Publication No.

FHWA-HRT-04-091
FOREWORD 

This report complements the American Association of State Highway and Transportation Officials 

(AASHTO) Strategic Highway Safety Plan to develop guidance on safety of nonsignalized and signalized 

intersections. The goal is to reduce the annual number of highway deaths. This guide is a 

comprehensive document that contains methods for evaluating the safety and operations of signalized 

intersections and tools to remedy deficiencies. The treatments in this guide range from low-cost 

measures such as improvements to signal timing and signage, to high-cost measures such as 

intersection reconstruction or grade separation. Topics covered include fundamental principles of user 

needs, geometric design, and traffic design and operation; safety and operational analysis techniques; 

and a wide variety of treatments to address existing or projected problems, including individual 

movements and approaches, pedestrian and bicycle treatments, and corridor techniques. It also includes 

coverage of alternative intersection forms that improve intersection performance through the use of 

indirect left turns and other treatments. Each treatment includes a discussion of safety, operational 

performance, multimodal issues, and physical and economic factors that the practitioner should consider. 

Although the guide has considerable focus on high-volume signalized intersections, many treatments also 

are applicable for lower volume intersections. The information contained in this guide is based on the 

latest research on available treatments and best practices in use by jurisdictions across the United 

States. Additional resources and references are highlighted for the student, practitioner, researcher, or 

decisionmaker who wishes to learn more about a particular subject. 

Copies of this report may be obtained from the Research and Technology Report Center, 9701 

Philadelphia Court, Unit Q, Lanham, MD 20706; telephone: 301–577–0818; fax: 301–577–1421; or the 

National Technical Information Service (NTIS), 5285 Port Royal Road, Springfield, VA 22161; telephone: 

703–487–4650; fax: 703–321–8547. 

Michael F. Trentacoste 

Director 

Office of Safety Research and Development 

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 its contents or use 

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

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers’ 

names appear in this report only because they are considered essential to the object of this 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. 
Technical Report Documentation Page 

1. Report No. 

FHWA-HRT-04-091 

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

5. Report Date 

August 2004 

4. Title and Subtitle 

Signalized Intersections: Informational Guide 

6. Performing Organization Code 

7. Author(s) 

Principal Investigator: Lee A. Rodegerdts 

Co-Investigators: Brandon Nevers, Bruce Robinson 

Co-Authors: John Ringert, Peter Koonce, Justin Bansen, Tina Nguyen, John 

McGill, Del Stewart, Jeff Suggett, Tim Neuman, Nick Antonucci, Kelly Hardy, 

Ken Courage 

8. Performing Organization Report No. 

Project 4770 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

Kittelson & Associates, Inc. 

610 SW Alder Street, Suite 700 

Portland, OR 97205 

Subconsultants: Synectics Transportation Consultants, Inc.; CH2M Hill, Inc.; and 

Ken Courage 

11. Contract or Grant No. 

Contract No. DTFH61-98-C-00075, 

Task Order No. B98C75-009 

13. Type of Report and Period Covered 

Informational Guide Book 

October 2001 to June 2004 

12. Sponsoring Agency Name and Address 

Federal Highway Administration 

Turner-Fairbank Highway Research Center 

6300 Georgetown Pike, HSR 20, Room No. T301 

McLean, VA 22101 14. Sponsoring Agency Code 

15. Supplementary Notes 

Joe G. Bared (Joe.Bared@fhwa.dot.gov) at the Turner-Fairbank Highway Research Center (http://www.tfhrc.gov) was the Technical 

Representative for the Federal Highway Administration (FHWA). Project focus group members contributed significantly to document

organization, content, and exhibits: Tom Hicks, Maryland State Highway Administration; Nick Kalivoda, Louisiana Department of 

Transportation; Nazir Lalani, Ventura County (California); John Mason, Pennsylvania State University; and Brian Walsh, Washington 

State Department of Transportation. In addition, many FHWA staff members participated as focus group members and/or provided 

comments throughout the project, including Carl Andersen, David Gibson, Hari Kalla, Ray Krammes, Barbara McMillen, Bill Prosser, 

Fred Ranck, Tamara Redmon, Essie Wagner, and Scott Wainwright. 

16. Abstract 

This guide provides a single, comprehensive document with methods for evaluating the safety and operations of signalized intersections 

and tools to remedy deficiencies. The treatments in this guide range from low-cost measures such as improvements to signal timing and 

signage, to high-cost measures such as intersection reconstruction or grade separation. Topics covered include fundamental principles of 

user needs, geometric design, and traffic design and operation; safety and operational analysis techniques; and a wide variety of 

treatments to address existing or projected problems, including individual movements and approaches, pedestrian and bicycle 

treatments, and corridor techniques. It also covers alternative intersection forms that improve intersection performance through the use 

of indirect left turns and other treatments. Each treatment includes a discussion of safety, operational performance, multimodal issues, 

and physical and economic factors that the practitioner should consider. Although the guide focuses primarily on high-volume signalized 

intersections, many treatments are applicable for lower volume intersections as well. The information contained in this guide is based on 

the latest research available on treatments and best practices in use by jurisdictions across the United States. Additional resources and 

references are highlighted for the student, practitioner, researcher, or decisionmaker who wishes to learn more about a particular subject. 

