General 

Considerations, Stopping Sight 

Distance, and Decision Sight 

Distance

Pg. 3-15, Sects. on Stopping Sight 

Distance Object & Passing Sight 

Distance Object

Pgs. 3-149 through 3-164, Sect. 

3.4.6 Vertical Curves

Pg. 3-175, Final Paragraph

Pgs. 421-423, Sect. on Sight 

Distance

Pg. 445, Sects. on Sight Distance & 

Alignment

Pg. 458, Para. 3

Pg. 678, Sect. on Vertical Control

Pgs. V-8-V-11, Sect. on Strategy 

3.1 B1: Provide Advance Warning 

Sings (T)

Pgs. 231-235, Sect. on Vertical 

Alignment

for a minimum pavement width (including shoulder) of 18 ft on arterial horizontal 

curves over 3 degrees of curvature (radius: 1,910 ft), (cf. Cirillo and Council, 1986). It is 

understood that limited-access highways already exceed this recommended lane-plusshoulder width. However, aging drivers often report a preference to travel on two-lane 

arterials, and these facilities may be deficient in this regard, especially in rural settings. 
Handbook for Designing Roadways for the Aging Population 273

CHAPTER 9—ROADWAY SEGMENTS

important finding in the selective attention literature, as noted above, is that aging adults 

respond much more slowly to stimuli that are unexpected (Hoyer and Familant, 1987), 

suggesting that aging adults might be particularly disadvantaged when an unexpected 

hazard appears in the road ahead. In fact, Stansifer and Castellan (1977) suggested that 

hazard recognition errors can be interpreted more as attention failures than as sensory 

deficiencies. The selective attention literature suggests that for adults of all ages, but 

particularly for aging people, the most relevant information should be signaled in a 

dramatic manner to ensure that it receives a high priority for processing. 

Next, appropriate vehicle control behaviors when unexpected hazards are encountered 

depend upon “speeded responding,” or how quickly an individual is able to respond 

to a relevant target, once identified. A timely braking response when one recognizes 

that the car ahead is stopped or that a red signal or STOP sign is present can determine 

whether or not there is a crash. Thus, reaction time or the ability to respond quickly to 

a stimulus is a critical aspect of successful driving. Mihal and Barrett (1976) measured 

simple, choice, and complex reaction time and reported that simple and choice reaction 

time were not correlated with crashes, but complex reaction time was. Moreover, when 

only aging adults were examined, the correlation with crash involvement increased 

from 0.27 for complex reaction for the total sample to 0.52, suggesting the relationship 

to be particularly marked for aging adults. There is nearly uniform agreement 

among researchers that reaction time increases with age. In particular, studies have 

demonstrated a significant and disproportionate slowing of response for aging adults 

versus young and middle-aged adults as uncertainty level increased for response 

preparation tasks. Preparatory intervals and length of precue viewing times appear to be 

crucial determinants of age-related differences in movement preparation and planning 

(Eisdorfer, 1975; Stelmach, Goggin, and Garcia-Colera, 1987; Goggin, Stelmach, and

Amrhein, 1989).

In summary, the age-related deficits in reaction time and various aspects of attention 

are not independent of one another, and more than one of these mechanisms is likely 

to reduce driving efficiency in the aging adult. Because of these deficits, sight-restricted 

locations pose a particular risk to aging drivers, presenting a need for treatments 

addressing both geometry and signing that can be reconciled with available highway 

research findings in this area. 

Unfortunately, there is a lack of conclusive data on this subject. Kostyniuk and Cleveland

(1986) analyzed the crash histories of 10 matched pairs of sites on 2-lane rural roadways. 

The 10 limited sight distance (vertical curve) locations were defined as those below the 

minimum stopping sight distance (SSD) recommended by AASHTO in 1965, and ranged 

from 118 ft to 308 ft. The control site locations were defined as those that more than met 

the standard (SSD greater than 700 ft). Seven of the limited sight distance sites had more 

crashes than the matched control sites, two were approximately equal, and one had fewer 

crashes (Pline, 1996). Overall, the set of sites with less than minimum SSD had over 50 

percent more crashes in the study period than the control sites.

Farber (1982) performed sensitivity analyses of the effects of change in eye height, object 

height, friction, and speed on SSD on crest vertical curves. He found that SSD was 

relatively insensitive to a reasonable range of changes in driver eye height, but was very 

sensitive to speed, friction, and reaction time. Thus, stopping distance on vertical curves 
274 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

that are of inadequate length or are substandard according to other design criteria, and 

where major redesign, repaving, or excavation is not feasible, could most efficiently be 

made safer by modifying a driver’s approach speed and/or reaction time. For 55 mph 

traffic, stopping distance increases 81 ft for every 1-s increase in reaction time. Similarly, 

stopping distance decreases about 26 ft for each 1 mph reduction in speed. A need for 

more effective traffic control countermeasures is thus highlighted.

A reevaluation of crest vertical curve length requirements was performed by Khasnabis

and Tad (1983). These researchers reviewed the historical changes in parameters that 

affect the computation of SSD and evaluated the effect of these changes on the length 

requirements of crest vertical curves. Principal conclusions were that further tests on 

reaction time are needed to more accurately reflect the changing age distribution and 

composition of the driving population. In addition, the validity of the assumption of 

a speed differential for wet pavement conditions between design speed and top driving 

speed is questionable, since there is very little evidence to substantiate the assumption 

that all motorists are likely to reduce their speed on wet pavements. Of particular 

interest, Khasnabis and Tad (1983) noted that the object height of 6 in appears to be

somewhat arbitrary, and stated that reducing the object height to 3 in would improve the 

safety elements of crest curves. 

In contrast, there are strong proponents of the position that the obstacle height criterion 

for design of vertical curves should be raised to 18 in, or the approximate height of a 

passenger vehicle’s rear taillights (see Neuman, 1989). Fambro, Fitzpatrick, and Koppa 

(1997) evaluated the 1994 AASHTO stopping sight distance model during the conduct 

of NCHRP project 4-42, and recommended that the object height be raised to 24 in (600 

mm) in future revisions to the Green Book. This treatment was adopted and reflects the 

height in the current Green Book (2011). The rationale provided by Fambro et al. (1997) 

includes the following points:

•	 Crashes involving small objects are extremely rare events and almost never result

in injuries to vehicle occupants.

•	 Small objects are beyond most drivers’ visual capabilities at the stopping sight

distances required for most rural highways, and especially at night.

•	 Large animals (e.g., cattle, deer) and other vehicles are more realistic and more

frequent hazards to drivers, and from a potential hazard standpoint, the critical 

object for stopping sight distance should be the smallest visible object during the 

day and at night that represents a hazard to the driver.

•	 Approximately 95 percent of the taillight heights and 90 percent of the headlight

heights exceed 600 mm, and therefore, 600 mm is recommended as the 

appropriate object height for determining required stopping sight distances except 

in those locations where the probability of rocks or other debris in the roadway is 

high. In these locations, a shorter object is appropriate.

While McGee (1995) has reported that available data are insufficient to definitively

establish the relationship between (limitations in) vertical alignment and highway safety, 

and on the surface it sounds reasonable to use a height criterion corresponding to the 

most commonly encountered obstacle on the road (i.e., another vehicle), this approach 

disproportionately penalizes aging drivers in those rare circumstances when a hazard 
Handbook for Designing Roadways for the Aging Population 275

CHAPTER 9—ROADWAY SEGMENTS

(of any type) appears unexpectedly due to sight-restricting geometry. Also, the simple 

argument that a conclusive relationship cannot be demonstrated as justification for 

changing current practice is somewhat disingenuous—a significant relationship between 

visual acuity and crash involvement has proven elusive, over decades of study, yet there is 

widespread acknowledgment that good vision is necessary for safe driving.

In consideration of potential countermeasures, since stopping distance is sensitive 

to decreases in speed and reaction time any traffic control device that lowers either 

parameter is beneficial. In one study, a LIMITED	SIGHT DISTANCE sign (W14-4

in the 1988 MUTCD) with a speed advisory was found to be understood by only 17 

percent of the 631 respondents who passed through the study sight (Christian, Barnack, 

and Karoly, 1981). Part of the problem may be that unlike the hazards cited by other

warning signs, the phrase “limited sight distance” has no tangible manifestation, and 

even when drivers have topped the crest of a vertical curve, they may not be aware of 

the extent to which their sight distance was reduced. Freedman, Staplin, Decina, and 

Farber (1984) developed and tested the effectiveness of both word and symbol alternative 

warning devices for use on crest vertical curves using drivers ages 16 to 75. The existing 

LIMITED SIGHT DISTANCE sign, with or without a supplementary	speed advisory	

panel, did not produce desirable driver responses (braking or slowing) as frequently, 

nor was it recalled, comprehended, recognized, or preferred as often as the alternatively 

worded SLOW HILL BLOCKS VIEW sign, or an alternative symbol sign that depicted

two vehicles approaching from opposite sides of a hill. 

The MUTCD 2009 states that the HILL sign (W7-1 or W7-1a) is intended for use in 

advance of a downgrade where the length, percent of grade, horizontal curvature, or 

other physical features require special precautions on the part of road users. While the 

LIMITED SIGHT DISTANCE sign is not included	in the 2009 MUTCD, practitioners

are aware of the need to alert drivers of sight restrictions due to vertical curvature, and 

continue to use the LIMITED SIGHT DISTANCE sign in many	jurisdictions. Since

the SLOW HILL BLOCKS VIEW sign is explicit in telling drivers what they should do

and why they should do it, its use is recommended over both the LIMITED	SIGHT

DISTANCE sign and the HILL sign. The HILL BLOCKS VIEW sign (W7-6) is included

in the 2009 MUTCD, and the guidance associated with its use states that it should be 

supplemented by an Advisory Speed (W13-1P) plaque indicating the recommended speed 

for traveling over the hillcrest based on available stopping sight distance 

Next, several studies have shown that the use of active sign elements, such as flashing 

warning lights for SLOW WHEN FLASHING and MAX SPEED ___ MPH messages

supplementing various standard warning signs, increases the conspicuity of the signs 

and results in greater speed reductions (Zegeer, 1975; Hanscom, 1976; Lanman, Lum, 

and Lyles, 1979; Lyles, 1981) as well as a 60 to 70 percent reduction of crashes at grade 

crossings compared with the static sign alone conditions (Hopkins and Holmstrom, 1976; 

Hopkins and White, 1977). According to Pline (1996), several agencies have experienced 

success with the use of flasher-augmented warning signs with the legend PREPARE TO 

STOP when there is limited sight distance to a signalized intersection, activated at the 

time of signal change (red phase).

Lyles (1980) compared the effects of warning signs at horizontal and crest vertical curves 
276 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

with limited sight distance (less than 500 ft). Five warning devices were evaluated: 

1. the standard intersection crossroad warning symbol sign; 

2.	 a warning sign with the message VEHICLES ENTERING;

3. a sequence of two warning signs and a regulatory sign (REDUCED SPEED 

AHEAD, crossroad symbol, and 35 mph speed limit sign); 

4.	 a VEHICLES ENTERING sign with constantly flashing warning lights; and

5.	 the same as (4) but with a WHEN FLASHING plate, with flashing warning lights

activated only in the presence of crossroad traffic. 

Overall, the standard crossroads and VEHICLES ENTERING signs had less speedreducing effect (0.5–2 mph) than the warning-warning-regulatory sequence and the signs 

with warning lights (4–5 mph). This trend was the same for both horizontal and vertical 

curves, and there was no significant difference between the warning-warning-regulatory 

sequence and the signs with warning lights. Motorists were twice as likely to recall the 

warning-warning-regulatory sequence and signs with warning lights than the standard 

signs. A van positioned at the crossroad was also reported to have been seen more often 

with these sign configurations.

If the combination of advance warning messages—in particular, PREPARE TO STOP—

and flashers appears to offer the greatest benefit, the activation of the flashers on the red 

phase only may be problematic. Drivers may associate the absence of flashers to signify 

an “all clear” condition, when a queue remains from the prior red phase. On the other 

hand, continuously activated flashers would provide no information about the status of 

the upcoming signal or traffic conditions (queue) resulting from a red signal, and could 

therefore breed disregard for the sign, because it carries false information. Therefore, the 

present treatment is to augment the sign panel with advance warning flashers (AWF) that 

are activated by the traffic signal controller prior to the onset of the yellow phase, and flash 

until the signal turns green, long enough for the expected queue to dissipate.

As reviewed above, there is ample reason for concern that at highway approach speeds, 

a safe response by aging drivers to a revealed obstacle at a crest vertical curve will be 

problematical. There is evidence of significant age-related decline in the capability to 

respond to unexpected hazards, specifically in the information processing requirements 

that precede a brake or steering action (object detection, recognition, and decision to 

respond). However, while analyses of curve length and sight distance requirements 

conclude that safety benefits will result from a lower object height criterion, crash data 

analyses have prompted a move in the opposite direction, toward a more liberal criterion. 

In fact, current standards (AASHTO, 2011) assume an obstacle height of 2.0 ft, in contrast 

to the previous value of only 6 in. At the same time, controlled braking rather than 

locked-wheel braking is assumed, which carries significance because stopping sight 

distance reflects not only a driver’s perception-reaction time (PRT) but also the assumed 

deceleration rate for a given design speed. With the widely recognized interrelationship 

between these parameters, and the stance reflected in the AASHTO 2011 design standards, 

the remaining variable—the driver’s PRT—accordingly is the subject of the initial 

treatment regarding vertical curves: at a minimum, a PRT value of 2.5 s should be used in 

the design of these roadway features. In addition, conspicuous and comprehensible warning 

devices should be especially beneficial to aging drivers in sight-restricted situations.
Handbook for Designing Roadways for the Aging Population 277

CHAPTER 9—ROADWAY SEGMENTS

35 Passing Zones

The safety and effectiveness of passing zones depend upon the specific geometric 

characteristics of the highway section, as well as on how drivers receive and process 

information provided by signs and pavement markings, integrate speed and distance 

information for opposing vehicles, and control their vehicles (brake and accelerate) 

during passing maneuvers. As the number of aging drivers in the population increases 

dramatically over the years 1995–2025, many situations are expected to arise where not 

only the slower-moving vehicle, but also the passing vehicle, is driven by an aging person.

The capabilities and behavior of aging drivers, in fact, vary with respect to younger 

drivers in several ways crucial to this discussion. Studies have shown that while driving 

speed decreases with driver age, the sizes of acceptable headways and gaps tend to 

increase with age. While motivational factors (e.g., sensation seeking, risk taking) have 

been shown to play a major role in influencing the higher speeds and shorter headways 

accepted by young drivers, they seem to play a less important role in aging driver 

behavior. Instead, the relatively slower speeds and longer headways and gaps accepted by 

aging drivers have been attributed to their compensating for decrements in cognitive and 

sensory abilities (Case, Hulbert, and Beers, 1970; Planek and Overend, 1973). 

The ability to judge gaps when passing in an oncoming lane is especially important. For 

some aging drivers, the ability to judge gaps in relation to vehicle speed and distance is 

diminished (McKnight and Stewart, 1990). Depth perception—i.e., the ability to judge

the distance, and changes in distance, of an object—decreases with age (Bell, Wolfe, 

and Bernholtz, 1972; Henderson and Burg, 1973, 1974; Shinar and Eberhard, 1976). 

Table 52. Cross-references of related entries for passing zones on two-lane highways.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Traffic Engineering

Handbook 

(2009)

Table 2B-1

Sects. 2B.28 & 2B.29

Tables 2C-1 through 2C-5

Sects. 2C.07 & 2C.45

Sect. 3B.02

Pg. 2-38, Para. 1

Pgs. 3-8 through 3-14, Sect. 3.2.4 Passing Sight 

Distance for Two-Lane Highways 

Pgs. 3-110 through 3-111, Sect. on Passing 

Sight Distance

Pgs. 3-132 through 3-140, Sect. 3.4.4 Methods 

for Increasing Passing Opportunities on TwoLane Roads

Pgs. 3-156 through 3-157, Sect. on Design 

controls: passing sight distance

Pg. 5-29, Sect. on Passing Sight Distance

Pgs. 6-4 through 6-5, Sect. on Sight Distance

Pg. 7-3, Sects. on Sight Distance & Alignment

Pgs. 7-7 through 7-8, Sect. 7.2.8 Provision for 

Passing 

Pgs. 7-16, Sect. on Climbing Lanes on 

Multilane Arterials

Pgs. 384-385, Sect. on No-Passing-Zone 

Markings

Pgs. 618-619, Sect. on No-Passing Zones

Pgs. 224-225, Sect. on Passing Sight Distance 

(PSD)
278 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

One study found that the angle of stereopsis (seconds of visual arc) required for a group 

of drivers age 75 and older to discriminate depth using a commercial vision tester was 

roughly twice as large as that needed for a group of drivers ages 18 to 55 to achieve the 

same level of performance (Staplin, Lococo, and Sim, 1993). McKnight and Stewart (1990)

reported that the inability to judge gaps is not necessarily associated with a high crash 

rate, to the extent that drivers can compensate for their deficiencies by accepting only 

inordinately large gaps. This tactic has a negative impact on operations as traffic volumes 

increase, however, and may not always be a feasible approach.

Judging in-depth motion is made difficult by the fact that when no lateral displacement 

occurs, the primary depth cue is the expansion or contraction of the image size of the 

oncoming vehicles (Hills, 1980). Studies of crossing-path crashes, where gap judgments 

of oncoming vehicle speed and distance are critical as in passing situations, indicate an 

age-related difficulty in the ability to detect angular movement. In laboratory studies, 

aging persons required significantly longer to perceive that a vehicle was moving closer 

(Hills, 1975). Staplin and Lyles (1991) reported research showing that, relative to younger 

drivers, older ones underestimate the speed of approaching vehicles. Similarly, Scialfa, 

Guzy, Leibowitz, Garvey, and Tyrrell (1991) showed that older adults tend to overestimate

approaching vehicle velocities at lower speeds and underestimate at higher speeds, relative 

to younger adults. Aging persons also apparently accept a gap to cross in front of an 

oncoming vehicle that is a more-or-less constant distance, regardless of the vehicle’s speed. 

Analyses of judgments of the “last possible safe moment” to cross in front of an oncoming 

vehicle showed that older men accepted a gap to cross at an average constant distance, 

whereas younger men allowed a constant time gap and thus increased distance at higher 

speeds (Hills and Johnson, 1980). A controlled field study showed that older drivers 

waiting (stationary) to turn left at an intersection accepted the same size gap regardless 

of the speed of the oncoming vehicle (30 mph and 60 mph [48 and 96.5 km/h]), while 

younger drivers accepted a gap that was 25 percent larger for a vehicle traveling at 60 mph 

(96.5 km/h) than their gap for a vehicle traveling at 30 mph (48 km/h) (Staplin et al., 1993).

The minimum passing sight distances listed in Table 3B-1 of the MUTCD (FHWA, 2009) 

for marking passing zones are shorter than the minimum passing sight distance values for 

the design of two-lane highways, as listed in Exhibit 3-7 of AASHTO’s 2004 Green Book; 

however, AASHTO revised its PSD values in the 2011 Green Book (Table 3-4) to match 

those found in the MUTCD. Although the minimum passing sight distances specified by 

AASHTO are based on observations of successful car-passing-car observations, Hughes 

et al. (1992) commented that the model does not take into account the abortive passing 

maneuver, nor does it consider the length of the impeding vehicle. Saito (1984) determined 

that the values specified by the MUTCD for minimum passing distance are inadequate for 

the abortive maneuver, while Ohene and Ardekani (1988) asserted that the MUTCD sight 

distance requirements are adequate for the driver to abort if the driver decelerates at a 

rate of 10.5 ft/s2

 for a 40-mph passing speed and at a rate of 12.8 ft/s2 for a 50-mph passing 

speed. In any event, it cannot be assumed that drivers will always use the maximum 

acceleration and deceleration capabilities of their vehicles, particularly aging drivers.

Consistent with the AASHTO operational model (AASHTO, 2011), passing sight distance 

is provided only at places where combinations of alignment and profile do not require the 

use of crest vertical curves. For horizontal curves, the minimum passing sight distance 
Handbook for Designing Roadways for the Aging Population 279

CHAPTER 9—ROADWAY SEGMENTS

for a two-lane road is about four times as great as the minimum stopping sight distance 

at the same speed (AASHTO, 2011). By comparison, the MUTCD defines passing 

sight distance for vertical curves as the distance at which an object 3.50 ft above the 

pavement surface can be seen from a point 3.50 ft above the pavement. For horizontal 

curves, passing sight distance is defined by the MUTCD as the distance measured 

along the centerline between two points 3.50 ft (1.07 m) above the pavement on a line 

tangent to the embankment or other obstruction that cuts off the view of the inside 

curve (MUTCD, 2009). The length of passing zones or the minimum distance between 

successive no-passing zones is specified as 400 ft (120 m) in the MUTCD; specifically, 

where the distance between successive no-passing zones is less than 400 ft, no-passing 

markings should connect the zones. As Hughes, Joshua, and McGee (1992) pointed

out, the MUTCD sight distance requirements were based on a “compromise between a 

delayed and a flying passing maneuver, traceable back to the AASHTO 1940 policy that 

reflected a compromise distance based on a passing maneuver such that the frequency 

of maneuvers requiring shorter distances was not great enough to seriously impair the 

usefulness of the highway.”

The basis for the minimum length of a passing zone is unknown, however, because 

research has indicated that for design speeds above 30 mph the distance required for 

one vehicle to pass another is much longer than 400 ft (Hughes et al., 1992). Weaver 

and Glennon (1972) reported that, in limited studies of short passing sections on main

rural highways, most drivers do not complete a pass even within an 800-ft section; and 

use of passing zones remains very low when their length is shorter than 900 ft. Not 

surprisingly, it has been mentioned in the literature (Hughes et al., 1992) that the current 

AASHTO and MUTCD passing sight distance values are probably too low. Several 

studies have indicated that both the MUTCD and AASHTO passing sight distances are 

too short to allow passenger cars to pass trucks and for trucks to pass trucks (Donaldson, 

1986; Fancher, 1986; Khasnabis, 1986).

Several research studies have been performed that have established and evaluated passing 

sight distance values for tangent sections of highways. As early as 1934, the National 

Bureau of Standards measured the time required for passing on level highways during 

light traffic and found that the time to complete the maneuver always ranged between 

5 and 7 s regardless of speed. Passing maneuvers were observed at speeds ranging from 

10 to 50 mph. They concluded that 900 ft of sight distance was required for passing at 

40 mph (64 km/h). Harwood and Glennon (1976) reported that drivers are reluctant to

use passing zones under 880 ft (268 m). They recommended that design and marking 

standards should be identical and include both minimum passing sight distances and 

minimum length of passing zones, with minimum passing sight distance values falling 

between the AASHTO and MUTCD values. Kaub (1990) presented a substantial amount

of data on passing maneuvers on a recreational two-lane, two-way highway in northern 

Wisconsin. Under low and high traffic volumes, respectively, he found that 24–35 percent 

and 24–50 percent of all passes were attempted in the presence of an opposing vehicle; 

the average time in the opposing lane (60 mph) was 12.2 s under low-traffic conditions 

and 11.3 s with high-traffic volumes.

Passing lanes, also referred to as overtaking lanes, are auxiliary lanes provided on twolane highways to enhance overtaking opportunities. Harwood, Hoban, and Warren 
280 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

(1988) reported that passing lanes provide an effective method for improving traffic 

operational problems resulting from the lack of passing opportunities, due to limited 

sight distance and heavy oncoming traffic volumes. In addition, passing lanes can be 

provided at a lower cost than that required to construct a four-lane highway. Based 

on Morrall and Hoban (1985), the design of overtaking lanes should include advance 

notification of the overtaking lane; a KEEP RIGHT UNLESS OVERTAKING sign at

the diverge point; advance notification of the merge and signs at the merge; and some 

identification for traffic in the opposing lane that they are facing an overtaking lane. 

They reported that there is general agreement that providing short overtaking lanes 

at regular spacing is more cost-effective than providing a few long passing lanes. This 

feature becomes increasingly attractive as the diversity of driving styles and driver 

capability levels grows, with more aggressive motorists accepting greater risks to overtake 

slower-moving vehicles.

Brewer, et al (2011) studied operational and safety effects of passing lane corridors 

(also called “Super 2” corridors) in Texas. Previous research (Wooldridge, et al. 2001) 

demonstrated that periodic passing lanes can improve operations on two-lane highways 

with average daily traffic (ADT) lower than 5000. Brewer’s research expanded on the 

Wooldridge research to develop design guidelines for passing lanes on two-lane highways 

with higher volumes, investigating the effects of volume, terrain, and heavy vehicles on 

traffic flow and safety. Results indicated that passing lanes provide added benefit at higher 

traffic volumes, reducing crashes, delay, and percent time spent following. Empirical 

Bayes analysis of crash data revealed a 35 percent reduction in expected non-intersection 

injury crashes. Simulation results indicated that most passing activity takes place within 

the first mile of the passing lane, so providing additional passing lanes can offer greater 

benefit than providing longer passing lanes. Whether adding new passing lanes or adding 

length to existing lanes, the incremental benefit diminished as additional length is 

provided and the highway more closely resembles a four-lane alignment. The simulation 

study also showed that the effects of ADT on operations were more substantial than the 

effects of terrain or truck percentage for the study corridor.

Finally, the benefits of fluorescent retroreflective sheeting for increased daytime and 

nighttime conspicuity are reported by Jenssen, Moen, Brekke, Augdal, and Sjøhaug 

(1996). They conducted a controlled field study of daytime and nighttime visibility 

performance of fluorescent and non-fluorescent yellow traffic signs, both fabricated with 

retroreflective sheeting that provides for high brightness at wide observation angles 

(ASTM D4956-01,Type IX). The subjects included younger (ages 18-25) and older (ages 

55-75) drivers. Under daytime conditions, the fluorescent yellow signs with Type IX 

sheeting provided a 295 ft increase in sign shape recognition distance over the nonfluorescent yellow signs with Type IX sheeting for the aging driver sample, and a 187 ft 

increase for the younger driver sample. At a speed of 62 mph, this additional detection 

distance would translate to 3.2 s of extra reaction time for the older drivers and 2.1 extra 

seconds of reaction time for the younger drivers. At nighttime, the signs fabricated with 

Type IX sheeting provided an additional sign shape recognition distance of 945 ft over 

signs fabricated with engineering grade sheeting (Type I), and an additional 489 ft of 

shape recognition distance over signs made with high intensity sheeting (Type III) for 

the older driver sample. The younger driver sample performed similarly, with increased 
Handbook for Designing Roadways for the Aging Population 281

CHAPTER 9—ROADWAY SEGMENTS

36 Lane Control Devices

sign shape recognition distances for the signs made with Type IX sheeting (1,010 ft 

over the signs made with Type I engineering grade sheeting, and 482 ft over the signs 

fabricated with Type III high intensity sheeting). These increased distances translate to 

an additional 5 to 10 seconds of reaction time, at a speed of 60 mph (100 km/h).

The age differences in driver capability and behavior noted earlier—i.e., age-related 

difficulties in judging gaps and in increased perception-reaction time, coupled with 

slower driving speeds—support a recommendation for use of the more conservative 

passing sight distance values specified by AASHTO (2004). In addition, a raised 

treatment to improve drivers’ preview of the end of a passing zone—the widely 

recognized NO PASSING ZONE pennant, either oversized or fabricated with fluorescent

yellow retroreflective sheeting that provides for high brightness at wide observation 

angles (e.g., Type IX) for added daytime and nighttime conspicuity— can reasonably 

be expected to facilitate aging drivers’ decisions and responses in situations where safe 

operations dictate that they should abort a passing maneuver. Finally, a recommendation 

to implement passing/overtaking lanes may be justified in terms of overall system safety 

and efficiency.

With the increasing need to provide more capacity on freeways and urban arterials, more 

jurisdictions are moving to the use of reversible lanes to accommodate peak-period traffic 

flows. The control of wrong-way movements on these facilities may be accomplished 

through the use of lane control signals (LCS). The MUTCD (section 4M.01) defines laneuse control signals as “special overhead signals that permit or prohibit the use of specific 

lanes of a street or highway or that indicate the impending prohibition of their use.” The 

meanings of LCS indications (steady downward green arrow, steady yellow X, and steady 

red X) are defined in MUTCD section 4M.02. LCS’s provide real-time information to 

motorists about which downstream lanes are open (green downward arrow), which are 

closed (red X) and which lanes are about to be closed (yellow X) either because of an 

incident downstream or because the lane is a reversible lane. Drivers should vacate lanes 

over which an LCS displays a yellow X, and they should not enter lanes designated by a 

red X. Safe and effective responses to these indications by aging drivers hinge upon the 

same visual target detection and recognition processes which have been documented 

elsewhere in this Handbook to decline systematically with advancing age. 

Ullman, et al. (1996) conducted legibility studies of commercially available lane-use 

control symbols (LCSs) being used in freeway traffic management systems throughout 

Texas. Subjects included drivers ages 16-44 and drivers age 65 and older. In the first 

Table 53. Cross-references of related entries for lane control devices.

Applications in Standard Reference Manuals

MUTCD

(2009)

AASHTO

Green Book

(2011)

Chapter 4M Pgs. 7-48 through 7-50, Section on Reverse Flow Operation

Pgs. 8-28 through 8-31, Section on Reverse-Flow Roadways
282 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

study, subjects were seated in the driver’s seat of a test vehicle that was 

positioned 460 m from an overhead sign structure that displayed three 

fiber optic LCSs mounted side by side. They were shown one symbol 

presented on one LCS for a 1.5-s duration, and were asked to describe 

the symbol and the color. If a subject could not correctly identify the 

color and symbol, he or she moved closer to the LCS, until the color 

and symbol could be correctly identified. The study was conducted 

during the day. The symbols on all three LCS heads measured 14 

in in height, but the arrangement of the pixels varied for the three 

sign manufacturers. Signal 1 utilized a single-stroke arrangement of 

pixels, arranged using 0-5 in lenses spaced 1 in apart. Signal 2 utilized 

a double-stroke arrangement of pixels, arranged using 0.6-in lenses 

spaced 1.5 in apart. Signal 3, besides displaying the three standard 

MUTCD symbols, was also able to display a yellow arrow pointing 

downward, or pointing to the left or right. Signal 3 utilized a doublestroke arrangement of pixels for the green arrow, the red X, and the 

yellow X, but utilized a single-stroke arrangement for the downward 

and diagonal yellow arrows. The lenses measured 0.15 in, and spacing 

was 0.7 in. Figure 94 presents the pixel layout of the three LCS heads 

used in this research. The legibility distances by symbol type are 

presented in Table 54, by signal type and driver age.

