HANDBOOK FOR 

Designing Roadways

for the AGING POPULATION

DESK REFERENCE

Interchanges Roadway

Segments

Intersections

Construction/

Work Zones

HighwayRail Grade

Crossings

Interchanges Roadway

Segments

Intersections

Construction/

Work Zones

HighwayRail Grade

Crossings
Desk Reference for Designing Roadways for the Aging Population

Handbook for Designing Roadways for the Aging Population

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.

Desk Reference for Designing Roadways for the Aging Population

Technical Report Documentation Page

1. Report No.

FHWA-SA-15-088

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

4. Title and Subtitle

Desk Reference to the Handbook for Designing Roadways for the 

Aging Population

5. Report Date

December 2015

6. Performing Organization Code

7. Authors 

Marcus Brewer (TTI), Lisa Bedsole (Leidos)

Authors of Previous Handbook

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

Leidos Texas A&M Transportation Institute

11251 Roger Bacon Drive 2935 Research Parkway

Reston, VA 20190 College Station, TX 77845

Performing Organization Name and Address for the Handbook

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.

DTFH61-10-D-00024

Contract or Grant No. for Handbook

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

Desk Reference

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 (FHWARD-97-135). The 2nd edition, titled Highway Design Handbook for Older Drivers and Pedestrians 

(FHWA-RD-01-103) was published in 2001. The 3rd edition, under a new title, incorporates new research 

findings and treatments to improve the safety of the transportation system for the aging population.

This Desk Reference serves as a companion document to the 3rd edition of the Handbook. It provides a 

shortened version of the technical information practitioners need to address problems for aging drivers 

and pedestrians. It also contains references to the specific pages in the Handbook where additional 

treatment details, supporting information, and references to national guidance documents can be found.

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

 100

22. Price

N/A

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

Desk Reference for Designing Roadways for the Aging Population

4 Handbook for Designing Roadways for the Aging Population

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 squareinches 645.2 square millimeters mm2

ft2 square feet 0.093 squaremeters m2

yd2 square yard 0.836 squaremeters m2

ac acres 0.405 hectares ha

mi2 squaremiles 2.59 square kilometers km2

fl oz

VOLUME fluidounces 29.57 milliliters

gallons 3.785 liters

cubic feet 0.028 cubicmeters

cubic yards 0.765 cubic

meters NOTE: volumes greater than 1000 L shall be

shown in m3

mL

gal L

ft3

m3

yd3

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")

o

F

TEMPERATURE (exact degrees) Fahrenheit 5 (F-32)/9 Celsius

or(F-32)/1.8

o

C

fc

fl

ILLUMINATION foot-candles 10.76 lux

foot-Lamberts 3.426 candela/m2

lx

cd/m2

lbf

lbf/in2

FORCE and PRESSURE or STRESS poundforce 4.45 newtons

poundforce per square inch 6.89 kilopascals

N

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 squareinches in2

m2 squaremeters 10.764 square feet ft2

m2 square meters 1.195 square yards yd2

ha hectares 2.47 acres ac

km2 square kilometers 0.386 squaremiles mi2

VOLUME mL milliliters 0.034 fluid ounces fl oz

L liters 0.264 gallons gal

m3 cubicmeters 35.314 cubic feet ft3

m3 cubicmeters 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 (2000lb) T

o

C

TEMPERATURE (exact degrees) Celsius 1.8C+32 Fahrenheit o

F

lx

cd/m2

ILLUMINATION lux 0.0929 foot-candles

candela/m2 0.2919 foot-Lamberts

f

c

fl

N

kPa

FORCE and PRESSURE or STRESS newtons 0.225 poundforce

kilopascals 0.145 poundforce per squareinch

lbf

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 March2003)
iii

Desk Reference for Designing Roadways for the Aging Population

Table of Contents

Chapter 1. Introduction to the Desk Reference .................................... 1

Overview ............................................................................................................................. 1

Knowing When to Implement these Recommendations.................................. 2

Organization fo the Desk Reference.......................................................................... 4

Chapter 2. Intersections.......................................................................... 7

1. Intersecting Angle (Skew) ................................................................................... 8

2. Receiving Lane (Throat) Width .......................................................................... 9

3. Channelization......................................................................................................... 9

4. Intersection Sight Distance...............................................................................11

5. Offset Left-Turn Lanes.........................................................................................12

6. Delineation of Edge Lines and Curbs............................................................15

7. Curb Radius.............................................................................................................17

8. Left-Turn Traffic Control for Signalized Intersections...............................18

9. Right-Turn Traffic Control for Signalized Intersections............................19

10. Street Name Signs................................................................................................20

11. Stop and Yield Signs............................................................................................22

12. Lane Assignment on Intersection Approach..............................................24

13. Traffic Signals.........................................................................................................25

14. Intersection Lighting...........................................................................................27

15. Pedestrian Crossings...........................................................................................28

16. Roundabouts..........................................................................................................30

17. Right-Turn Channelization Design .................................................................34

18. Combination Lane-Use/Destination Overhead Guide Signs................34

19. Signal Head Visibility ...........................................................................................35

20. High-Visibility Crosswalks..................................................................................36

21. Supplemental Pavement Marking for Stop and Yield Signs.................36

22. Reduced Left-Turn-Conflict Intersections....................................................37

23. Accessible Pedestrian Signal (APS) Treatments.........................................38

24. Flashing Yellow Arrow.........................................................................................38

Chapter 3. Interchanges........................................................................ 39

25. Exit Signs and Markings.....................................................................................40

26. Freeway Entrance Traffic Control Devices....................................................41

27. Delineation .............................................................................................................43

28. Acceleration/Deceleration Lane Design.......................................................44

29. Interchange Lighting...........................................................................................46

30. Restricted or Prohibited Movements............................................................46
iv

Desk Reference for Designing Roadways for the Aging Population

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

Junctions.................................................................................................................49