17. Key Words 

Signalized Intersections, Intersection Safety, Intersection Design, Intersection 

Performance, Intersection Treatments 

18. Distribution Statement 

19. Security Classif. (of this report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified 

21. No. of Pages 

369 

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
ii Federal Highway Administration

SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol 

LENGTH 

in inches 25.4 millimeters mm 

ft feet 0.305 meters m 

yd yards 0.914 meters m 

mi miles 1.61 kilometers km 

AREA 

in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2

ac acres 0.405 hectares ha 

mi2 square miles 2.59 square kilometers km2

VOLUME 

fl oz fluid ounces 29.57 milliliters mL 

gal gallons 3.785 liters L 

ft3 cubic feet 0.028 cubic meters m3 

yd3 cubic yards 0.765 cubic meters m3 

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

MASS 

oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg

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

TEMPERATURE (exact degrees) o

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

or (F-32)/1.8 

ILLUMINATION 

fc foot-candles 10.76 lux lx 

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS 

lbf poundforce 4.45 newtons N 

lbf/in2 poundforce per square inch 6.89 kilopascals kPa 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

LENGTH

mm millimeters 0.039 inches in 

m meters 3.28 feet ft 

m meters 1.09 yards yd 

km kilometers 0.621 miles mi 

AREA mm2

 square millimeters 0.0016 square inches in2 

m2 square meters 10.764 square feet ft2 

m2 square meters 1.195 square yards yd2 

ha hectares 2.47 acres ac 

km2 square kilometers 0.386 square miles mi2 

VOLUME 

mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft3 

m3 cubic meters 1.307 cubic yards yd3 

MASS 

g grams 0.035 ounces oz

kg kilograms 2.202 pounds lb

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

TEMPERATURE (exact degrees) o

C Celsius 1.8C+32 Fahrenheit oF 

ILLUMINATION 

lx lux 0.0929 foot-candles fc 

cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS 

N newtons 0.225 poundforce lbf 

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for th International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E e 380. 

(Revised March 2003)
Signalized Intersections: Informational Guide iii 

Table of Contents

TABLE OF CONTENTS 

1.0 INTRODUCTION.................................................................................................................... 3 

 1.1 Background .................................................................................................................. 3 

 1.2 Scope of Guide............................................................................................................. 4 

 1.3 Audience for this Guide ................................................................................................ 5 

 1.4 Organization of the Guidelines ..................................................................................... 5 

PART I FUNDAMENTALS ............................................................................................................. 9 

2.0 ROAD USER NEEDS........................................................................................................... 13 

 2.1 Overview of Human Factors....................................................................................... 13 

 2.1.1 Positive Guidance.......................................................................................... 14 

 2.1.2 Roadway Safety ............................................................................................ 15 

 2.2 Intersection Users....................................................................................................... 16 

 2.2.1 Human Factors Common to All Road Users................................................. 16 

 2.2.2 Motorists ........................................................................................................ 20 

 2.2.3 Bicyclists........................................................................................................ 23 

 2.2.4 Pedestrians.................................................................................................... 27 

 2.3 Applying Human Factors ............................................................................................ 32 

3.0 GEOMETRIC DESIGN......................................................................................................... 37

3.1 Channelization............................................................................................................ 37 

3.2 Number of Intersection Legs ...................................................................................... 44 

3.3 Intersection Angle....................................................................................................... 45

3.4 Horizontal and Vertical Alignment .............................................................................. 46 

3.5 Corner Radius and Curb Ramp Design ..................................................................... 46 

 3.5.1 Corner Radius ............................................................................................... 47 

 3.5.2 Curb Ramp Design........................................................................................ 47 

 3.5.3 Detectable Warnings ..................................................................................... 51 

3.6 Sight Distance ............................................................................................................ 53 

 3.6.1 Stopping Sight Distance ................................................................................ 53 

 3.6.2 Decision Sight Distance ................................................................................ 53 

 3.6.3 Intersection Sight Distance............................................................................ 54 

3.7 Pedestrian Facilities ................................................................................................... 54 

3.8 Bicycle Facilities ......................................................................................................... 55 

4.0 TRAFFIC DESIGN AND ILLUMINATION ............................................................................ 59 

4.1 Traffic Signal Control Type......................................................................................... 59 

4.2 Traffic Signal Phasing................................................................................................. 59 

 4.2.1 “Permissive-Only” Left-Turn Phasing ............................................................ 60 

 4.2.2 “Protected-Only” Left-Turn Phasing .............................................................. 62 

 4.2.3 Protected-Permissive Left-Turn Phasing ...................................................... 63 

 4.2.4 Split Phasing.................................................................................................. 67 

 4.2.5 Prohibited Left-Turn Phasing......................................................................... 70 

 4.2.6 Right-Turn Phasing........................................................................................ 70 

4.3 Vehicle and Pedestrian Displays................................................................................ 72 

 4.3.1 Vehicle Displays ............................................................................................ 72 

 4.3.2 Pedestrian Displays....................................................................................... 76 

4.4 Traffic Signal Pole Layout........................................................................................... 77 

4.5 Traffic Signal Controller.............................................................................................. 78 

4.6 Detection Devices....................................................................................................... 79 

 4.6.1 Vehicle Detection........................................................................................... 79 

 4.6.2 Pedestrian Detection ..................................................................................... 83 
iv Federal Highway Administration 

4.7 Basic Signal Timing Parameters ................................................................................ 83 

 4.7.1 Pedestrian Timing.......................................................................................... 84 

 4.7.2 Vehicle Timing—Green Interval .................................................................... 84 

 4.7.3 Vehicle Timing—Detector Timing.................................................................. 85 

 4.7.4 Vehicle Timing—Vehicle Clearance.............................................................. 85 

 4.7.5 Vehicle Timing—Cycle Length ...................................................................... 86 

4.8 Signing and Pavement Marking Design ..................................................................... 86 

4.9 Illumination Design ..................................................................................................... 90 

 4.9.1 Illuminance .................................................................................................... 91 

 4.9.2 Veiling Illuminance......................................................................................... 92 

PART II PROJECT PROCESS AND ANALYSIS METHODS ..................................................... 95 

5.0 PROJECT PROCESS.......................................................................................................... 99

5.1 Project Initiation .......................................................................................................... 99 

5.2 Identify Stakeholder Interests and Objectives............................................................ 99 

 5.2.1 Intersection Users........................................................................................ 100 

 5.2.2 Adjacent Property/Business Owners........................................................... 100 

 5.2.3 Facility Managers ........................................................................................ 100 

 5.2.4 Other Decisionmakers................................................................................. 100 

5.3 Data Collection ......................................................................................................... 101