Results indicate that median legibility distances for the older drivers 

viewing the red X, yellow X, and green arrow were 298 to 649 ft shorter 

than those for the younger drivers. The biggest discrepancies between 

younger and older drivers were for the red X on Signal 2 and the green 

down arrow on Signal 1. Signal 3 produced the most uniform legibility 

distances for all symbols. The authors state that comments from the 

older drivers indicated that the double-stroke pixel arrangement 

combined with the larger pixel lenses on Signal 2 caused irradiation 

effects, resulting in older drivers’ inability to identify the shape of the 

red “glow” until they were 50 percent closer to the signal than younger 

drivers. The actual cause of the poor legibility of the green down arrow 

on Signal 1 for older drivers was unknown, but hypothesized by the 

researchers to be a result of being slightly more “blue” than the green 

down arrows on the other two signals. Figure 94. Pixel layout of LCD Heads 

employed in research conducted by 

Ullman et al. (1996)

Table 54. Median legibility distance (meters) of lane control signals, as a function of driver age, LCS type, and LCS 

symbol (Ullman, Parma, Peoples, Trout, and Tallamraju, 1996).

Driver

Age

Signal 1 Signal 2 Signal 3

Red 

X

Yellow 

X

Green 

Down 

Arrow

Red 

X

Yellow 

X

Green 

Down 

Arrow

Red 

X

Yellow 

X

Green 

Down 

Arrow

Yellow 

Diagonal 

Arrow

Yellow 

Down 

Arrow

Young/Middle 

Aged (16-44) 366 457 396 335 457 457 427 457 457 427 457

Older (65+) 274 274 198 168 350 290 305 274 335 396 427
Handbook for Designing Roadways for the Aging Population 283

CHAPTER 9—ROADWAY SEGMENTS

On the other hand, although the yellow downward and diagonal arrows displayed on 

Signal 3 are not standard MUTCD symbols for LCS’s, they showed the highest legibility 

distance of all symbols for the older drivers, and yielded a legibility distance that was 30 

m shorter than younger drivers’ legibility distance. These symbols were created with a 

single line of closely spaced small pixels. The legibility distance was greater than that 

of the double-stroke yellow X presented on the same display. Results of a preliminary 

field study conducted in this same project indicated that the yellow X and yellow down/

diagonal arrows were interchangeable, resulting in similar proportions of drivers exiting 

a closed lane. 

The authors also studied the effects of age, dirt accumulation, and regular maintenance 

on LCS legibility. The combined effect of age and dirt accumulation significantly reduced 

the visibility of the green arrow and red X for both younger and older driver groups. The 

signal had been installed for 6 years, and had an 18-month accumulation of dirt, since its 

last cleaning. Subjects viewed the symbols before and after cleaning and replacement of 

each of the 50-watt halogen light bulbs in the signal face. The legibility distances before 

maintenance and cleaning ranged from 600 to 1,099 ft for drivers under age 45, and 351 

to 899 ft for drivers age 65 and older. After maintenance and cleaning, visibility distances 

increased significantly for both driver groups. Median visibility distances for the 

younger drivers ranged from 850 to 1,250 ft, and for the older drivers ranged from 699 

to 1,099 ft. There appears to be permanent loss of visibility of the red and green symbols 

over time; after maintenance, the legibility distances for both driver groups were twothirds to three-fourths of those shown for the new LCS. The effect of dirt and signal age 

did not affect legibility distance of the yellow X.
284 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

37 Lane Drop Markings

Description of Practice: Pavement markings in advance of a lane drop are used 

to supplement the warning sign messages that indicate the lane is a dropped 

lane. Section 3B.04 of the 2009 MUTCD discusses standards and guidance for 

dotted white lane line markings and other lane-drop markings. Note that this is a 

different marking application than lane reduction markings, which are described 

in Section 3B.09.

Anticipated Benefits to Aging Road Users: As the result of normal aging, drivers 

may be at higher risk of failing to detect advance warning signs posted at the 

side of the road due to loss of visual sensitivity in the periphery; a narrowing 

of the attentional (or “useful”) field of view; or a reduced ability to engage in a 

search of the visual periphery when, for example, road or weather conditions 

increase demands for path guidance information. To the extent that aging drivers 

experience any of these limitations, they should derive an extra benefit from 

advance warning messages presented as pavement markings—if these markings are 

applied and maintained at contrast levels sufficient to ensure legibility to an “aging 

design driver.”

38 Contrast Markings on 

Concrete Pavement

Description of Practice: Duplicate black markings applied immediately upstream 

or downstream from broken line longitudinal markings (staggered markings), 

or black contrast marking surrounding either side of broken or continuous 

longitudinal markings, are used to increase the visibility of markings on concrete 

and other light colored pavements. Routine use of such “contrast markings” occurs 

in Arkansas, Colorado, Georgia, Idaho, Missouri, North Carolina, Oklahoma,

Pennsylvania, Texas, Utah, Virginia, Wisconsin, and the District of Columbia. 

The use of supplemental contrast markings is included as an option in the 2009 

MUTCD.

Anticipated Benefits to Aging Road Users: Any treatment that improves the 

contrast and therefore the detectability of lane, gore, and other longitudinal 

pavement markings, whether broken or continuous, will have a disproportionate 

benefit to aging drivers, who as a group experience diminished contrast sensitivity 

due to normal changes in the lens of the eye and also evidence a higher prevalence 

of ocular diseases. 

PROMISING PRACTICES
Handbook for Designing Roadways for the Aging Population 285

CHAPTER 9—ROADWAY SEGMENTS

39 Utilize Highly Retroreflective 

Marking Material 

Description of Practice: Oversize glass beads in traditional paint markings, 

profiled thermoplastic markings, and preformed pavement marking tape designed 

for rumble strip applications all offer strategies to increase the retroreflectivity and 

thus the visibility of pavement markings at night and in wet weather conditions. 

Preformed pavement marking tape is utilized statewide in Iowa and on Detroitarea freeways in Michigan. Virginia utilizes the pavement marking tape on all 

interstate routes. 

Anticipated Benefits to Aging Road Users: Any treatment that improves the 

contrast and therefore the detectability of lane and road edge boundaries will have 

a disproportionate benefit to aging drivers, who as a group experience diminished 

contrast sensitivity due to normal changes in the lens of the eye and also evidence a 

higher prevalence of ocular diseases. The continuous guidance information offered 

by treatments that enhance the contrast of pavement markings is especially helpful 

to aging drivers under adverse visibility conditions and when there is only a brief 

preview of changing roadway geometry downstream.

40 Curve Warning Markings

Description of Practice: Curve warning markings on the pavement in advance 

of horizontal curves are used to supplement warning sign messages such as the 

Curve Ahead sign and other curve delineation devices such as chevron signs. Such 

advance markings are currently in use in many locations in the country, including 

Irvine, California and Williamston, Michigan. 

Anticipated Benefits to Aging Road Users: As the result of normal aging, drivers 

may be at higher risk of failing to detect advance curve warning signs posted at 

the side of the road due to loss of visual sensitivity in the periphery; a narrowing 

of the attentional (or “useful”) field of view; or a reduced ability to engage in a 

search of the visual periphery when, for example, road or weather conditions 

increase demands for path guidance information. To the extent that aging drivers 

experience any of these limitations, they should derive an extra benefit from 

advance warning messages presented as pavement markings—if these markings are 

applied and maintained at contrast levels sufficient to ensure legibility to an “aging 

design driver.”
286 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

41 Road Diets

Description of Practice: The classic roadway reconfiguration commonly referred 

to as a “road diet” involves converting an undivided four-lane roadway into three 

lanes made up of two through lanes and a center two-way left turn lane. The 

reduction of lanes allows the roadway to be reallocated for other uses such as bike 

lanes, pedestrian crossing islands, and/or parking. Midblock locations tend to 

experience higher travel speeds, contributing to increased injury and fatality rates. 

More than 80 percent of pedestrians hit by vehicles traveling at 40 mph or faster 

will die, while less than 10 percent will die when hit at 20 mph or less. (FHWA 

Office of Safety 2012)

Road diets can be low-cost treatments if planned in conjunction with 

reconstruction or simple overlay projects, since a road diet mostly consists of 

restriping. Roadways with Average Daily Traffic (ADT) of 20,000 or less may be 

good candidates for a road diet and should be evaluated for feasibility. It has been 

shown that roads with 15,000 ADT or less had very good results in the areas of 

safety, operations, and livability. Driveway density, transit routes, the number and 

design of intersections along the corridor, as well as operational characteristics are 

some considerations to be evaluated before deciding to implement a road diet. 

It is a good practice to know well in advance when road reconstruction and overlay 

projects will be initiated so an evaluation can be conducted. It is important to 

analyze and understand the effects of the proposed change, obtain input from the 

community stakeholders, and ensure the appropriate elements are included in the 

project. Improvements to intersection turn lanes, signing, pavement markings, 

traffic control devices, transit stops, and pedestrian and bicyclist facilities may be 

needed to support this concept. It should be noted that the classic four-to-threelane road diet is very compatible with single-lane roundabouts.

Anticipated Benefits to Aging Road Users: Road diets have multiple safety and 

operational benefits for vehicles as well as pedestrians, such as:

•	 Decreasing vehicle travel lanes for pedestrians to cross, therefore reducing the

multiple-threat crash (when one vehicle stops for a pedestrian in a travel lane 

on a multi-lane road, but the motorist in the next lane does not, resulting in a 

crash) for pedestrians.

•	 Providing room for a pedestrian crossing island.

•	 Improving safety for bicyclists when bike lanes are added (such lanes also

create a buffer space between pedestrians and vehicles).

•	 Providing the opportunity for on-street parking (also a buffer between

pedestrians and vehicles).

•	 Reducing rear-end and side-swipe crashes.

•	 Improving speed limit compliance and decreasing crash severity when crashes

do occur.
Handbook for Designing Roadways for the Aging Population 287

CHAPTER 9—ROADWAY SEGMENTS

When appropriately applied, road diets have generated benefits to users of all 

modes of transportation, including bicyclists, pedestrians, and motorists. The 

resulting benefits include reduced vehicle speeds, improved mobility and access, 

reduced collisions and injuries, and improved livability and quality of life. When 

modified from four travel lanes to two travel lanes with a two-way left-turn lane, 

roadways have experienced a 29 percent reduction in all roadway crashes. The 

benefits to pedestrians include reduced crossing distance and fewer midblock 

crossing locations, which account for more than 70 percent of pedestrian fatalities. 

(FHWA Office of Safety 2012) A Michigan study (Taylor 2004) compared beforeafter crash data for eight corridors treated with road diets and found that the 

weighted average number of crashes per year declined by 25 percent and injury 

crashes by 30 percent, but for crashes specifically involving aging drivers, the 

weighted average number of crashes per year declined by 39 percent and injury 

crashes by 48 percent.

42 High Friction Surface 

Treatments (HFSTs)

Description of Practice: Horizontal curves made up only 5 percent of the 

country’s highway miles in 2008. Yet, more than 25 percent of highway fatalities in 

the United States occur at or near horizontal curves each year. While some of the 

factors contributing to these crashes include excessive vehicle speed or distracted 

driving and driver error, at some locations, the deterioration of pavement surface 

friction may also be a contributing factor. Variable friction creates the need to 

consider pavement improvements for surface characteristics, particularly for 

friction, at certain locations in order to increase safety.

High friction surface treatments (HFSTs) are the site-specific application composed 

of “tough” polish-resistant, abrasion-resistant aggregates bonded to the pavement 

surface using a resin that restores and maintains pavement friction where the need 

for a safer pavement surface is the greatest. Maintaining the appropriate amount of 

pavement friction is critical for safe driving. Vehicles traversing horizontal curves 

require a greater side force friction, and vehicles at intersections require greater 

longitudinal force friction.

HFSTs have been used on horizontal and vertical curves, at intersections, at on 

and off-ramps, and on bridge decks. HFSTs are known to reduce crashes, have 

a significant benefit/cost ratio, are relatively low-cost compared to geometric 

improvements, are durable and long-lasting, produce negligible environmental 

impacts and have minimal impact to traffic. HFSTs have been tried and proven 

in over 40 states, and they are a recommended treatment as part of FHWA’s Every 

Day Counts initiative (FHWA, 2012). 

HFSTs can be placed manually or mechanically depending on the size of the 

project. Costs typically run $20 to $40 per square yard, depending on the size 

of the project. Friction values immediately increase with HFST and retain their 
288 Handbook for Designing Roadways for the Aging Population

CHAPTER 9—ROADWAY SEGMENTS

values over much longer time periods (7-10 years) than typical pavement mixes. 

Because HFSTs are placed on the pavement, there is seldom any need for right-ofway or environmental approvals, which lead to a quick solution at a reduced cost 

compared to geometric improvements. This in turn leads to a reduction in crashes 

and can be used proactively on other areas with similar geometrics. (ATSSA, 2013)

Anticipated Benefits to Aging Road Users: A higher friction surface amplifies 

braking and expedites the reduction in vehicle speeds, helping drivers retain 

control. Furthermore, it meets the need underscored by AASHTO’s 2011 Green 

Book to provide skid resistant pavements for wet, snow and ice covered surfaces to 

address side friction needs. While these benefits have been shown for the driving 

population as a whole, they are expected to be at least as applicable for aging 

drivers to help offset declining reaction times in steering and braking.
Handbook for Designing Roadways for the Aging Population 289

CHAPTER 10

Construction/Work Zones

The following discussion presents the rationale and supporting evidence for Handbook 

treatments pertaining to these seven proven and promising practices.

Proven Practices

43. Signing and Advance Warning

44. Portable Changeable (Variable) Message Signs

45.	 Channelization (Path Guidance)

46. Delineation of Crossovers/Alternate Travel Paths

47. Temporary Pavement Markings

Promising Practices

48. Increased Letter Height for Temporary Work Zone Signs

49. Work Zone Road Safety Audits
43 Signing and Advance Warning

290 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

Minimum requirements for safely negotiating a lane closure include an awareness 

of a decrease in pavement width ahead, and of the direction of the lateral shift in the 

travel path; a detection of traffic control devices marking the location of the lane drop 

(beginning of taper); a timely decision about the most appropriate maneuver, taking 

other nearby traffic into account; and smooth vehicle control through maneuver 

execution. In the vicinity of a lane closure, the longer the information needs supporting 

these requirements remain unmet for the least capable drivers within the traffic stream, 

the less likely is a smooth transition through the work area for all drivers (Goodwin,

1975). The more time that is required for aging drivers to prepare and initiate a merging 

maneuver, the more dense following traffic (including the adjacent lane) is likely to 

become; this, in turn, will make gap judgments and maneuver decisions at the point of a 

lane closure more difficult, and will increase the likelihood of erratic vehicle movements 

resulting in conflicts between motorists. 

Relevant alterations in aging adults’ cognitive-motor processes include: failure to use 

advance preparatory information (Botwinick, 1965); difficulty in processing stimuli that 

are spatially incompatible (Rabbitt, 1968); initiation deficit in dealing with increased 

task complexity (Jordan and Rabbitt, 1977); and inability to regulate performance speed 

(Rabbitt, 1979; Salthouse, 1979; Salthouse and Somberg, 1982). Stelmach, Goggin, and

Garcia-Colera (1987) found that older adults showed disproportionate response slowing

when compared with younger subjects, when there was low expectancy for a required 

movement. When subjects obtained full information about an upcoming response, 

reaction time (RT) was faster in all age groups. Stelmach et al. (1987) concluded that 

Table 55. Cross-references of related entries for signing and advance warning. 

Applications in Standard Reference Manuals

MUTCD

(2009)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Sect. 6C.05

Sect. 6C.06

Sects. 6F.16 & 6F.17

Sects. 6F.81 to 6F.83

Sect. 6F.61

Sect. 6F.63

Sect. 6G.04 

Sect. 6G.10

Sects. 6G.12 through 6G.19

Tables 6C-1 & 6C-3

Figs. 6H-3, 6H-5, 6H-6, 6H-10 through 6H-12, 6H15, 6H-16, 6H-18, 6H-19, & 6H-21 through 6H-46 

plus associated notes with each fig.

Pgs. V-8-V-11, Sect. on Strategy 

3.1 B1: Provide advance Warning 

Signs (T)

Pgs. V-26-V-27, Sect. on Strategy 3.1 

B11: Improve Traffic Control at Work 

Zones (T)

Pgs. 357-376, Sects. IIA through IID

Pgs. 391-392, Sect. on Older Drivers 

and Pedestrians

PROVEN PRACTICES
Handbook for Designing Roadways for the Aging Population 291

CHAPTER 10—CONSTRUCTION/WORK ZONES

aging drivers may be particularly disadvantaged when they are required to initiate a 

movement in which there is no opportunity to prepare a response. Preparatory intervals 

and length of precue viewing times are determining factors in age-related differences in 

movement preparation and planning (Goggin, Stelmach, and Amrhein, 1989). When

preparatory intervals are manipulated such that aging adults have longer stimulus 

exposure and longer intervals between stimuli, they profit from the longer inspection 

times by performing better and exhibiting less slowness of movement (Eisdorfer, 1975; 

Goggin et al., 1989). Since aging drivers benefit from longer exposure to stimuli, Winter

(1985) proposed that signs should be spaced farther apart to allow drivers enough time 

to view information and decide which action to take. Increased viewing time will reduce 

response uncertainty and decrease aging drivers’ RT.

In focus group discussions consisting of 81 drivers ages 65 to 86, pavement width 

transitions were identified as sources of difficulty by 50 percent of the participants 

(Staplin, et al., 1997). The drivers participating in these discussions suggested longer 

merging areas to give them more opportunity to find a safe gap and the use of multiple 

warning signs to allow them to plan their maneuver at an earlier point upstream. Use 

of multiple signs to give advance notice of downstream work zones and of required 

maneuvers was also offered as a desired change by aging drivers participating in an 

earlier focus group (Staplin, Lococo, and Sim, 1990). 

Lyles (1981) conducted studies on two-lane rural roads to evaluate the effectiveness of 

alternate signing sequences for providing warning to motorists of construction and 

maintenance activities that required a lane closure. The signs tested included a standard 

MUTCD warning sequence, the same sequence augmented with continuously flashing 

warning lights on the signs, and a sequence of symbol signs (WORKER and RIGHT

LANE CLOSED). The most effective sign sequence was one that was flasher augmented; 

this treatment was twice as effective as similar signs with no warning lights in slowing 

vehicles in the vicinity of the lane closure. 

The use of word messages on signs in highway work areas raises sign legibility issues 

for aging drivers. In research conducted to improve the legibility of the RIGHT/LEFT

LANE CLOSED and ROAD CONSTRUCTION series signs using test subjects in three 

age groups (18–44, 45–64, and 65 and older), Kuemmel (1992) concluded the following

for black on orange (negative contrast) signs: (1) signs that increased both letter size 

and stroke width (SW) while maintaining or increasing the standard alphabet letter 

series resulted in the best improvement; (2) increasing letter size while decreasing the 

alphabet series (e.g., from C to B) reduces sign legibility, particularly at night; (3) the use 

of letter series E, with its 21-percent increase in SW-to-letter height over 8-in series C 

letters, appears to overcome the problems of irradiation (or overglow phenomenon) with 

high intensity retroreflective materials, thus increasing night legibility; (4) the legibility 

distance of the ROAD CONSTRUCTION signs can be increased by changing the word 

“construction” to “work,” and increasing the letter size from 175-mm (7-in) series C to 

200-mm (8-in) series C; and (5) for the RIGHT LANE CLOSED series, use of symbol

signs will have to supplement word legend signs, and for the CENTER LANE CLOSED 

series, redundant signs will have to be employed if a 48-in maximum sign size is to be 

maintained. The author pointed out that the minimum required visibility distance 

(MRVD) for both signs is 331 ft at 55 mph and 369 ft at 65 mph. The legibility distances 
292 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

obtained in this study for the current standard construction work zone signs ranged from 

650 ft for the best observers to 140 ft for the worst observers. In addition, 85th percentile 

values were closer to the minimum legibility distances than they were to the maximum 

legibility distances. This finding reinforces the need for redundant signing during the 

approach to a work zone.

Several studies have centered on the use of fluorescent orange signs for work zone 

applications, particularly as their increased conspicuity may benefit aging drivers with 

diminished visual capabilities by providing longer detection distances. Jenssen, et al. 

(1996) state that fluorescent materials have the potential to increase daytime conspicuity 

through increased contrast, while the nighttime brightness is sustained through a 

microprismatic retroreflective system. Burns and Pavelka (1995) explain that the high 

visibility of fluorescent materials is due to their ability to absorb energy in the near 

ultraviolet and visible region of the electromagnetic spectrum, and then to re-emit 

the energy as longer wavelength, visible light. Conventional colorants don’t have this 

property. During the daylight hours from dawn to dusk, there is always sufficient solar 

energy to elicit light emission from fluorescent materials, irrespective of the cloud cover. 

Therefore, fluorescent colors maintain a significant daytime visibility advantage over 

ordinary colors in all types of weather. Improvements in legibility distance have also 

been found using signs with fluorescent orange microprismatic sheeting (sheeting that 

provides for high retroreflectance overall, particularly at widest available observation 

angles).

Chrysler, Carlson, and Hawkins (2002) conducted a controlled field study to determine 

nighttime sign legibility distance for small ground-mounted signs as a function of 

retroreflective sheeting type, font, and color. Study methods and results presented here 

are limited to those describing orange signs. Two font types, both using 6-in black letters 

were compared, with all signs created using 4-letter words chosen from the MUTCD. The 

baseline font was Highway Series D. D-Modified font, created for Alabama DOT for use 

on work zone signs with a thicker stroke width than Highway Series D, was also used. 

Three types of retroreflective sheeting were used: 

•	 ASTM Type III (high-intensity encapsulated lens glass bead material), orange.

•	 ASTM Type VIII (super-high-intensity microprismatic material), fluorescent

orange.

•	 ASTM Type IX (very-high-intensity microprismatic material), fluorescent orange.

Participants in the Chrysler et al. (2002) study included 12 licensed drivers ages 55 to 64 

and 12 licensed drivers ages 65 to 75, with males and females equally represented in both 

groups. Binocular acuity for 21 participants was 20/25 or better, one subject had acuity of 

20/30, one had 20/40 acuity, and one had 20/50 acuity. Subjects drove a passenger sedan 

around a closed course at 30 mph at night using low-beam headlights (HB4 halogen), 

while attempting to read ground-mounted signs on the right shoulder. Subjects were 

accompanied by an experimenter who sat in the front passenger seat. Subjects were told 

to say the word as soon as they could correctly identify it, but were also told that there 

was no penalty for being wrong, and that it was OK to guess. All signs were offset 14 ft

from the right edge line with a height of 8 ft to the center of the sign. 
Handbook for Designing Roadways for the Aging Population 293

CHAPTER 10—CONSTRUCTION/WORK ZONES

Chrysler et al. (2002) found no significant differences in legibility distance as a function 

of font type, with the mean of 160 ft for D-Modified, and a mean of 167 ft for Highway 

Series D. The difference in performance between the two microprismatic sheetings was 

not significant (Type VIII mean legibility distance = 175 ft and Type IX mean = 169 ft), 

but both produced significantly longer distances than Type III (mean = 148 ft). There 

were no significant effects of age on legibility distance for the orange signs. Based 

on their findings of superior legibility performance with fluorescent microprismatic 

sheeting, Chrysler et al. (2002) recommended its use for work zone signs over the use of 

Type III orange sheeting. They also recommended a more conservative legibility index of 

33 ft/in (in place of the standard of 40 ft/in) based on their study findings which averaged 

24 to 34 feet of legibility per inch of letter height across the 4 sheeting colors evaluated.

Jenssen et al. (1996) conducted a controlled field study using 35 younger subjects (ages 

18 to 25) and 44 older subjects (ages 55 to 75) to compare the detection distance, color 

recognition distance, and the legibility distance of fluorescent signs to traditional signs, 

under daytime and nighttime conditions. In this study, subjects sat in an open-ended 

container on a railway car that moved at a speed of 9 mph along a set of unused railroad 

tracks. Subjects used a response form and were trained to look for specific signs. They 

activated a response lever that sent a signal to a distance-measuring computer, and then 

recorded what they observed in the categories provided on their response forms for sign 

detection, shape, color, symbol, and text. The signs of interest for this discussion were 

those with an orange background and black text. 

Signs with fluorescent orange Type VII retroreflective sheeting were compared to signs 

with standard orange Type VII retroreflective sheeting, signs with standard orange Type 

III high intensity grade retroreflective sheeting, and signs with standard orange Type 

I engineering grade retroreflective sheeting. In the daytime, only signs with Type VII 

optics were used. The Norwegian town names “LENSVIK,” “LAKSVIK,” or “LEKSVIK,”

appeared in randomized order on the signs. The height, angle, and distance of the 

signs relative to the track were adjusted according to standards for Norwegian two-lane 

roadways, to ensure realistic viewing positions. Signs were always placed on the right 

side of the track. For nighttime trials, original headlights for a Volkswagen Golf type 1

vehicle (placed on the railcar at the standard vehicle headlight orientation) were used. 

Detection, shape recognition, color recognition, and content recognition were 

accomplished at significantly greater distances for fluorescent orange retroreflective signs 

than for the standard orange retroreflective signs, for both younger and older subjects 

under daytime conditions. The mean detection distance for all subjects during daytime 

conditions for the fluorescent orange retroreflective signs was 2,697 ft, compared to 

2,569 ft for standard orange retroreflective signs. This difference in detection distance 

was statistically significant. The difference in mean detection distance was larger for 

the older subjects than for the younger subjects; however, both age groups demonstrated 

significantly longer detection distances when viewing the fluorescent orange 

retroreflective signs. The mean shape recognition distance across all subjects during the 

daytime was 2,441 ft for the fluorescent orange retroreflective signs and 2,136 ft for the 

standard orange retroreflective signs. Younger subjects were able to correctly recognize 

the shape of fluorescent signs at an average distance that was 335 ft longer than for the 

standard signs, and older subjects demonstrated an average shape recognition distance 
294 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

difference of 194 ft. Fluorescent signs also showed significantly longer correct color 

recognition distances (1,916 ft across age groups) than standard signs (1,539 ft across 

age groups). Color recognition distances were 429 ft longer for younger subjects, and 

350 ft longer for older subjects when viewing the fluorescent signs during the daytime 

compared to the standard signs. In terms of legibility distances during daytime, across 

all subjects, the fluorescent signs significantly outperformed the non-fluorescent signs, 

with a difference in mean legibility distance of 43 ft.

At nighttime, there were no significant differences in detection, shape recognition, color 

recognition, or contents recognition distances between fluorescent orange retroreflective 

signs with Type VII sheeting and standard (non-fluorescent) orange retroreflective signs 

with Type VII sheeting, for either age group. However, comparisons between the three 

types of retroreflective sheeting indicated that the signs with Type VII sheeting produced 

detection distances that were 138 ft longer than the signs with high intensity grade 

sheeting, and 203 ft longer than the signs with engineering grade sheeting, for the older 

drivers. For the younger drivers, detection distances for the signs with Type VII sheeting 

were 62 ft longer than those produced by the signs with high intensity grade sheeting, and 

118 ft longer than those produced by the signs with engineering grade sheeting. 

The mean sign detection distance, shape recognition distance, color recognition distance, 

and contents recognition distance are presented in Table 56, as a function of subject age 

group and lighting condition (day vs. night) for the signs with standard orange Type VII 

sheeting and for the signs with fluorescent orange Type VII sheeting.

Burns and Pavelka (1995) conducted a field study using 14 drivers ages 19 to 57 (median 

age: 40 years), to compare the visibility and conspicuity of durable retroreflective 

Table 56. Subject performance as a function of sheeting type (fluorescent orange Type VII vs. standard 

orange Type VII), as a function of subject age group and lighting condition (Jenssen, Moen, Brekke, Augdal, 

and Sjøhaug, 1996). 

Lighting 

Condition Age Group

Sign Color 

(Type VII 

Sheeting)

Mean Distance (m)

Sign 

Detection

Shape 

Recognition

Color 

Recognition

Contents 

Recognition

Daytime

Young

Standard 

Orange 828 707 518 123

Fluorescent 

Orange 851 808 648 131

Old

Standard 

Orange 726 591 410 92

Fluorescent 

Orange 776 650 516 108

Nighttime

Young

Standard 

Orange 838 707 592 88

Fluorescent 

Orange 815 623 548 93

Old

Standard 

Orange 771 589 471 92

Fluorescent 

Orange 758 555 430 66
Handbook for Designing Roadways for the Aging Population 295

CHAPTER 10—CONSTRUCTION/WORK ZONES

fluorescent sheetings (orange, red, yellow, and yellow-green) to the same color standard 

highway sheeting (orange, red, yellow, yellow-green, and green), at midday and at dusk. 

Circular targets with an area measuring 0.01 ft2

 were viewed in pairs (one fluorescent 

and one standard highway color sign) against a 4-ft by 4-ft background. The background 

consisted of a complex camouflage pattern made up of 23 percent light green, 34 percent 

green, 25 percent brown, and 18 percent black. The targets were placed 1 ft apart, and 

were viewed at four distances during the daytime (394 ft, 295 ft, 197 ft, and 98 ft). At dusk 

(15 min before sunset, and 15 min after sunset), signs were viewed only at 98 ft. Subjects 

viewed the target pairs while seated in a vehicle that had the headlights turned off. An 

electronic shutter system provided a viewing duration of 2 s. After each target pair was 

viewed, subjects provided responses to indicate: 

1. number of targets detected (0, 1, or 2); 

2. target location (left or right); 

3. target color (left color and right color); and 

4. attention-getting value (was one target perceived more easily, or did one target 

attract your attention more than the other?).

During the daytime, the durable fluorescent targets evaluated in the Burns and Pavelka 

(1995) study were detected with a higher frequency (close to 100 percent) and at greater 

distances than the standard highway colors. At midday (facing north on an overcast day) 

from a distance of 396 ft, 93 percent of the subjects were able to detect the fluorescent 

orange targets; however, only 43 percent of the subjects could detect the standard orange 

targets at this distance under the same lighting conditions. At 90 m, 100 percent of the 

subjects detected the fluorescent signs, compared to 92 percent who detected the standard 

orange signs. At dusk (15 min after sunset) at a distance of 100 ft, the fluorescent orange 

signs were detected by 96 percent of the subjects and the standard orange signs were 

detected by 85 percent of the subjects. 

The fluorescent signs also showed greater color recognition than the standard highway 

signs at all distances. During midday (overcast facing north), the fluorescent orange signs 

were correctly identified by 61 percent of the subjects at 120 m, 58 percent of the subjects 

at 90 m, 86 percent of the subjects at 60 m, and 82 percent of the subjects at 30 m. By 

comparison, the standard orange signs were identified correctly by 7 percent, 23 percent, 

64 percent, and 93 percent of the subjects at the same distances. At dusk (15 minutes 

before sunset) at 30 m, the fluorescent orange signs were correctly identified as orange by 

74 percent of the subjects, compared to 62 percent of the subjects for the standard orange 

signs.