32. Wrong-Way Driving Countermeasures.........................................................50

Chapter 4. Roadway Segments............................................................. 51

33. Horizontal Curves.................................................................................................52

34. Vertical Curves.......................................................................................................54

35. Passing Zones........................................................................................................55

36. Lane Control Devices...........................................................................................56

37. Lane Drop Markings............................................................................................57

38. Contrast Markings on Concrete Pavement .................................................58

39. Utilize Highly Retroreflective Marking Material.........................................58

40. Curve Warning Markings....................................................................................59

41. Road Diets...............................................................................................................59

42. High Friction Surface Treatments...................................................................60

Chapter 5. Construction/Work Zones .................................................. 61

43. Signing and Advance Warning ........................................................................62

44. Portable Changeable (Variable) Message Signs........................................64

45. Channelization (Path Guidance)......................................................................66

46. Delineation of Crossovers/Alternate Travel Paths.....................................67

47. Temporary Pavement Markings......................................................................68

48. Increased Letter Height for Temporary Work Zone Signs......................69

49. Work Zone Road Safety Audit (WZRSA)........................................................69

Chapter 6. Highway-Rail Grade Crossing............................................. 71

50. Passive Traffic Control Devices.........................................................................72

51. Lighting....................................................................................................................73

Glossary.................................................................................................. 75
Handbook for Designing Roadways for the Aging Population

INTRODUCTION

Chapter 1. Introduction to the Desk Reference

Overview ............................................................................................................................. 1

Knowing When to Implement these Recommendations.................................. 2

Organization of the Desk Reference.......................................................................... 4

Desk Reference for Designing Roadways for the Aging Population
Desk Reference for Designing Roadways for the Aging Population

INTRODUCTION TO THE DESK REFERENCE

Handbook for Designing Roadways for the Aging Population

1

CHAPTER 1

Introduction to the Desk Reference

Overview 

This Desk Reference serves as a companion document 

to the Handbook for Designing Roadways for the Aging 

Population (the Handbook). It provides a quick reference 

to Part I of the Handbook and is ideal for use in the field or 

as an abbreviated information resource. While each design element 

from the Handbook is briefly described and illustrated in this desk 

reference, practitioners should refer to the corresponding section in 

the Handbook for more details and complete discussion.

This Desk Reference is organized in the following categories:

Chapter 2 — Intersections

Chapter 3 — Interchanges

Chapter 4 — Roadway Segments

Chapter 5 — Construction/Work Zones

Chapter 6 — Highway-Rail Grade Crossings

Within each chapter (category) is a list of the design elements that 

will be presented. For each design element, the Desk Reference 

illustrates the recommended treatments. 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 they are currently 

being used by one or more agencies, and, although 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. 

Keep in mind that this Desk Reference is a condensed version of 

the corresponding material in the Handbook; practitioners should 

refer to the same treatment in the Handbook for additional details, 

examples, illustrations, and image sources.
INTRODUCTION TO THE DESK REFERENCE

Desk Reference for Designing Roadways for the Aging Population

2

Also note that the drawings included in this Desk Reference are for 

illustrative purposes only; they are not to scale and should not be 

used for design purposes. 

Knowing When to Implement these 

Recommendations

Implementing the treatments in this Desk Reference will 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. 

The engineering enhancements described in this document should 

benefit all road users. Special justification may be required for 

implementation of Handbook practices. To this end, below is a threestep procedure outlining responses plus brief written comments to 

support engineering judgment. Please refer to the Handbook for a 

set of optional worksheets for documenting each step.

Step 1: Problem Identification [see Project Review Worksheet on 

page 7 of the Handbook]

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 work sheet 

that appears on page 7 of the Handbook, problem identification 

can be accomplished by answering YES or NO to the following four 

questions:
INTRODUCTION TO THE DESK REFERENCE

3

Desk Reference for Designing Roadways for the Aging Population

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 (noninstitutionalized) 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.
INTRODUCTION TO THE DESK REFERENCE

Desk Reference for Designing Roadways for the Aging Population

4

Step 2: Identification of Design Elements and Treatments [see 

worksheet on page 9 of the Handbook]

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 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). See the Handbook for a more indepth discussion of the identification process.

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

the Handbook]

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.

Organization

Like the Handbook for Designing Roadways for the Aging Population 

(Handbook), this Desk Reference includes recommended treatments 

for 33 traffic control or geometric design elements divided among 

five categories. The five categories of treatment are as follows:

• Intersections,
INTRODUCTION TO THE DESK REFERENCE

5

Desk Reference for Designing Roadways for the Aging Population

• 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 the original 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.

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 Manual on Uniform Traffic Control Devices (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 Desk Reference are not always consistent with those 

prescribed in the MUTCD. When employing treatments included 

in this Desk Reference and Handbook, only MUTCD-approved 

lettering styles, arrows and symbols should be used.
INTRODUCTION TO THE DESK REFERENCE

Desk Reference for Designing Roadways for the Aging Population

6

Additionally, any highway agency wishing to implement a treatment 

that has not been included in the most recent edition of the MUTCD 

must request experimentation approval from the FHWA.

Handbook References — This Desk Reference contains references 

below each treatment that indicate where the rationale and 

supporting evidence for this treatment can be found. This includes 

references to those national design guides that practitioners often 

turn to for guidance on the use and implementation of the treatment.

INTERSECTIONS

Handbook for Designing Roadways for the Aging Population

1

Intersecting Angle (Skew)

Intersection skew angle in degrees is 

the absolute value of the difference 

between 90 degrees and the actual 

intersection angle.

A. Unrestricted Right-of-Way

Where right-of-way is not 

restricted, all intersecting 

roadways should meet at a 

90-degree angle (as indicated in 

Figure 3).

B. Restricted Right-of-Way

Where right-of-way is restricted, 

intersecting roadways should 

meet at an angle of not less than 

75 degrees (as indicated in Figure 

4).

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).

The rationale and supporting evidence 

for these treatments begins on page 96 

of the Handbook.