 5.3.1 Office Review .............................................................................................. 101 

 5.3.2 Field Investigation........................................................................................ 101 

5.4 Problem Identification............................................................................................... 102 

 5.4.1 Establish Performance Measures and Criteria............................................ 105 

 5.4.2 Summarize Operational and Safety Conditions .......................................... 107 

 5.4.3 Develop Problem Statement ....................................................................... 107 

5.5 Identify Problem Cause ............................................................................................ 108 

5.6 Treatment Selection ................................................................................................. 109 

 5.6.1 Identify Range of Treatments ...................................................................... 109 

 5.6.2 Evaluate Treatments ................................................................................... 110 

 5.6.3 Assess Potential To Introduce Undesirable Effects .................................... 110 

 5.6.4 Determine Costs and Implementation Issues ............................................. 110 

5.7 In-Service Assessments........................................................................................... 111 

 5.7.1 Followup Plan.............................................................................................. 111 

 5.7.2 Monitoring Program..................................................................................... 111 

6.0 SAFETY ANALYSIS METHODS........................................................................................ 115 

6.1 Balancing Safety and Mobility .................................................................................. 115 

6.2 Selection of an Intersection ...................................................................................... 116 

 6.2.1 Collision Frequency..................................................................................... 119 

 6.2.2 Collision Rate .............................................................................................. 119 

 6.2.3 Combined Collision Frequency and Rate Method ...................................... 120 

 6.2.4 Collision Severity Method............................................................................ 120 

 6.2.5 Critical Collision Rate .................................................................................. 121 

 6.2.6 Risk Analysis Methods ................................................................................ 121 

 6.2.7 Safety Performance Functions .................................................................... 122 

 6.2.8 Empirical Bayes Method.............................................................................. 122 

 6.2.9 Conclusions................................................................................................. 123 

6.3 Identification of Potential Problems .......................................................................... 125 

 6.3.1 Safety Diagnosis.......................................................................................... 125 

 6.3.2 Assemble Collision Data ............................................................................. 126 

 6.3.3 Analyze/Diagnose Collision Data ................................................................ 128 

 6.3.4 Determine Overrepresentation.................................................................... 129 

 6.3.5 Conduct Site Visit(s).................................................................................... 132 

 6.3.6 Deciding on Further Analysis ...................................................................... 134 
Signalized Intersections: Informational Guide v 

Table of Contents

 6.3.7 Conducting Further Studies......................................................................... 134 

 6.3.8 Defining the Problem Statement ................................................................. 135 

6.4 Identification of Possible Treatments ....................................................................... 136 

 6.4.1 List Possible Treatments ............................................................................. 136 

 6.4.2 Screen Treatments...................................................................................... 138 

 6.4.3 Selecting a Collision Modification Factor or Study Finding ......................... 139 

 6.4.4 Quantify Safety Benefit................................................................................ 140 

 6.4.5 Selected Treatment(s)................................................................................. 142 

6.5 Improvement Plan Development .............................................................................. 142 

7.0 OPERATIONAL ANALYSIS METHODS............................................................................ 145 

7.1 Operational Measures of Effectiveness ................................................................... 146 

 7.1.1 Motor Vehicle Capacity and Volume-to-Capacity Ratio .............................. 147 

 7.1.2 Motor Vehicle Delay and Level of Service .................................................. 148 

 7.1.3 Motor Vehicle Queue................................................................................... 148 

 7.1.4 Transit Level of Service............................................................................... 149 

 7.1.5 Bicycle Level of Service............................................................................... 149 

 7.1.6 Pedestrian Level of Service......................................................................... 150 

7.2 Traffic Operations Elements..................................................................................... 151 

 7.2.1 Traffic Volume Characteristics .................................................................... 151 

 7.2.2 Intersection Geometry ................................................................................. 152 

 7.2.3 Signal Timing............................................................................................... 152 

7.3 Rules of Thumb for Sizing an Intersection ............................................................... 153 

7.4 Critical Movement Analysis ...................................................................................... 154 

7.5 HCM Operational Procedure for Signalized Intersections ....................................... 157 

7.6 Arterial and Network Signal Timing Models ............................................................. 157 

7.7 Microscopic Simulation Models ................................................................................ 158 

PART III TREATMENTS............................................................................................................. 159 

8.0 SYSTEM-WIDE TREATMENTS ........................................................................................ 163 

 8.1 Median Treatments................................................................................................... 163 

 8.1.1 Description................................................................................................... 163 

 8.1.2 Applicability.................................................................................................. 163 

 8.1.3 Key Design Features................................................................................... 163 

 8.1.4 Safety Performance..................................................................................... 169 

 8.1.5 Operational Performance ............................................................................ 169 

 8.1.6 Multimodal Impacts...................................................................................... 169 

 8.1.7 Physical Impacts.......................................................................................... 170 

 8.1.8 Socioeconomic Impacts .............................................................................. 170 

 8.1.9 Enforcement, Education, and Maintenance ................................................ 170 

 8.1.10 Summary ..................................................................................................... 170 

 8.2 Access Management................................................................................................ 171 

 8.2.1 Description................................................................................................... 171 

 8.2.2 Applicability.................................................................................................. 172 

 8.2.3 Design Features .......................................................................................... 172 

 8.2.4 Safety Performance..................................................................................... 177 

 8.2.5 Operational Performance ............................................................................ 177 

 8.2.6 Multimodal Impacts...................................................................................... 178 

 8.2.7 Physical Impacts.......................................................................................... 178 

 8.2.8 Socioeconomic Impacts .............................................................................. 178 

 8.2.9 Enforcement, Education, and Maintenance ................................................ 178 

 8.2.10 Summary ..................................................................................................... 178 
vi Federal Highway Administration 

 8.3 Signal Coordination .................................................................................................. 179 

 8.3.1 Description................................................................................................... 179 

 8.3.2 Applicability.................................................................................................. 179 