The fluorescent orange sign in each pair of viewings was subjectively determined to be 

more conspicuous (more attention-getting) than the standard orange highway sign, 

at 30 m, under all lighting conditions (midday, 15 min before sunset, and 15 min after 

sunset). Luminance measurements were taken of the targets and their backgrounds, so 

that a contrast ratio could be calculated. The fluorescent signs always produced a higher 

contrast ratio than the standard signs. The contrast ratios for the fluorescent orange 

and standard orange signs are shown in Table 57, under the various, natural lighting 

conditions utilized in the study.
296 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

Table 57. Luminance contrast ratio ([Lt-Lb]/Lb) under different lighting conditions, for 

fluorescent orange and standard highway orange signs (Burns and Pavelka, 1995).

Color

Sign Direction and Lighting Condition

South facing 

midday—clear

North facing 

midday—overcast

North facing 

dusk—overcast

Fluorescent Orange 5.4 4.4 1.0

Standard Orange 1.8 2.0 0.5

The authors concluded that fluorescent orange signs are more conspicuous than standard 

highway orange sign colors during the daytime (as were the other fluorescent colors); 

are detected with higher frequency; and are recognized with greater accuracy at farther 

distances. Fluorescent signs provide a greater contrast with the background scene, and 

therefore should be considered as a countermeasure to address problems that aging 

drivers have in the detection and recognition of traffic signs when viewed against a 

cluttered background.

Finally, Hummer and Scheffler (1999) conducted a field study at seven long-term work 

zones in North Carolina with left lane drops on multilane highways, to determine 

whether the increase in the conspicuity of fluorescent orange signs leads to positive 

operational changes in driver behavior. All seven sites were left lane drops on four-lane 

highways (with standard lane and shoulder widths), with the following sequence of 

orange signs (in pairs, with one sign on each side of the highway):

•	 Two fluorescent BEGIN WORK ZONE text message signs located 0.4 to 1.2 mi

from the taper.

•	 Two text message LEFT LANE CLOSED AHEAD signs located 0.25 to 0.68 mi

from the taper.

•	 Two symbol message LEFT LANE CLOSED AHEAD signs located 0.1 to 0.31 mi

from the taper.

•	 Two text message LEFT LANE CLOSED signs at the beginning of the taper.

Six sites had 55 mph speed limits and wide grassy medians, and one site had a 65 mph 

speed limit. Before the study was conducted, both treatment and control sites existed as 

work zones with standard orange signs, except for the first sign in the pair, which was 

fluorescent. In the “before” period, five operational measures were collected on this 

standard set of signs. In the “after” period, the standard orange signs were replaced with 

fluorescent signs (same size and message) at the “treatment sites,” and the same measures 

were recorded at these treatment sites, as well as at the “control sites” where the standard 

signs were left in place. Two weeks elapsed before data were collected in the “after” 

period, to eliminate novelty effects. The operational measures included: 

1. traffic conflicts (one vehicle brakes or swerves to avoid hitting another); 

2. percentage of all vehicles in the left lane; 

3. percentage of trucks in the left lane; 

4. mean speed; and 

5. speed variance. 
Handbook for Designing Roadways for the Aging Population 297

CHAPTER 10—CONSTRUCTION/WORK ZONES

These data were collected at the beginning of the taper, at the BEGIN WORK ZONE sign,

and at the midpoint of the approach.

With regard to traffic conflicts, a reduction from 153 to 136 at the treatment sites (with 

fluorescent signs) was observed in the before and after periods, respectively, while an 

increase from 160 to 187 was observed at the control sites (with standard signs) in the 

before and after periods. This reduction in conflict frequency was statistically significant, 

when sites without potential confounding factors were removed from the analysis. 

Regarding the number of vehicles in the left lane, there was a significant reduction in 

the percentage of vehicles at the midpoint of the work zone approach at the sites with 

fluorescent signs (more than a 5 percent reduction, or 100+ fewer vehicles); similarly, an 

increase in the percentage of trucks that moved out of the left lane before the midpoint 

(16 more trucks, or 30 percent more than expected) and at the taper (12 more trucks than 

expected) was observed at the sites with fluorescent signs, compared to sites with the 

standard orange signs. 

Differences in mean speeds were not statistically significant; speeds increased by 

approximately 1 mph at the midpoint and taper of treatment sites, and decreased 

by the same amounts at the control sites. However, speed variance decreased at the 

midpoint and at the taper of the treatment sites (with fluorescent signs), relative to speeds 

monitored at the control sites (with standard orange signs). 

Hummer and Scheffler (1999) state that the operational changes documented during their 

study would translate to fewer collisions in work zones that display fluorescent orange 

signs compared to those that display the standard orange signs. Although the overall 

reduction in traffic conflicts in this study was small (approximately 7 percent), they 

recommend that agencies use fluorescent orange sheeting on warning signs in work zones 

similar to those studied, as well as for work zones where warning drivers is as critical 

or more critical than it was in the current study. These would include long-term work 

zones where there is flagging, temporary traffic signals, sharp lane shifts, and changed 

merging patterns, as well as in many temporary and moving work zones. Hummer 

and Scheffler (1999) state that fluorescent orange sheeting costs only a few dollars more 

per sign installation than standard orange sheeting, and even if work zone collision 

frequencies declined by only one or two percent, the benefit-to-cost relationship would 

be substantial. 

Next, a number of studies have been performed to determine the effectiveness and 

motorist comprehension of static signs and changeable message signs (CMS’s)—also 

referred to as variable message signs (VMS’s)—for lane closures. A general indication of 

the importance of CMS’s to accomplish lane control in advance of work zones is provided 

by a field study on a four-lane section of I-35 in San Antonio conducted by Dudek, 

Richards, and Faulkner (1981) to evaluate the effects of CMS messages on lane changes 

at a work-zone lane closure. The measure of effectiveness used to evaluate the CMS was 

the percentage of vehicles that remained in the closed (median) lane as traffic progressed 

toward the cone taper. The results indicated that the CMS did encourage drivers to vacate 

or avoid the closed lane, compared with driver responses at the same site without use of 

the CMS. The percent volumes in the closed lane were significantly lower when a lane-
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closure message was displayed than during periods when the sign was blank. Specifically, 

there was a 46 percent greater reduction in the lane volume attributable to the CMS.

During the conduct of field studies for NCHRP project 3-21(2), the relative proportions 

of traffic in the through and closed lanes approaching construction lane closures were 

observed for a sample of more than 196,500 vehicles (Transportation Research Board, 

1981). Data gathered in Georgia, Colorado, and California were used to compare these

lane distributions between baseline (no CMS) conditions and various CMS applications. 

A fourth data set, gathered in South Carolina, was used to determine relative effects 

between certain CMS message alternatives (i.e., speed and closure, speed and merge, 

closure and merge advisories), and various placement configurations (i.e., one CMS at 

2,000 ft in advance; or one CMS at 3,960-ft advance placement; or two CMS devices, one 

at each advance location; or one CMS placed at 3,960 ft in advance of the taper and an 

additional arrow panel at the 2,000-ft location). Findings indicated increased preparatory 

lane change activity, smoother lane-change profiles, and significantly fewer “late exits” 

(exit from a closed lane within 100 ft of closure) in locations where a CMS was applied at 

the 3,960-ft advance location and an arrow panel at the 2,000-ft location. 

Additional studies of flashing arrow panels at construction sites have shown that they are 

effective in shifting approaching traffic out of a closed lane (Bates, 1974; Shah and Ray, 

1976; Graham, Migletz, and Glennon, 1978; Bryden, 1979; Faulkner and Dudek, 1981). 

These studies found that arrow panels were effective because they promote early merging 

into the open lane and fewer vehicles remained in the closed lane at the start of the laneclosure taper. A basis thus exists to assert that a CMS used to give advance notice of 

the need to exit a lane, followed by the application of an arrow panel, would be of clear 

benefit to drivers with diminished capabilities resulting from aging, inattentiveness, or 

transient impairment (e.g., due to fatigue, alcohol, or drugs). While the specific location 

of the arrow panel in this approach should be consistent with the signing sequence 

indicated in the MUTCD Part 6H (Figure 6H-33 for divided highways), placement at the 

beginning of the taper is suggested by the findings reported above.

Mace, Finkle, and Pennak (1996) conducted a static and a dynamic field study to 

determine the minimum and optimum lamp intensities needed for arrow panel legibility 

(left arrow or chevron vs. right arrow or chevron presentation) during the day, and 

minimum and maximum intensity for nighttime operations to minimize glare effects. 

The authors cite the work of Faulkner and Dudek (1982), who found that sight distances 

to arrow panels (AP’s) influences driver behavior, such that when AP’s are used too far 

in advance of a lane closure, (e.g., 4,000 ft, drivers tend to return to a vacated lane. Also, 

if sight distance is less than 1,500 ft, an advance supplemental AP is desirable. While no 

data exist to document problems in the safe use of AP’s by aging drivers, the following 

recommendations (see Table 58) suggested by Mace et al. (1996) for arrow panel lamp 

intensity provide a useful reference for practitioners. These values ensure visibility for 

DSD’s of 1,500 and 930 ft, for high-speed and low-speed roadways, respectively. 
Handbook for Designing Roadways for the Aging Population 299

CHAPTER 10—CONSTRUCTION/WORK ZONES

Table 58. Recommended minimum on- and off-axis lamp intensities of arrow panels to ensure 

daytime visibility by aging drivers, and the maximum intensity recommended for nighttime 

operations to ensure safe levels of discomfort and disability glare for aging drivers, for highspeed (≥45 mph) and low-speed (<45 mph) roadways (Mace, Finkle, and Pennak, 1996).

Situation Luminous Intensity Requirements (cd per lamp)

Minimum On-Axis Minimum Off-Axis Maximum Hot Spot

Low-Speed Day 300 60 n/a

High-Speed Day 500 100 n/a

Low-Speed Night 90 18 370

High-Speed Night 150 30 370

A questionnaire also was completed during the conduct of NCHRP Project 3-21(2), by 

489 subjects ranging in age from under 20 to 80 to gather measures of driver detection, 

recognition, and comprehension of the CMS devices. Twenty percent of the drivers were 

age 60 and older. Five tested message conditions were: 

1.	 speed and closure advisory (MAX SPEED 45 MPH/RIGHT LANE CLOSED);

2.	 speed and merge advisory (MAX SPEED 45 MPH/MERGE LEFT);

3.	 merge and closure advisory (RIGHT LANE CLOSED/MERGE LEFT);

4. speed advisory only (SLOW TO 45 MPH); and 

5.	 closure advisory only (RIGHT LANE CLOSED AHEAD). 

Drivers consistently reported that the speed advisory and lane closure message 

combination was most helpful, was the easiest to read, best met their information needs, 

and would be most likely to cause them to change lanes early and reduce speed.

A human factors laboratory study was conducted to determine which CMS message 

alternatives would be most likely to enhance motorists’ compliance with lane control 

messages in work zones (Gish, 1995). The subjects were divided into two age groups

consisting of 24 subjects each: the youngest drivers had a mean age of 23.1 years (range: 

16–33), and the oldest drivers had a mean age of 70.2 years (range: 65–84). The results of 

this study indicated that older drivers were more likely to reduce their speed and change 

lanes than the younger drivers, and that both older and younger drivers’ compliance 

with lane-change messages was strongly influenced by surrounding vehicles and by the 

visibility of the lane closures themselves, which exerts a strong influence on message 

credibility. Other factors, such as traffic density, static displays, and merge arrows 

(arrow panels), influence driver compliance with CMS messages. To optimize lanechange compliance, Gish (1995) recommended that static displays, merge arrows, and

other devices be used in addition to CMS messages. A need to study the long-term 

effectiveness on nonstandard messages was also indicated, and potential improvements 

in work-zone safety and operations through the use of condition-responsive (real-time) 

traffic control systems that provide continuously updated information to motorists (for 

enhanced credibility) were identified.
44 Portable Changeable 

(Variable) Message Signs

300 Handbook for Designing Roadways for the Aging Population

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The effectiveness of changeable message signs (CMSs), gauged in terms of observable 

driver behaviors that traffic management procedures are designed to elicit, rests upon a 

set of reasonably well-understood human factors. A motorist information system must 

be rational, relevant, and reliable. Driver sensory/perceptual and cognitive capabilities 

must be thoughtfully considered to ensure that a message will be acquired and then 

understood, recalled, and applied by the driver within a desired timeframe; the message 

must seem to clearly apply to the driver and to reflect current conditions to be credible; 

and it must be accurate in describing what the driver experiences downstream. The 

credibility of a highway advisory message certainly depends in part upon a presentation 

strategy that is “rational,” but it also must be perceived to be relevant to the individual 

motorist, and reliable to the point of being virtually error-free. Reliability requirements—

being dependent on real-time data on operations as input to the traffic control system—

are most difficult to meet, but probably the most important if high rates of compliance in 

drivers’ vehicle control decisions are ever to be realized. 

A motorist’s ability to use highway information is governed by: (1) information 

acquisition, or how well the source can be seen or heard; and (2) information processing, 

or the speed and accuracy with which the message content can be understood, and its 

ease of recall by the motorist after message presentation is completed. 

In the acquisition of CMS information, a visual task, the key factors are: (1) its 

conspicuity, or “attention-getting value” to the motorist; (2) the size, brightness (contrast), 

stroke width-to-height ratio, and spacing of individual characters of text, which together 

determine the legibility of the message; (3) the placement of the CMS device—overhead 

versus one side versus both sides of the highway—which affects its likelihood of being 

blocked from a motorist’s view by other vehicles, as well as the “eyes away from the road” 

time required to fixate upon the message; and (4) the exposure time, or available viewing 

time, of each message phase presented on a CMS.

Conspicuity is generally not a problem for any type of CMS under low-traffic volumes, 

although under high volumes with a significant mix of heavy vehicles, a motorist may 

fail to notice a roadside device because of obscuration. Good conspicuity is achieved

by overhead devices under all conditions. While the attention value of a CMS display 

Table 59. Cross-references of related entries for portable changeable (variable) message signs.

Applications in Standard Reference Manuals

MUTCD

(2009)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Chapter 2L

Sects. 6F.60 & 6F.61

Figs. 6H-4, 6H-17, 6H-22, 6H-23, 6H-24, 6H-30 

through 6H-35, 6H-37 through 6H-39, 6H-42, & 

6H-44 plus associated notes with each fig.

Pgs. V-26-V-27, Sect. on Strategy 

3.1 B11: Improve Traffic Control at 

Work Zones (T)

Pg. 368, Para. 7

Pg. 371, Sect. on Changeable 

Message Signs
Handbook for Designing Roadways for the Aging Population 301

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can be maximized by flashing operations, research by Dudek et al. (2006) indicates 

this strategy may detract from message comprehension, and is thus discouraged as a 

standard operating procedure. In rare circumstances, for a unit of information deemed 

particularly critical by the highway authority, the flashing of a single text element within 

a message at a slow rate may be justified. Also, if the CMS in question always has some 

type of message displayed, then slowly flashing (e.g., two cycles per phase) the problem 

statement line only may be warranted to attract attention. A preferred strategy under 

such circumstances would be to activate a flashing warning light separate from, though 

clearly attached to, the CMS.

If it is standard policy to leave the signs blank, then the mere display of a message will 

capture the driver’s attention, without the need to resort to flashing elements. Indeed, 

driving simulator study findings argue against the use of flashing message elements on 

CMS’s with rare exceptions, as noted above (Dudek, Schrock, Ullman, and Chrysler, 

2006). By extension, the use of these devices to display any content except highway safety 

advisories or traffic control messages should be universally prohibited. 

The legibility of a CMS is influenced by the same factors influencing character and 

message legibility of static signs, including the key factor of driver visual performance 

capability. Letter acuity declines during adulthood (Pitts, 1982) and aging adults’ loss in 

acuity is accentuated under conditions of low contrast, low luminance, and where there 

is crowding of visual contours (Sloane, Owsley, Nash, and Helms, 1987; Adams, Wong, 

Wong, and Gould, 1988). In any event, the legibility for current CMS’s is determined

primarily by the technology and the device configuration (numbers of rows, characters 

per row, and number, size, and spacing of pixels per character) as fabricated by a given 

manufacturer, and for all practical purposes can be treated as a fixed factor—modified 

by environmental considerations—in considering whether a particular system as 

implemented in the field will meet motorists’ needs.

For any given speed, aging drivers’ needs dictate a legibility distance that permits the 

entire CMS message to be read twice in its entirety. As a general rule, at least 1,000 ft 

of legibility distance for a motorist with 20/40 visual acuity should be provided on a 55 

mph facility. Of the studies that assessed various character matrix forms (number of 

elements per character cell), most found a 7 x 9 element matrix to be necessary when 

using lowercase letters, because of the descenders and ascenders, but a 5 x 7 font was 

generally deemed acceptable with uppercase-only lettering. The MUTCD recommends 

a minimum legibility requirement of 0.5 mi for trailer– or large-truck-mounted Portable 

Changeable Message Signs, and a minimum letter height of 18 in (Section 6F.60). Given

that the most common format for a portable sign is 18-in tall characters arranged in 

three lines of eight characters, this provides for a legibility distance of 147 ft/in of letter 

height. The MUTCD provides for the use of smaller letter heights (minimum of 10 in) 

on CMSs mounted on service patrol trucks, provided that the message is legible from 

at least 650 ft. This provides for a legibility distance of 65 ft/in. Other variables found 

to significantly affect CMS legibility for aging observers are font, letter width-to-height 

ratio, contrast orientation, letter height, case, and stroke width (Jenkins, 1991; Mace, 

Garvey, and Heckard, 1994). The most consistent finding across studies evaluating

CMS design elements was that the results found for aging drivers were quantitatively 

but not qualitatively different from those of their younger counterparts. That is, if a 
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manipulation of a variable resulted in an improved score for younger observers, it almost 

invariably improved aging observer performance.

Garvey and Mace (1996) conducted several laboratory and controlled field studies to

determine optimum legibility requirements of CMS’s, particularly for aging drivers. The 

laboratory studies included 24 “young” subjects ages 16 to 40 (mean age: 26.6); 25 “old” 

subjects ages 62 to 73 (mean age: 67.9); and 21 “old-old” subjects age 74 and older (mean 

age: 77.2). The first laboratory study used a CMS simulator that was programmed on a 

PC, simulating nighttime viewing conditions. Only positive contrast signs (light letters 

against a dark background) were used. The objectives were: (1) to determine the optimum 

width-to-height ratio (W:H) and stroke-width-to height ratio (SW:H); (2) to identify the 

CMS font that produced the smallest size legibility thresholds; and (3) to determine the 

effect of color on legibility. Six different sizes of each sign were evaluated. The dependent 

variable in the study was the threshold size at which a character became legible, which 

was converted into a legibility index (LI) reported in ft/in (m/cm). Seven combinations 

of CMS matrix size, W:H, and SW:H combinations were evaluated to determine the 

optimum character legibility, as shown in Table 60.

Results indicated that for all conditions, the younger group performed significantly better 

(smaller letter size required for legibility) than both older groups, and the “old” group 

performed better than the “old-old” group. The authors indicated that, generally, what 

worked well for one age group worked well for all ages. Across all age groups, increasing 

the width-to-height ratio (W:H) of a character from 0.7 to 1.0 increased the legibility 

index (LI) by 7 ft/in. This provides an advantage of 38 meters of legibility for the wider 

letter when using an 18 in letter height, or 1.5 s at 55 mph. A significant stroke-widthto height (SW:H) effect was also found. For the narrow letters (W:H = 0.8), a thinner 

stroke performed better than a wider stroke by 5 ft/in. This effect was not significant 

with wider letters. There were no significant differences in legibility index as a function 

of matrix density. Therefore, for uppercase 

letters, increasing the number of elements 

beyond the standard 5 x 7 format did not 

improve legibility. The authors state that 

a typical CMS font with a W:H of 1.0 and 

a SW:H of 0.13 is optimal for the three age 

groups studied, from the median to the 85th 

percentile observer. Their data indicate that 

the 85th percentile old-old observer was 

capable of reading such a letter at the LI 

typically expected of CMS’s (35 ft/in).

In another laboratory study using the same 

subjects and test apparatus, Garvey and

Mace (1996) found that the fonts typically used by CMS manufacturers performed well, 

with the exception of “double stroke” characters within a 5 x 7 character matrix. A 

double-stroke font provided a LI of 43 ft/in for young observers compared to 57 ft/in 

for the typical CMS font. For old-old observers, the double stroke font provided a LI of 

32 ft/in compared to the typical CMS font that provided 38 ft/in. Across all age groups, 

the double-stroke font resulted in a decrement in LI of 10 ft/in.

Table 60. Variables evaluated by Garvey and Mace (1996) using a 

CMS simulator to determine the optimum character legibility.

Matrix 

Size

Width-to-Height Ratio 

(W:H)

Stroke-Width-to-Height 

Ratio (SW:H)

5 x 7 1.0 0.13

5 x 7 0.8 0.13

5 x 7 0.7 0.13

15 x 15 1.0 0.13

15 x 15 1.0 0.20

12 x 15 0.8 0.13

12 x 15 0.8 0.20
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CHAPTER 10—CONSTRUCTION/WORK ZONES

In the final laboratory study of CMS character legibility, Garvey and Mace (1996) found

significant effects of contrast orientation on letter legibility. Positive-contrast stimuli 

(lighter colored letters on a dark background) produced a LI of 12 ft/in higher than 

negative-contrast stimuli (dark letters on a lighter background). This improvement is 

equal to an additional 220 ft of legibility distance for an 18-in letter height, or 2.75 s at 

55 mph. White-on-black signs performed similarly to yellow-on-black signs, except 

for the highest-percentile old-old group, where yellow-on-black signs were significantly 

better than white-on-black. Red-on-black signs performed as well as the other two 

colors for the young observers, but were found to be significantly less legible than 

yellow or white on black signs for both groups of older observers. The authors point 

out that the reduced performance of the color red for aging subjects is likely due to its 

lower luminance, and as people age, they become more sensitive to changes in target 

luminance. The obtained LI by sign color and observer age and percentile is shown in 

Table 61.

In a dynamic field study, Garvey and Mace (1996) employed older and younger drivers

to evaluate legibility distance and detection distance of six portable CMS’s. Participants 

included 33 “young” subjects ages 19 to 40; 25 “old” subjects ages 59 to 72; and 26 “oldold” subjects ages 73 to 82. Other independent variables included contrast orientation 

(positive or negative); character height (18 in or 42 in); lighting condition (backlit, 

frontlit, overcast, or rain); character luminance—day (350, 570, 850, or 1,200 cd/m2

); 

character luminance—night (30, 80, 130, 200, 570, 1,200 cd/m2

); inter-letter spacing—

night (single or double); and sign lighting—night (internal vs. external or backlight vs. 

LED).

Table 61. Legibility index obtained by Garvey and Mace (1996) in a laboratory study of 

CMS character legibility, as a function of driver age, sign color, and percent of drivers 

accommodated.

Driver Age

Percent 

Accommodated

Legibility Index (ft/in)

Yellow on 

Black

White on 

Black

Red on 

Black

16-40

50 61.6 61.6 63.3

75 58.3 55.0 56.6

85 48.3 51.6 53.3

90 45.0 45.0 46.6

95 40.0 43.3 35.0

62-73

50 53.3 55.0 48.3

75 48.3 50.0 40.0

85 46.6 43.3 38.2

90 43.3 43.3 38.2

95 35.0 41.6 31.6

74+

50 45.0 45.0 40.0

75 41.6 38.2 33.3

85 40.0 33.3 30.0

90 35.0 31.6 28.3

95 30.0 30.0 30.0
304 Handbook for Designing Roadways for the Aging Population

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Significant findings in the field study included the following:

•	 At night, positive contrast messages (yellow on black) produced significantly longer

legibility distances, representing a 29 percent improvement over negative contrast 

messages (black on yellow). The mean legibility distance for positive contrast 

messages was 497 ft, and the mean legibility distance for negative contrast messages 

was 386 ft. The “old-old” group showed significantly shorter legibility distances 

compared to the “young” and “old” groups, which were not significantly different 

from one another. 

•	 Increasing luminance during daytime up to 850 cd/m2 produced significantly 

longer legibility distances; however, increasing the luminance from 850 to 

1,200 cd/m2

 did not significantly increase legibility distance. At night, the effects 

of increasing luminance were random, with the lowest and highest luminances 

both producing legibility distances of approximately 800 ft. Also, there was 

no significant interaction between character luminance and age group. Note: 

Important guidance on procedures for valid measurement of CMS character 

luminance is provided by Garvey and Mace (1996).

Next, the “target value,” legibility, and viewing comfort of light-emitting diodes (LEDs) 

and fiber-optic CMS technologies were compared with flip-disk and conventional 

overhead guide signs in a field study conducted by Upchurch, et al. (1991). Younger (ages 

18 to 31) and older (ages 60 to 79) subjects in this study demonstrated mean daytime target 

values for fiber-optic, LED, and flip-disk technologies that all were significantly better 

(longer) than the values for conventional overhead signs. Under nighttime conditions, 

however, the poorest performance (shortest distances) was demonstrated by both age 

groups for the flip-disk technology, falling below the conventional sign values as well. 

The fiber-optic and LED signs again exceeded the conventional signs, based on nighttime 

mean target value, with the fiber-optic technology showing a slight superiority for aging 

drivers. Under backlight (sun behind sign) and washout (sun behind driver) conditions, 

target values for all sign types decreased substantially and the differences among 

sign types diminished, but the fiber-optic technology still resulted in the best overall 

performance, across age groups.

Legibility distance results tended to favor the conventional signs, followed by the fiberoptic signs, LED signs, and flip-disk technology. Mean daytime legibility distances for 

each sign type in this study were as follows: fiber-optic—61 ft/in; LED—42 ft/in; flipdisk—39 ft/in and conventional—88 ft/in. Under nighttime conditions, the conventional 

signs again could be read at the longest mean distances, followed closely by the fiberoptic and LED signs, with the flip-disk technology showing the poorest performance. 

Backlight conditions favored the fiber-optic technology, and washout conditions favored 

the conventional signs; in both cases, however, the flip-disk technology resulted in the 

shortest legibility distances. Using a threshold for minimal acceptable legibility distance 

of 628 ft, the study concluded that flip-disk signs are deficient under all conditions except 

midday daytime viewing, LED signs are deficient under both backlight and washout 

sun conditions, and fiber-optic signs are deficient only with the sun glare present under 

backlight conditions.

Mean discomfort ratings were consistent with these patterns of results. Fiber-optic and 
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conventional signs were assigned the best (lowest discomfort) ratings under daytime 

conditions, by younger and older drivers alike. LED signs caused slightly more 

discomfort for aging subjects, and flip-disk signs resulted in the highest discomfort 

ratings, especially for aging drivers. Under nighttime conditions, only the flip-disk 

technology resulted in high discomfort ratings. Discomfort ratings were more even, and 

much higher, across sign types under backlight conditions where the sun was behind the 

sign, though flip-disk signs still were rated the worst by both age groups. Under washout 

conditions, subjects reported little discomfort for either the fiber-optic or conventional 

signs, but much greater and roughly equivalent levels of discomfort with the LED and 

flip-disk technologies.

Table 62 contains legibility distances from the Upchurch et al. (1991) study. For aging 

drivers, the legibility distances are lower due to the well-documented degradation of 

visual performance with age. Unfortunately, this is the only study that has assessed 

legibility distances for aging observers. The legibility distances for conventional bulb 

matrix and LED/flip-disk hybrid CMS’s were estimated from the results of the Upchurch 

data and data cited in Dudek (1991).

Table 62. Day and night predicted legibility distances for various sign technologies (Upchurch 

et al., 1991).

Sign Technology 

(Character Height)

Daytime Legibility Distances Nighttime Legibility 

Distances

Younger 

Observers

Older 

Observers

Younger 

Observers

Older 

Observers

Fiber-optic 

16 in 1,006 ft 959 ft 687 ft 667 ft

Light-emitting diodes 

17.8 in * 812 ft 681 ft 794 ft 602 ft

Flip-disk 

18 in 731 ft 667 ft 363 ft 348 ft

Bulb matrix 

18 in 800 ft 671 ft 750 ft 569 ft

Hybrid LED/flip-disk 

18 in 731 ft 667 ft 794 ft 602 ft

* Legibility distance of this technology decreases over time, because as LED’s age, they become less bright. 

The aging driver legibility distances in Table 62 should be assumed to represent the 

legibility distances for the various types of technology represented. This ensures that the 

needs of aging drivers have been met. The results suggest that flip-disk CMS’s should not 

be used at night along roadways where average speeds reach or exceed about 55 mph. 

Although the bulb matrix CMS was assessed by Upchurch et al. (1991), no legibility 

distances for that sign were reported. Legibility distances for this type of CMS have 

been obtained; however, it is unknown whether any aging observers have been used in 

assessing legibility distances. Dudek (1991) cited a study in which bulb matrix CMS’s 

provided legibility distances of 800 ft during the day and 750 ft at night. These distances 

are similar to the legibility distances obtained by Upchurch et al. (1991) for LED-type 

CMS’s using younger observers. Until psychophysical data can be obtained for aging 

observers viewing bulb matrix signs, the legibility distances for aging observers are 
306 Handbook for Designing Roadways for the Aging Population

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assumed to be roughly 671 ft during the day and 569 ft at night. These estimates are 

based on applying the ratio of older-to-younger legibility distances for the LED-type 

display. 

There are also a number of hybrid CMS’s that were not included in the Upchurch et al. 

study. Hybrid CMS’s apply various combinations of sign technologies listed in Table 62 

within a single sign. Product literature for one manufacturer’s hybrid LED/flip-disk 

sign states that the sign provides 900 ft of legibility distance during the day and greater 

than 900 ft at night, using character heights of 18 in. Unfortunately, the methods used 

to obtain these legibility distances are unknown. Since the sign uses the reflective flipdisk technology during daytime and the LED’s at night, the legibility distances for aging 

observers for the daytime flip-disk in Table 62 (667 ft) should be used as a more realistic 

estimate of legibility distance with LED/flip-disk hybrids. For nighttime viewing, use the 

nighttime LED legibility distance (602 feet) in Table 62. 

CMS placement affects information acquisition under heavy traffic conditions where 

a center lane driver’s view of a roadside device may be obscured for lengthy intervals. 

If a facility has more than two lanes, a consideration may be given to placement of a 

portable CMS in the median—space permitting and where glare from opposing vehicles 

is absent or minimal due to a large glare angle—rather than on the right shoulder, since 

lane control practices for heavy trucks are common throughout many corridors. Aging 

drivers participating in focus groups have reported difficulty seeing portable changeable 

message signs positioned on the shoulders of multilane roadways, unless they are driving 

in the right lane. This suggests that signs be elevated as high as possible so that they 

can be seen across multiple lanes of traffic, and that multiple CMS’s be used with the 

same message — the first to attract attention, and the second further downstream to 

communicate the message (Kihl, 2005; Kihl, et al., 2004).