1

90

75

Figure 3. 

Example 

90° angle of 

intersection

Figure 4. 

Example 

75° angle of 

intersection

Figure 5. Skewed 

signalized intersection 

with prohibition of right 

turn on red

PROVENPRACTICES

Design 

Element – 

each design 

element is 

numbered 

consistently 

with those in 

the Handbook 

to allow 

for quick. 

reference.

Category – 

identifies 

the current 

section of 

the guide.

Figures – 

figures 

are used 

throughout 

the guide to 

illustrate the 

recommendations. 

They are 

numbered 

for easy 

reference.

Treatment – 

each 

recommended 

treatment 

is identified 

with a letter 

for quick 

reference.

References –

Each practice 

refers back to 

the page in 

the Handbook 

where greater 

detail can be 

found.

Note – Numbers are consistent with the complete 

Handbook for easy cross-reference.
INTERSECTIONS

Chapter 2. Intersections 

1. Intersecting Angle (Skew) ................................................................................... 8

2. Receiving Lane (Throat) Width .......................................................................... 9

3. Channelization......................................................................................................... 9

4. Intersection Sight Distance...............................................................................11

5. Offset Left-Turn Lanes.........................................................................................12

6. Delineation of Edge Lines and Curbs............................................................15

7. Curb Radius.............................................................................................................17

8. Left-Turn Traffic Control for Signalized Intersections...............................18

9. Right-Turn Traffic Control for Signalized Intersections............................19

10. Street Name Signs................................................................................................20

11. Stop and Yield Signs............................................................................................22

12. Lane Assignment on Intersection Approach..............................................24

13. Traffic Signals.........................................................................................................25

14. Intersection Lighting...........................................................................................27

15. Pedestrian Crossings...........................................................................................28

16. Roundabouts..........................................................................................................30

17. Right-Turn Channelization Design .................................................................34

18. Combination Lane-Use/Destination Overhead Guide Signs................34

19. Signal Head Visibility ...........................................................................................35

20. High-Visibility Crosswalks..................................................................................36

21. Supplemental Pavement Marking for Stop and Yield Signs.................36

22. Reduced Left-Turn-Conflict Intersections....................................................37

23. Accessible Pedestrian Signal (APS) Treatments.........................................38

24. Flashing Yellow Arrow.........................................................................................38

Desk Reference for Designing Roadways for the Aging Population
INTERSECTIONS

7

Desk Reference for Designing Roadways for the Aging Population

CHAPTER 2

Intersections

This section of the Desk Reference illustrates 

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. Following these proven 

practices, eight additional promising practices are addressed. 

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
INTERSECTIONS

8

Desk Reference for Designing Roadways for the Aging Population

Intersecting Angle (Skew)

Intersection skew angle in degrees is 

the absolute value of the difference 

between 90 degrees and the actual 

intersection angle.

A. Unrestricted Right-of-Way

Where right-of-way is not restricted, all intersecting roadways 

should meet at a 90-degree angle 

(as indicated in Figure 3).

B. Restricted Right-of-Way

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

an angle of not less than 75 degrees 

(as indicated in Figure 4).

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).

The rationale and supporting evidence 

for these treatments begins on page 96 

of the Handbook.

1

90

75

Figure 3. 

Example 

90° angle of 

intersection

Figure 4. 

Example 

75° angle of 

intersection

Figure 5. Skewed 

signalized intersection 

with prohibition of right 

turn on red

PROVEN PRACTICES
INTERSECTIONS

9

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for this treatment begins on 

page 99 of the Handbook.

Channelization

A. Left- and Right-Turn Lanes

Raised channelization with sloping curbs (see Figure 7) is 

recommended instead of pavement markings alone for turn 

lane treatments on all roadways with operating speeds of less 

than 45 mph.

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 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. 

2

3

16 ft

Recommended Receiving Lane Width

4–5 ft

Bicycle Lane/

Paved Shoulder

11–12 ft Travel Lane

Figure 6. Recommended receiving lane width
INTERSECTIONS

10

Desk Reference for Designing Roadways for the Aging Population

Contrast should be calculated according to this formula:

* 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.

C. Acceleration Lane

If right-turn channelization is present, 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.

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.

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.

Figure 7. Vertical curb 

(top), sloping curb 

(bottom)

Luminancestripe - Luminancepavement

Luminancepavement

Luminance contrast (C) =
INTERSECTIONS

11

Desk Reference for Designing Roadways for the Aging Population

F. Median Channelization

To reduce unexpected midblock conflicts with opposing 

vehicles, the use of channelized left-turn lanes in combination 

with continuous raised-curb 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.

The rationale and supporting evidence for these treatments begins 

on page 102 of the Handbook.

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, as defined in the AASHTO Green Book (2011):

• 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.

The rationale and supporting evidence for these treatments begins 

on page 107 of the Handbook.

4
INTERSECTIONS

12

Desk Reference for Designing Roadways for the Aging Population

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. 

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.

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 leftturn traffic includes a moderate to heavy volume of large trucks.

5

Figure 8. Left-turn lanes with positive offset
INTERSECTIONS

13

Desk Reference for Designing Roadways for the Aging Population

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

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

1 ft = 0.305 m

D. Signs and Markings

At intersections where the left-turn lane treatment 

results in channelized offset left-turn lanes, the following 

countermeasures (see Figure 9) are recommended to reduce 

the potential for wrong-way maneuvers by drivers turning left 

from a stop-controlled 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.

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

sheeting, to provide increased sign conspicuity and 

legibility for older drivers. 

D-3. Retroreflective lane-use arrows.

D-4. Retroreflective pavement marking extensions of the 

center line that scribe a path through the turn, except 

where extensions for opposing movements cross.
INTERSECTIONS

14

Desk Reference for Designing Roadways for the Aging Population

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

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.