 8.3.3 Safety Performance..................................................................................... 180 

 8.3.4 Operational Performance ............................................................................ 180 

 8.3.5 Multimodal Impacts...................................................................................... 181 

 8.3.6 Physical Impacts.......................................................................................... 181 

 8.3.7 Socioeconomic Impacts .............................................................................. 181 

 8.3.8 Enforcement, Education, and Maintenance ................................................ 181 

 8.3.9 Summary ..................................................................................................... 181 

 8.4 Signal Preemption and/or Priority............................................................................. 181 

 8.4.1 Description................................................................................................... 181 

 8.4.2 Emergency Vehicle Preemption.................................................................. 182 

 8.4.3 Applicability.................................................................................................. 182 

 8.4.4 Safety Performance..................................................................................... 183 

 8.4.5 Operational Performance ............................................................................ 183 

 8.4.6 Multimodal Impacts...................................................................................... 183 

 8.4.7 Physical Impacts.......................................................................................... 183 

 8.4.8 Socioeconomic Impacts .............................................................................. 183 

 8.4.9 Enforcement, Education, and Maintenance ................................................ 183 

 8.4.10 Summary ..................................................................................................... 183 

9.0 INTERSECTION-WIDE TREATMENTS ............................................................................ 187 

 9.1 Pedestrian Treatments ............................................................................................. 187 

 9.1.1 Reduce Curb Radius ................................................................................... 187 

 9.1.2 Provide Curb Extensions............................................................................. 190 

 9.1.3 Modify Stop Bar Location ............................................................................ 192 

 9.1.4 Improve Pedestrian Signal Displays............................................................ 194 

 9.1.5 Modify Pedestrian Signal Phasing............................................................... 196 

 9.1.6 Grade-Separate Pedestrian Movements..................................................... 199 

 9.2 Bicycle Treatments................................................................................................... 201 

 9.2.1 Provide Bicycle Box..................................................................................... 201 

 9.2.2 Provide Bike Lanes......................................................................................202 

 9.3 Transit Treatments ................................................................................................... 203 

 9.3.1 Relocate Transit Stop.................................................................................. 203 

 9.4 Traffic Control Treatments........................................................................................ 205 

 9.4.1 Change Signal Control from Pre-Timed to Actuated................................... 205 

 9.4.2 Modify Yellow Change Interval and/or Red Clearance Interval .................. 208 

 9.4.3 Modify Cycle Length.................................................................................... 211 

 9.4.4 Late Night/Early Morning Flash Removal.................................................... 212 

 9.5 Street Lighting and Illumination ................................................................................ 214 

 9.5.1 Provide or Upgrade Illumination.................................................................. 214 

10.0 ALTERNATIVE INTERSECTION TREATMENTS ............................................................. 221 

 10.1 Intersection Reconfiguration and Realignment Treatments..................................... 222 

 10.1.1 Remove Intersection Skew Angle ............................................................... 222 

 10.1.2 Remove Deflection in Travel Path for Through Vehicles ............................ 225 

 10.1.3 Convert Four-Leg Intersection to Two T-Intersections................................ 227 

 10.1.4 Convert Two T-Intersections to Four-Leg Intersection................................ 229 

 10.1.5 Close Intersection Leg................................................................................. 230 
Signalized Intersections: Informational Guide vii 

Table of Contents

 10.2 Indirect Left-Turn Treatments................................................................................... 232 

 10.2.1 Jughandle .................................................................................................... 232 

 10.2.2 Median U-Turn Crossover........................................................................... 242 

 10.2.3 Continuous Flow Intersection...................................................................... 249 

 10.2.4 Quadrant Roadway Intersection.................................................................. 256 

 10.2.5 Super-Street Median Crossover.................................................................. 260 

 10.3 Grade Separation Treatments.................................................................................. 264 

 10.3.1 Split Intersection.......................................................................................... 265 

 10.3.2 Diamond Interchange ..................................................................................269 

11.0 APPROACH TREATMENTS.............................................................................................. 279 

 11.1 Signal Head Placement and Visibility....................................................................... 279 

 11.1.1 Convert to Mast Arm or Span Wire Mounted Signal Heads........................ 280 

 11.1.2 Add Near-Side Signal Heads ...................................................................... 281 

 11.1.3 Increase Size of Signal Heads .................................................................... 282 

 11.1.4 Use Two Red Signal Sections..................................................................... 284 

 11.1.5 Increase Number of Signal Heads .............................................................. 286 

 11.1.6 Provide Backplates...................................................................................... 288 

 11.1.7 Provide Advance Warning........................................................................... 290 

 11.2 Signing and Speed Control Treatments ................................................................... 292 

 11.2.1 Improve Signing........................................................................................... 292 

 11.2.2 Reduce Operating Speed............................................................................ 294 

 11.3 Roadway Surface Improvements ............................................................................. 294 

 11.3.1 Improve Pavement Surface......................................................................... 294 

 11.3.2 Provide Rumble Strips................................................................................. 297 

 11.3.3 Improve Cross Section ................................................................................ 298 

 11.3.4 Remove Obstacles from Clear Zone........................................................... 300 

 11.4 Sight Distance Treatments ....................................................................................... 301 

 11.4.1 Improve Sight Lines..................................................................................... 301 

12.0 INDIVIDUAL MOVEMENT TREATMENTS........................................................................ 307 

 12.1 Left-Turn Treatments................................................................................................ 307 

 12.1.1 Add Single Left-Turn Lane .......................................................................... 307 

 12.1.2 Multiple Left-Turn Lanes.............................................................................. 318 

 12.1.3 Turn Prohibition ........................................................................................... 322 

 12.2 Through Lane Treatments........................................................................................ 324 

 12.2.1 Provide Auxiliary Through Lanes ................................................................ 324 

 12.2.2 Delineate Through Path .............................................................................. 326 

 12.3 Right-Turn Treatments ............................................................................................. 328 