A motorist’s reading time for a CMS message dictates the required exposure time at a 

given speed. Exposure time is the length of time a driver is within the legibility distance 

of the message. The minimum recommended exposure time per page (phase) for a threeline CMS is 3 s, aside from a consideration of any particular set of driver characteristics. 

However, while some jurisdictions have selected briefer exposure times, the increasing 

numbers of aging drivers on limited-access highways makes an even stronger case for the 

3 s minimum per page. Reading time is the time it actually takes a driver to read a sign 

message. In instrumented vehicle studies conducted in light traffic with familiar drivers 

on a rural freeway, reading times averaged 1 to 1.5 s per unit of information (Mast and 

Ballas, 1976). Reading times under “loaded” driving conditions would be higher, such 

as under extreme geometry, heavy traffic volumes, large volume of truck traffic, traffic 

conflicts, or poor climatological conditions. Field research using unfamiliar drivers has 

indicated that a minimum exposure time of 1 s per short word (four to eight characters) 

or 2 s per unit of information, whichever is larger, should be used (Carvell, Turner, and 

Dudek, 1978; Messer, Stockton, and Mounce, 1978; Weaver, et al., 1978; Dudek, et al., 

1981). A unit of information is a data item given in a message, which can answer one of 

the following questions: (1) what happened? (2) where? (3) what is the effect on traffic? 

(4) for whom is the advisory intended? and (5) what driver action is advised? Thus, the 

exposure time for a three-line message could vary from 3 s to as much as 6 s, with each 
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phase of a portable CMS at the lower end of this range and with each permanent CMS 

phase (page) at the upper end, due to differences in the number of characters per line. 

Reducing the exposure time per phase is warranted only when information is being 

repeated. For example, a three-line message may be displayed for only 2.5 s if it is a 

second phase of a two-phase message which repeats one or two lines from the first phase. 

If the second phase presents new information, the recommended minimum exposure 

time for both phases remains 3 s. 

For a given operating speed, exposure will increase with increasing legibility distance. 

For example, an overhead sign message that is legible at 650 ft will be exposed to drivers 

traveling at 55 mph for approximately 8 s. With a legibility distance of 1,000 ft, the 

message will be exposed for about 12 s. Permanent CMSs generally have legibility 

distances in the higher range of 900–1,200 ft. However, there is a point at which a sign 

becomes unreadable during a driver’s approach to a CMS, which reduces the legibility 

distance, particularly for side-mounted CMSs. This unreadable distance, which is 

dependent on the number of lanes and the sign technology, as well as how far the sign 

is set back from the roadway edge or how high above the roadway it is mounted, ranges 

from 280 ft to 420 ft. In an existing system, therefore, required exposure times dictate 

the maximum length of message that can be displayed, and in all cases, it is desirable that 

motorists be able to read the entire message on an (unobstructed) CMS twice.

The calculated maximum exposure duration of a message should not exceed 9 s. For 

two-phase messages, a separate requirement is needed to meet the needs of drivers. In 

this case, 3 s is added to the required exposure time because of the asynchrony between 

the time the driver can read the CMS and the onset of CMS phase displayed. In other 

words, the phase that the driver reads initially may have already been displayed for 2 s 

by the time he or she can read it. Thus, the driver will not have enough time to read this 

phase and will need to view that phase again. The net result is that 3 s needs to be added 

to the required exposure time to allow drivers to read the phase that first came into view 

a second time. Since the maximum recommended exposure time is 9 s, only 6 s of actual 

message reading time is allowed on a two-phase CMS, whereas the full 9 s can be used for 

a single-phase message. The important point here is that single-phase messages can more 

efficiently convey information to drivers. When use of a single-phase CMS is not possible 

because of message length, multiple devices with a single phase on each device will be 

superior to multiple phases on a single device. Part 6 of the 2009 MUTCD (Section 6F.60) 

states that when multiple portable changeable message signs are needed, they should be 

placed on the same side of the roadway and they should be separated from each other by 

a distance of at least 1,000 feet on freeways and expressways, and by a distance of at least 

500 feet on other types of highways.

For these reasons, the maximum number of phases used to display a message on a 

permanent CMS should be two. The most effective format for CMS message presentation 

is a single phase which consists of a maximum of three units of information, but if 

two phases are required, each should be worded so that it can stand alone and still be 

understood. Portable CMS devices, though limited to fewer characters per line, should 

also be restricted to two phases. At high speeds (55 mph), a driver may only have 2.8 to 

4.6 s to read a message on a side-mounted CMS, depending on the available legibility 

distance. For this reason, messages should be restricted to one phase at high speeds. 
308 Handbook for Designing Roadways for the Aging Population

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Recommendations against the use of flashing messages and message elements have 

been made, based on the findings of a driving simulator study using older and younger 

drivers (Dudek, et al., 2006). In this study, 64 drivers ages 18 to 80 viewed CMS messages 

presented on the right side of a simulated roadway, while following a lead vehicle that 

varied its speed before, during, and after the display of a CMS, as well as at times when 

there was no CMS. One-phase, three-line messages were presented on the CMS in 

one of three formats: 1) all three lines flashing; (2) flashing the top line of a three-line 

message; and (3) all three lines static. The flash rate for the dynamic messages was 1.5 s 

on and 0.5 s off. There were no significant differences in average reading time between 

signs with all three lines flashing (7.2 s) and static messages (7.2 s), but average reading 

time for messages where the top line flashed were significantly longer than for static 

messages (7.8 s vs. 7.1 s). Comprehension for three-line flashing messages was lower (but 

not significantly) than for three-line static messages, for subjects’ first exposure to the 

flashing display, which suggests that flashing all three lines may have an adverse effect on 

drivers unfamiliar with this mode of CMS display. Comprehension was even lower on 

signs where only the top line flashed, but the differences were not statistically significant. 

Significantly more participants preferred the static message over the three-line flashing 

message (60% to 40%). The most common reason cited by participants who preferred the 

flashing mode was that it caught their attention. The most common reason for those who 

preferred a static message was that it gave the driver more time to read the message and 

was easier to read. Participants were evenly split (50-50) in their preference for three-line 

static vs. first line flashing on a three-line message, but opponents of the first-line flashing 

message indicated that the flashing line was distracting. There were no significant 

differences in driver performance measures collected in the simulator (e.g., acceleration 

noise, lane positioning, or headway) as a function of message display format. There were 

no age effects on reading time, message comprehension, display preference, or driver 

performance.

The motorist’s need for rapid understanding and integration of message components 

also focuses attention on the formatting of multiword text displays. The main concern 

is with “units of information” (i.e., where and how to divide phrases) and with the use of 

abbreviations and contractions in CMS messages. These formatting issues are discussed 

below.

Work zones constitute driving situations that require a high amount of controlled 

processing, and data show that cognitive ability scores that measure processing efficiency 

decline with age (Ackerman, 1987). In fact, sensory memory, working memory, and 

divided attention all show a decline with aging and must be considered in the display 

of messages on CMSs. This reinforces the conclusion that a message should be limited 

to a single phase, or certainty no more than two, because multiple phases will interfere 

with message comprehension. There is also considerable evidence that aging adults have 

poorer working memory function than younger adults (Salthouse, 1991; Salthouse and 

Babcock, 1991). This indicates that message length should be limited to the fewest, most 

relevant units possible.

Finally, aging adults are particularly disadvantaged when they are required to use 

working memory to manage multiple tasks (Ponds, Brouwer, and van Wolffelaar, 1988). 
Handbook for Designing Roadways for the Aging Population 309

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Van Wolffelaar, Brouwer, and Rothengatter (1990) found that there is a disproportionately 

greater problem for aging adults in divided attention situations and directly linked this to 

a higher crash rate for aging adults in time-pressured, complex traffic situations.

The minimum required information for traffic management includes: (1) a statement of 

the problem; and (2) the action statement(s) (i.e., a driver needs to know what to do and 

one good reason for doing it). Additional elements are included as needed for a specific 

situation. The key here is not to burden the driver with unnecessary information. Only 

about two-thirds of drivers are able to recall completely four pieces of information 

(problem, effect, attention, and action); however, 80–90 percent can recall the action 

message (Huchingson, Koppa, and Dudek, 1978). Two problems in message presentation

must be avoided: (1) providing too much information in too short a time; and (2) 

providing ambiguous information that leaves either the intent of the message or the 

desired driver response uncertain.

The first problem does not refer solely to reading time difficulties, as discussed above; 

instead, it refers to the number of ideas, or “information units,” contained in a message. 

Certainly, the number of words displayed on a sign is important, but so is the manner 

in which words are grouped. Units containing one word (DELAY), two words (DELAY 

AHEAD), or many words (MAJOR DELAY AT HIGH STREET) are equally difficult to

remember when the display is no longer in sight. However, a series of, say, six units of 

information in a message displayed on a permanent CMS will be easier to remember if 

presented in two phases of three units each than if all six units are presented on a single 

phase. Studies have concluded that no more than three units of information should be 

displayed on one sequence when all three units must be recalled by drivers (Huchingson 

et al., 1978; Dudek et al., 1981; Gish, 1995).

Gish (1995) conducted a human factors laboratory study addressing the perceived

timeliness, accuracy, and credibility of CMS messages using both younger (ages 16 to 

33) and older (ages 65 to 84) test subjects. Results showed that correct recall of the first 

CMS phase (a downstream speed advisory) was nearly 100 percent for both age groups. 

However, successive phases of information (containing downstream delay and route 

diversion information) were recalled less accurately. For the delay information (second 

phase), correct recall for the younger subjects was about 82 percent, versus 60 percent 

for the older subjects. For route numbers (third phase), correct recall was 55 percent for 

the younger subjects and 19 percent for older subjects. These results reinforce the earlier 

recommendation that a maximum of two phases should be used.

Aging drivers participating in focus groups stated that CMS’s with multiple phases were 

difficult, if not impossible to read. They stated that even when there was enough time to 

read two phases, once both were read, it was easy to forget what the first phase indicated 

(Kihl, 2005). Further, these focus group participants indicated that there was no need to

offer explanations on the signs; just provide direction to the driver.

When a message must be divided into two phases, it is desirable to repeat key words from 

the first phase on the second phase, to provide assurance that all drivers see the message 

at least once. This also allows information rehearsal, as provided by an additional 

“learning trial,” which will facilitate message recall when the device is no longer in sight. 
310 Handbook for Designing Roadways for the Aging Population

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A recommended standard practice is therefore to put the problem on line 1, the location 

on line 2, and alternate either the effect and action or diversion information on line three, 

repeating lines 1 and 2 on both phases.

The second type of problem can occur when an unfamiliar word or abbreviation is 

used, when a word is hyphenated or a phrase is divided inappropriately, or when an 

abbreviation or a word can mean different things in different word pairings or contexts. 

Ambiguity occurs, for example, when CENTER LANE is used on a freeway with four 

or more lanes in one direction. Another example is the use of LANE CLOSED versus 

LANE BLOCKED, to denote a prolonged closure for construction/maintenance versus

a temporary blockage due to a crash or stall. To foster the most simple and consistent 

practice for motorists, LANE CLOSED is recommended under both roadwork and 

incident conditions, because at the time the message is displayed, the lane is effectively 

closed. Finally, neither FREEWAY BLOCKED nor FREEWAY CLOSED should ever be

used when at least one lane is open to traffic.

Abbreviations also have the potential to be misunderstood by some percentage of 

drivers, exacerbating message comprehension problems for individuals with (agerelated) diminished capabilities. It has been determined that certain abbreviations 

are understood by at least 85 percent of the driving public independent of the specific 

context (e.g., BLVD = boulevard). A second category of abbreviations are understood 

by at least 75 percent of the driving population but only with a prompt word, (e.g., LOC 

means “local” when shown with “traffic”). Other abbreviations are prone to be frequently 

confused with another word (e.g., WRNG could mean either “warning” or “wrong”) and

should be avoided. Following are lists of abbreviations in three categories, extracted from 

Dudek et al. (1981) and Durkop and Dudek (2001):

1 those that are acceptable (understood by at least 85 percent of the driving 

population) when shown alone (Table 63);

2. those that are not acceptable and, therefore, should not be used (Table 64); and

3. those that require a prompt word (Table 65). Table 63 also includes abbreviations 

taken from the MUTCD, as well as common contractions used in the English 

language.

Most of the abbreviations in these tables have been incorporated into the MUTCD

(FHWA, 2009), as Tables 1A-1 to 1A-3 in section 1A.15; Section 6F.60 of the MUTCD

states that when abbreviations are used on CMS’s, they should be easily understood, and 

refers the practitioner to section 1A.15.
Handbook for Designing Roadways for the Aging Population 311

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Table 64. Abbreviations and phrases that are “not acceptable.” Source: Dudek, et al. (1981); 

Durkop and Dudek (2001).

Abbreviation Intended Word Common Misinterpretation

ACC Accident Access (Road)

ALT RT Alternate Routes Don’t know meaning

CLRS Clears Colors

DLY Delay Daily

EX Exit Don’t know meaning

FDR Feeder Federal

FEED RD Feeder Road Feed Road

FRNTG RD Frontage Road Front Road

L Left Lane (Merge)

LT Light (Traffic) Left

MAJ CONG Major Congestion Major Construction

PARK Parking Park

POLL Pollution (Index) Poll

RD WK Road Work Road Walk

RED Reduce Red

STAD Stadium Standard

VIC OF Vicinity of Don’t know meaning

WRNG Warning Wrong

Table 63. “Acceptable” abbreviations and phrases for frequently used words. Source: Dudek, et 

al. (1981), Durkop and Dudek (2001).

Word Abbreviation Word Abbreviation

Alternate ALT Left Lane LFT LN

Avenue AVE Major Accident MAJ ACCDT

Boulevard BLVD Maintenance MAINT

Can Not CAN’T Normal NORM

Center CNTR Parking PKING

Center Lane CTR LN Parking Lot PRK LOT

Do Not DON’T Right Lane RGT LN

Emergency EMER Road RD

Emergency Vehicle EMER VEH Service SERV

Entrance, Enter ENT Shoulder SHLDR

Expressway EXPWY Slippery SLIP

Freeway FRWY, FWY Speed SPD

Highway HWY Street ST

Information INFO Traffic TRAF

It Is IT’S Travelers TRVLRS

Junction JCT Warning WARN

Lane Closed LN CLSD Weight Limit WT LIMIT

Left LFT Will Not WON’T
312 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

Table 65. Abbreviations that are “acceptable with a prompt.” Source: Dudek, et al. (1981), 

Durkop and Dudek (2001).

Word+ Abbreviation Prompt

Access ACCES Road

Ahead AHD Fog*

Blocked BLKD Lane*

Bridge BRDG [Name]*

Condition COND Traffic*

Congested CONG Traffic*

Construction CONST Ahead

Downtown DWNTN Traffic*

Eastbound E-BND Traffic

Exit EXT Next*

Express EXP Lane

Hazardous HAZ Road

Interstate I [Number]

Local LOC Traffic

Major MAJ Accident

Mile MI [Number]*

Minor MNR Accident

Minute(s) MIN [Number]*

Northbound N-BND Traffic

Oversized OVRSZ Load

Prepare PREP To Stop

Pavement PVMT Wet*

Quality QLTY Air*

Roadwork RDWK Ahead [Distance]

Route RTE Best*, Detour*

Southbound S-BND Traffic

Temporary TEMP Route

Township TWNSHP Limits

Turnpike TRNPK [Name]*

Upper, Lower UPR, LWR Level

Vehicle VEH Stalled*

Westbound W-BND Traffic

Cardinal Directions N, E, S, W [Number]

* Prompt word should precede abbreviation.

+ The words and abbreviations shown in normal type are understood by at least 85 percent of the driving population. 

Those shown in boldface type are understood by at least 75 percent of the driving population, and public 

education is recommended prior to their usage.
Handbook for Designing Roadways for the Aging Population 313

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45 Channelization (Path Guidance)

Channelization systems include the use of cones, posts, tubular markers, barricades, 

panels, drums, amber-flashing and steady-burn lights, and standard and raised/recessed 

pavement markings. They are used to direct motorists into the open lanes and to guide 

them through the work area. They must provide a long detection distance and be highly 

conspicuous under both day and night conditions. Using data collected by the police, it 

has been estimated that anywhere from 80 to 86 percent of the crashes in work zones can 

be attributed to driver error (Nemeth and Migletz, 1978; Hargroves and Martin, 1980). 

Hargroves and Martin (1980) found that crashes with fixed objects within a work zone 

account for a greater percentage than other crash types, such as rear-end or sideswipe. 

Nemeth and Migletz (1978) found that nighttime crashes are concentrated in the taper 

area. Humphreys, Maulden, and Sullivan (1979) identified the most significant problems 

with channelization in work zones as: (1) failure to use, or hazardous use of, temporary 

concrete barriers; and (2) inadequate or inconsistent use of devices and methods in 

closing roadways and establishing lane-closure tapers. 

Aging drivers, like alcohol-impaired and fatigued drivers, show reduced sensitivity 

to contrast. Olson (1988) pointed out that the brightness of a traffic control device is 

the main factor in its attention-getting capability: in a visually complex environment, 

the brightness must be increased by a factor of 10 to achieve conspicuity equivalent to 

that found in a low-complexity environment. A major problem at night is reduction in 

contrast sensitivity, which makes it difficult to see even large objects when they cannot 

be distinguished from their background. Aging drivers also have difficulty processing 

information due to less effective scanning behavior and eye movements, diminished 

visual field size, difficulty in selective attention, and slower decision making. Inconsistent 

use of drums and traffic cones to delineate the travel path may be a particular problem for 

aging drivers, especially when applied in the presence of remnants of old lane markings, 

because such inconsistency is confusing and aging drivers (and inattentive drivers) are 

not able to react as quickly to conflicting traffic cues (National Transportation Safety 

Board, 1992). To compensate for their slower information-processing capabilities, their 

Table 66. Cross-references of related entries for channelization (path guidance).

Applications in Standard Reference Manuals

MUTCD 

(2009)

NCHRP 500-Volume 9

(2004)

Traffic Engineering

Handbook 

(2009)

Sect. 6B.01

Sects. 6C.05, 6C.08, 6D.01, 6F.13, 6F.14, 

6F.21 through 6F.24, 6F.32, & 6F.63 & 

6F.81

Sects. 6G.04 & 6G.07

Sect. 6G.10 through 6G.18 

Figs. 6H-3, 6H-5 through 6H-7, 6H-10 

through 6H-12, 6H-15, 6H-18, 6H-21 

through 6H-34, 6H-36 through 6H-44, & 

6H-46 plus associated notes for each fig.

Pgs. V-26-V-27, Sect. on Strategy 3.1 

B11: Improve Traffic Control at Work 

Zones (T)

Pg. 663 Paras. 6-7
314 Handbook for Designing Roadways for the Aging Population

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reduced visual capabilities, and their slower reaction time, aging drivers often drive more 

slowly. Although driver age was not studied, Hargroves and Martin (1980) found that 

slow-moving vehicles were overrepresented in work-zone crashes. Aging drivers also 

show reductions in lane-keeping ability, which is further compromised when they are 

required to attend to other tasks, in unfamiliar surroundings. Finally, steering abilities 

may be adversely affected by physical problems such as arthritis.

McGee and Knapp (1979) performed an analytic study to develop a performance

requirement/standard for the detection and recognition of retroreflective devices (cones, 

drums, panels, and barricades) used in work zones. The performance standard developed 

in this study, presented in terms of visibility requirements (i.e., the distance at which 

motorists should be able to detect and recognize the devices at night) and established 

using the principles of driver information needs and the requirement for decision sight 

distance, calls for a minimum visibility distance of 900 ft when illuminated by the low 

beams of standard automobile headlights at night under normal atmospheric conditions. 

Pain, McGee, and Knapp (1981) evaluated the effectiveness of traffic cones and tubular

markers, vertical panels, drums, barricades, and steady-burn lights in laboratory studies, 

in controlled field studies, and at actual construction sites. Two-hundred fifty-four 

subjects between the ages of 17 and 60+ participated; over half of the subjects were 

between ages 21 and 40, and 7 percent of the subjects were age 60 or older. Overall, 

there were no major differences between the device categories in the daytime. At night, 

barricades, panels, drums, cones, and tubular markers were also equivalent when 

the optimized cone and tubular marker retroreflectorization was used (two bands 

of retroreflective material for cones and one band for tubular markers totaling 150 

to 200 in2

, or roughly the amount provided by a 12- to 14-in collar) of retroreflective 

material with SIA of at least 250. However, tubular markers and cones with 6 in of 

collar resulted in diminished nighttime performance. The variables manipulated in 

the cone optimization study included amount of retroreflectorization (69, 138, 207, 276, 

and 345 in2

), [corresponding to single bands measuring 6-, 10-, 14-, 17-, and 20-in wide; 

number of bands of retroreflective material (1, 2, or 3); 3 types of retroreflectorization 

plus 1 internally illuminated cone (polycarbonate Reflexite with SIA of 2000 at entrance 

angle -4° and observation angle 0.1°, high intensity with SIA of 300 at entrance angle 

-4° and observation angle 0.1°, and polycarbonate Reflexite plus vinyl Reflexite); color 

of retroreflectorization (white and yellow), 3 sizes (18-, 28-, and 36- in tall); 3 device 

spacings (half, regular, and double-speed limit). The variables manipulated in the tubular 

marker study included amount of retroreflectorization (14, 28, 43, 57, and 71 percent of 

area covered, corresponding to bands measuring 150-, 300-, 450-, 600-, and 950-mm 

wide); number of bands (1, 2, 4, 6, or 8); the same retroreflectorization levels and colors 

as for the cone study, 3 sizes (18-, 28-, and 42-in tall); and the same device spacings as 

described for the cone study.

In comparing the meaning of chevrons versus stripes, Pain et al. (1981) found 

that diagonal, horizontal, and vertical stripes conveyed no consistent directional 

information; chevrons, though less easily detected than the stripe patterns, effectively 

and unambiguously indicated that a movement to the left or right was required. Since 

diagonal, horizontal, and vertical stripes conveyed no consistent direction information; 

Pain et al. (1981) concluded that there was no reason to have a diagonal stripe pattern for 
Handbook for Designing Roadways for the Aging Population 315

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left and right “sidedness.” They pointed out, however, that only one direction of diagonal 

should be allowed in an array so there is always a consistent pattern or image on devices. 

In terms of device spacing, comparisons of regular speed-limit spacing (55 ft in the test), 

half-spacing (27.5 ft), and double-spacing (110 ft) of Type I barricades and 8-in x 24-in) 

panels showed that changes in spacing produced little impact on driver behavior. There 

was no significant speed or lateral placement differences between half, regular, and double 

speed-limit spacing during the day. At night, however, when devices were placed at halfspacing, they produced a speed reduction, apparently from the illusion that the motorist 

was going faster than he or she actually was. Devices placed at double-spacing tended not 

to perform as well as when they were placed at regular speed-limit spacing, as drivers made 

lane changes and detected arrays of traffic control devices sooner with shorter spacing. 

From these findings, Pain et al. (1981) recommended that: (1) all devices be placed at speed 

limit spacing for most conditions and, in all cases, along the taper or transition section; 

(2) if there is no construction work or hazard in the closed lane for a substantial length, 

or traffic delays, the spacing can be increased to no more than twice the speed limit; and 

(3) shorter spacing may prove to be useful where speed reduction is desired. 

Device-specific findings by Pain et al. (1981) are as follows:

•	 Traffic cones. (1) They perform as well as other devices during daytime, with long 

detection distance and adequate lane-change distances. (2) Bigger is better: 36-in 

cones are more effective than 28-in cones; 28-in cones are better than 18-in) cones 

(and 18-in cones should not be used on high-speed facilities); (3) At night, 150 to 

200 in2

, or roughly the amount in a 12- to 14-in collar of highly retroreflective 

material (with specific intensity per unit area [SIA] of at least 250), is needed 

for effectiveness. Even higher brightness materials enhance driver response 

characteristics and are preferable. (4) Under both day and night conditions, 

the 2-band configuration outperformed the 3-band configuration, and both 

outperformed the 1-band configuration; therefore, two bands of retroreflective 

material are preferable on cones.

•	 Tubular Markers. (1) During daytime, 28-in and 42-in tubular markers are as 

effective as cones, but 18-in tubular markers are ineffective and not recommended 

for lane closures or diversions on high-speed facilities. (2) At night, tubular markers 

with at least a 12-in highly retroreflective band are equally as effective as cones. 

(3) The 1-band configuration outperformed the 2- and 3-band configurations for 

tubular markers

•	 Vertical panels. (1) Laboratory results showed that compared with the barricade, 

the vertical panel is more easily detectable. (2) Vertical panels are equally as 

effective (detectable) as Type I barricades, and vertical panels promote earlier lane 

changing than barricades. (3) The minimum width dimensions of the panel should 

be 300 mm (12 in) rather than 200 mm (8 in), especially when used at night and on 

high-speed facilities. 

•	 Drums. (1) Drums are highly visible and detectable from long distances, during 

both day and night. (2) Drums promote lane changing further upstream of the taper 

than other devices. (3) Drums are associated with a speed reduction. (4) Drums are 

a dangerous object when hit. 
316 Handbook for Designing Roadways for the Aging Population

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•	 Barricades. (1) The Type I barricade is as effective as other devices. (2) The Type 

II barricade is no more detectable than the Type I barricade. (3) The 12-in x 36-in 

barricade is more conspicuous than the 8-in x 24-in barricade. 

Other findings were reported for comparisons of steady-burn lights and Type II and Type 

III sheeting. The steady-burn lights provided the longest detection distances at night 

compared with all other materials, and they more than tripled the distance (or zone) 

in which lane changing occurred before the taper. In comparisons of Type II sheeting 

and Type III sheeting on cone and tubular marker optimization tests, Type III was 

significantly better at night on a flat road. Narrow-angle sheeting, even though offering 

high brightness, was not effective under certain sight geometry characteristics, such as 

hills and curves. Type III sheeting and steady-burn lights were comparable in terms of 

point-of-lane-change and array detection distance; however, the authors noted that the 

effect of vertical or horizontal curvature must be considered. 

There have been mixed results regarding the effectiveness of steady-burn lights in 

highway work zones. The use of steady-burn lights mounted on channelizing devices has 

been shown to significantly influence driver behavior in some work-zone configurations, 

and they are particularly effective in left-lane closures (KLD Associates, 1992). Although

drivers age 55 and older consistently showed poorer performance than younger drivers in 

all study conditions, evidence was found that the use of lights improved the performance 

of aging test subjects. The variables manipulated in this study included work-zone 

configuration (left-lane, right-lane, and shoulder closures), device type (panels versus 

drums), and light placement (every device, alternate devices, no lights). Drivers of all 

ages were able to identify lane and shoulder closures from greater distances when lights 

were used on channelization devices, as opposed to when the channelizing devices 

were used alone. Steady-burn lights produced a higher percentage of correct responses 

(determining the direction the channelizing devices were leading) for all driver age 

groups when used in left-lane closures than in right-lane closures. Interestingly, the use 

of lights on every other drum or vertical panel (placement on alternate devices) generated 

more correct responses than the use of lights on consecutive devices. More generally, 

the literature suggests that in environments characterized by high-speed operations, 

compromised visibility due to inclement weather, and/or complex maneuvers required 

as a result of work-zone configuration, the deployment of steady-burn lights should be 

considered on all channelizing devices used for right-lane closures. 

However, Pant, Huang, and Krishnamurthy (1992) obtained a different result when they

examined the lane-changing behavior of motorists in advance of tapered sections as 

they drove an instrumented vehicle through work zones during the day, at night when 

steady-burn lights were placed on drums, and at night when the steady-burn lights were 

removed. They measured the traffic volume at several locations in each lane in advance 

of the taper. Results showed that the steady-burn lights had little effect on driver behavior 

in the work zones studied. It was concluded by Pant et al. that steady-burn lights have 

little value in work zones that employ drums with high intensity sheeting and a flashing 

arrow panel as channelizing devices.

Opiela and Knoblauch (1990) conducted laboratory and field studies to determine the

optimal spacing and use of devices for channelization purposes in the taper or tangent 
Handbook for Designing Roadways for the Aging Population 317

CHAPTER 10—CONSTRUCTION/WORK ZONES

sections of work zones. In the laboratory study, the recognition distances of eight different 

device types, spaced at the standard distance and at 1.5 and 2.0 times the standard 

distance, were measured for 240 subjects. Results indicated variability between the 

performance of most channelizing devices across the spacings tested. Right- and left-lane 

closures were then used at six actual work zones, to test the various device spacings under 

both day and night conditions. Field data were collected at four points equally spaced over 

2,000 ft before the work zone and the activity at the start of the taper for the lane closure, 

according to the premise that the most effective treatment would minimize the percentage 

of traffic in the closed lane at the start of the taper. Statistical analysis of 2,100 observation 

periods lasting 5 minutes each showed that neither type of device (round drums, oblong 

drums, Type II barricades, and cones with retroreflective collars) nor device spacings (55, 

80, and 110 ft) had a significant effect on driver lane-changing behavior. 

Cottrell (1981) also found that driver lane-change response was not strongly dependent on 

the channelizing device employed in a work-zone taper. The objective of this study was 

to evaluate the effectiveness of alternative orange-and-white chevron patterns on vertical 

panels and barricades that form an arrow pointing in the direction in which traffic is 

being diverted, compared with traffic cones, simulated drum vertical panels, and Type 

II barricades and vertical panels with standard orange-and-white striping patterns. The 

measure of effectiveness was the position of lane changing relative to the transition taper. 

Although the subjective evaluation revealed that chevron patterns were preferred over the 

presently used patterns because of their clear directional message, the positions of lane 

changing were similar for the stripes and chevrons. With respect to the spacing of devices, 

it was generally found that lane changes occurred more frequently at greater distances 

from the taper when the devices were spaced every 40 ft, as opposed to every 80 ft. 

In a supplemental test, the effectiveness of the concrete safety-shaped barrier (CSSB), 

also referred to as a “Jersey” barrier in some jurisdictions, was compared with that of 

the channelizing devices studied (Cottrell, 1981). The barrier was marked with steadyburn warning lights and 6-in reflectors and had a slope of 16:1 for the 192-ft taper. The 

CSSB was rated equal to the cone during the daytime and lower than all other devices 

based on the lane-change positions. It was recommended that a supplemental taper of 

channelization devices be used with the CSSB. In a study of concrete barrier visibility, 

Pain et al. (1981) found that retroreflectors were superior to retroreflectorized tape. 

Logically, the most conspicuous types of retroreflective devices, such as those containing 

cube-corner lenses, will be potentially the most effective in this regard. 