D-6. Delineation of median noses using retroreflective 

treatments to increase their visibility and improve driver 

understanding of the intersection design and function.
INTERSECTIONS

15

Desk Reference for Designing Roadways for the Aging Population

E. Pedestrian Accommodations

At intersections where there are high pedestrian volumes, and 

the offset left-turn treatment results in a crossing width that 

would require a pedestrian walking at 3.0 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 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 to separate the left-turn lane from opposing 

travel lanes. 

The rationale and supporting evidence for these treatments begins 

on page 122 of the Handbook.

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.

6

Figure 10. Pedestrian Crossing 

Island (or Refuge Area)

6ft minimum 

width
INTERSECTIONS

16

Desk Reference for Designing Roadways for the Aging Population

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

3.0 or higher.

 Contrast should be calculated according to the formula 

shown for Treatment 3: Channelization on page 10.

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 lowmounted 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.

The rationale and supporting evidence for these treatments begins 

on page 129 of the Handbook.

Figure 11. Raised median island with 

yellow marking on the vertical face 

and top surface
INTERSECTIONS

17

Desk Reference for Designing Roadways for the Aging Population

Curb Radius

A. Simple Radius

Where roadways intersect at 90 degrees and are joined with a 

simple radius curve, a corner curb radius between 25 and 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).

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).

The rationale and supporting evidence for these treatments begins 

on page 132 of the Handbook.

7

Figure 12. Comparison of curb radii

Simple Curve

25 ft Radius

20ft Curve

with 1:10 Tapers 

and 2.5 ft Offsets

3-Centered 

Compound Curve

Radius = 100 ft, 20 ft,

100 ft
INTERSECTIONS

18

Desk Reference for Designing Roadways for the Aging Population

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 left-turning 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 leftturn lanes (see Design Element 5) or other geometric design 

features, or where a pattern of permissive left-turn crashes 

occurs.

B. Permissive Left-Turn Signing

If circular green is used as 

the permissive indication 

of a protected/permissive 

left- turn, 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).

C. Advance Signing

Where practical, an additional 

R10-12 sign 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 of the Handbook.]

8

Figure 13. MUTCD R10-12 sign 

adjacent to left-turn signal face

Figure 14. (MUTCD R10-31P)
INTERSECTIONS

19

Desk Reference for Designing Roadways for the Aging Population

D. Lead versus Lag Phasing

A leading protected left-turn phase is recommended wherever 

protected left-turn signal operation is implemented (as 

opposed to a lagging protected left-turn phase).

The rationale and supporting evidence for these treatments begins 

on page 135 of the Handbook.

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 addition to the MUTCD 

recommended practice of installing 

an R10-11 series sign near the appropriate signal head.

B. Skewed Signalized Intersections

As discussed in Treatment 1: Intersecting Angle (Skew), 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 4), prohibit right turn on

red (RTOR).

9

Figure 15. (MUTCD R10-11)
INTERSECTIONS

20

Desk Reference for Designing Roadways for the Aging Population

C. Pedestrian Protection

Posting 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 yellowgreen for this sign.)

The rationale and supporting evidence for these treatments begins 

on page 148 of the Handbook.

Street Name Signs

A. Letter Heights and Sign Border

Minimum letter heights of 6 

in for uppercase letters and 

4.5 in for lowercase letters are 

recommended for use on groundmounted 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.

10

Figure 17. (MUTCD R10-15)

Figure 18. (MUTCD D3-1)
INTERSECTIONS

21

Desk Reference for Designing Roadways for the Aging Population

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.

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 being 

used to provide adequate preparation 

time for any lane 

change and/or turning maneuvers (see 

Figure 20).

Figure 19. Intersection 

Warning W2-1 Sign and 

W16-8P Supplemental 

Advance Street Name 

Plaque

Figure 20. (MUTCD D3-2)

Scott Blvd Lincoln Ave
INTERSECTIONS

22

Desk Reference for Designing Roadways for the Aging Population

 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.

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 retroreflectivity should be used to provide increased 

sign conspicuity and legibility for aging drivers. 

The rationale and supporting evidence for these treatments begins 

on page 152 of the Handbook.

Stop and Yield Signs

A. Sign Size

The minimum sign size required by the 2009 MUTCD for STOP 

(R1-1) and YIELD (R1-2) signs is as follows:

• 30 in for single-lane applications and 36 in for multi-lane 

applications of STOP signs.

• 36 in for single-lane applications, 48 in for multi-lane 

applications, and 60 in for freeway applications of 

YIELD signs.

Larger R1-1 (36-in for single-lane applications, or 48-in in any 

location) signs may be used where engineering judgment 

indicates that greater emphasis or visibility is required.

11
INTERSECTIONS

23

Desk Reference for Designing Roadways for the Aging Population

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.

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.

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 

distance of at least 2.5 s. [See timespeed-distance table on page 5 of 

the Handbook.]

Figure 21. (MUTCD W4-4P)

Figure 22. (MUTCD W3-1)
INTERSECTIONS

24

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for these treatments begins 

on page 160 of the Handbook.

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.

12

Figure 23. Mast-arm mounted lane-use control signs
INTERSECTIONS

25

Desk Reference for Designing Roadways for the Aging Population

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-speed-distance 

table on page 5 of the Handbook.] R3-5 and R3-6 series signs 

should be mounted overhead wherever practical.

The rationale and supporting evidence for these treatments begins 

on page 170 of the Handbook.

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.

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:

13
INTERSECTIONS

26

Desk Reference for Designing Roadways for the Aging Population

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

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). 

C. Backplates

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.

Details on dimensions of reflective strips are provided in the 

Handbook on page 36.

The rationale and supporting evidence for these treatments begins 

on page 173 of the Handbook.

r = W + L 

1.47V

r = P + L 

1.47V
INTERSECTIONS

27

Desk Reference for Designing Roadways for the Aging Population

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.

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.

The rationale and supporting evidence for these treatments begins 

on page 181 of the Handbook.