 12.1.1 Add Single Right-Turn Lane ........................................................................ 328 

 12.1.2 Provide Double Right-Turn Lanes............................................................... 333 

 12.1.3 Provide Channelized Right-Turn Lane ........................................................ 334 

 12.4 Variable Lane Use Treatments................................................................................. 336 

 12.4.1 Provide Reversible Lanes ........................................................................... 336 

 12.4.2 Provide Variable Lane Use Assignments.................................................... 338 

REFERENCES............................................................................................................................. 341 

BIBLIOGRAPHY (OTHER REFERENCES) ................................................................................ 353 
viii Federal Highway Administration 

LIST OF FIGURES 

Figure Page

CHAPTER 2 

1 Traffic controls such as official signs need to be close to the road, distinctive from 

other information presentations, brief, and explicit. This photo provides an example 

of signs that are close to the road but may be confused with background information.... 17 

2 In terms of both official signs and advertising displays, too many displays may have the 

effect of causing drivers to “tune out,” and recall will be poor. This photo shows an 

example of sign clutter where the regulatory sign is difficult to isolate from the 

background advertising signs ........................................................................................... 17 

3 Enforcement cameras, as shown in the photo above, are used at signalized intersections 

to identify red light runners................................................................................................ 23

4 Typical dimensions of a bicyclist.......................................................................................... 25

5 Bicyclist conflicts at signalized intersections........................................................................ 27 

6 Examples of pedestrians of various abilities preparing to cross an intersection ................. 28 

7 Typical dimensions for a turning wheelchair........................................................................ 29 

8 Crosswalks are used by a variety of users with different speed characteristics. 

Pedestrian walking speeds generally range between 0.8 to 1.8 m/s (2.5 to 6.0 ft/s) ....... 30 

9 Pedestrian conflicts at signalized intersections.................................................................... 31 

CHAPTER 3 

10 The photograph shows a raised median that restricts left-turn egress movements from a 

driveway located between two signalized intersections ................................................... 38 

11 Pavement markings can be used to delineate travel lanes within wide intersections as 

shown in the photograph................................................................................................... 39 

12 Various right-turn treatments may be used, depending on the speed environment............ 40 

13 Providing a dedicated left-turn lane reduces potential collisions between left-turning 

and through vehicles, increasing the capacity of the approach for both left and 

through traffic .................................................................................................................... 41 

14 The photo shows how double left-turn and double right-turn lanes can be used to 

accommodate high-priority movements............................................................................ 42 

15 Intersection skew increases both the intersection width and pedestrian crossing distance 43 

16 The photograph illustrates a multileg intersection................................................................ 44 

17 Potential conflicts at intersections with three and four legs ................................................. 45 

18 Curb ramp components........................................................................................................ 48 

19 Examples of preferred designs ............................................................................................ 50 

20 Examples of acceptable curb ramp designs ........................................................................ 50 

21 Examples of inaccessible designs ....................................................................................... 50 

22 This crosswalk design incorporates the use of detectable warning surfaces into the curb 

ramps to facilitate navigation by a visually impaired pedestrian....................................... 51 

CHAPTER 4 

23 Standard NEMA ring-and-barrier structure .......................................................................... 60 

24 Typical phasing diagram for “permissive-only” left-turn phasing ......................................... 61 

25 Possible signal head arrangements for “permissive-only” left-turn phasing........................ 62 

26 Typical phasing diagram for “protected-only” left-turn phasing............................................ 63 

27 Possible signal head arrangements for “protected-only” left-turn phasing .......................... 63 

28 Typical phasing diagram for protected-permissive left-turn phasing ................................... 64 

29 Possible signal head and signing arrangement for protected-permissive left-turn phasing 64 

30 Illustration of the yellow trap................................................................................................. 66 

31 The protected-permissive left-turn display known as “Dallas display” uses louvers to 

restrict visibility of the left-turn display to adjacent lanes.................................................. 67 
Signalized Intersections: Informational Guide ix 

Table of Contents

Figure Page

CHAPTER 4, CONTINUED 

32 Typical phasing diagrams for split phasing .......................................................................... 69 

33 Common signal head arrangement for split phasing ........................................................... 70 

34 Typical phasing diagram illustrating a right-turn overlap ..................................................... 71 

35 Common signal head and signing arrangement for right-turn-overlap phasing .................. 72 

36 Examples showing five optional signal head locations ........................................................ 74 

37 Pedestrian signal indicators ................................................................................................. 76 

38 Example of advance street name sign for upcoming intersection ....................................... 87 

39 Example of advance street name sign for two closely spaced intersections....................... 88 

40 Example of signing for a left-hand land trap ........................................................................ 88 

41 Example of advance overhead signs indicating lane use for various destinations.............. 89 

42 Example of pavement legends indicating destination route numbers 

(“horizontal signage”)........................................................................................................ 90 

CHAPTER 6 

43 Exclusion of property-damage-only collisions (such as this one from an analysis) may 

mask valuable information .............................................................................................. 117 

44 The potential for error in coding the location of a collision should be understood............. 118 

45 Selecting a candidate intersection using a combined collision frequency/collision rate 

method, where each diamond represents an intersection.............................................. 120 

46 Example of SPF curve........................................................................................................122 

47 Identification of potential problems..................................................................................... 126

48 The original police collision report may contain valuable information regarding collisions 

that have occurred at the intersection............................................................................. 127 

49 Possible taxonomy for collision type classification............................................................. 131 

50 Conducting a site visit ........................................................................................................ 133 

51 Examples of problem statements....................................................................................... 135 

52 Identification of possible treatments.................................................................................. 136 

CHAPTER 7 

53 Still reproduction of a graphic from an animated traffic operations model......................... 146 

54 Overview of intersection traffic analysis models ................................................................ 147 

55 Pedestrian LOS based on cycle length and minimum effective pedestrian green time .... 151 

56 Graphical summary of the Quick Estimation Method......................................................... 155 

CHAPTER 8 

57 Issues associated with intersections with a narrow median .............................................. 164 

58 Issues associated with intersections with a wide median.................................................. 165 

59 Median pedestrian treatments............................................................................................ 167 