Overall, Pain et al. (1981) concluded that most devices show relatively successful detection 

and path guidance performance. However, a major deterrent to effectiveness is not the 

device itself; instead, poor positioning, dirt, and overturned devices destroy the visual 

line or path created by the channelizing devices. Therefore, although use of appropriate 

devices is important, of equal importance is conscientious set-up and care of channelizing 

devices used in the work zones.

In consideration of the threat posed to drivers by passenger compartment intrusion or 

interference with vehicle control, or the threat to workers and other traffic from impact 

debris, plastic drums, cones, tubular markers, and vertical panels used as channelizing 

devices presented no hazards in full-scale vehicle crash tests (Bryden, 1990). However, 
318 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

Delineation of Crossovers/

Alternate Travel Paths

46

Studies have established that: (1) a substantial proportion of construction work-zone 

crashes occur in the taper and the crossover, where channelizing devices are usually 

located; (2) darkness is associated with an increase in the frequency of crashes in these 

areas; and (3) construction zones are associated with increases in the incidence of fixedobject, rear-end, and head-on crashes (Graham, Paulsen, and Glennon, 1977). Nemeth

and Rathi (1983), studying crash types in construction zones on the Ohio Turnpike, 

found that 52.4 percent of the crashes were with fixed objects, and 68.3 percent of the 

Table 67. Cross-references of related entries for delineation of crossovers/alternative travel paths.

Applications in Standard Reference Manuals

MUTCD 

(2009)

AASHTO

Green Book

(2011)

Sects. 6F.80 through 6F.83

Sects. 6F.76, 6F.84, 6F.85

Sects. 6F.69, 6F.70, & 6F.79

Sect. 6G.04

Sect. 6G.11

Sect. 6G.12

Sect. 6G.14

Figs. 6H-7, 6H-9, 6H-19, 6H-20, 6H-39 through 6H-41, & 6H45 plus associated notes for each fig.

Ch. 6I

Pgs. V-26-V-27, Sect. on Strategy 3.1 B11: Improve Traffic 

Control at Work Zones (T)

Types I and II barricades and portable signs and supports formed impact debris, which 

was often thrown long distances through work zones, posing a threat to workers and 

other traffic. The American Traffic Safety Services Association (ATSSA) is opposed to 

the use of metal drums in work zones as channelizing devices, as they pose a hazard 

to motorists as well as workers in the zone (TranSafety, 1987). They suggest the use of 

plastic drums, which are safer. Riedel (1986) described studies showing that a substantial 

number of work-zone crashes occur in the taper and the crossover where channelization 

devices are located. The frequency of crashes involving drums has led to the use of 

forgiving devices such as plastic drums, which in tests have been shown to be safer than 

steel drums. Juergens (1972) noted that because barricades are inherently fixed-object 

hazards, they should not be used as primary delineation to guide traffic. Further, they 

should not be used unless the construction hazard the motorist may encounter is greater 

than the hazard of striking the barricades. A concern with the use of steady-burn 

lights mounted on channelizing devices was highlighted in full-scale vehicle crash tests 

evaluating the performance of work-zone traffic control devices, where warning lights 

attached to these devices were thrown free, posing a potential threat to workers and other 

traffic (Bryden, 1990).
Handbook for Designing Roadways for the Aging Population 319

CHAPTER 10—CONSTRUCTION/WORK ZONES

crossover crashes involved collisions with channelizing devices or other objects. In 

this study, 69.4 percent of the crashes at the first curve of a crossover occurred at night. 

Nemeth and Migletz (1978) found that 60.7 percent of single-vehicle fixed-object crashes 

were collisions with drums and 29.8 percent of all crashes involved collisions with drums. 

They also found that the proportion of crashes involving construction objects (drums) at 

night is significantly higher than the proportion of daylight construction object crashes. 

The results of these studies highlight the need for highly conspicuous and properly 

installed and maintained channelizing devices. 

The relationships between functional capabilities of aging drivers and their performance 

that are likely to be of greatest operational significance as they approach and negotiate a 

crossover in a work zone can be summarized as follows. Age-related declines in acuity 

(both static and dynamic) and contrast sensitivity will delay recognition of channelizing 

devices and pavement markings and will delay comprehension of the information 

provided by advance warning signs. This information loss in the early stages of the 

driver’s vehicle control task will be compounded by attentional and decision making 

deficits shown to increase with increasing age, with age differences in performance 

magnified as serial processing demands for conflict avoidance and compliance with 

traffic control messages increase during the approach to the work zone. Age-related 

decrements in the “useful field of view,” selective attention, and divided attention, and 

attention-switching capabilities will slow the initiation of a driver’s response when a lane 

change is required prior to the transition zone, or maneuvering through channelization 

across the median. In addition, less efficient working memory processes may translate 

into riskier operations for aging drivers in unfamiliar areas if concurrent search for and 

recognition of navigational cues is required, as such demands disproportionately tax 

“spare capacity” for lanekeeping and conflict avoidance for aging operators. Finally, 

the execution of vehicle-turning movements becomes more difficult for aging drivers as 

bone and muscle mass decrease, joint flexibility is lost, and range of motion diminishes. 

Simple reaction time, while not significantly slower for aging drivers responding to 

expected stimuli under nominal operating conditions, suffers operationally significant 

decrements with each additional response to an unexpected stimulus, e.g., as required 

in emergency situations. In addition, aging drivers’ increased sensitivity to glare and 

reduced dark adaptation ability will compound the difficulties described above while 

driving at night.

The National Transportation Safety Board (NTSB) has expressed concern about the lack 

of positive separation of opposing traffic in work zones (NTSB, 1992). The NTSB uses 

“positive barrier,” or “positive separation of traffic,” to refer to the use of concrete barriers 

to separate traffic. (A number of States distinguish between these terms, using “positive 

separation” to describe various channelization treatments which do not necessarily 

involve use of a physical concrete barrier.) The NTSB (1992) emphasizes that, “Fatal 

crash rates increase significantly when an interstate highway is switched from a fourlane, divided operation to a two-lane, two-way operation (TLTWO) during construction 

work.” Research on the use of channelization and barrier delineation for TLTWO’s is 

described below.

A crossover requires a change in direction and may require a reduction in speed. This 

requires adequate advance warning of the lane and speed reduction, conspicuous and 
320 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

unambiguous delineation/channelization in the transition zone, and conspicuous 

separation of opposing traffic the length of the TLTWO. One survey of drivers in 

Houston and Dallas, Texas by Hawkins, Kacir, and Ogden (1992) found that only half

of the respondents correctly understood that they should turn before reaching the 

CROSSOVER sign (D13-1) when this device was shown in a field placement in an arterial 

work zone. Of course, the D13-1 sign panel is identified in the MUTCD as a device 

used in permanent installations on divided highways, not as a temporary device for 

use in construction zones. The poor comprehension of motorists for such an explicit 

message is alarming, nevertheless, and suggests the need for heightened conspicuity of 

guidance information in this situation. Hawkins et al. recommended that the spacing 

of channelizing devices be decreased in the vicinity of a crossover to reduce drivers’ 

confusion.

Next, Pang and Yu (1981) conducted a study to verify whether concrete barriers were 

justified at transition zones adjacent to TLTWO’s on normally divided highways, based 

on crash experience in several construction zone TLTWO’s. They found that 34 of the 

44 total crashes that occurred in TLTWO’s were within the transition zone. Four headon crashes occurred on two-way, two-lane segments away from the transitions. The 

transition zone was defined as the roadway section at which traffic flow was converted 

from a four- to a two-lane operation and vice versa. The absence of opposing traffic 

precluded the occurrence of head-on crashes during the study period; however, more 

than one-half of the crashes (56 percent) had the potential of becoming head-on 

collisions. The authors concluded that on relatively low-volume highways, delineation 

devices appear to be adequate at transition zones, assuming they are placed properly. A 

regression analysis provided by Pang (1979) indicated that as annual average daily traffic 

increases, the crash rate at transition zones also increases, with a concurrent increase in 

the head-on crash rate at the transition zone. 

Project duration and approach speed are two other variables that appear to affect the 

head-on crash rate at transitions (Pang and Yu, 1981). Graham (1977) concluded that as

project duration increases, the crash rate at the transitions decreases. Expectancy issues 

were highlighted as a plausible explanation. Pang and Yu (1981) reported that because the 

crash rate in the transition zone increases with shorter project duration, concrete barriers 

may be necessary for short-term projects. However, long-term projects are expected to 

have a greater number of crashes owing to a longer period of exposure. Thus, installation 

of concrete barriers would be more economically justified for long-term projects than for 

short-term ones. With regard to approach speed, it can be expected that as speed to the 

transition increases, the chances of a head-on collision would also increase, due to the 

tendency of vehicles to stray out of their lanes at curves such as those present in transition 

zones. Pang and Yu (1981) suggested that concrete barriers appear to be justified at 

transition zones where approach speeds are high. 

The conspicuity of concrete safety shaped barriers (CSSB’s) is an important issue. Their 

composition provides little contrast with the roadway pavement, making them difficult 

to see at night, particularly in the rain, and under opposing headlight glare conditions. 

Proper barrier delineation treatments will provide drivers with a defined path during 

darkness and adverse weather conditions. Standard barrier delineation treatments 

include Type C steady-burn warning lights on top of the barrier, retroreflective devices 
Handbook for Designing Roadways for the Aging Population 321

CHAPTER 10—CONSTRUCTION/WORK ZONES

on the top or side of the barrier, vertical panels placed on top of the temporary concrete 

barrier, and retroreflective pavement markings on the side of the barrier. The results 

of studies of barrier delineation in work zones have been mixed (Ullman and Dudek, 

1988). For instance, Mullowney (1978) suggested that delineation should be mounted on 

the top of the barrier so it will retain its reflectivity longer and require less maintenance. 

However, Ogwoaba (1986) recommended side-mounted concrete barrier delineation so 

that the delineators are not masked by oncoming headlight glare. The size and brightness 

of delineators is another controversial topic, with some studies suggesting the use of 

larger but less bright devices (Davis, 1983; Bracket, et al., 1984; Kahn, 1985) and others

recommending smaller, brighter reflectors (Mullowney, 1978; Ogwoaba, 1986). Kahn

(1985) found that the delineation of portable concrete barriers improved considerably 

through the use of cylindrical reflectors on top and smaller units on the side of the 

barrier at 25-ft intervals. Delineator spacings ranging from 25 ft to 200 ft (7.6 m to 61 m) 

have been recommended by various studies. 

Ullman and Dudek (1988) conducted a study of five barrier delineation treatments, 

using observations of driver performance to determine how different delineator types, 

spacings, and mounting positions on the barrier affect nighttime traffic operating in the 

travel lane next to the barrier. An additional objective of the study was to determine 

how the visibility and brightness of different types of delineators deteriorate over time 

because of dirt and road film; in a controlled field study, drivers ages 18 to 56 were asked 

to provide subjective evaluations of delineator brightness. The study was not conducted 

at a work zone, but was conducted on an illuminated urban freeway with four lanes in 

each direction. The CSSB was located 1 ft from the inside travel lane. The five delineation 

treatments were: (1) top-mounted cube-corner lenses at 200-ft spacing; (2) side-mounted 

cube-corner lenses at 50-ft spacing; (3) top-mounted retroretroreflective brackets at 

50-ft spacing; (4) side-mounted retroreflective brackets at 200-ft spacing; and (5) topmounted retroreflective cylinders at 50-ft spacing. The cube-corner reflector (treatments 

1 and 2) had a diameter of 3.25 in. The brackets (treatments 3 and 4) were 3 in (75 mm) 

high and 4.25 in wide, and were covered with high intensity sheeting. The cylindrical 

tube (treatment 5) had a diameter of 3 in and was 6 in high, and was wrapped with high 

intensity sheeting. Before-and-after data were obtained for the following measures of 

effectiveness: lane distribution, lane straddling, and lateral distance from the left rear tire 

to the bottom of the CSSB. 

Results of the driver performance data collected by Ullman and Dudek (1988) showed 

that the treatments had very little practical effect on lane distribution. Lane-straddling 

rates at all of the treatment segments were low during the higher volume nighttime 

hours; however, a significant increase in lane straddling occurred for Treatment 2. The 

data suggested that the combination of close delineator spacing and the side-mounted 

position may make some drivers too apprehensive of driving near the barrier. Lateral 

distance data showed significant differences during the higher volume nighttime hours 

for Treatment 4 and Treatment 5. Lateral distance distributions shifted away from the 

barrier at Treatment 4 and closer to the barrier at Treatment 5. Subjective evaluations 

for clean delineators showed brightness rankings to be the same for all treatments. 

Treatments 1–4 received adequate ratings from at least 80 percent of the subjects, while 

Treatment 5 was rated adequate by only 50 percent of the subjects. With respect to each 

treatment’s relative effectiveness in helping drivers maintain a safe travel path next to 
322 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

the CSSB, the rankings did not differ significantly; however, Treatment 5 again received 

the worst score. Subjects stated that side-mounted delineators were preferable to topmounted delineators because side-mounted delineation provided a more direct line of 

sight, a better indication of the location of the wall, and a more realistic perception of the 

lane width. For dirt-covered delineators, Treatment 2 was rated as brightest and most 

effective, while Treatment 5 was rated as dimmest and least effective. Although further 

research was deemed necessary, the study authors recommended the use of cube-corner 

lenses for delineating CSSB’s in narrow freeway median applications, because these 

delineators do not lose their reflectivity due to dirt and grime as quickly as those covered 

with high intensity sheeting. In addition, for situations with limited lateral clearance, as 

is common with TLTWO’s, top-mounted delineation is recommended, because sidemounted close delineator spacing results in lane straddling if the barrier is located close 

to the travel lanes. Although subjects indicated a preference for close spacings, driver 

performance data did not show any differences between 50-ft and 200-ft spacing. The 

authors recommended that a 200-ft spacing be considered maximum, and that closer 

spacings may be necessary for CSSB’s on sharp curves. The treatments were also deemed 

appropriate for CSSB’s in work zones.

On divided highways with narrow medians, which are often created when barriers 

are used in crossover situations in work zones, drivers are subject to blinding glare 

from opposing vehicle headlights. This is particularly problematic for aging drivers 

who have a reduction in their dark adaptation ability and increased sensitivity to 

glare. This results in reduced visibility of roadway alignment and channelization, 

and increases the possibility of crashes. Glare screens can solve the problem, as well

as reduce rubbernecking and its associated problems. The Pennsylvania Department 

of Transportation discontinued the use of the standard glare-control mesh screen in 

1976, based on maintenance difficulties, and has employed a paddle-type system in its 

place (Maurer, 1984). The system consists of plastic airfoil-shaped paddles, which when 

mounted resembles a picket fence. Results of a 5-year study have shown that the paddletype system reduces headlight glare satisfactorily and is more cost-effective, both in terms 

of installation and maintenance, than metal mesh screen. The system was also found 

to be beneficial as a temporary control for channelizing traffic around a construction 

work zone, when screening was placed at the transition or the taper zone at the ends 

of the work zone (Maurer, 1984). Kelly and Bryden (1983) reported that a glare screen

consisting of individual plastic louvers 36 in high, mounted vertically on a guiderail or 

median barrier spaced at 24-in centers, performed as expected in two safety improvement 

projects.
Handbook for Designing Roadways for the Aging Population 323

CHAPTER 10—CONSTRUCTION/WORK ZONES

47 Temporary Pavement Markings

Preconstruction centerlines and edge lines that are not obliterated may confuse drivers 

about the exact locations of lanes. The National Transportation Safety Board (1992) has 

reported that although guidelines exist for proper signing and striping in construction 

areas, the traffic control techniques used in many jurisdictions are not in compliance 

with the guidelines. Lewis (1985) stated that if drivers are presented with conflicting 

information (as may be the case in a work zone), they will generally choose to follow the 

pavement, as the pavement itself is a primary source of information for drivers. This 

points to a need for unambiguous pavement delineation patterns in work zones, to 

provide clear guidance—particularly at night and under adverse weather conditions—

and to accommodate drivers with visual limitations such as those associated with normal 

aging.

The research findings that have the greatest bearing on age differences in drivers’ ability 

to acquire and use information provided by roadway delineation are a decline in spatial 

contrast sensitivity and acuity for aging drivers, and a general slowing of responses 

because of deficits in visual search ability that slows discrimination of more important 

from less important information in a driving scene. 

Discrimination of the boundaries of the traveled way often involves only slight 

differences in the brightness of the road surface versus the shoulder or surrounding 

land. The ability to obtain such “edge information” depends upon a driver’s sensitivity to 

contrast. Age differences in contrast sensitivity, beginning at approximately age 40 and 

becoming progressively more exaggerated with advancing age, demonstrate significant 

decrements in performance for aging persons (Owsley, Sekuler, and Siemsen, 1983). 

Under constant viewing conditions, aging observers have lower contrast sensitivity 

especially in situations where there is a reduction in ambient light levels. A 60-year-old 

driver requires 2.5 times the contrast needed by a 23-year-old driver (Blackwell and 

Blackwell, 1971).

Age decrements in visual search and scanning capabilities are widely reported in 

gerontological research. Rackoff and Mourant (1979) measured visual search patterns 

for 10 young (ages 21–29) and 13 older (ages 60–70) subjects as they drove on a freeway 

under day and night conditions in low to moderate traffic. They reported that differences 

Table 68. Cross-references of related entries for temporary pavement markings.

Applications in Standard Reference Manuals

MUTCD

(2009)

NCHRP 500-Volume 9

(2004)

Traffic Engineering

Handbook 

(2009)

Sects. 6F.63, 6F.64, 6F.65

Sects. 6F.77, 6F.78, 6F.79

Sect. 6G.06

Figs. 6H-7, 6H-12, 6H-14, 6H-24, 6H-29, 

6H-32 through 6H-34, 6H-36, 6H-38 

through 6H-42, & 6H-44 plus associated 

notes for each fig..

Pgs. V-26-V-27, Sect. on Strategy 3.1 

B11: Improve Traffic Control at Work 

Zones (T)

Pg. 669, Sect. on Pavement Markings
324 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

between young and older test subjects’ performance were most apparent at night, and 

that older subjects required more time to acquire the minimum information needed for 

vehicle control. Thus, older drivers require delineation information that is optimal from 

the standpoints of both attention conspicuity and search conspicuity downstream, and 

that provides unambiguous path guidance cues for moment-to-moment steering control. 

Uncertainty about roadway heading and lane position has been cited by older driver 

focus group members as reasons for driving slower, for erratic maneuvers caused by 

last-second steering corrections, and for simply avoiding nighttime operations (Staplin, 

Lococo, and Sim, 1990). An exaggeration of the difficulties older drivers have in rapidly 

discerning the correct travel path may be expected in construction zones, where drivers 

must respond to temporary pavement markings that are often in competition with 

preexisting stripes and/or misleading informal cues provided by variation in the surface 

characteristics of the road, shoulder, or median. 

These diminished capabilities must be considered in relation to specific information 

needs, when negotiating work zones, while also taking into account the time (distance) 

in which these needs must be satisfied. The information needs may be loosely contrasted 

according to the discrimination of continuous versus discrete roadway features (i.e., 

the perception and recognition of the boundaries of the traveled way, as opposed to a 

singular location which must be avoided (e.g., an island, barrier, or abutment) or where a 

path selection decision must be acted upon (e.g., a ramp gore, pavement width transition 

point, or intersection)). Furthermore, delineation must provide information to a driver 

permitting roadway feature recognition both at “long” preview distances up to and 

sometimes exceeding 5 s travel time, and at the more immediate proximities (i.e., within 

1 s travel time) where attention is directed for instant-to-instant vehicle control responses.

An investigation of age-related differences in the required contrast for pavement 

delineation showed that an aging driver (ages 65–80) test sample required a level of 

contrast 20–30 percent higher than a young/middle-aged (ages 19–49) comparison group 

(Staplin et al., 1990). The differences became exaggerated with glare as an independent 

variable. An inevitable consequence of these age differences is an increased reliance on 

delineation elements for path guidance by aging drivers under nighttime conditions, 

especially against oncoming glare. The “long preview” and the instant-to-instant steering 

control cues provided by pavement markings are critical to aging drivers under these 

circumstances.

Raised pavement markers (RPMs) used for delineation of the centerline and edge lines 

in construction zones have been found to provide improved wet weather and nighttime 

reflectivity, and are particularly useful when lanes are diverted from their original path 

(Spencer, 1978). Davis (1983) reported that, compared with conventional pavement 

markings (e.g., paint), day-night/wet-night visible RPMs improved construction zone 

traffic performance significantly. In this study, the markers were associated with 

decreased lane-change frequency and night lane encroachments. In before-and-after 

comparisons of crash frequencies in two construction projects, the number of crashes 

and fatalities decreased as a function of RPM installation (Niessner, 1978). In a study 

investigating vehicle guidance through work zones, Shepard (1989) recommended that 

closely spaced RPMs should be used as a supplement to existing pavement striping in 

areas where the roadway alignment changes.
Handbook for Designing Roadways for the Aging Population 325

CHAPTER 10—CONSTRUCTION/WORK ZONES

Dudek, Huchingson, and Woods (1986) conducted a study on a test track to examine 

the effectiveness of temporary pavement markings for use in work zones. Ten candidate 

treatments were tested during the day, and the most effective treatments were examined 

at night. All treatments were tested only under dry weather/dry road conditions. The 

candidate treatments are presented in Table 69 and included patterns with stripes, RPM’s, 

and combinations of stripes and RPM’s. Treatment 1 was the control condition in the 

study. 

Table 69. Temporary pavement marking treatments evaluated by Dudek, Huchingson, and 

Woods (1986).

Treatment Description

1* 4-ft stripes (4 in wide) with 36-ft gaps (control condition)

2* 2-ft stripes (4 in wide) with 38-ft gaps

3* 8-ft stripes (4 in wide) with 32-ft gaps

4* 2-ft stripes (4 in wide) with 18-ft gaps

5* Four nonreflective RPM’s at 3-1/3-ft intervals with 30-ft gaps and one retroreflective 

marker centered in alternate gaps at 80-ft intervals

6* Three nonretroreflective and one retroreflective RPM at 3-1/3-ft intervals with 30-ft 

gaps

7 2-ft stripes (4 in wide) with 48-ft gaps

8 Treatment 2 plus RPM’s at 80-ft intervals

9* Two nonretroreflective RPM’s at 4-ft intervals with 36-ft gaps plus one retroreflective 

RPM centered in each 36-ft gap

10 1-ft stripes (4 in wide) with 19-ft gaps

* Treatments evaluated both day and night

Results of both daylight and nighttime testing indicated that there were no practical 

differences between treatments when comparing measures of effectiveness developed 

from speed and distance measurements. Practical differences were arbitrarily defined 

as at least 4 mph for speed measures and 1 ft for distance measures. The greatest number 

of erratic maneuvers during daylight occurred for treatments 7 and 8, which consisted 

of 2-ft stripes and long gaps. Drivers referred to 2-ft stripes as dots. The subjective data 

indicated that Treatments 5, 6, and 9 were preferred, under both daylight and nighttime 

conditions. Reasons given were that RPMs clearly identify curves, are highly visible at 

a great distance, provide noise and vibration when drivers cross them, and stand out 

more than tape markings. Of the treatments without RPMs, Treatment 3 was the drivers’ 

choice, for both lighting conditions, while Treatment 2 was rated as least effective. 

It should be noted that for temporary pavement markings, the MUTCD specifies in 

section 6F.78 that the same cycle length as permanent markings be used (30 ft), with 

markings at least 2 ft long, and that half-cycle lengths with a minimum of 2-ft stripes 

may be used for roadways with severe curvature.

Because subjects tend to perform best when in a controlled, test-track setting and because 

the range of performance measures are not always sensitive enough to discern small 

differences between candidate treatments, Dudek, et al. (1988) conducted field studies to 

compare the safety and operational effectiveness of 1-ft, 2-ft, and 4-ft temporary broken 

line pavement markings on 40-ft centers in work zones. The study was conducted at 
326 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

night on rural two-lane, two-way highways with 2.0-degree horizontal curvatures, level 

to rolling terrain, and average speeds between 50 mph and 62 mph. In terms of speed, 

lateral distance, encroachment, erratic maneuver, and speed profile data for the sample 

of vehicles with headways of 4 s or more, there were no differences in driver performance 

between the 1-ft, 2-ft, and 4-ft striping patterns. Analysis of subjective evaluations of the 

effectiveness of the markings found that the 1-ft stripe was generally rated as poorest, 

but its mean ranking was not significantly different from that of the 2-ft and 4-ft stripes. 

Drivers generally preferred the longer stripes, but there was no evidence that the 2-ft or 

4-ft stripes were superior to the 1-ft stripe. 

In a discussion of the conditions present during this research, Ward (1988) stated that 

all sites had 12-ft lanes with 4-ft to 10-ft shoulders, the marking material was highly 

retroreflective yellow tape laid over very black new pavement overlays, and there were 

no edge lines; therefore, the drivers’ focus was a “brilliant ribbon of yellow to follow,” 

resulting in no difference in driver performance between the three stripe lengths. Most 

important was that none of the treatments were judged as extremely effective, although 

the 1-ft stripe was rated as poorest, and there was a slight preference for the 4-ft lengths. 

This is consistent with results obtained by Dudek et al. (1986), where subjects rated 8-ft 

stripes with 32-ft gaps as the best striping treatment (when RPM’s were not available). In 

the Dudek et al. (1986) study, drivers preferred the treatments with longer stripes, shorter 

gaps, and RPM’s. Hence, the results of the Dudek et al. (1988) study may be applicable 

only to pavement overlay projects on two-lane, two-way rural roadways, and may not 

translate to other highway work-zone situations.

Harkey, Mera, and Byington (1992) conducted a study to determine the effects of shortterm (interim) pavement markings on driver performance under day, night, wet, and 

dry weather conditions. The three marking patterns tested included: (1) 2-ft stripes with 

38-ft gaps and no edge lines; (2) 4-ft stripes with 36-ft gaps and no edge lines; and (3) 10-ft 

stripes with 30-ft gaps and edge lines. The measures of effectiveness included lateral 

placement of the vehicle on the roadway, vehicle speed, number of edge line and lane 

line encroachments, and number of erratic maneuvers (e.g., sudden speed or directional 

changes and brake applications). For each operational measure, the 10-ft markings 

resulted in better driver performance than either the 2-ft or 4-ft temporary marking 

patterns. Drivers traveled 0.76 mph slower on segments with 4-ft markings and 2.02 mph 

slower on segments marked with 2-ft markings than on segments marked with 10-ft 

stripes and edge lines. In addition, compared with the 10-ft pattern, drivers encroached 

over the lane or edge line 66 percent more often in the presence of the 4-ft temporary 

marking and 139 percent more often in the presence of the 2-ft markings. These values 

increased dramatically under night and wet-weather conditions. Comparisons of driver 

performance between the 4-ft and 2-ft markings showed the following: (1) the speed 

at which drivers traveled decreased as the length of the lane line decreased; (2) drivers 

positioned their vehicles closer to the center of the lane as the length of the line increased; 

(3) the variability of vehicle placement within the lane increased as the length of the lane 

line decreased; (4) the number of encroachments increased as the length of the lane line 

decreased; and (5) all operational measures were negatively affected by adverse weather 

conditions. Results provided evidence of significant decreases in driver performance 

associated with both the 2-ft and the 4-ft markings, but drivers performed better with the 

4-ft stripes compared to the 2-ft stripes. The results suggested that while it may not be 
Handbook for Designing Roadways for the Aging Population 327

CHAPTER 10—CONSTRUCTION/WORK ZONES

practical to place full markings (10-ft segments with 30-ft gaps as specified by MUTCD

Section 3A.06) on a temporary basis, measures should be taken to prevent reductions in 

driver performance which result in increased crash potential. Such measures include 

the use of longer temporary markings, the addition of RPM’s for improved performance 

under adverse weather conditions, and the appropriate use of warning signs to indicate a 

change in the pavement marking pattern.
328 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

48 Increased Letter Height for 

Temporary Work Zone Signs

Description of Practice: Studies have shown that 25-30 percent of crashes within 

a work zone happen in the advance warning area or transition area. Most of them 

are rear-end or side-swipe types of crashes. Some of them are preventable with 

more perception/reaction time. A Caltrans sign comparison study concluded 

that for aging drivers, early recognition of the proposed sign could result in an 

additional 1.5 seconds of response time (Caltrans 2012). 

Work zone warning signs notify road users of specific situations or conditions 

on or adjacent to a roadway that might not otherwise be apparent. A solution 

is needed to improve sign legibility without increasing the cost of providing 

temporary traffic control. To improve and enhance roadway safety in and around 

work zones, the largest warning signs practical should be used. However, due to 

the limitations of the most commonly available portable sign stands, the work zone 

warning signs are limited to a maximum of 48 in by 48 in. If larger sign sizes are 

used, they will require larger portable sign stands resulting in a significant increase 

in cost to provide traffic control in and around work zones. 

The California MUTCD recommends the use of larger-than-standard sign, symbol 

and legend sizes where roadway or road user conditions require greater emphasis. 

In order to increase sign legibility for TTC zone warning signs, a suggested solution 

was to identify signs that can have larger legends displayed on some “action” words 

without increasing the overall sign size maximum of 48 in by 48 in. The proposal 

calls for increasing the number patch from 8-in to 10-in numbers, and the words 

“LEFT”, “RIGHT”, and “CLOSED” from 6-in to 8-in letters. (See Figure 95.)

Figure 95. Current (left) and proposed modified (right) temporary work zone sign in 

California. (Caltrans 2012)

PROMISING PRACTICES
Handbook for Designing Roadways for the Aging Population 329

CHAPTER 10—CONSTRUCTION/WORK ZONES

Anticipated Benefits to Aging Road Users: As with signs in other driving 

environments, larger legend size would increase sign legibility and improve work 

zone safety. Initial results of a Caltrans study indicate that drivers were able to read 

the modified signs from approximately 100 ft further away. While benefitting all 

road users, it may especially help aging road users as the larger legend size of action 

words will gain quicker comprehension of the sign message and from a longer 

distance, increasing their decision making and response time to the intended 

action required by the sign.

49 Work Zone Road Safety Audits

Description of Practice: Work zones have increased potential for violating a 

driver’s expectations, which can be especially hazardous for the aging population 

because of their diminished visual acuity. According to the Fatality Analysis 

Reporting System (FARS), 609 people were killed in motor vehicle crashes in work 

zones in 2012. Of those 609 fatalities, 45 were age 65 and older. A Work Zone 

Road Safety Audit (WZRSA) is a tool agencies can use to help reduce fatalities and 

serious injury crashes in work zones. It is the formal safety performance evaluation 

of a work zone by an independent, multidisciplinary team. It detects and reports 

on potential road safety issues and identifies opportunities to improve the safety of 

workers and all roadway users, including the aging population.

A Work Zone RSA follows the eight-step process of an RSA combined with 

characteristics of a typical work zone inspection or process review. 