14

Figure 24. Yellow retroreflective backplates
INTERSECTIONS

28

Desk Reference for Designing Roadways for the Aging Population

Pedestrian Crossings

A. Walking Speed

Use a walking speed of 3.0 s to calculate total crossing time 

(WALK interval plus pedestrian clearance interval). 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.

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) 

s p e c i f i c a t i o n s 

should 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).

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:

15

Figure 25. Pedestrian crossing at 

channelized right-turn lane
INTERSECTIONS

29

Desk Reference for Designing Roadways for the Aging Population

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

R10-3e, R10-3f, R10-3g, or R10-3i. Examples of R10-3e, 

R10-3f are shown in Figure 26; other examples are shown 

in the Handbook.

C-2. For two-stage crossings using a pedestrian refuge island, 

use MUTCD R10-3d 

or R10-3h on the 

corners of the intersection and the 

placards defined 

above the median 

refuge island.

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 rightturning vehicles to come 

into conflict with crossing 

pedestrians.

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 

3.0 s, may be calculated using the formula:

Figure 26. (MUTCD R10-3 Series) 

R10-3e, R10-3f

Figure 27. Recommended placement 

of MUTCD R10-15 sign

R10-3g R10-3h

R10-3e

R10-3i

R10-3c R10-3d R10-3f 

R10-3b 
INTERSECTIONS

30

Desk Reference for Designing Roadways for the Aging Population

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.

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 7.0 s.

The rationale and supporting evidence for these treatments begins 

on page 185 of the Handbook.

Roundabouts

Roundabouts should be considered as part of the engineering 

study in the design of new intersections and the redesign of 

existing intersections. When a State or local highway authority 

has determined through an engineering study to install a 

modern roundabout, include the following (see Figure 29):

16

Figure 28. Countdown 

pedestrian signal
INTERSECTIONS

31

Desk Reference for Designing Roadways for the Aging Population

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.

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.

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

Figure 29. Key geometric design elements and traffic control 

devices for roundabouts
INTERSECTIONS

32

Desk Reference for Designing Roadways for the Aging Population

C. Splitter Islands

Raised splitter islands, as opposed to pavement markings, 

should be used to delineate the channelization. The pedestrian 

crosswalk area should be designed at street level (crosswalk cut 

through a splitter island).

D. Conspicuity

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 

the formula shown for Treatment 3: Channelization on 

page 10.

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.

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).

Figure 30. (MUTCD W2-6)
INTERSECTIONS

33

Desk Reference for Designing Roadways for the Aging Population

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).

The rationale and supporting evidence for these treatments begins 

on page 197 of the Handbook.

Figure 31. Roundabout directional arrow sign

Figure 32. Placement of Roundabout Circulation Plaques

Central

Island

(Optional)

Central

Island
INTERSECTIONS

34

Desk Reference for Designing Roadways for the Aging Population

Right-Turn Channelization Design

Consider 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, as shown in the Preferred example on the right of Figure 33. 

Traffic control devices at the end of the channelization should be 

visible to vehicles entering the channelized lane.

The rationale and supporting evidence for these treatments can be 

found beginning on page 215 of the Handbook.

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 

17

18

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

PROMISING PRACTICES
INTERSECTIONS

35

Desk Reference for Designing Roadways for the Aging Population

used as overhead combination 

lane use destination guide signs 

and are described in Section 

2D.33 of the 2009 MUTCD (see 

Figure 34).

The rationale and supporting 

evidence for these treatments 

can be found beginning on 

page 215 of the Handbook.

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. 

The rationale and supporting evidence for these treatments can be 

found beginning on page 216 of the Handbook.

19

Figure 34. Combination Lane Use/

Destination Guide Sign (MUTCD 

D15-1)

Figure 35. Example Of One Signal Head Per Lane

OR
INTERSECTIONS

36

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 216 of the Handbook.

Supplemental Pavement Marking for Stop and 

Yield Signs

Use the “STOP AHEAD” pavement marking to supplement stop 

ahead signs (W3-1) and either the “YIELD AHEAD” pavement 

marking or the yield ahead triangle symbol pavement markings to 

supplement yield ahead signs (W3-2). See Section 3B.20 of the 2009 

MUTCD and Figure 37.

The rationale and supporting evidence for these treatments can be 

found beginning on page 217 of the Handbook.

20

21

Figure 36. High-Visibility 

(“Ladder”) Crosswalk

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

6 ft

30

inches

13 ft

Direction

of travel

8 inches

Direction

of travel
INTERSECTIONS

37

Desk Reference for Designing Roadways for the Aging Population

Reduced Left-Turn-Conflict 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 restricted-crossing U-turn 

(RCUT) intersection (see Figure 39) have features that minimize 

the operational delay and potential for crashes due to left turns. 

These innovative intersection designs should be considered for 

suitability during the engineering study for new and reconstructed 

intersections. Additional details are provided in the Handbook.

The rationale and supporting evidence for these treatments can be 

found beginning on page 218 of the Handbook.

22

Figure 39. Diagram of Restricted Crossing U-Turn Intersection

Figure 38. Diagram of Median U-Turn Intersection
INTERSECTIONS

38

Desk Reference for Designing Roadways for the Aging Population

Accessible Pedestrian Signal (APS) Treatments

A. Pushbutton-Activated Extended Pedestrian 

Crossing Phase

 At crosswalks frequently used by 

aging pedestrians, consider installing 

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 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. 

The rationale and supporting evidence for these treatments can be 

found beginning on page 219 of the Handbook.

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.

23

24

Figure 40. 