60 Median pedestrian signal treatments ................................................................................. 168 

61 This refuge island enables two-stage pedestrian crossings .............................................. 169 

62 Comparison of physical and functional areas of an intersection........................................ 172 

63 Diagram of the upstream functional area of an intersection .............................................. 173 

64 Access points near signalized intersections ...................................................................... 175 

65 Access management requiring U-turns at a downstream signalized intersection............. 176 

66 Access management requiring U-turns at an unsignalized, directional median opening.. 176 

CHAPTER 9 

67 A curb radius from 4.6 m (15 ft) to 15.2 m (50 ft) increases the pedestrian crossing 

distance from 18.9 m (62 ft) to 30.5 m (100 ft), all else being equal .............................. 188 

68 Intersection with curb extension......................................................................................... 191

69 Examples of countdown and animated eyes pedestrian signal displays........................... 195 

70 A pedestrian grade separation treatment........................................................................... 200 

71 Typical lighting layouts ....................................................................................................... 215 
x Federal Highway Administration 

Figure Page

CHAPTER 10 

72 Illustration of conflict points for a four-leg signalized intersection...................................... 222 

73 Diagrams of different types of intersection realignment.....................................................223 

74 Example of deflection in travel paths for through vehicles................................................. 226 

75 Conflict point diagram for two closely spaced T-intersections........................................... 228 

76 Diagram of a jughandle intersection................................................................................... 233 

77 Vehicular movements at a jughandle intersection ............................................................. 233 

78 Example of a jughandle intersection .................................................................................. 234 

79 Another example of a jughandle intersection..................................................................... 234 

80 Design layout of near-side jughandle................................................................................. 236 

81 Design layout of far-side jughandle.................................................................................... 237 

82 Example of jughandle and associated signing................................................................... 238 

83 Signal phasing of a jughandle intersection ........................................................................ 239 

84 Conflict point diagram for a four-leg signalized intersection with two jughandles ............. 240 

85 Diagram of a median U-turn crossover from the main line ................................................ 242 

86 Vehicular movements at a median U-turn intersection ...................................................... 243 

87 Example of median U-turn signing in Michigan.................................................................. 244 

88 Diagram of general placement of a median U-turn crossover ........................................... 245 

89 Diagram of a median U-turn crossover from the main line with a narrow median............. 245 

90 Conflict diagram for a four-leg signalized intersection with median U-turns...................... 247 

91 Diagram of a continuous flow intersection ......................................................................... 250 

92 Vehicular movements at a continuous flow intersection .................................................... 250 

93 Continuous flow intersection .............................................................................................. 251 

94 Displaced left turn at a continuous flow intersection.......................................................... 251 

95 Signal phasing of a continuous flow intersection ............................................................... 252 

96 Conflict diagram for a continuous flow intersection with displaced left turns on the major 

street only........................................................................................................................ 253 

97 Diagram of a quadrant roadway intersection ..................................................................... 257 

98 Vehicular movements at a quadrant roadway intersection................................................ 257 

99 Signal phasing of a quadrant roadway intersection ........................................................... 258 

100 Conflict point diagram for four-leg signalized intersection with quadrant roadway............ 259 

101 Illustration of super-street median crossover..................................................................... 261 

102 Vehicular movements at a super-street median crossover................................................ 261 

103 Signal phasing of a super-street median crossover........................................................... 262 

104 Conflict diagram for a super-street median crossover ....................................................... 263 

105 Illustration of a split intersection......................................................................................... 266 

106 Conflict point diagram for a split intersection ..................................................................... 267 

107 Diagram of a single-point interchange ............................................................................... 270 

108 Diagram of a compressed diamond interchange ............................................................... 271 

109 Typical signal phasing of a single-point interchange ......................................................... 271 

110 Typical signal phasing of a compressed diamond interchange ......................................... 272 

111 Single-point diamond interchange conflict point diagram .................................................. 273 

112 Compressed diamond interchange conflict point diagram................................................. 274 

CHAPTER 11 

113 Signal head with a double red signal indication................................................................. 285 

114 Lane-aligned signal heads ................................................................................................. 287 

115 Illustration of sight distance triangles ................................................................................. 302 
Signalized Intersections: Informational Guide xi 

Table of Contents

Figure Page

CHAPTER 12 

116 Diagram of a single left-turn lane ....................................................................................... 308 

117 Narrow (2.4-m (8-ft) left-turn lanes may be used effectively in retrofit situations .............. 311 

118 Example of positive offset .................................................................................................. 312 

119 Intersection with turn paths delineated for dual left-turn lanes in Tucson, AZ (Kolb Road/ 

22nd Street), June 1998 ................................................................................................. 321 

120 Diagram of an auxiliary through lane ................................................................................. 324 

121 Example of delineated paths.............................................................................................. 327 

122 Diagram of a typical right-turn lane .................................................................................... 328

123 Narrow (2.4-m (8-ft) right-turn lanes may be used effectively in retrofit situations ............ 330 

124 Example illustration of a channelized right-turn lane ......................................................... 334 

125 Example use of variable lane use sign to add a third left-turn lane during certain 

times of day..................................................................................................................... 339 

126 Example use of variable lane use sign to add a second right-turn lane along a corridor 

during certain times of day.............................................................................................. 339 
xii Federal Highway Administration 

LIST OF TABLES 

Table Page

CHAPTER 1 

1 Summary of motor vehicle crashes related to junction and severity in the United States 

during 2002 ......................................................................................................................... 3 

2 Organization of the guide ....................................................................................................... 6 

3 List of intersection treatments discussed in this document.................................................... 7 

CHAPTER 2 

4 Estimated number of registered vehicles by type, 2002 ...................................................... 20 

5 Fatalities and injuries by mode, 2001................................................................................... 21 