Step 1: Identify Project or Active Work Zone to be Audited

Step 2: Select the WZRSA Team

Step 3: Conduct a Pre-audit Meeting to Review Project Information and Drawings

Step 4: Conduct a Review of Project Data and Perform a Field Review

Step 5: Conduct Audit Analysis and Prepare Report of Findings

Step 6: Present Audit Findings to Road Owner

Step 7: Road Owner Prepares Formal Response

Step 8: Incorporate Findings into the Project and Evaluate Results

One of the key features of a WZRSA is that it is performed by a multidisciplinary 

team focused on safety issues. Team members with various backgrounds and 

experiences can identify issues that may otherwise be overlooked. WZRSA teams 

may review the potential for safety enhancements to roadway and work zone 

elements, human factor considerations, enforcement and emergency services issues, 

and facility operations, whether they currently exist or are planned. 
330 Handbook for Designing Roadways for the Aging Population

CHAPTER 10—CONSTRUCTION/WORK ZONES

Anticipated Benefits to Aging Road Users: Recommendations from a WZRSA can 

potentially affect roadway users and workers immediately, improve the safety of the 

work zone being audited, and improve an agency’s overall work zone development and 

deployment process. The Work Zone Road Safety Audit Guidelines and Prompt Lists is a 

publication that includes guidance on how to conduct an RSA at all phases of work zone 

planning, design and deployment. The document explains the importance of the Work 

Zone RSA and navigates practitioners through the RSA process. Executing WZRSAs 

can make a work zone safer, mitigate the potential for risk claims, reduce the societal 

cost of crashes, reduce project costs, mitigate congestion, and lessen crash severity levels, 

including those that particularly affect aging drivers. 
Handbook for Designing Roadways for the Aging Population 331

CHAPTER 11

Highway-Rail Grade Crossings

The following discussion presents the rationale and supporting evidence for Handbook

treatments pertaining to these two proven practices.

Proven Practices

50. Passive Traffic Control Devices

51. Lighting
50 Passive Traffic Control Devices

332 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

50

For the approximately two-thirds of highway-rail grade crossings that are controlled 

by passive devices, “recognition errors” have been cited as the most frequent error 

type, accounting for 77 to 85 percent of the errors at Crossbuck-only crossings (Berg, 

Knoblauch, and Hueke, 1982). This category of driver error was defined broadly by

the study authors as “a breakdown in the detection and/or perception of the necessary 

information to negotiate the crossing safely.” Given the vast body of evidence that

sensory and perceptual capabilities decline as a function of age, it is reasonable to assert 

that the tasks of detecting an approaching train and judging its distance and speed pose 

exaggerated difficulty for aging drivers. Older drivers are also slower than their younger 

counterparts to process information (Berg et al., 1982), which was cited as a significant 

contributing factor by these researchers in decision errors—i.e., the “breakdown in the 

analysis of information or an incorrect choice of action”—at rail crossings by elderly 

and inexperienced drivers. Fambro (1999) similarly underscores these problems which 

disproportionately affect aging road users in his comprehensive literature review, while 

summarizing a large body of research directed at engineering countermeasures to 

improve driver understanding of and behavior at grade crossings.

Studies in this area have examined how changes in signing, delineation, the use of 

Table 70. Cross-References of Related Entries for Passive Traffic Control Devices.

Applications in Standard Reference Manuals

MUTCD

(2009)

NCHRP 500 – Volume 9

(2004)

Railroad-Highway Grade Crossing Handbook

(1986)

Traffic Engineering 

Handbook

(2009)

Sect. 1A.13, Highway-Rail 

Grade Crossing 

Sects. 8A.01 & 8A.04

Figs. 8B-8 & 8B-9

Sects. 8B.03 through 8B.12

Fig. 8B-2, 8B-3

Sects. 8B.17, 8B.20 through 

8B.23, 8B.27, 8B.28

Fig. 8B-4

Sects. 8A.06, 8B.16, 8B.19, 

8B.26.

Pg. 5-10, Sect. 5.2.6 RailroadHighway Grade Crossings

Pgs. 5-21 through 5-22, Sect. 

5.3.6 Railroad-Highway Grade 

Crossings 

Pg. 6-10, Sect. 6.2.6 RailroadHighway Grade Crossings 

Pg. 6-19, Sect. 6.3.6 RailroadHighway Grade Crossings

Pg. 7-26, Sect. 7.2.16 

Railroad-Highway Grade 

Crossings 

Pg. 7-39, Sect. 7.3.7 RailroadHighway Grade Crossings 

Pgs. 9-185 through 9-192, 

Sect. 9.12.3 Crossing Design

Pg. 10, Para. 3

Pg. 11, Para 4

Pg. 12, Para. 2

Pg. 29, Para. 3

Pg. 30, Table 8

Pg. 31, Paras. 5-6

Pg. 33, Paras. 2 & 4

Pg. 53, Fig. 7

Pg. 57-58, Figs. 9-10

Pgs. 66-69, Sects. on New 

Hampshire Index & NCHRP 50

Pg. 71, Tables 19-20

Pg. 78, Para. 2

Pgs. 80-81, Para. 6 & Fig. 15

Pg. 83, Para. 5

Pg. 84, Para. 5, 4th bullet

Pg. 87, Para. 4, Last bullet

Pgs. 96-103, Sect. on Passive 

Traffic Control Devices

Pgs.173-176, Item 1 of each 

economic type analysis 

Pgs. 177-180, Sect. on 

Resource Allocation Procedure

Pg. 188, Para. 4 

Pgs. 196-199, Part of Sect. on 

Traffic Control Devices

Pgs. 201-202, Figs. 100-103

Pg. 206, Paras. 2-3

Pg. 215, Para. 4

Pg. 217, Para. 5

Pg. 219, Para 4, 2nd bullet

Pg. 220, Sect. on Improved 

Signing

Pg. 226, Paras. 4 & 8

Pg. 227, Para. 1

Pgs. 147, Table 5-7

Pg. 398, Item 1

Pg. 425, Final Paragraph

Pgs. 634-635, Sect. on 

Railroad-Highway Grade 

Crossing Control

PROVEN PRACTICES
Handbook for Designing Roadways for the Aging Population 333

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

rumble strips and the introduction of nighttime illumination can variously affect drivers’ 

allocation of attention; looking behaviors; braking/deceleration during approach to a 

highway-rail grade crossing; and maneuver decisions to negotiate the crossing; as well as 

the actual vehicle-train crash experience at a site.

To begin, simply detecting the presence of a passive crossing, where the need to slow 

and look for a train is indicated, can be problematic, especially at night. Fambro (1999) 

cites the work of Russell and Konz (1980) who found that placement of the Crossbuck

sign (R15-1) does not make the best use of the vehicle’s headlight beam pattern, which 

is aimed to the right and down. They state that certain combinations of headlight angle 

and roadway geometry at the crossing may result in a Crossbuck sign luminance of zero. 

The MUTCD states that the sign height above the ground (9 ft) may be varied as required 

by local conditions. Russell and Konz (1980) recommend lowering the Crossbuck by 2 ft,

which would increase the illuminance by 50 percent at 150 ft and 69 percent at 250 ft. 

Russell and Rys (1994) conducted a small field study that confirmed that, from a distance 

of 350 ft, a Crossbuck at a height of 9 ft measured to the center and 6 ft from the right 

pavement edge received 8.4 percent of the vehicle headlight illuminance, compared to 

14.2 percent if the Crossbuck were lowered to 7 ft above ground level, and 44 percent if 

the Crossbuck were lowered to 3 ft above the ground. Russell and Rys conclude that 

placement of the Crossbuck as low as possible and using retroreflective tape on the 

full length of the Crossbuck posts would make the best use of the greater headlight 

illuminance levels present near the ground.

Related work by Russell and Kent (1993) indicates that the conspicuity of passive grade

crossings may be affected by adopting more effective delineation practices. These 

researchers conducted a before-after study to evaluate the effectiveness of five lowcost passive warning systems, implemented at six different sites. The warning systems 

included combinations of conventional signing (YIELD) and an enhanced delineation 

treatment; experimental signing (the “Buckeye Crossbuck,” also termed the “Conrail 

Shield”) as shown in Figure 96, plus an enhanced delineation treatment; two systems 

utilizing signing alone; and the enhanced delineation treatment alone. The enhanced 

delineation treatment included Type VII (ASTM D 4956-01) retroreflective tape that 

provides for high brightness on straight approaches as well as at wide observation angles 

(with SIA values ranging between 800 and 1,000), placed on both sides of both Crossbuck 

posts, and Type 2, flexible roadside retroreflective delineators with high intensity 

sheeting, placed on the right side of each approach, spaced 50 ft apart from the advance 

warning sign to the Crossbuck post (a total distance of 1,200 ft), and extending an equal 

distance beyond the Crossbuck post.

The measures of effectiveness in the Russell and Kent (1993) study included: approach

speeds; brake light activations; and head movements toward the tracks. One “before” 

study was conducted prior to installation of the new treatments, and two “after” studies 

were conducted, one at 2 months and the other at 7 months after treatment installation. 

Each observation period lasted for 3 to 4 days, from 2:30 p.m. until 5:30 p.m., and 

from 9:00 p.m. until 12 midnight. Results indicated that only the locations where the 

delineation system alone (roadside delineators and high-brightness tape on both sides 

of the crossbuck posts) was installed showed statistically significant, long-term positive 

changes in more than one variable (deceleration rates and looking behavior). The 

Figure 96. 

Experimental 

Enhanced Crossbuck 

Sign, Referred to 

as the “Buckeye 

Crossbuck” or 

“Conrail Shield”
334 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

researchers indicated that the added retroreflective devices and tape on the Crossbuck 

posts provide high values of reflected light at all distances, especially under low-beam 

headlight conditions, concluding that the delineation treatment showed the most 

permanent improvement in driver behavior of the low-cost systems tested, and would be 

effective at grade crossings on highways in rural areas, particularly at night. 

Brich (1995) similarly concluded that the use of very high intensity retroreflective 

sheeting (e.g., ASTM D 4956-01 Type IX) applied to both the front and back sides of the 

Crossbuck posts for the entire length of the post, plus double-sided Crossbucks (blades) 

also with very high intensity retroreflective sheeting resulted in superior conspicuity of 

the crossing, compared to systems that contained double-sided Crossbucks with Type 

IX sheeting, plus Type IX sheeting on only the back side of the posts (full length); or 

double-sided Crossbucks with Type IX sheeting, plus Type IX sheeting placed on the 

back of the posts in a 4-ft long strip; or single-sided Crossbucks with a strip of Type IX 

sheeting on the back side of the Crossbuck blades and also on the front and back of the 

posts (full length); or single-sided Crossbucks with a strip of Type VII sheeting on the 

back of the Crossbuck blades and also on the back side of the posts (applied 3 ft above 

ground level to the center of the Crossbuck blades). Both the Type VII and IX sheeting 

materials provide high brightness at wide observation angles, but Type IX is designed 

to provide high brightness at shorter viewing distances (in the 300- to 600-ft range). To 

delineate the Crossbuck posts, a strip of 2-in wide sheeting was applied to a 3-in wide, 

9-ft tall aluminum strip that was mounted on the front and the back of the Crossbuck 

post, or to the back of the post only, depending on the treatment being evaluated. The 

study by Brich (1995) was conducted in a laboratory using videotaped images of varying 

treatments filmed under low- and high-beam headlight illumination at night, during the 

approach to rail grade crossings. A train was also filmed traveling through each crossing. 

Comments obtained from the subjects in the Brich (1995) study indicated that marking 

the full length of the Crossbuck posts on the front and the back results in: (1) visually 

stabilizing the Crossbuck and tying it to the ground, which provides a valuable reference 

point; and (2) it makes the part of the far-side post below the undercarriage of a moving 

train in the crossing visible, causing a flickering effect that alerts a motorist of the 

presence of a train. It was concluded that using double-sided Crossbucks and marking 

the full length of both sides of both posts increases the visibility of the crossing; increases 

driver depth perception of the crossing; and increases the ability of a driver to detect a 

train in the crossing. The cost of a double-sided Crossbuck with Type IX sheeting in 1995 

was $87.50 and the cost of sheeting and aluminum to apply to the post was $18.74 per 

Crossbuck assembly. Since most crossings use two Crossbuck assemblies, the cost per 

crossing (Crossbuck, post, aluminum strip, and retroreflective material) was $212.48, in 

1995 dollars.

The MUTCD (FHWA, 2009) includes the requirement to use a strip of retroreflective 

sheeting that is at least 2-in wide, on the front and back of each Crossbuck support post, 

for the full length of the post. In addition, it states that a strip of retroreflective sheeting 

shall be applied to the back of the Crossbuck blades, except in locations where Crossbuck 

signs are installed back-to-back.

The largest body of work has been directed toward improving performance under 

daytime conditions, seeking to improve conspicuity for advance warning devices as 
Handbook for Designing Roadways for the Aging Population 335

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

well as devices at the crossing, but principally focusing upon motorists’ understanding 

of signs at highway-rail grade crossings. Uses of novel sign designs, combinations, 

materials, and placements have been evaluated, plus expanded applications of 

conventional devices—particularly STOP signs.

Research has indicated that driver comprehension of highway-rail grade crossing signs 

is poor. Even when the signs are conspicuous, they don’t provide any information 

about what drivers should do when approaching or crossing the tracks. The MUTCD

(2009) specifies that a railroad crossing sign (Crossbuck, R15-1) is a regulatory sign, and 

indicates that as a minimum, one sign shall be used on each roadway approach to every 

grade crossing, alone or in combination with other traffic control devices. Although the 

Crossbuck is, in effect, a YIELD sign, and motorists have the obligation to so interpret 

it, drivers do not have a clear understanding of what their responsibilities are when 

encountering the Crossbuck sign (Fambro et al., 1997). Lerner, Ratte, and Walker (1990) 

indicate that across studies, the majority of subjects (54 to 84 percent) believe that the 

appropriate behavior at a passive crossing is to stop; however, observational studies 

indicate that drivers routinely disregard this “rule.” 

One area of research has attempted to enhance the conspicuity and comprehensibility of 

the Crossbuck sign. Two enhanced Crossbuck signs have been evaluated in the State of 

Ohio (Zwahlen and Schnell, 2000). The Buckeye Crossbuck (also known as the Conrail 

Shield) is a standard Crossbuck sign with a supplemental reflectorized aluminum shield 

with a red vertical YIELD legend, mounted at headlight level. The 38-in high shield 

(reflectorized with white microprismatic sheeting on both sides) contains a 9-in wide 

center section (YIELD) with two 12-in side panels that are bent away from the center 

panel at 45-degree angles (see Figure 96). These panels contain alternating stripes of 

red and white highly retroreflective sheeting, with narrow mirrored strips between the 

stripes. This device costs approximately $300 per crossing. The Buckeye Crossbuck 

and the Standard Improved Crossbuck were evaluated on a statewide basis in Ohio 

with respect to their potential to alter driver risk taking behavior, their crash reduction 

potential, user acceptance, and photometric performance at night. The Standard 

Improved Crossbuck consists of a wooden post that is reflectorized on all four sides and 

aluminum blades that are reflectorized on both front and back with white microprismatic 

long-distance performance (Type VII) sheeting and the standard black legend. The 

Standard Crossbuck consists of a non-reflectorized wooden post and aluminum blades 

equipped with white encapsulated retroreflective sheeting material (Type III) and the 

standard black legend. 

For the driver risk-taking portion of the study, motorist near-collision and violation video 

data were collected along four selected rail corridors during 1995 in the before-condition 

(Standard Crossbuck condition). In the after-condition (1996-1997) half of the Current 

Standard Crossbucks were replaced with the Buckeye Crossbuck and the other half 

were replaced with the Standard Improved Crossbuck. A total of 3,833 passive railroad 

crossing approaches were recorded under both the before and after condition. Motorists 

were categorized as either compliant (yielded to an approaching train blowing its whistle) 

or non-compliant (drove over the crossing although an approaching train was blowing its 

whistle). Results of the driver risk-taking study indicated that the new crossbuck devices 

did not provide increased compliance over the standard crossbuck (56.1 percent non-
336 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

compliant vs. 54.6 percent non-compliant). However, none of the driver violations in the 

before or after period were closer than 5 seconds. Both new crossbuck designs provided 

temporal distributions that were slightly shifted towards longer risk acceptance times 

(median value = 25 seconds) when compared to the temporal distributions obtained with 

the Current Standard Crossbuck design (median value = 20 seconds). The increased 

time difference for the Buckeye Crossbuck compared to the Standard Crossbuck was 

significantly significant (p<0.0186). The crash analysis showed a statistically significant 

superiority (p<.0.047) of the Buckeye Crossbuck (157 crashes) over the Standard 

Improved Crossbuck (192 crashes) from 1994 to 1999, a 22.3 percent decrease. The crash 

analysis included every public passive railroad/highway grade crossing in Ohio; all 

crossings were equipped with either the Buckeye Crossbuck or the Standard Improved 

Crossbuck, which were evenly matched in terms of their number of installations. The 

user acceptance survey included 374 returned surveys out of 1,009 sent to randomly 

sampled licensed Ohio drivers. Findings indicated an overwhelming preference of the 

Buckeye Crossbuck over the Standard Improved Crossbuck. The majority of road users 

perceived that the additional area of the shield with the vertical “Yield” legend was 

useful in warning an approaching driver about the presence of a public passive railway/

highway crossing. Road users indicated that the Buckeye Crossbuck should be adopted 

as a warning device at public passive crossings. The Buckeye Crossbuck provided the 

strongest visual signal among the measured crossbucks at night and during the day. 

Based on their study findings, Zwahlen and Schnell (2000) recommended amending 

the National standard for crossbucks at passive railroad/highway grade crossings in the 

MUTCD, including the Buckeye Crossbuck as an alternative design, with the following 

modification. They recommended that the sheeting material of choice for the whole 

Buckeye Crossbuck should be a microprismatic sheeting material with a high angularity 

(Type VII Visual Impact performance, instead of Type VII Long Distance Performance).

Bridwell, et al. (1993) conducted a laboratory study that employed 42 young/middleaged subjects (ages 25 to 45 years) and 42 older subjects (ages 65 to 85) who viewed slides 

of 7 railroad crossing signs. The signs included the standard Crossbuck sign (R15-1); 

the standard Crossbuck sign with a red and white striped (barber) pole; the standard 

Crossbuck sign with a standard YIELD sign mounted below; the standard Crossbuck 

with the Conrail Shield mounted below; the Canadian Crossbuck (Crossbuck with white 

panel, red border, and no text); the Canadian Crossbuck with the Conrail Shield mounted 

below; and a standard YIELD sign with a black and white regulatory sign below reading 

“TO TRAINS.” Sign recognition distance, conspicuity distance (except for the YIELD 

TO TRAINS sign) and driver comprehension data were collected. Although there 

were no significant differences in recognition distance between the signs, the authors 

suggest that this may be more a result of the testing conditions (laboratory) than of the 

signs themselves. They recommend that a field study be conducted to measure actual 

recognition distances. In terms of conspicuity distance, the worst performing signs 

were the two that contained only the Crossbuck (standard R15-1 and the Canadian 

Crossbuck). The standard Crossbuck when supplemented with the YIELD sign, or the 

Conrail Shield, or a barber-striped pole was noticed significantly more often. 

For the comprehension portion of the Bridwell et al. (1993) study, drivers were asked 

about what they thought the sign meant, and what they should do if they encountered 
Handbook for Designing Roadways for the Aging Population 337

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

such a sign on the roadway. Drivers who didn’t know what the meaning of a sign was 

(i.e., “there is a railroad crossing”) were shown the Advanced Railroad Crossing (W10-1) 

warning sign to help put the Crossbuck sign “in context.” Several drivers required this 

“in context” information to correctly identify the meaning of the Canadian Crossbuck, 

the Canadian Crossbuck with the Conrail Shield, and the YIELD TO TRAINS sign. Data 

were therefore presented for percent-correct for sign meaning before and after being 

shown the Advance Railroad Crossing sign. Responses were always correct (100 percent 

comprehension) before the Advance sign for three of the signs: the standard Crossbuck, 

the standard Crossbuck sign with the barber pole, and the standard Crossbuck with the 

YIELD sign. For the other four signs, the “before” data for percent correct responses 

were as follows: standard Crossbuck with Conrail Shield (83.3 percent), Canadian 

Crossbuck (91.7 percent); Canadian Crossbuck with Conrail Shield (58.3 percent); and 

YIELD TO TRAINS sign (66.7 percent). After presentation of the Advanced Railroad 

Crossing sign, comprehension improved for three signs: all drivers understood the 

meaning of the Canadian Crossbuck and the YIELD TO TRAINS sign (100 percent 

correct comprehension), and comprehension improved from 58.3 percent correct to 

83.3 percent correct for the Canadian Crossbuck with the Conrail Shield. In terms of 

knowing what to do when encountering such a sign, the two best signs (83.3 percent 

correct for the standard Crossbuck with the YIELD sign and the YIELD TO TRAINS 

sign) significantly outperformed the two worst signs (the standard Crossbuck [41.6 

percent correct] and the Canadian Crossbuck [33.3 percent correct]). The other three 

signs were understood correctly half of the time. After being shown the Advance 

Railroad Crossing sign, the only sign that showed significant improvement in driver 

understanding of the correct action was the YIELD TO TRAINS sign, which increased to 

100 percent identification of the correct action. 

Bridwell et al. (1993) conclude that a change in the current standard Crossbuck sign 

for passive crossings appears necessary, based on study findings that it is neither well 

understood nor well noticed. They recommend further testing in the field for the 

standard Crossbuck sign supplemented with the standard YIELD sign, the standard 

Crossbuck sign supplemented with the Conrail Shield (which has the words “YIELD”), 

and the standard YIELD sign with the supplemental plaque that reads “TO TRAINS.” 

The Canadian Crossbuck should be omitted from further testing, as it performed worse 

than the standard Crossbuck. 

Fambro (1999) conducted five focus groups containing 10 participants each, who were 

selected to provide a range of ages. Focus groups were conducted in College Station, 

Corsicana, and Arlington, Texas and in De Kalb and St. Charles, Illinois. During

the sessions, participants were asked to provide their reactions to the following eight 

traffic control devices described as proposed enhancements to passive warning devices 

at highway-rail grade crossings: (1) Buckeye Crossbuck; (2) LOOK FOR TRAINS sign;

(3) YIELD TO TRAINS sign; (4) a vehicle-activated strobe light; (5) illumination; (6) 

rumble strips; (7) additional retroreflective material and/or devices on Crossbuck and 

support posts; and (8) roadway traffic signals. None of the passive signing systems 

were recommended by focus group participants as promising, although the Buckeye 

Crossbuck was rated as an excellent alternative in one of the five focus groups. 

In the Fambro et al. (1997) survey of 1,010 drivers conducted to determine driver 
338 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

understanding of traffic control devices at highway-rail crossings, 82 percent of the 

respondents correctly identified the meaning of the “YIELD TO TRAINS” experimental 

sign (i.e., “Yield the right-of-way if a train is approaching a crossing”). In the focus group 

sessions conducted by Fambro (1999), the “YIELD TO TRAINS” signs were not rated 

as promising alternative traffic control devices. However, he recommends their use at 

passive grade crossings in rural areas, to alert and warn drivers that they are approaching 

a critical safety decision point. The sign consists of a standard YIELD sign, with a 

supplemental panel with the phrase, “TO TRAINS.” The sign combination can be placed 

on the standard Crossbuck sign or used on a separate pole at the crossing. Fambro’s 

recommendation is based on a before-after study conducted in Texas, which found a 

significant decrease in approach speed at two of six sites; significant increases in looking 

behavior at three of eight sites; and no significant decrease in looking behavior at any of 

the eight sites evaluated (Fambro, Beitler, and Hubbard, 1994).

The above recommendations with combinations involving the standard R1-2 sign focuses 

attention on the use of traffic control devices whose meanings are familiar to drivers. 

Section 8B.04 of the MUTCD (2009) indicates that, while the Crossbuck Assembly is 

required, STOP or YIELD signs may be used in addition to the Crossbuck Assembly at 

passive grade crossings at the discretion of the responsible State or Local jurisdiction. It 

further states that a YIELD sign shall be the default traffic control device for Crossbuck 

Assemblies on all highway approaches to passive grade crossings unless an engineering 

study performed by the regulatory agency or highway authority having jurisdiction over 

the roadway approach determines that a STOP sign is appropriate. Engineering studies 

should take into account such factors as the line of sight to approaching rail traffic (giving 

due consideration to seasonal crops or vegetation beyond both the highway and railroad 

or LRT rights-of-ways), the number of tracks, the speeds of trains or LRT equipment and 

highway vehicles, and the crash history at the grade crossing. The YIELD or STOP sign 

may be installed on the same support as the Crossbuck sign or it may be installed on a 

separate support; in either case the YIELD or STOP sign is considered to be a part of the 

Crossbuck Assembly.

The use of STOP signs at passive crossings has been a controversial issue for over 40 years 

(Russell and Burnham, 1999). One camp (including Russell and Burnham) maintains 

that the indiscriminate use of STOP signs at all passive crossings would serve to breed 

driver disrespect for STOP signs as well as for highway-rail grade crossings. Russell and 

Burnham (1999) cite the research of Bezkorovainy-Holsinger (1966) and Burnham (1994) 

who observed that approximately 84 percent of drivers at STOP-controlled highway-rail 

grade crossings violated the law, and either did not stop at all, or performed a rolling stop. 

This view is contrasted against that of the National Transportation Safety Board (NTSB), 

who in 1998 recommended that States install STOP signs at all passive grade crossings 

unless a traffic engineering analysis determines that installation of a STOP sign would 

reduce the level of safety at a crossing. Farr and Hitz (1985) found that STOP signs 

reduced crossing crashes by approximately 35 percent, based on analysis of data included 

in the Department of Transportation (DOT)-Association of American Railroads (AAR) 

Rail-Highway Crossing Inventory and the Federal Railroad Administration (FRA) 

Railroad Accident/Incident Reporting System for the years 1975 through 1980. Eck and 

Shanmugam (1987) used the National Rail-Highway Crossing Inventory and FRA crash 
Handbook for Designing Roadways for the Aging Population 339

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

files to compare low-volume road grade crossing characteristics with high-volume road 

grade crossing characteristics. They found that exposure-based crash rates at low-volume 

road grade crossings were much higher than at higher-volume road grade crossings, and 

that magnitudes of crash reductions following upgrades from no signs or Crossbucks only 

to STOP signs were higher for the low-volume crossings. 

Earlier work in this area has also influenced current thinking, particularly the Sanders, 

McGee, and Yoo (1978) study which determined advantages and disadvantages of the

selective use of highway STOP signs as safety improvements at highway-rail grade 

crossings, and developed guidelines for their use. They performed crash analyses to 

compare crash rates for crossings with Crossbucks only to crash rates for crossings with 

Crossbucks and standard highway STOP signs. Results indicated that crash rates for 

STOP-sign crossings were lower than rates for Crossbuck-only crossings, given higher 

vehicle-train exposure. Sanders et al. (1978) also performed field studies to compare 

driver behaviors for Crossbuck-only crossings to driver behaviors for similar crossings 

where a standard highway STOP sign was installed in addition to the Crossbuck. Driver 

behaviors included looking behavior, speed profiles, and observance of STOP signs. 

Looking behavior was obtained by Sanders et al. (1978) for 1,413 drivers at 8 Crossbuckonly sites in 4 States, and for 3,073 drivers at 18 sites with both a STOP sign and a 

Crossbuck sign in 5 States. They found that 83 percent of the drivers looked for trains at 

the locations with STOP signs, but only 42 percent looked for trains at the Crossbuck-only 

sites. Speed profile measures indicated that drivers approaching a STOP-sign crossing 

began their deceleration closer to the crossing than did drivers approaching a Crossbuck 

crossing. Also, vehicle speeds just prior to the crossing were considerably lower at the 

STOP-sign crossing. Sanders et al. (1978) observed that while STOP sign observance 

(compliance) at stop-controlled highway-rail crossings was less than at highway 

intersections (60 percent vs 80 percent), there was no transfer of adverse stopping behavior 

between the rail-grade crossing and a nearby stop-controlled highway intersection.

Applying the results of Sanders et al. (1978) to the goal of accommodating age-related 

driver difficulties is hampered by lack of knowledge about the age of drivers sampled 

in their research. In addition, the driver behaviors adopted as outcome variables were 

affected by factors other than signing practices and site characteristics. For example, 

looking behavior was affected by the level of enforcement at STOP sign controlled 

crossings. Their principal conclusion still is worth noting: STOP signs should be applied 

selectively only at hazardous passive grade crossings (restricted sight triangle; ADT<2000; 

3+ train crossings per day) and should not be used indiscriminately at all passive grade 

crossings.

Fambro, et al. (1997) conducted a field study using 10 younger drivers (ages 18 to 25), 10 

middle-aged drivers (ages 30 to 45), and 10 older drivers (ages 55 and older), to document 

looking behavior and deceleration at rail grade crossings. This study was predicated upon 

the belief that looking behavior in both directions and a significant reduction in speed are 

the key safety goals at passive crossings, because no warning devices are activated when a 

train is approaching the crossing. The passive site with the greatest percentage of drivers 

who looked in both directions before crossing (97 percent) was a site controlled by a STOP 

sign. All of the young and middle-aged drivers looked both ways at this site, and 9 of the 

10 older drivers looked both ways. Three of the 30 drivers did not stop at the STOP sign 
340 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

(although they slowed considerably), and 10 drivers performed a rolling stop. At the other 

two passive sites (marked with Crossbuck signs only, and no advance railroad crossing 

sign), 70 percent of the drivers did not look in both directions at one site (70 percent of 

younger, 80 percent of middle-aged, and 60 percent of older drivers), and 17 percent did 

not look in both directions at the other site (20 percent of the younger, 10 percent of the 

middle-aged, and 20 percent of the older drivers).

It may be noted that stopping before reaching the tracks provides the driver who may 

have difficulty dividing attention (e.g., the aging driver), with the ability to focus on the 

single task of looking for a train. For example, Lerner, Ratte, and Walker (1990) note 

that in the Knoblauch et al. (1982) study, relatively few crashes occurred at a roadwayrail grade crossing because a driver who was stopped (at a passive crossing or at an active 

crossing with flashing lights) misjudged a gap and proceeded to cross. The large majority 

of decision errors were made by drivers in moving cars. Expecting to stop and seeing a 

STOP sign at a passive crossing would also remove the potential for vehicle-to-vehicle 

(rear-end) crashes. Related is the fact that 15 to 25 percent of drivers expect all crossings 

to be actively controlled (Fambro, 1999; Lerner et al., 1990). This erroneous perception 

results in drivers assuming that it is safe to cross (without slowing or looking both ways) 

when there are no lights flashing, even when there are no lights present at the crossing. A 

STOP sign at a passive crossing will eliminate this expectancy and provide positive and 

unambiguous guidance, removing the need to look for the absence of active warnings for 

clues about what behavior is appropriate. Also, as Lerner et al. (1990) note, response time 

is faster to detect the presence of a TCD as opposed to its absence. 