(MUTCD R10-32P)

Indicates Flashing

Figure 41. Typical 

arrangements of 

signal faces with 

flashing yellow 

arrow indications 

for permissive leftturn movements
INTERCHANGES

Chapter 3. Interchanges

25. Exit Signs and Markings.....................................................................................40

26. Freeway Entrance Traffic Control Devices....................................................41

27. Delineation .............................................................................................................43

28. Acceleration/Deceleration Lane Design.......................................................44

29. Interchange Lighting...........................................................................................46

30. Restricted or Prohibited Movements............................................................46

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

Junctions.................................................................................................................49

32. Wrong-Way Driving Countermeasures.........................................................50

Desk Reference for Designing Roadways for the Aging Population
INTERCHANGES

39

Desk Reference for Designing Roadways for the Aging Population

CHAPTER 3

Interchanges

This section of the Desk Reference focuses on treatments 

for highway design elements in six areas to enhance the 

performance of aging drivers at interchanges. After the 

last design element, two promising practice treatments 

are also presented. 

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

INTERCHANGES

Handbook for Designing Roadways for the Aging Population
INTERCHANGES

40

Desk Reference for Designing Roadways for the Aging Population

Exit Signs and Markings

A. Letter Size

Assume a minimum specific ratio of 1 inch of letter height 

per 30 feet of legibility distance for new or reconstructed 

installations and for sign replacement at interchanges and on 

their approaches.

B. Mixed-Case Lettering

It is required by the 2009 MUTCD that mixed-case lettering be 

used for destination and street names.

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).

25

Figure 42. Example Overhead Arrow-per-Lane Sign

PROVEN PRACTICES
INTERCHANGES

41

Desk Reference for Designing Roadways for the Aging Population

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. 

D. Retroreflective Sheeting

Microprismatic retroreflective sheeting should be used on 

overhead and ground-mounted guide signs.

The rationale and supporting evidence for these treatments can be 

found beginning on page 224 of the Handbook. 

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.

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 

26

Figure 43. (MUTCD D13-3)
INTERCHANGES

42

Desk Reference for Designing Roadways for the Aging Population

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.

Figure 44. Recommended signs and markings for adjacent entrance/exit 

ramps at a crossroad intersection
INTERCHANGES

43

Desk Reference for Designing Roadways for the Aging Population

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).

The rationale and supporting evidence for these treatments can be 

found beginning on page 235 of the Handbook.

Delineation

A. Delineators/Raised 

Pavement Markers

Delineation in the vicinity 

of the exit gore at nonilluminated and partially 

illuminated interchanges 

should include, as a minimum, raised pavement 

markers and retroreflective post- mounted 

delineators as shown in 

Figure 46.

27

Figure 46. Recommended 

raised pavement markers 

and post-mounted 

delineators at an exit gore

Figure 45. Advance 

ground-mounted 

diagrammatic sign

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)
INTERCHANGES

44

Desk Reference for Designing Roadways for the Aging Population

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.

C. Chevrons/PostMounted Delineators

Post-mounted delineators and/or chevrons 

should be applied to 

delineate the controlling curvature on 

exit ramps, as illustrated 

in Figure 47.

The rationale and supporting evidence for these treatments can be 

found beginning on page 238 of the Handbook.

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. A parallel 

style entrance lane length of at least 1,200 ft, plus a taper, is 

desirable.

B. Location of Exit Ramps

The AASHTO (2011) decision sight distance values (instead 

of stopping sight distance) should be consistently applied in 

28

Figure 47. Placement of chevrons on 

the controlling curve of an exit ramp
INTERCHANGES

45

Desk Reference for Designing Roadways for the Aging Population

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

locating ramp exits downstream from sight-restricting vertical 

or horizontal curvature on the mainline.

The rationale and supporting evidence for these treatments can be 

found beginning on page 243 of the Handbook.

Legend

 Direction of travel A Length of acceleration lane plus taper
INTERCHANGES

46

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for this treatment can be 

found beginning on page 248 of the Handbook.

Restricted or Prohibited Movements

A. Signing Practices

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.

A-2. To provide increased sign conspicuity and legibility for 

aging drivers, use retroreflective fluorescent red sheeting 

materials that provide for high retroreflectance overall.

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).

29

30
INTERCHANGES

47

Desk Reference for Designing Roadways for the Aging Population

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.

Figure 49. Recommended signing for restricted movements 

on an exit ramp

Exit Ramp

Entrace Ramp

Legend

Direction of travel

Wrong-way arrows

Optional
INTERCHANGES

48

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 252 of the Handbook.
INTERCHANGES

49

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 257 of the Handbook.

31

Figure 50. Route Shield Markings At Freeway Junctions

PROMISING PRACTICES
INTERCHANGES

50

Desk Reference for Designing Roadways for the Aging Population

Wrong-Way Driving Countermeasures

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. Those treatments include: 

• Conducting a Road Safety Audit (RSA) to examine the 

performance of the interchange and determine appropriate 

countermeasures to employ. 

• Using the Wrong-Way Driving (WWD) Prompt list to 

focus specific attention on wrong-way driving issues and 

contributing factors. 

• Referring to American Traffic Safety Services Association 

publication that describes promising practices in wrongway driving countermeasures (ATSSA, 2012); a review of that 

document should be included during the consideration of 

potential WWD treatments to implement.

The rationale and supporting evidence for these treatments can be 

found beginning on page 257 of the Handbook.

32
SEGMENTS

ROADWAY 

Chapter 4. Roadway Segments

33. Horizontal Curves.................................................................................................52

34. Vertical Curves.......................................................................................................54

35. Passing Zones........................................................................................................55

36. Lane Control Devices...........................................................................................56

37. Lane Drop Markings............................................................................................57

38. Contrast Markings on Concrete Pavement .................................................58

39. Utilize Highly Retroreflective Marking Material.........................................58

40. Curve Warning Markings....................................................................................59

41. Road Diets...............................................................................................................59

42. High Friction Surface Treatments...................................................................60

Desk Reference for Designing Roadways for the Aging Population
ROADWAY SEGMENTS

51

Desk Reference for Designing Roadways for the Aging Population

CHAPTER 4

Roadway Segments

This section of the Desk Reference illustrates treatments 

designed to facilitated the safety of aging drivers on 

specific types of roadway segments. It contains four 

proven practices and six treatments that promise to 

support the needs of aging drivers. 