6 Total motor vehicle crashes and injury/fatal collisions at signalized intersections by total 

ADT entering the intersection ........................................................................................... 21 

7 Proportion of crashes by collision type at signalized intersections...................................... 22 

8 Typical dimensions for a sample of types of pedestrians .................................................... 29 

CHAPTER 3 

9 Summary of best practices for curb ramp design and associated rationale........................ 49 

10 Requirements for detectable warning surfaces.................................................................... 52 

11 Design values for stopping sight distance............................................................................ 53 

12 Design values for decision sight distance for selected avoidance maneuvers.................... 54 

CHAPTER 4 

13 Advantages and disadvantages of various configurations for displaying vehicle signal 

indications ......................................................................................................................... 77 

14 Traffic signal controller advantages and disadvantages...................................................... 79 

15 Strengths and weaknesses of commercially available detector technologies..................... 81 

16 Location of advanced vehicle detectors............................................................................... 83 

17 Recommended illuminance for the intersection of continuously lighted urban streets........ 92 

18 RP-8-00 guidance for roadway and pedestrian/area classification for purposes of 

determining intersection illumination levels ...................................................................... 93 

CHAPTER 5 

19 Example stakeholder interests and objectives................................................................... 101 

20 User characteristics............................................................................................................ 103 

21 Operational characteristics.................................................................................................103 

22 Safety characteristics ......................................................................................................... 104 

23 Geometric, traffic signal control, and land use characteristics........................................... 104 

24 Policy and background information.................................................................................... 105 

25 Common concerns raised by stakeholders........................................................................ 105 

26 Example performance measures and criteria .................................................................... 106 

27 Possible causes of intersection problems.......................................................................... 109 

CHAPTER 6 

28 Suggested weighting for collision severity method ............................................................ 121 

29 Common methods of assessing safety at a location.......................................................... 124 

30 Chi-square test values and corresponding confidence levels ........................................... 129 

31 Collision types commonly identified, possible causes, and associated treatments........... 138 

32 Example calculation of safety benefit of adding a right-turn lane ...................................... 141 
Signalized Intersections: Informational Guide xiii 

Table of Contents

Table Page

CHAPTER 7 

33 Motor vehicle LOS thresholds at signalized intersections ................................................. 148 

34 Bicycle LOS thresholds at signalized intersections ........................................................... 150 

35 Pedestrian LOS thresholds at signalized intersections......................................................150 

36 Planning-level guidelines for sizing an intersection ........................................................... 153 

37 V/C ratio threshold descriptions for the Quick Estimation Method..................................... 156 

CHAPTER 8 

38 Summary of issues for providing median treatments......................................................... 171 

39 Relative crash rates for unsignalized intersection access spacing.................................... 177 

40 Summary of issues for providing access management .....................................................179 

41 Selected findings of safety benefits associated with signal coordination or progression .. 180 

42 Summary of issues for providing signal coordination ........................................................ 181 

43 Summary of issues for providing signal preemption and/or priority................................... 184 

CHAPTER 9 

44 Summary of issues for curb radius reduction..................................................................... 190 

45 Summary of issues for curb extensions ............................................................................. 192 

46 Summary of issues for stop bar alterations........................................................................194 

47 Safety benefits associated with addition of pedestrian signals: Selected findings ............ 195 

48 Summary of issues for pedestrian signal display improvements....................................... 196 

49 Summary of issues for pedestrian signal phasing modifications ....................................... 199 

50 Summary of issues for pedestrian grade separation ......................................................... 201 

51 Summary of issues for providing a bicycle box.................................................................. 202 

52 Summary of issues for providing bicycle lanes.................................................................. 203 

53 Summary of issues for near-side/far-side transit stops......................................................205 

54 Safety benefits associated with upgrading an intersection from pre-timed to actuated 

operation: Selected findings............................................................................................ 207 

55 Summary of issues for providing signal actuation.............................................................. 208 

56 Safety benefits associated with modifying clearance intervals: Selected findings ............ 210 

57 Summary of issues for modifying yellow/red clearance intervals ...................................... 211 

58 Summary of issues for cycle length modifications ............................................................. 212 

59 Safety benefits associated with removal of signal from late night/early morning flash 

mode: Selected findings.................................................................................................. 213 

60 Summary of issues for flash mode removal....................................................................... 214 

61 Safety benefits associated with providing illumination: Selected findings ......................... 216 

62 Summary of issues for providing illumination..................................................................... 217 

CHAPTER 10 

63 Summary of issues for removing intersection skew........................................................... 225 

64 Summary of issues for removing deflection of vehicle path............................................... 227 

65 Number of conflict points at a four-leg signalized intersection compared to two closely 

spaced T-intersections.................................................................................................... 227 

66 Safety benefits of converting a four-leg signalized intersection to two T-intersections: 

Expert opinion .................................................................................................................228 

67 Summary of issues for converting a four-leg intersection to two T-intersections .............. 229 

68 Summary of issues for converting two T-intersections to one four-leg intersection .......... 230 

69 Safety benefits associated with street closures: Selected findings.................................... 231 

70 Summary of issues for closing an intersection approach leg............................................. 232 

71 Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a jughandle ......................................................................... 240 

72 Safety benefits of converting a four-leg signalized intersection to a four-leg signalized 

intersection with two jughandles: Expert opinion............................................................ 240 

73 Summary of issues for jughandles..................................................................................... 242 
xiv Federal Highway Administration 

Table Page

CHAPTER 10, CONTINUED 

74 Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a median U-turn crossover configuration............................ 246 

75 Safety benefits of converting a four-leg signalized intersection to median U-turn 

crossover configuration: Expert opinion.......................................................................... 247 

76 Summary of issues for median U-turn crossovers............................................................. 249 

77 Number of conflict points at a four-leg signalized intersection compared to a continuous 

flow intersection with displaced left turns on the major street only................................. 253 