Together, the findings and conclusions in the paragraphs above should provide guidance 

for the selective use of the R1-1 sign at highway-rail grade crossings, by informing the 

engineering judgment called out in the MUTCD for application of these devices.

As described in Chapter I (Design Element 12 Stop and Yield Signing), highway signs 

with fluorescent sheeting have been found to be more conspicuous and can be detected 

at a further distance than signs with standard sheeting of the same color. Of particular 

interest is a study by Burns and Pavelka (1995), who found that signs with fluorescent red 

sheeting had greater detection and color recognition distances at dusk than signs made 

with standard red sheeting. The results of this study suggest that the use of fluorescent red 

sheeting on YIELD signs at highway-rail grade crossings (and on STOP signs, where they 

are deemed appropriate), would serve to increase their conspicuity both under daytime 

and low luminance conditions, and would be of particular benefit to aging drivers, who 

suffer from decreases in contrast sensitivity.

Other research pertaining to signing for highway-rail grade crossings for which data from 

aging drivers has been obtained has addressed comprehension of the Railroad Advance 

Warning sign and the Parallel Railroad Advance Warning sign. Picha, Hawkins, and 

Womack (1995) conducted a survey of 747 drivers ranging in age from 16 to 65 and older 

who were renewing their drivers’ licenses in seven Texas cities. Of the 747 participants, 54 

were ages 55 to 64 (7.3 percent of the sample) and 31 were age 65 or older (4.2 percent of 

the sample). A multiple choice question was included regarding the meaning of the W10-1 

(Railroad Advance Warning) sign and the W10-3 (Parallel Railroad Advance Warning) 

sign. No advantages for alternative designs to the standard W10-1 were demonstrated in 

this research; however, an alternative to the current W10-3 was recommended. 
Handbook for Designing Roadways for the Aging Population 341

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

The standard Parallel Railroad Advance Warning sign (W10-3) and three Alternative 

designs were shown to the same driver sample. (See Figure 97.) Alternative 1 was a yellow 

diamond sign that consisted of the same elements present in the standard design, except 

that the roadway outline was drawn (as opposed to thick solid lines), and a bent right 

arrow was drawn within the roadway lines to indicate that a right turn would lead to 

railroad tracks. Alternative 2 was the standard W10-1 sign (Advance RR Crossing) with 

a supplemental plaque containing an arrow that pointed to the right. Alternative 3 was 

the same as Alternative 2 except the supplemental panel contained a bent right-pointing 

arrow. The correct response, “you will cross a railroad track if you turn right at the 

intersection,” was provided by 84.1 percent of the participants who saw the standard sign; 

88.1 percent of the respondents who saw Alternative 1; 90.5 percent of the respondents 

who saw Alternative 2; and 87.2 percent of the respondents who saw Alternative 3. A 

higher percentage of respondents indicated that they did not know what the standard 

sign meant (10.2 percent) than the alternative designs (6.2 percent for Alternative 1; 3.2 

percent for Alternative 2; and 1.6 percent for Alternative 3). Thus, the standard W10-

3 sign had the lowest correct response rate and the highest “not sure” rate, although 

these differences did not reach statistical significance. While suggestive, further work is 

deemed necessary to justify a treatment in this Handbook.

The next category of countermeasures reviewed, targeting speed reductions by drivers 

approaching highway-rail grade crossings, is the application of rumble strips. Fambro’s 

(1999) review indicates that in Kentucky, rumble strips were effective in reducing

collisions and near misses, with no indication of motorists avoiding the rumble strips; 

however, in Georgia, about 12 drivers per day “drove around” the strips (Skinner, 1971;

Parsonson and Rinalducci, 1982). Parsonson and Rinalducci (1982) recommend that at 

grade crossings, rumble strips should be applied only at nonresidential locations where 

unfamiliar drivers are the prevalent group. Fambro states that the potential benefits 

of rumble strips at roadway-rail grade crossings include: decreased approach speeds; 

increased awareness of warning signs; and increased awareness of a potentially hazardous 

intersection. He recommends their use for passive crossings on rural, low-volume 

roadways and provides the following guidelines: 

•	 Three to four rumble strip pads of 5 to 20 rumble strips should be used, with the

first pad placed 2 to 3 s before the advance warning sign to direct the driver’s 

attention to the sign. 

Figure 97. Standard MUTCD W10-3 Sign and Alternative Sign Designs Evaluated by Picha, 

Hawkins, and Womack (1995)
342 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

•	 Subsequent pads should be placed with decreasing spacing and numbers to create

the sensation of acceleration. 

•	 The last pad should be placed at least 250 ft before the crossing to avoid creating a

pavement condition that might interfere with braking.

Another view is provided by Lerner, Ratte, and Walker (1990), who caution that 

distorting the driver’s perception of approach speed with progressively decreasing 

spacings of rumble strips, in an effort to encourage slowing on the approach to a crossing, 

could actually encourage a driver to speed up and try to beat a train. While this behavior 

has not typically been associated with aging drivers either in the research literature or 

anecdotally, it raises a more general concern that any present recommendation regarding 

the use of rumble strips would be premature. 

Finally, a novel treatment to attract motorists’ attention to highway-rail grade crossings is 

the use of a vehicle-activated strobe light on a sign assembly. The vehicle-activated strobe 

light causes short bursts of flashing light when a vehicle passes over detectors placed in 

the roadway. In research conducted by the Texas Transportation Institute, the strobe is 

mounted on top of a standard railroad advance warning sign, and the vehicle detector is 

placed approximately 8 seconds before the advance warning sign (Fambro, Schull, Noyce, 

and Rahman (1997). The strobe flashes three to five times to direct the driver’s attention 

toward the advance warning sign, and it should stop flashing 2 to 3 seconds before the 

driver reaches the sign to allow time to read the sign. 

Fambro et al. (1997) evaluated this treatment in a controlled field study using 7 younger 

drivers (age 25 or younger), 12 middle-aged drivers (ages 25 to 54) and 7 older drivers (age 

55 and older). Head movements toward the sign and braking reactions were recorded by 

in–vehicle observers to the advance railroad crossing sign alone, to the advance railroad 

crossing sign supplemented with a strobe light, and to an advance railroad warning sign 

supplemented with a standard flashing beacon. The sign sheeting was engineering grade, 

making it retroreflective. There were no differences in head movements (indicating 

no differences in attention-getting value) as a function of the sign system; however, 54 

percent of the drivers exhibited braking in response to signs enhanced with either the 

strobe light or the flashers, compared to 31 percent who exhibited braking to the standard 

sign without enhancements. Drivers also responded to a questionnaire and participated 

in a focus group discussion. Three drivers (11 percent) thought that the strobe-enhanced 

sign indicated that a train was ahead, and 9 drivers (35 percent) thought that the 

flashing beacon indicated the presence of a train. The authors mention a concern with 

this interpretation; drivers at passive crossings who do not see trains approaching after 

encountering strobe- or flasher-enhanced warning signs may begin to disrespect active 

devices at crossings that do indicate the presence of a train. Seven drivers (27 percent) 

indicated that the strobe light was confusing, and 11 drivers (42 percent) thought the 

flasher-enhanced sign was confusing. With special attention to the problems of aging 

drivers, including the difficulties in decision making and delays in response time when 

confronted with unusual or unexpected situations, such results were not sufficiently 

encouraging to warrant a recommendation in this Handbook.
Handbook for Designing Roadways for the Aging Population 343

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

51 Lighting

Aging drivers, with their decreased contrast sensitivity, and need for increasing levels 

of light for night driving tasks, would be expected to benefit disproportionately from 

increasing the detectability and conspicuity of railroad crossing signing, and of the 

crossing itself. Another strategy is to add illumination to passive crossings. In one 

before-after study of 52 highway-rail grade crossings (Russell and Konz, 1980), adding

illumination to passive crossings resulted in an 85 percent reduction in the mean number 

of crashes per week (where the vehicle ran into a train already at the crossing). The 

importance of illumination at passive highway-rail grade crossings was also highlighted 

by Fambro (1999).

Mather (1991) evaluated the 7-year crash history of 35 passive highway-rail grade 

crossings in Oregon that were illuminated as a low-cost alternative for improving 

crossing safety at night. The eligibility criteria for the installation of illumination were: 

(1) the crossing must have regular nighttime train movements (4 p.m. to 7 a.m.), and 

(2) the crossing is too low on the statewide crossing priority list (low train or vehicle 

traffic volumes) to qualify for automatic warning devices. Crash data indicate that 

before illumination, 18 train-vehicle crashes occurred at 13 crossings during the hours 

of darkness. After illumination, only 3 train-vehicle crashes occurred at two crossings 

during the hours of darkness. 

The cost of installation across the 34 crossings averaged $1,931 per crossing, and ranged 

from $386 to $9,384 (where a 1-mi long ditch was dug to provide electrical power to the 

site). The goal was $2,000 per crossing (a substantial reduction of the costs associated 

with installing active warning devices, estimated to be in excess of $100,000 per crossing, 

according to Bridwell et al., 1993). Monthly maintenance costs averaged $15 per 

luminaire per pole. 

The installation specifications for illumination at the crossings reported on by Mather 

(1991) are as follows.

At least one luminaire shall be mounted on each side of the track at the crossing. 

Luminaires should be located so that protective devices at the crossing will be directly 

illuminated.

•	 Luminaires shall be oriented toward the railroad track to provide at least 10.76 lux

[1 footcandle (fc)] of illumination on the vertical plane 5 ft from the centerline of 

the track. Maximum permissible level of illumination and exact orientation of the 

Table 71. Cross-References of Related Entries for Lighting.

Applications in Standard Reference Manuals

MUTCD

(2009)

NCHRP 500 – Volume 9

(2004)

Traffic Engineering 

Handbook

(2009)

Pgs. V-22-V-23, Sect. on Strategy 3.1 B8: Improve 

Roadway Delineation (T)

Pgs. 55-56, Sect. on Control of 

Distribution Above Maximum 

Candlepower

Pgs. 140-143, Sects. on Illumination 

& Miscellaneous Improvements
344 Handbook for Designing Roadways for the Aging Population

CHAPTER 11—HIGHWAY-RAIL GRADE CROSSINGS

luminaire will be determined on a case-by-case basis. Factors at the site, including 

the ambient level of nighttime illumination, need to be considered. The maximum 

level of illumination is related to the level of lighting on the roadway approaches. 

The level of illumination should be sufficient to alert drivers to the crossing ahead 

and to any railroad equipment occupying the crossing, but should not be so bright 

as to create a blinding effect for motorists in the area immediately beyond the 

crossing. Cutoffs will normally be used on luminaires to minimize this blinding 

effect.

Luminaires should illuminate an area along the track that is 50 percent wider than the 

traveled width of the road. The illumination should cover a distance equal to the normal 

height of rail equipment (at least 15 ft above the top of the rail).

Poles holding luminaires should be located so that they can be maintained from the 

roadway right-of-way.

Mather (1991) states that it was difficult to convince highway authorities and electrical 

companies that the luminaires should be aligned toward the railroad tracks instead of 

the roadway. However, through meetings and demonstrations, all parties eventually 

agreed that the luminaires were more effective if they were aligned toward the track. 

Light readings taken at all tracks showed that a higher percentage of the installations 

complied with the 10.76 lux (1 fc) standard for illumination where the luminaires faced 

the railroad tracks. Mather provided the following specifications for the installations. 

For single-track crossings, poles were located 25 ft from both the road and the centerline 

of the railroad track. Two-hundred-watt, high-pressure sodium luminaires were placed 

at least 30 ft above the top of the rail on 6- to 16-ft long arms. If a railroad signal system 

was involved, full cutoff luminaires were used. For multiple-track crossings, 400-watt, 

high-pressure sodium luminaires were placed at least 40 ft above the top of the rail. If a 

considerable distance separated the tracks, it was desirable to install a luminaire between 

the tracks. Semicutoff luminaires were used because they spread the light over a larger 

area of the crossing. This treatment was needed at crossings with three or more tracks, 

and those with severe angles of intersection.
Handbook for Designing Roadways for the Aging Population 345

APPENDIX A

Supplemental Technical Notes

Aging And Driver Capabilities

Many aspects of sensory and cognitive function needed to drive safely deteriorate in later 

adulthood. In fact, recent data indicate that aging adults are in the highest risk category 

for crashes when figures are based on crashes per number of miles driven. Among the 

senses, the importance of vision is paramount. To respond appropriately to all manner 

of stimuli in the roadway environment, a driver must first detect and recognize physical 

features of the roadway, traffic control devices, other vehicles, non-motorized users, and 

a wide variety of other objects and potential hazards of a static and dynamic nature. 

On rare occasions, critical information concerning the presence or position of traffic is 

conveyed to a road user solely through an auditory signal; in the vast majority of cases, 

however, the visual system is preeminent at this (input) stage of processing. 

Age-related changes in the lens of the eye, combined with pathology (for example, 

glaucoma, cataracts, diabetic retinopathy, and macular degeneration), result in the 

diminished capabilities that are described below. 

Reductions in Acuity

This is the ability needed to discriminate high contrast features; it is necessary for reading 

information on road signs. Visual acuity of 20/40 with or without corrective lenses for 

both eyes or one blind eye is the predominant minimum standard for driver licensing 

for passenger car drivers throughout the U.S. However, there are an increasing number 

of states (including Pennsylvania, Maryland, New Jersey, Florida, Illinois, and others) 

that will grant a restricted license to low-vision drivers with acuities as poor as 20/70 

to 20/100. Restrictions may include daytime only, area, and speed limitations. Added 

to reductions in acuity, aging is also associated with yellowing of the eyes’ lenses and 

increased density (or thickening). This affects the way color is perceived and also reduces 

the amount of light that reaches the retina, which makes seeing in low light conditions 

more difficult. 

Reductions in Contrast Sensitivity 

This is the ability needed to detect low-contrast features; it is necessary to see worn 

lane lines, detect (non retroreflectorized) curbs and median boundaries, and see 

other road users at dusk. Some people have 20/20 acuity but still have “cloudy” or 

washed-out vision. Contrast sensitivity makes it possible to distinguish an object from 

its background. It begins to decline after about age 40, as a result of normal aging. 

Individuals age 61+ have an increasing risk for the development of cataracts and other 

sight-threatening or visually disabling eye conditions that reduce contrast sensitivity. 

Many people with reductions in contrast sensitivity are not aware that their vision is 

impaired, and contrast sensitivity is not a standard test in most DMVs for licensing.
346 Handbook for Designing Roadways for the Aging Population

APPENDIX A—SUPPLEMENTAL TECHNICAL NOTES

Reductions in Visual Field

This is the ability to see objects in the periphery; it is necessary for detecting signs, 

signals, vehicles, pedestrians, cyclists, etc., outside of a limited field of view directly 

ahead. A limitation in visual field size is a physiological limitation—the person’s visual 

system is not capable of detecting a stimulus outside of his or her visual field.

Restrictions in the Area of Visual Attention

This is the ability to see potential conflicts in the periphery, and to discriminate relevant 

from irrelevant information; it is necessary for responding quickly and appropriately to 

a constantly changing traffic scene. Sometimes termed “useful field of view,” “functional 

field of view,” or “attentional window,” this refers to a subset of the total field of view. 

Restrictions in the area of visual attention can lead to “looked but didn’t see” crashes, 

where stimuli can be detected, but cannot be recognized and understood sufficiently 

to permit a timely driver response. As such, this term represents a limitation at the 

attentional stage of visual information processing, rather than a physiological limitation. 

Increased Sensitivity to Glare

This refers to the ability to see in the presence of oncoming headlights, at night, or in the 

presence of sun glare in daytime. Glare introduces stray light into the eye; it reduces the

contrast of important safety targets.

Slower Dark Adaptation

This is the ability needed to see targets when moving from areas of light to dark, which 

may occur at highway interchanges or moving from commercialized areas to noncommercialized areas.

Decreased Motion Sensitivity

This ability is needed to accurately estimate closing speeds and distances; it is necessary, 

for example, for judging gaps to safely perform left turns at intersections with oncoming 

traffic, to cross an intersecting traffic stream from a minor road or driveway, or to merge 

with traffic.

Hearing Sensitivity

While driving is primarily a visual task, sounds sometimes give drivers the first 

awareness that a problem or condition demanding a timely driver response exists, 

including not only emergency sounds such as sirens, but also sounds that signify 

problems with brakes, tires, or other mechanical problems. In addition, it is to be 

expected that hearing will play an increasingly important role in the future, as new 

technologies are introduced in vehicles to provide aging drivers with navigational 

assistance or early warning of hazards. Pedestrians with visual impairments, regardless 

of age, also depend on auditory cues to detect approaching traffic at intersections, and 

rely on auditory signals at crosswalks if they are present. A decreased sensitivity to 

sound, particularly at higher frequencies, accompanies normal aging.
Handbook for Designing Roadways for the Aging Population 347

APPENDIX A—SUPPLEMENTAL TECHNICAL NOTES

Compounding the varied age-related deficits in visual performance that are a part of 

normal aging, an overall slowing of mental processes occurs as individuals continue 

to age into their seventies and beyond. Declines have been demonstrated in a number 

of specific mental activities that are related to driver and pedestrian safety, such as 

attentional, decisional, and response-selection functions. These are described below.

Selective Attention

This refers to the ability to filter out less critical information and continuously re-focus 

on the most critical information (for example, detecting a lane-use restricted message 

on an approach to a busy intersection; detecting a pedestrian crossing while watching 

oncoming traffic to locate a safe gap).

Divided Attention

This refers to the ability to perform multiple tasks simultaneously and process 

information from multiple sources (for example, lane-keeping, reading signs, noticing 

traffic signals and changing phases, while maintaining a safe headway with other traffic 

during an intersection approach).

Perception-Reaction Time

This is the time required to make a decision about what response is appropriate for 

specific highway design elements and traffic conditions, and then make a vehicle control 

movement such as steering and/or braking. As the overall speed of mental processing of 

information slows with aging, PRT increases. As the complexity of the driving situation 

increases, PRT increases disproportionately for aging motorists.

Working Memory

This refers to the ability to store, manipulate, and retrieve information for later use while 

driving (e.g., carrying out a series of navigational instructions while negotiating in heavy 

traffic; or remembering, integrating, and understanding successive phases of a changeable 

message sign).

Finally, it has been well established that physical capabilities decline as a function of age 

and also as a function of general health. Aging (as well as disease and disuse) brings about 

changes in the components and structure of the cartilage near the joints, underlying 

bones, ligaments and muscles. These changes impair the ability of the musculoskeletal 

system to perform driving acts. The physical capabilities (motor functions) needed for 

safe and effective vehicle control are described below.

Limb Strength, Flexibility, Sensitivity, and/or Range of Motion

These abilities are needed to quickly shift (the right foot) from accelerator to brake pedal 

when the situation demands, to apply correct pressure for appropriate speed control, and 

for arm movements to safely maneuver the car around obstacles.
348 Handbook for Designing Roadways for the Aging Population

APPENDIX A—SUPPLEMENTAL TECHNICAL NOTES

Head/Neck and Trunk Flexibility

A key ability of a driver is to rapidly glance in each direction from which a vehicle 

conflict may be expected in a given situation; this includes the familiar “left-right-left” 

check before crossing an intersection, as well as looking over one’s shoulder before 

merging with traffic or changing lanes.
Handbook for Designing Roadways for the Aging Population 349

APPENDIX B

Photograph and Image Credits

Figure # Caption Credit 

Cover 1 (in-lane freeway route shield markings) Jim Lyle, Texas A&M Transportation Institute

Cover 2 (crosswalk markings) Kay Fitzpatrick, Texas A&M Transportation 

Institute

Cover 3 (work zone cones) Tom Saunders, Virginia Department of 

Transportation

Cover 4 (curve warning markings) Marcus Brewer/Debbie Murillo, Texas A&M 

Transportation Institute

Cover 5 (railroad crossing devices) Ben Sperry, Texas A&M Transportation 

Institute

1 Elements included for each Handbook treatment Debbie Murillo, Texas A&M Transportation 

Institute

2 Percentage of crashes involving drivers and 

pedestrians by age at intersections (Hauer, 1988).

Ezra Hauer, TRB Special Report 218 (1988)

3 Example 90° angle of intersection. Debbie Murillo, Texas A&M Transportation 

Institute

4 Example 75° angle of intersection. Debbie Murillo, Texas A&M Transportation 

Institute

5 Skewed signalized intersection with prohibition of 

right turn on red

Debbie Murillo, Texas A&M Transportation 

Institute

6 Recommended receiving lane width. Debbie Murillo, Texas A&M Transportation 

Institute

7 Vertical Curb (top), Sloping Curb (bottom) David Harkey, Highway Safety Resource 

Center, University of North Carolina

8 Left-turn lanes with positive offset Debbie Murillo, Texas A&M Transportation 

Institute

9 Recommended signs and markings for intersections 

with channelized offset left-turn lanes

Debbie Murillo, Texas A&M Transportation 

Institute

10 Pedestrian Crossing Island (or Refuge Area) Debbie Murillo, Texas A&M Transportation 

Institute

11 Raised median island with yellow marking on the 

vertical face and top surface.

David Harkey, Highway Safety Resource 

Center, University of North Carolina

12 Comparison of curb radii Debbie Murillo, Texas A&M Transportation 

Institute

13 MUTCD R10-12 sign adjacent to left-turn signal face. Marcus Brewer, Texas A&M Transportation 

Institute
350 Handbook for Designing Roadways for the Aging Population

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS

Figure # Caption Credit 

14 (MUTCD R10-31P) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

15 (MUTCD R10-11) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

16 Skewed signalized intersection with prohibition of 

right turn on red

Debbie Murillo, Texas A&M Transportation 

Institute

17 (MUTCD R10-15) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

18 (MUTCD D3-1) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

19 Intersection Warning W2-1 Sign and W16-8P 

Supplemental Advance Street Name Plaque

Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

20 (MUTCD D3-2) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

21 (MUTCD W4-4P) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

22 (MUTCD W3-1) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

23 Mast-arm mounted lane-use control signs Alan Pate, Battelle

24 Yellow retroreflective backplates Mark Doctor, Federal Highway 

Administration

25 Pedestrian crossing at channelized right-turn lane. Debbie Murillo, Texas A&M Transportation 

Institute

26 (MUTCD R10-3 Series) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

27 Recommended placement of MUTCD R10-15 sign. Debbie Murillo, Texas A&M Transportation 

Institute

28 Countdown pedestrian signal David Harkey, Highway Safety Resource 

Center, University of North Carolina

29 Key geometric design elements and traffic control 

devices for roundabouts

Debbie Murillo, Texas A&M Transportation 

Institute
Handbook for Designing Roadways for the Aging Population 351

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS

Figure # Caption Credit 

30 (MUTCD W2-6) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

31 Roundabout directional arrow sign Debbie Murillo, Texas A&M Transportation 

Institute

32 Placement of Roundabout Circulation Plaques Debbie Murillo, Texas A&M Transportation 

Institute

33 Right-Turn Channelization Design Debbie Murillo, Texas A&M Transportation 

Institute

34 Combination Lane Use/Destination Guide Sign 

(MUTCD D15-1).

Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

35 Example of one signal head per lane Marcus Brewer, Texas A&M Transportation 

Institute

36 High-visibility (”ladder”) crosswalk Kay Fitzpatrick, Texas A&M Transportation 

Institute

37 Yield Ahead Triangle Symbols David Harkey, Highway Safety Resource 

Center, University of North Carolina

38 Diagram of Median U-Turn Intersection Debbie Murillo, Texas A&M Transportation 

Institute

39 Diagram of Restricted Crossing U-Turn Intersection Debbie Murillo, Texas A&M Transportation 

Institute

40 (MUTCD R10-32P) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

41 Typical arrangements of signal faces with flashing 

yellow arrow indications for permissive left-turn 

movements

Flashing Yellow Arrow information page, 

City of Bryan website, Bryan, Texas (2014) 

www.bryantx.gov

42 Example Overhead Arrow-per-Lane Sign. Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

43 (MUTCD D13-3) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

44 Recommended signs and markings for adjacent 

entrance/exit ramps at a crossroad intersection

Debbie Murillo, Texas A&M Transportation 

Institute

45 Advance ground-mounted diagrammatic sign. David Harkey, Highway Safety Resource 

Center, University of North Carolina

46 Recommended raised pavement markers and postmounted delineators at an exit goreDebbie Murillo, Texas A&M Transportation 

Institute
352 Handbook for Designing Roadways for the Aging Population

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS

Figure # Caption Credit 

47 Placement of chevrons on the controlling curve of an 

exit ramp

Debbie Murillo, Texas A&M Transportation 

Institute

48 Recommended markings for acceleration lanes from 

entrance ramps onto freeways.

Debbie Murillo, Texas A&M Transportation 

Institute

49 Recommended signing for restricted movements on 

an exit ramp

Debbie Murillo, Texas A&M Transportation 

Institute

50 Route Shield Markings At Freeway Junctions Jim Lyle, Texas A&M Transportation Institute

51 White edge lines, centerline RPMs, and chevrons on a 

horizontal curve

Adam Pike, Texas A&M Transportation 

Institute

52 (MUTCD W7-6 and W13-1P). Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

53 (MUTCD W3-4 and W16-13). Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

54 (MUTCD W14-3) Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

55 Lane Control Signal (adapted from Ullman et al. 1996) Ullman, G.L., Parma, K.D., Peoples, M.D., 

Trout, N.D., and Tallamraju, S.S. Visibility, 

Spacing, and Operation of Freeway Lane 

Control Signals. (1996)

56 Dotted Lane Line Markings at Freeway Lane Drop Marcus Brewer, Texas A&M Transportation 

Institute

57 Contrast Markings on Light Colored Pavement Marcus Brewer, Texas A&M Transportation 

Institute

58 Curve Warning Markings Marcus Brewer/Debbie Murillo, Texas A&M 

Transportation Institute

59 Example of Road Diet Virginia Department of Transportation

60 High Friction Surface Treatment on a Horizontal 

Curve

Ken Kochevar, Federal Highway 

Administration

61 Flashing arrow panel at lane closure taper. Debbie Murillo, Texas A&M Transportation 

Institute

62 Changeable message sign upstream of lane closure 

taper

Debbie Murillo, Texas A&M Transportation 

Institute

63 Redundant static signs upstream of lane closure 

taper

Debbie Murillo, Texas A&M Transportation 

Institute

64 Phase 1 (Top) and Phase 2 (Bottom) Debbie Murillo, Texas A&M Transportation 

Institute

65 Use of approved abbreviation in one-phase message Debbie Murillo, Texas A&M Transportation 

Institute
Handbook for Designing Roadways for the Aging Population 353

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS

Figure # Caption Credit 

66 Traffic cone for nighttime work zone operations. Debbie Murillo, Texas A&M Transportation 

Institute

67 Temporary work zone sign with increased letter 

height.

Caltrans, Office of Signs, Markings and 

California MUTCD. Challenge Area: CA-14 — 

Improve Work Zone Safety. (2012)

68 Recommended placement of post-mounted 

delineators

Debbie Murillo, Texas A&M Transportation 

Institute

69 Turning Path Taken by Left-Turning Vehicles (from 

Staplin et al., 1997).

Staplin, L., Harkey, D., Lococo, K., and 

Tarawneh, M. Intersection Geometric Design 

and Operational Guidelines for Older Drivers 

and Pedestrians, Volume I: Final Report. (1997)

70 Intersection Geometries Examined in a Field Study of 

Right-Turn Channelization (Staplin et al., 1997).

Staplin, L., Harkey, D., Lococo, K., and 

Tarawneh, M. Intersection Geometric Design 

and Operational Guidelines for Older Drivers 

and Pedestrians, Volume I: Final Report. (1997)

71 Sight Distance for Left and Right Turns for Passenger 

Car Drivers at Yield-Control Intersections (Harwood 

et al., 1993).

Harwood, D.W., Mason, J.W., Jr., Pietrucha, 

M.T., Brydia, R.E., Hostetter, R.S., and 

Gittings, G.L. Intersection Sight Distance. 

(1993)

72 Spatial relationships that determine available sight 

distance

McCoy, P.T., Navarro, U.R., and Witt, W.E. 

“Guidelines for Offsetting Opposing 

Left-Turn Lanes on Four-Lane Divided 

Roadways.” Transportation Research Record 

1356. (1992)

73 Comparison of Required Intersection Sight Distance 

Values from the Modified AASHTO Model (with J 

= 2.5 S) and the Gap Acceptance Model (with Gap 

Values of 5.5 S, 7.0, 7.5 S, and 8.0 S).

Staplin, L., Harkey, D., Lococo, K., and 

Tarawneh, M. Intersection Geometric Design 

and Operational Guidelines for Older Drivers 

and Pedestrians, Volume I: Final Report. (1997)

74 Alignment of Left-Turn Lanes for Negative and 

Positive Offset

David Harkey, Highway Safety Resource 

Center, University of North Carolina

75 Alternative Left-Turn Treatments for Rural and 

Suburban Divided Highways

Bonneson, J.A., McCoy, P.T., and Truby, J.E. 

“Safety Improvements at Intersections 

on Rural Expressways: A Survey of 

State Departments of Transportation.” 

Transportation Research Record 1385. (1993)

76 Sight Distance Restrictions for a Positioned and 

Unpositioned Left-Turning Driver at an Aligned 

Intersection with an Opposing Left-Turning Vehicle.

Staplin, L., Harkey, D., Lococo, K., and 

Tarawneh, M. Intersection Geometric Design 

and Operational Guidelines for Older Drivers 

and Pedestrians, Volume I: Final Report. (1997)

77 Left-Turn Lane Offset Design Values Necessary to 

Achieve Unrestricted Sight Distances Calculated with 

Either the Modified AASHTO Model (J = 2.5 s) or the 

Gap Acceptance Model (G = 8.0 s).

Staplin, L., Harkey, D., Lococo, K., and 

Tarawneh, M. Intersection Geometric Design 

and Operational Guidelines for Older Drivers 

and Pedestrians, Volume I: Final Report. (1997)
354 Handbook for Designing Roadways for the Aging Population

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS

Figure # Caption Credit 

78 Alternative Curb Radii Evaluated in Laboratory 

Preference Study of Intersection Geometries

Staplin, L., Harkey, D., Lococo, K., and 

Tarawneh, M. Intersection Geometric Design 

and Operational Guidelines for Older Drivers 

and Pedestrians, Volume I: Final Report. (1997)

79 Novel Sign Tested as a Countermeasure to Reduce 

RTOR Violations and Pedestrian Conflicts

Zegeer, C.V. and Cynecki, M.J. “Evaluation 

of Countermeasures Related to RTOR 

Accidents that Involve Pedestrians.” 