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

ROADWAY SEGMENTS

Handbook for Designing Roadways for the Aging Population
ROADWAY SEGMENTS

52

Desk Reference for Designing Roadways for the Aging Population

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 inservice 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 inservice contrast level for edgelines on horizontal curves 

is 3.75.

Contrast should be calculated according to the formula shown 

for Treatment 3: Channelization on page 10.

33

Figure 51. White edge lines, centerline RPMs, and chevrons on a 

horizontal curve

PROVEN PRACTICES
ROADWAY SEGMENTS

53

Desk Reference for Designing Roadways for the Aging Population

B. Retroreflective Pavement Markers

B-1. For curves with radii greater than 1,640 ft and less than 

3,280 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 of the Handbook.] 

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.

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. 

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)

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
ROADWAY SEGMENTS

54

Desk Reference for Designing Roadways for the Aging Population

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 1,900 ft.

The rationale and supporting evidence for this treatment can be 

found beginning on page 260 of the Handbook.

Vertical Curves

A. Perception-Reaction Time

Strict adherence to a perception-reaction time (PRT) of at least 

2.5 s for a roadway hazard obscured by vertical curvature should 

be used in the design of new and reconstructed facilities.

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.

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) be used along with a warning beacon 

34

Figure 52. (MUTCD 

W7-6 and W13-1P)
ROADWAY SEGMENTS

55

Desk Reference for Designing Roadways for the Aging Population

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 timespeed-distance table on page 5 of the 

Handbook.]

The rationale and supporting evidence for these treatments can be 

found beginning on page 272 of the Handbook.

Passing Zones

A. Passing Sight Distance

To accommodate age-related difficulties in judging gaps and 

longer decision making 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.)

35

Figure 53. (MUTCD W3-4 

and W16-13)

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
ROADWAY SEGMENTS

56

Desk Reference for Designing Roadways for the Aging Population

B. Pennant

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) pennant 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).

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 277 of the Handbook.

Lane Control Devices

A. Pixel Specifications

To increase the legibility distance 

of overhead lane-control signal 

indications for prohibited 

movements (red X), use a doublestroke arrangement of pixels that 

are small (approximating 0.15 

in diameter) and closely spaced 

(approximating 0.70 in center-tocenter), as shown in Figure 55.

The rationale and supporting evidence for these treatments can be 

found beginning on page 281 of the Handbook.

36

Figure 54. 

(MUTCD W14-3)

Figure 55. Lane control 

signal (adapted from 

Ullman et al. 1996)
ROADWAY SEGMENTS

57

Desk Reference for Designing Roadways for the Aging Population

Lane Drop Markings

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 284 of the Handbook.

37

Figure 56. Dotted lane line markings at freeway lane drop

PROMISING PRACTICES
ROADWAY SEGMENTS

58

Desk Reference for Designing Roadways for the Aging Population

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).

The rationale and supporting evidence for these treatments can be 

found beginning on page 284 of the Handbook.

Utilize Highly Retroreflective Marking Material

To maintain visibility under adverse driving conditions, use highly 

retroreflective marking material.

The rationale and supporting evidence for these treatments can be 

found beginning on page 285 of the Handbook.

38

39

Figure 57. Contrast markings on light colored pavement
ROADWAY SEGMENTS

59

Desk Reference for Designing Roadways for the Aging Population

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 285 of the Handbook.

Road Diets

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. An example of a 

completed road diet is shown in Figure 59. 

The rationale and supporting evidence for these treatments can be 

found beginning on page 286 of the Handbook.

40

41

Figure 58. Curve warning markings (MUTCD:5)
ROADWAY SEGMENTS

60

Desk Reference for Designing Roadways for the Aging Population

High Friction Surface Treatments

High friction surface treatments (HFST) 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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 287 of the Handbook.

42

Figure 60. High friction surface treatment on a horizontal curve

Figure 59. Example of road diet
CONSTRUCTION 

WORK ZONES

Chapter 5. Construction /Work Zones

43. Signing and Advance Warning ........................................................................62

44. Portable Changeable (Variable) Message Signs........................................64

45. Channelization (Path Guidance)......................................................................66

46. Delineation of Crossovers/Alternate Travel Paths.....................................67

47. Temporary Pavement Markings......................................................................68

48. Increased Letter Height for Temporary Work Zone Signs......................69

49. Work Zone Road Safety Audit (WZRSA)........................................................69

Desk Reference for Designing Roadways for the Aging Population
CONSTRUCTION/WORK ZONES

61

Desk Reference for Designing Roadways for the Aging Population

CHAPTER 5

Construction/Work Zones

This section of the Desk Reference examines treatments 

to enhance the performance of aging drivers as they 

approach and travel through construction/work zones. It 

addresses five specific proven design elements and two 

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 Audit (WZRSA)

CONSTRUCTION/WORK ZONES

Handbook for Designing Roadways for the Aging Population
CONSTRUCTION/WORK ZONES

62

Desk Reference for Designing Roadways for the Aging Population

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.

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 

43

Figure 61. Flashing arrow 

panel at lane closure taper

Figure 62. Changeable 

message sign upstream of 

lane closure taper

Shoulder

taper

Work

vehicle

Truckmounted

attenuator

(optional)

PROVEN PRACTICES
CONSTRUCTION/WORK ZONES

63

Desk Reference for Designing Roadways for the Aging Population

Figure 63. Redundant static signs upstream of lane closure taper

are equipped with flashing warning lights throughout the 

entire time period of the lane closure (see Figure 63).

C. Sign Sheeting

To increase the legibility distance of ground-mounted workzone signs, the use of fluorescent orange is recommended over 

the use of beaded high-intensity orange sheeting.

D. Legibility Distance

A minimum specific ratio of 1 inch of letter height per 30 feet of 

legibility distance should be used.

The rationale and supporting evidence for these treatments can be 

found beginning on page 290 of the Handbook.
CONSTRUCTION/WORK ZONES

64

Desk Reference for Designing Roadways for the Aging Population

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.

B. Display Time

Each phase of a CMS message 

should be displayed for a minimum 

of 3 s.

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. 

C-2. For CMS messages split into 

two phases, a total of no 

more than four unique units 

of information should be 

presented.

44

Figure 64. Phase 1 (Top) 

and Phase 2 (Bottom)

Figure 65. Use of 

approved abbreviation in 

one-phase message

LEFT

LANE

CLOSED

ROAD

2 MILES

WORK

LEFT LN

CLOSED

IN 2 MI
CONSTRUCTION/WORK ZONES

65

Desk Reference for Designing Roadways for the Aging Population

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.

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.

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-toheight ratio of 0.13.

F. Sign Height

Portable changeable message signs should be elevated to 

a height sufficient to be seen across multiple lanes of (samedirection) traffic by approaching passenger car drivers.

The rationale and supporting evidence for these treatments can be 

found beginning on page 300 of the Handbook.
CONSTRUCTION/WORK ZONES

66

Desk Reference for Designing Roadways for the Aging Population

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).

A-2. Tubular markers 

—42 in high, with 

a single band of 

retroreflective material at least 12 in 

wide for nighttime 

operations.

A-3. Vertical (striped) 

panels—12 in wide.

A-4. Barricades—12 in x 36 in minimum dimension.

A-5. Drums—18 in x 36 in, with high-brightness sheeting 

for the orange and white retroreflective stripes (as per 

MUTCD guidelines).

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 

45

Figure 66. Traffic cone for nighttime 

work zone operations

6 inches

2 inches

3 to 4 inches

6 inches

Retroreflective

band

36 inches
CONSTRUCTION/WORK ZONES

67

Desk Reference for Designing Roadways for the Aging Population

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).

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 313 of the Handbook.

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 work zones, for all 

roadway classes except residential.

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).

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).

46
CONSTRUCTION/WORK ZONES

68

Desk Reference for Designing Roadways for the Aging Population

D. Screens

It is recommended for construction/work zones on highvolume 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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 318 of the Handbook.

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.

The rationale and supporting evidence for this treatment can be 

found beginning on page 323 of the Handbook.

47
CONSTRUCTION/WORK ZONES

69

Desk Reference for Designing Roadways for the Aging Population

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).

The rationale and supporting 

evidence for these treatments 

can be found beginning on page 

328 of the Handbook.

Work Zone Road Safety 

Audit (WZRSA)

Work Zone Road Safety Audit Guidelines and Prompt Lists include 

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 329 of the Handbook.

48

49 Figure 67. Temporary work zone 

sign with increased letter height

PROMISING PRACTICES

HIGHWAY-RAIL

 GRADE CROSSING

Chapter 6. Highway-Rail Grade Crossing

50. Passive Traffic Control Devices.........................................................................72

51. Lighting....................................................................................................................73

Desk Reference for Designing Roadways for the Aging Population
HIGHWAY-RAIL GRADE CROSSING

71

Desk Reference for Designing Roadways for the Aging Population

CHAPTER 6

Highway-Rail Grade Crossing

This section of the Desk Reference highlights two specific 

treatments that have proven to enhance the performance 

of aging drivers at highway-rail grade crossings.

PROVEN PRACTICES 

50. Passive Traffic Control Devices

51. Lighting
HIGHWAY-RAIL GRADE CROSSING

72

Desk Reference for Designing Roadways for the Aging Population

Passive Traffic Control Devices

A. Post-Mounted Delineators

For rural passive grade crossings that are not illuminated, the 

approach should 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).

The rationale 

and supporting 

evidence for these 

treatments can be 

found beginning 

on page 332 of the 

Handbook.

50

Figure 68. Recommended placement of postmounted delineators

Post-mounted

Delineators

50 ft spacing

(with high performance

retroreflective sheeting)

PROVEN PRACTICES
HIGHWAY-RAIL GRADE CROSSING

73

Desk Reference for Designing Roadways for the Aging Population

Lighting

A. Luminaire Type/Alignment

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.

The rationale and supporting evidence for these treatments can be 

found beginning on page 343 of the Handbook.

51

GLOSSARY

Glossary

Desk Reference for Designing Roadways for the Aging Population
75

Desk Reference for Designing Roadways for the Aging Population

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.
76

Desk Reference for Designing Roadways for the Aging Population

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.

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.
77

Desk Reference for Designing Roadways for the Aging Population

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.

Composite photometry. Light measurement applied to a highmast 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.
78

Desk Reference for Designing Roadways for the Aging Population

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.
79

Desk Reference for Designing Roadways for the Aging Population

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.

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.
80

Desk Reference for Designing Roadways for the Aging Population

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 diagonaltype 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.

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.
81

Desk Reference for Designing Roadways for the Aging Population

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 right- of-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.
82

Desk Reference for Designing Roadways for the Aging Population

Interchange (grade separation). A system of interconnecting 

roadways that provides for the movement of traffic between two or 

more highways on different levels.

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.
83

Desk Reference for Designing Roadways for the Aging Population

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.

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.
84

Desk Reference for Designing Roadways for the Aging Population

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.
85

Desk Reference for Designing Roadways for the Aging Population

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.
86

Desk Reference for Designing Roadways for the Aging Population

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 bi- directional, and are 

fastened into the pavement with the reflector surface visible above 

the road surface.

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.
87

Desk Reference for Designing Roadways for the Aging Population

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 off- ramp 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.

 Slip ramp. A diagonal ramp, more properly called a cross connection, 

which connects with a parallel frontage road.
88

Desk Reference for Designing Roadways for the Aging Population

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 speed- change 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.
89

Desk Reference for Designing Roadways for the Aging Population

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.

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.
90

Desk Reference for Designing Roadways for the Aging Population

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.
91

Desk Reference for Designing Roadways for the Aging Population

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.