Transportation Research Record 1059. (1986)

80 Recommended Wording For Educational Placards For 

One-Stage And Two-Stage Crossings

Knoblauch, R., Nitzburg, M., Dewar, 

R., Templer, A. and Pietrucha, M. Older 

Pedestrian Characteristics for Use in Highway 

Design. (1995)

81 One Way and Chevron Sign Combination Used in 

Central Island of Roundabout

Jacquemart, G. Synthesis of Highway 

Practice 264: Synthesis of Roundabout 

Practice in the United States. (1998)

82 Roundabout Advance Warning Sign Recommended 

by Lord et al

Lord, D., Van Schalwyk, L., Chrysler, S., and 

Staplin, L. “A Strategy to Reduce Older 

Driver Injuries at Intersections Using More 

Accommodating Roundabout Design 

Practices.” Accident Analysis and Prevention, 

39(3), pp 427-432. (2007)

83 Lane Control Sign Recommended by Lord et al Lord, D., Van Schalwyk, L., Chrysler, S., and 

Staplin, L. “A Strategy to Reduce Older 

Driver Injuries at Intersections Using More 

Accommodating Roundabout Design 

Practices.” Accident Analysis and Prevention, 

39(3), pp 427-432. (2007)

84 Roundabout Sign Recommended by Lord et al Lord, D., Van Schalwyk, L., Chrysler, S., and 

Staplin, L. “A Strategy to Reduce Older 

Driver Injuries at Intersections Using More 

Accommodating Roundabout Design 

Practices.” Accident Analysis and Prevention, 

39(3), pp 427-432. (2007)

85 Yield Sign Treatment Recommended by Lord et al Lord, D., Van Schalwyk, L., Chrysler, S., and 

Staplin, L. “A Strategy to Reduce Older 

Driver Injuries at Intersections Using More 

Accommodating Roundabout Design 

Practices.” Accident Analysis and Prevention, 

39(3), pp 427-432. (2007)

86 Exit Treatment Recommended by Lord et al Lord, D., Van Schalwyk, L., Chrysler, S., and 

Staplin, L. “A Strategy to Reduce Older 

Driver Injuries at Intersections Using More 

Accommodating Roundabout Design 

Practices.” Accident Analysis and Prevention, 

39(3), pp 427-432. (2007)
Handbook for Designing Roadways for the Aging Population 355

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS

Figure # Caption Credit 

87 Example of continental crosswalk markings K. Fitzpatrick, S.T. Chrysler, V. Iragavarapu, E. 

Park. (2010) Crosswalk Marking Field Visibility 

Study. Research Report. FHWA-HRT-10-068. 

Federal Highway Administration, 

Washington, DC.

88 Example of bar pairs crosswalk markings K. Fitzpatrick, S.T. Chrysler, V. Iragavarapu, E. 

Park. (2010) Crosswalk Marking Field Visibility 

Study. Research Report. FHWA-HRT-10-068. 

Federal Highway Administration, 

Washington, DC.

89 Diagram of Median U-Turn Intersection Debbie Murillo, Texas A&M Transportation 

Institute

90 Diagram of Restricted Crossing U-Turn Intersection Debbie Murillo, Texas A&M Transportation 

Institute

91 Supplemental Plaque Used with Extended Crossing 

Time Feature for APS

Federal Highway Administration, Manual on 

Uniform Traffic Control Devices for Streets and 

Highways, 2009 Edition.

92 Example of MUTCD diagrammatic sign (a) 

and modified diagrammatic sign (b) used in 

comprehension evaluation

Brackett, Q., Huchingson, R.D., Trout, N.D., 

and Womack, K. “Study of Urban Guide Sign 

Deficiencies.” Transportation Research Record 

1368. (1992)

93 Ground-Mounted Diagrammatic Guide Sign for 

Urban Multilane Arterial, Used by Zwahlen et al

Zwahlen, Helmut T., Russ, Andrew, Roth, 

James M., and Schnell, Thomas. (2003) 

“Evaluation of the Effectiveness of Ground 

Mounted Diagrammatic Advance Guide 

Signs For Freeway Entrance Ramps”, Paper 

No. 03-3315, presented at the 82nd Annual 

Transportation Research Board Meeting, 

National Academy of Sciences, Washington, 

DC.

94 Pixel layout of LCD Heads employed in research 

conducted by Ullman et al.

Ullman, G.L., Parma, K.D., Peoples, M.D., 

Trout, N.D., and Tallamraju, S.S. Visibility, 

Spacing, and Operation of Freeway Lane 

Control Signals. (1996)

95 Current (left) and proposed modified (right) 

temporary work zone sign in California.

Caltrans, Office of Signs, Markings and 

California MUTCD. Challenge Area: CA-14 — 

Improve Work Zone Safety. (2012)

96 Experimental Enhanced Crossbuck Sign, Referred to 

as the “Buckeye Crossbuck” or “Conrail Shield”.

Russell, E.R. and Kent, W. Highway-Rail 

Crossing Safety Demonstrations. (1993). 

97 Standard MUTCD W10-3 Sign and Alternative Sign 

Designs Evaluated by Picha, Hawkins, and Womack

Picha, D.L., Hawkins, H.G., and Womack, K.N. 

Motorist Understanding of Alternative Designs 

for Traffic Signs. (1995)
356 Handbook for Designing Roadways for the Aging Population

APPENDIX B—PHOTOGRAPH AND IMAGE CREDITS
Handbook for Designing Roadways for the Aging Population 357

APPENDIX C

Glossary

AAAFTS. American Automobile Association Foundation for Traffic Safety.

AADT. Annual Average Daily Traffic.

AASHTO. American Association of State and Highway Transportation Officials.

Ambient conditions. The visual background or surrounding atmospheric and visibility 

conditions.

Angular motion sensitivity. The ability of an observer to detect changes in the apparent 

distance and direction of movement of an object as a function of the change in the 

angular size of the visual stimulus on the observer’s retina.

Angular velocity threshold. The rate of change in angular size of a visual stimulus that 

is necessary for an observer to discern that an object’s motion has increased or 

decreased. 

Annual average daily traffic (AADT). The total volume passing a point or segment of a 

highway facility in both directions for 1 year divided by the number of days in the 

year.

Apron. The mountable portion of the central island of a roundabout that is adjacent to 

the circulatory roadway. An apron is generally required on smaller roundabouts to 

accommodate the wheel tracking of large vehicles.

ASTM. American Society for Testing and Materials.

ATSSA. American Traffic Safety Services Association.

Attraction signing. Information/supplemental signs featuring logos or verbal messages 

pointing out places to visit or food, gas, and rest stop locations.

Barnes Dance timing. Type of exclusive signal timing phase where pedestrians may also 

cross diagonally in addition to crossing either street. Also referred to as scramble 

timing.

Brake reaction time. The interval between the instant that the driver recognizes the 

presence of an object or hazard on the roadway ahead and the instant that the driver 

actually applies the brakes.

Brightness. A term that refers to human perception of luminance. Whereas luminance 

is a photometrically measured quantity, brightness describes how intense a light 

source or lighted surface appears to the human eye. 

 Buttonhook ramp. J-shaped ramp that connects to a parallel or diagonal street or 

frontage road, which is often well removed from the interchange structure and other 

ramps.
358 Handbook for Designing Roadways for the Aging Population

APPENDIX C—GLOSSARY

Candela (cd). A measure of luminous intensity.

Central island. The raised area in the center of a roundabout around which traffic 

circulates.

Changeable message sign (CMS). Sometimes called portable changeable or variable 

message sign. This traffic control device has the flexibility to display a variety of 

messages to fit the needs of the traffic and highway situation.

Channelization. The separation or regulation of conflicting traffic movement into 

definite paths of travel by the use of pavement markings, raised islands, or other 

suitable means, to facilitate the safe and orderly movement of both vehicles and 

pedestrians.

Chevron signs. A chevron symbol (sideways “V”) in black, against standard yellow 

background, on a vertical rectangle. Used as an alternate or supplement to standard 

delineators and to large arrow signs. 

CIE. Commission Internationale de l’Éclairage (International Commission on Street/

Highway Lighting).

Circulatory roadway. The curved path used by vehicles to travel in a counterclockwise 

fashion around the central island of a roundabout.

Circulatory roadway width. The width between the outer edge of the circulatory 

roadway and the central island, not including the width of any apron.

Cloverleaf interchange. A form of interchange that provides indirect right-turn 

movements in all four quadrants by means of loops. Generally used where the

turning and weaving volumes are relatively low. This type of interchange eliminates 

all crossing conflicts found in a diamond interchange but requires more area. The 

cloverleaf type of interchange can have one or two points of entry and exit on each 

through roadway.

Coefficient of luminous intensity (RI

). The ratio of the luminous intensity (I) of a 

retroreflectometer in the direction of observation to the illuminance E at the 

retroreflectometer on a plane perpendicular to the direction of the incident light, 

expressed in candelas per lux.

Coefficient of retroreflected luminance (RL

). A measure of retroreflection most 

often used to describe the retroreflectivity of pavement markings. Coefficient of 

retroreflected luminance is defined as the coefficient of luminous intensity per unit 

area. 

Coefficient of retroreflection (RA). A measure of retroreflection used more often to refer 

to the retroreflectivity of highway signs. Coefficient of retroreflection is defined 

as the ratio of the coefficient of luminous intensity (RI

) of a plane retroreflecting 

surface to its area (A), expressed in candelas per lux per square meter.

Complete interchange lighting (CIL). Includes lighting in the interchange area on both 

the acceleration and deceleration areas plus the ramps through the terminus.
Handbook for Designing Roadways for the Aging Population 359

APPENDIX C—GLOSSARY

Composite photometry. Light measurement applied to a high-mast lighting system 

that employs a counterbeam arrangement, to take advantage of the efficiency with 

which pavement luminance can be increased with light directed upstream, while 

enhancing positive contrast through additivity of vehicle headlighting with the light 

directed downstream.

Concrete safety-shaped barrier (CSSB). A tapered concrete barrier used as a highway 

divider in narrow medians to prevent vehicle crossovers into oncoming traffic. It 

is referred to as a Jersey Barrier in some jurisdictions, as its first application was on 

the New Jersey Turnpike. CSSB’s can be either permanent barriers or temporary 

portable barriers used in work zone applications.

Conspicuity. A measure of the likelihood that a driver will notice a certain target at a 

given distance against a certain background. 

Contrast. See luminance contrast.

Contrast sensitivity. Ability to perceive a lightness or brightness difference between 

two areas. Frequently measured for a range of target patterns differing in value 

along some dimension such as pattern element size and portrayed graphically in a 

contrast sensitivity function in which the reciprocal of contrast threshold is plotted 

against pattern spatial frequency or against visual angle subtended at the eye by 

pattern elements (such as bars).

Critical gap. The gap (distance to nearest vehicle) in oncoming or cross traffic that a 

driver will accept to initiate a turning or crossing maneuver 50 percent of the time it 

is presented, typically measured in seconds.

Crossbuck. White X-shaped retroreflectorized highway-rail grade crossing sign with the 

words RAILROAD CROSSING in black lettering, located alongside the highway

at the railroad tracks. At multiple track crossings a sign indicating the number of 

tracks will be on the post of the Crossbuck.

Cutoff. A luminaire light distribution is designed as cutoff when the candlepower per 

1,000 lamp lumens does not numerically exceed 25 (2.5 percent) at an angle of 

90 degrees above nadir (horizontal); and 100 (10 percent) at a vertical angle of 80 

degrees above nadir. This applies to any lateral angle around the luminaire.

Dark adaptation. Adjustment of the eye to low levels of illumination, which results in 

increased sensitivity to light.

Decision sight distance (DSD). The distance required for a driver to detect an 

unexpected or otherwise difficult-to-perceive information source or hazard in a 

roadway environment that may be visually cluttered, recognize the hazard or its 

threat potential, select an appropriate speed and path, and initiate and complete the 

required safety maneuver safely and efficiently.

Deflection. The change in trajectory of a vehicle imposed by geometric features of the 

roadway.

Depth perception. The ability to distinguish the relative distance of objects in visual 

space, used to interpret their motion over multiple observations.
360 Handbook for Designing Roadways for the Aging Population

APPENDIX C—GLOSSARY

Diamond interchange. The simplest and perhaps most common type of interchange. 

This type of interchange contains a one-way diagonal-type ramp in one or more of 

the quadrants. The diamond interchange provides for all movements to and from 

the intersecting road.

Diverge steering (DS) zone. Used with interchange/ramp exit models, it is the distance 

upstream from the exit gore at which a driver begins to diverge from the freeway. 

Divided attention. The ability of a driver to allocate attention among tasks or stimuli in 

the roadway environment, where more than one task or stimulus is perceived to be 

important to safe performance at a given time.

Divided highway. Roadway that is separated by a median. 

Downstream. The direction toward which traffic is flowing.

Dynamic visual acuity. Acuteness or clarity of vision for an object that has angular 

movement relative to the observer. Acuity depends on sharpness of retinal focus, 

sensitivity of nervous elements, oculomotor coordination, interpretative faculty of 

the brain, and contextual variables.

Edgeline visibility. The detection/recognition of painted pavement surface delineation 

along roadway edges demarcating the outside edge of the travel lane.

Entry width. The width of the entry to a roundabout, where it meets the inscribed circle, 

measured perpendicularly from the right edge of the entry to the intersection point 

of the left edge line and the inscribed circle.

Exit gore area. The area located immediately between the left edge of a ramp pavement 

and the right edge of the mainline roadway pavement at a merge or diverge area.

Flared approach. The widening of an approach at a roundabout, resulting in multiple 

lanes at entry to provide additional capacity at the yield line and storage.

FARS. Fatal Analysis Reporting System.

FHWA. Federal Highway Administration.

Footcandle. The English system’s unit of illuminance. One footcandle is the illuminance 

on a surface that is everywhere one foot from a uniform point source of light of one 

candle and equal to one lumen per square foot. One footcandle equals 10.76 lux.

Footlambert. A unit of luminance equivalent to 1 lumen per square foot. 

Full diamond interchange. Interchange with a one-way diagonal-type ramp in each 

quadrant. 

Gap acceptance. The decision by a driver that there is sufficient time and/or distance 

ahead of an approaching vehicle to allow safe performance of a desired crossing or 

merging maneuver.
Handbook for Designing Roadways for the Aging Population 361

APPENDIX C—GLOSSARY

Gap judgments. The judgment of a driver of the time and/or distance ahead of an 

approaching vehicle traveling in a lane that the driver wishes to turn across or 

merge into. 

Gap search and acceptance (GSA) zone. Used with interchange/ramp entry models, it is 

the zone in which the driver searches, evaluates, and accepts or rejects the available 

lags or gaps in the traffic stream for execution of a merging maneuver. 

Guard (guide) rail. Protective barrier along a roadway to prevent vehicles from leaving 

the roadway. 

Half-diamond interchange. An interchange with a one-way diagonal-type ramp in two 

adjacent quadrants. This type of interchange is appropriate to situations in which 

traffic demand is predominantly in one direction. 

High-mast lighting. Illumination of a large area by means of a cluster of 3 to 12 

luminaires which are designed to be mounted in fixed orientation at the top of a 

high mast (generally 18 to 46+ m [80 to 150+ ft] or higher). 

High-spatial-frequency stimulus. A visual target characterized by fine detail.

Highway-rail grade crossing. The general area where a highway and a railroad’s rightof-way cross at the same level, including the railroad tracks, highway, and traffic 

control devices for highway traffic traversing the area.

Horizontal alignment. The linear (tangent) character or specific degree of curvature 

describing the geometry of a defined section of highway in plain view. 

IIHS. Insurance Institute for Highway Safety.

Illuminance. The density of luminous flux (rate of emission of luminous energy flow of a 

light source in all directions) incident on a surface; the quotient of the flux divided 

by the area of the surface, when the surface is uniformly illuminated.

Illumination. The amount of light falling onto a surface. 

Initial acceleration (IA) zone. Used with interchange/ramp entry models, it is the zone 

in which the driver accelerates to reduce the speed differential between the ramp 

vehicle and the freeway vehicles to an acceptable level for completing the merge 

process. 

Inscribed circle diameter. The basic parameter used to define the size of a roundabout, 

measured between the outer edges of the circulatory roadway. It is the diameter of 

the largest circle that can be inscribed within the outline of the intersection.

In-service brightness level (ISBL). The brightness level of a delineation treatment at 

an intermediate point in its anticipated service life; this value varies by type of 

delineator, type of wear (traffic level), and environmental conditions.

Interchange (grade separation). A system of interconnecting roadways that provides for 

the movement of traffic between two or more highways on different levels.
362 Handbook for Designing Roadways for the Aging Population

APPENDIX C—GLOSSARY

Intersecting angle (skew). The angle formed by the intersection of two roadways (other 

than a 90-degree angle). 

Intersection (at grade). The general area where two or more highways join or cross 

without grade separation, including the roadway and roadside facilities for traffic 

movements within it.

Intersection sight distance (ISD). The unobstructed view of an entire (at-grade) 

intersection and sufficient lengths of the intersecting highway to permit control of 

the vehicle to avoid collisions during through and turning movements. 

ISTEA. Intermodal Surface Transportation Efficiency Act. 

TEH. Institute of Transportation Engineers.

Joint flexibility. An aspect of the physical condition of the driver that can be assessed 

to determine whether the driver has sufficient strength to turn the steering wheel, 

apply the brakes, and generally control the vehicle.

Lane control signals. Special overhead signals that permit or prohibit the use of specific 

lanes of a street or highway or that indicate the impending prohibition of their use.

Leading pedestrian interval (LPI). Also known as, “pedestrian head start,” and 

“delayed vehicle green,” an LPI allows pedestrians to begin crossing an intersection 

a few seconds before the vehicular green interval begins. This allows pedestrians 

to establish their presence in the crosswalk before the turning vehicles, thereby 

enhancing the pedestrian right of way.

Legibility index (LI). Used to describe the relative legibility of different letter styles, 

it is calculated from the distance at which a character, word, or message is legible 

divided by the size of the letters on the sign.

Limited sight distance. A restricted preview of the traveled way downstream due to 

a crest vertical curve or horizontal curvature of the roadway, or to blockage or 

obstruction by a natural or manmade roadway feature or by (an)other vehicle(s).

Luminaire. A complete lighting unit consisting of a lamp or lamps together with the 

parts designed to distribute the light, to position and protect the lamps, and to 

connect the lamps to the power supply. 

Luminance. The luminous intensity or brightness of any surface in a given direction, per 

unit of projected area of the surface as viewed from that direction, independent of 

viewing distance. The SI unit is the candela per square meter.

Luminance contrast. The difference between the luminance of a target area and a 

surrounding background area, divided by the background luminance alone (e.g., 

lane marking minus lane pavement surface, divided by pavement surface.)

Lux. The metric unit of illuminance. One lux is equal to the illuminance corresponding 

to a luminous flux density of one lumen per square meter. 
Handbook for Designing Roadways for the Aging Population 363

APPENDIX C—GLOSSARY

Measures of effectiveness (MOE’s). Descriptions of driver or traffic behavior which 

quantify the level of safety or the quality of service provided by a facility or 

treatment to drivers, passengers, or pedestrians; examples include vehicle 

speed, trajectory, delay, and similar measures, especially crashes, plus indices 

of performance such as reaction time. In research studies, the MOE’s are the 

dependent measures (e.g., the effects/behaviors resulting from introduction of a 

treatment or countermeasure).

Median barriers. A longitudinal system of physical barriers used to prevent an errant 

vehicle from crossing the portion of a divided highway separating traffic moving in 

opposite directions.

Merge steering control (MSC) zone. Used with interchange/ramp entry models, it is the 

zone in which the driver enters the freeway and positions the vehicle in the nearest 

lane on the mainline.

Minimum required visibility distance (MRVD). The distance necessary to permit 

detection and comprehension, plus driver decision-making, response selection, and 

completion of a vehicle maneuver, if necessary. 

Mountable. Geometric features (e.g., curbs) that can be driven upon by vehicles without

damage, but not intended to be in the normal path of traffic.

MUTCD. Manual on Uniform Traffic Control Devices for Streets and Highways.

NCHRP. National Cooperative Highway Research Program.

Nearside priority. Priority given to drivers entering the circle of a roundabout.

Negative offset. A term used to describe the alignment of opposing left-turn lanes at an 

intersection; this geometry exists when the left boundary of one left-turn lane, when 

extended across the intersection, falls to the right of the right-facing boundary of 

the opposite left-turn lane. 

NHTSA. National Highway Traffic Safety Administration.

Non-cutoff. The luminaire light distribution category when there is no candlepower 

limitation in the zone above maximum candlepower. 

No turn on red (NTOR). This message on signs is used to indicate that a right turn on 

red (or left turn on red for one-way streets) is not permitted at an intersection.

NTSB. National Transportation Safety Board.

Ocular media. The internal structure of the eye, including the aqueous, through 

which light entering through the cornea must be transmitted before reaching the 

photosensitive retina. 

Ocular transmittance. The amount of light reaching the retina relative to the amount 

incident upon the cornea.
364 Handbook for Designing Roadways for the Aging Population

APPENDIX C—GLOSSARY

Offside priority. Priority given to traffic already in the circle of a roundabout.

Osteoarthritis. A degenerative form of arthritis. 

Parclo loop ramp. A (partial cloverleaf) interchange with loops in advance of the minor 

road with direction of travel on the freeway; and in the same interchange area, an 

interchange with loops beyond the minor road.

Partial interchange lighting (PIL). Lighting on an interchange that consists of a few 

luminaires located in the general areas where entrance and exit ramps connect with 

the through traffic lanes of a freeway (between the entry gore and the end of the 

acceleration ramp or exit gore and the beginning of the deceleration ramp). 

Passive crossing control devices. Non-activated traffic control devices, including signs, 

pavement markings, and other devices located at or in advance of crossings to 

indicate the presence of a crossing and the possibility of a train.

Peak intensity. The maximum strength of a traffic signal maintained through a defined 

viewing angle; measured in candelas. 

Pedestrian control device. A special type of device (including pedestrian signal 

indications and sign panels) intended for the exclusive purpose of controlling 

pedestrian traffic in crosswalks.

Pedestrian crosswalk. An extension of a sidewalk across an intersection or across a 

roadway at a midblock location to accommodate pedestrian movement.

Pedestrian refuge. An at-grade opening within a median island that allows pedestrians 

to safely wait for an acceptable gap in traffic. 

Perception-reaction time (PRT). The interval between a driver’s detection of a target 

stimulus or event and the initiation of a vehicle control movement in response to the 

stimulus or event.

Positive offset. A term used to describe the alignment of opposing left-turn lanes at an 

intersection; this geometry exists when the left boundary of one left-turn lane, when 

extended across the intersection, falls to the left of the right-facing boundary of the 

opposite left-turn lane. 

Post-mounted delineators (PMD’s). Retroreflective devices located in a series at the 

side of a roadway to indicate alignment. Each delineator consists of a flat reflecting 

surface, typically a vertical rectangle, mounted on a supporting post.

Raised. Geometric features (e.g., curbs) with a sharp elevation change that are not

intended to be driven upon by vehicles at any time.

Raised pavement markers (RPM’s). Used as positioning guides and/or as supplements 

or substitutes for other types of markings, these markers conform to the color 

of the marking for which they serve as a positioning guide, can be mono- or bidirectional, and are fastened into the pavement with the reflector surface visible 

above the road surface.
Handbook for Designing Roadways for the Aging Population 365

APPENDIX C—GLOSSARY

Reaction time (RT). The time from the onset of a stimulus to the beginning of a driver’s 

(or pedestrian’s) response to the stimulus, by a simple movement of a limb or other 

body part.

Retroreflective. Capable of returning light to its source.

Rheumatoid arthritis. A usually chronic disease of unknown cause characterized 

by pain, stiffness, inflammation, swelling, and sometimes destruction of joints. 

Drivers with this condition sometimes require compensatory equipment for their 

vehicle. In acute conditions, individuals should not drive because of weakness and 

extreme tenderness in the joints of the wrists and hands.

Right turn on red (RTOR). Unless otherwise specified by traffic signal control signing, 

this practice permits a driver to proceed with a right turn on a red signal after 

stopping at signalized intersections. It provides increased capacity and operational 

efficiency at a low cost. 

Roundabouts. Circular intersections with specific design and traffic control features that 

include yield control of entering traffic, channelized approaches, and appropriate 

geometric curvature to ensure that travel speeds on the circulating roadway are 

typically less than 50 km/h (30 mph).

Route marker reassurance assembly. Consists of a cardinal direction marker (i.e., east, 

west, north, and south) and a route marker.

Saccadic movement. A change in visual fixation from one point to another by means of 

a quick, abrupt movement of the eye.

Scissors off-ramp. A condition where one-way traffic streams cross by merging and 

diverging maneuvers onto exit ramps. Drivers tend to go straight ahead onto an offramp instead of turning left.

Selective attention. The ability, on an ongoing moment-to-moment basis while driving, 

to identify and allocate attention to the most relevant information, especially 

embedded when within a visually complex scene and in the presence of a number of 

distractors.

Senile miosis. An aging characteristic involving an excessive smallness or contraction of 

the pupil of the eye.

Short range delineation. Delineation that is useful to the driver for tracking the 

roadway at night under poor visibility conditions.

Sight distance. The length of highway visible to the driver.

Sight triangle. In plan view, the area defined by the point of intersection of two 

roadways, and by the driver’s line of sight from the point of approach along one 

leg of the intersection, to the farthest unobstructed location on another leg of the 

intersection.

Situational awareness. The selective attention to and perception of environmental 

elements within a specified space and time envelope, the comprehension of their 

meaning, and the projection of their status in the near future. 
366 Handbook for Designing Roadways for the Aging Population

APPENDIX C—GLOSSARY

Slip ramp. A diagonal ramp, more properly called a cross connection, which connects 

with a parallel frontage road. 

Small target visibility (STV). A proposed criterion for roadway lighting. The concept 

assumes that increased target visibility results in both increased nighttime safety 

and improved nighttime driver performance, a surrogate for reduced crash risk. 

Speed-change lane (SCL). Used in interchange/ramp exit models, it refers to the speedchange maneuver on deceleration lanes segmented components.

Splitter island. A raised or painted area on an approach to a roundabout used to 

separate entering from exiting traffic, deflect and slow entering traffic, and provide 

storage space for pedestrians crossing the road in two stages. It is also referred to as 

a median island or separator island.

Steering control (SC) zone. Used with interchange/ramp entry models, it is the zone 

where positioning of the vehicle along a path from the controlling ramp curvature 

onto the speed-change lane is accomplished.

Stereopsis. Binocular visual perception of three-dimensional space based on retinal 

disparity.

Stopping sight distance (SSD). The sight distance required to permit drivers to see an 

obstacle soon enough to stop for it under a defined set of reasonable worst-case 

conditions, without the performance of any avoidance maneuver or change in travel 

path; the calculation of SSD depends upon speed, gradient, road surface and tire 

conditions, and assumptions about the perception-reaction time of the driver.

Temporary pavement marking treatment. This treatment primarily involves the 

application of paint or tape striping and has been shown to be important for 

effective vehicle guidance at highway work sites. 

Threshold contrast. The minimum difference in luminance of a target and luminance 

of that target’s background at which the target is visible. Also defined as the 

luminance contrast detectable during some specific fraction of the times it is 

presented to an observer, usually 50 percent.

T-intersection. An intersection that involves three legs, where one leg is perpendicular 

to the other two legs. There are several types of this intersection, such as plain, with 

turning lanes, and channelized.

Traffic control device (TCD). The prime, and often the only, means of communicating 

with the driving public. These devices (e.g., signs, markings, signals, islands) 

must be used discriminately, uniformly, and effectively to ensure correct driver 

interpretation and response. 

Transient adaptation factor. A reduction in target contrast caused by the process of 

transient visual adaptation.

Transient visual adaptation (TVA). The process in which the (driver’s) eye fixates upon 

roadway locations or surrounding environments at different luminance levels, 

continuously adapting to higher and lower levels; this process temporarily reduces 

contrast sensitivity.
Handbook for Designing Roadways for the Aging Population 367

APPENDIX C—GLOSSARY

TRB. Transportation Research Board.

Trumpet interchange. A three-leg interchange where a connecting highway terminates 

and where only a small amount of traffic moves between the terminating highway 

and one of the two legs of the freeway. The trumpet is laid out so that this minor 

traffic moves via a 200-degree loop. 

Two-quadrant cloverleaf interchange. A type of partial cloverleaf where most traffic 

leaving one highway turns to the same leg of the intersecting highway.

TWLTL. Two-way, left-turn lane.

Two-way stop-control. Stop signs are present on the approaches of the minor street and 

drivers on the minor street (or a driver turning left from the major street) must wait 

for a gap in the major-street traffic to complete a maneuver.

Upstream. The direction from which traffic is flowing.

Useful field of view. Also known as the “functional field of view”, or “attentional 

window,” this area refers to a subset of the total field of view where stimuli can not 

only be detected, but can be recognized and understood sufficiently to permit a 

timely driver response. As such, this term represents an aspect of visual information 

processing, rather than a measure of visual sensitivity.

Variable message sign (VMS). See changeable message sign.

Veiling glare. Stray light entering the eye that reduces the contrast of a target upon 

which the driver has fixated; this may result from the driver’s direct view of light 

sources, such as opposing headlights or roadway luminaires, or from light reflected 

from surfaces near the target’s location.

Vertical curve. The parabolic curve connecting the two approach grades on either side of 

a hill.

Visual accommodation. The process by which the eye changes focus from one distance 

to another

Visual acuity. The ability of an observer to resolve fine pattern detail. Acuity is usually 

specified in terms of decimal acuity, defined as the reciprocal of the smallest 

resolvable pattern detail in minutes of arc of visual angle. “Normal” or average 

acuity is considered to be 1.0 (a resolution of 1-min arc). 

Visual adaptation. The process by which the retina becomes accustomed to more or less 

light than it was exposed to during an immediately preceding period. It results in a 

change in the sensitivity of the eye to light.

Visual clear (VC) zone. Used with interchange/ramp entry models, this refers to the 

zone that provides a buffer between the driver and the end of the acceleration lane, 

where the driver can either merge onto the freeway in a forced maneuver or abort 

the merge and begin to decelerate at a reasonable rate.
368 Handbook for Designing Roadways for the Aging Population

APPENDIX C—GLOSSARY

Yield line. A pavement marking used to mark the point of entry from an approach 

into the circulatory roadway of a roundabout, and is generally marked along the 

inscribed circle. Entering vehicles must yield to any circulating traffic coming from 

the left before crossing this line into the circulating roadway.

Zebra crossing. A crossing marked by transverse white stripes where vehicles are 

required to yield to pedestrians.
Handbook for Designing Roadways for the Aging Population 369

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