78 Safety benefits of converting a four-leg signalized intersection to a CFI: Expert opinion.. 254 

79 Summary of issues for continuous flow intersections ........................................................ 256 

80 Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a quadrant roadway ............................................................ 258 

81 Safety benefits of adding a quadrant roadway to a four-leg signalized intersection: 

Expert opinion .................................................................................................................259 

82 Summary of issues for quadrant roadways........................................................................ 260 

83 Number of conflict points at a four-leg signalized intersection compared to a super-street 

median crossover............................................................................................................ 263

84 Safety benefits of converting a four-leg signalized intersection compared to a super-street 

median crossover: Expert opinion .................................................................................. 263 

85 Summary of issues for super-street median crossovers....................................................264 

86 Number of conflict points at a four-leg signalized intersection compared to a split 

intersection...................................................................................................................... 267 

87 Safety benefits of converting a four-leg signalized intersection to a split intersection: 

Expert opinion .................................................................................................................268 

88 Summary of issues for split intersections...........................................................................269 

89 Number of conflict points at a four-leg signalized intersection compared to a 

compressed diamond and single-point diamond interchange ........................................ 273 

90 Safety benefits of converting a four-leg signalized intersection to a 

compressed diamond and single-point diamond interchange: Expert opinion............... 275 

91 Summary of issues for single-point and compressed diamond interchanges ................... 276 

CHAPTER 11 

92 Summary of approach treatments...................................................................................... 279 

93 Safety benefits associated with using mast arms: Selected findings................................. 280 

94 Summary of issues for using mast arm/span wire mounted signal heads......................... 281 

95 Summary of issues for supplemental near-side traffic signal heads ................................. 282 

96 Safety benefits associated with using 300-mm (12-inch) signal lenses: Selected 

findings............................................................................................................................ 283 

97 Summary of issues for increasing the size of signal heads...............................................284 

98 Safety benefits associated with using a double red indication (red “T”) display: Selected 

findings............................................................................................................................ 285 

99 Summary of issues for using two red signal sections ........................................................ 286 

100 Safety benefits associated with addition of a signal head: Selected findings.................... 288 

101 Summary of issues for adding a signal head ..................................................................... 288 

102 Safety benefits associated with the use of signal backplates: Selected findings .............. 289 

103 Summary of issues for using signal head backplates........................................................ 290 

104 Safety benefits associated with advance warning signs and flashers: Selected findings . 291 

105 Summary of issues related to advance warning treatments .............................................. 292 

106 Safety benefits associated with sign treatments: Selected findings .................................. 293 

107 Summary of issues for improving signing .......................................................................... 294 

108 Safety benefits associated with nonskid treatments, drainage improvements, or 

resurfacing: Selected findings......................................................................................... 296 

109 Summary of issues for pavement treatments .................................................................... 297 

110 Safety benefits associated with rumble strips: Selected findings ...................................... 297 
Signalized Intersections: Informational Guide xv 

Table of Contents

Table Page

CHAPTER 11, CONTINUED 

111 Summary of issues for rumble strips.................................................................................. 298 

112 Summary of issues for cross section improvements ......................................................... 300 

113 Summary of issues for removing obstacles from the clear zone ....................................... 301 

114 Expected reduction in number of crashes per intersection per year by increased sight 

distance........................................................................................................................... 303 

115 Safety benefits associated with sight distance improvements: Selected findings ............. 303 

116 Summary of issues for visibility improvements .................................................................. 304 

CHAPTER 12 

117 Rule-of-thumb intersection capacities assuming various exclusive left-turn treatments ... 309 

118 Guidelines for use of left-turn phasing ............................................................................... 313 

119 Guidelines for selection of type of left-turn phasing........................................................... 314 

120 Minimum recommended sight distance for allowing permissive left turns......................... 315 

121 Safety benefits associated with left-turn lane design improvements: Selected findings ... 316 

122 Summary of issues for left-turn lanes................................................................................. 317 

123 Safety benefits associated with multiple left-turn lanes: Selected findings........................ 319 

124 Summary of issues for multiple left-turn lanes ...................................................................322 

125 Safety benefits associated with left-turn operational treatments: Selected findings.......... 323 

126 Summary of issues for turn prohibitions............................................................................. 324 

127 Summary of issues for auxiliary through lanes .................................................................. 326 

128 Summary of issues for path delineation............................................................................. 327 

129 Right-turn lane volume warrants ........................................................................................ 329 

130 Safety benefits associated with right-turn improvements: Selected findings..................... 331 

131 Summary of issues for right-turn lanes .............................................................................. 332 

132 Summary of issues for double right-turn lanes .................................................................. 334 

133 Safety benefits associated with right-turn channelization: Selected findings .................... 335 

134 Summary of issues for channelized right-turn lanes..........................................................336 

135 Summary of issues for reversible lanes ............................................................................. 338 

136 Summary of issues for variable lane use ........................................................................... 340 
 
Signalized Intersections: Informational Guide 

Introduction 

1

CHAPTER 1 

INTRODUCTION 

TABLE OF CONTENTS 

1.0 INTRODUCTION ....................................................................................................................3 

 1.1 Background...................................................................................................................3 

 1.2 Scope of Guide .............................................................................................................4 

 1.3 Audience for this Guide.................................................................................................5 

 1.4 Organization of the Guidelines......................................................................................5 

LIST OF TABLES 

Table Page

1 Summary of motor vehicle crashes related to junction and severity in the United States 

during 2002..........................................................................................................................3 

2 Organization of the guide........................................................................................................6 

3 List of intersection treatments discussed in this document ....................................................7 

Signalized Intersections: Informational Guide 3

Introduction

1.0 INTRODUCTION 

This guide provides a single, comprehensive document with methods for evaluating the 

safety and operations of signalized intersections and tools to remedy deficiencies. The 

treatments in this guide range from low-cost measures such as improvements to signal timing 

and signage, to high-cost measures such as intersection reconstruction or grade separation. 

While some treatments apply only to higher volume intersections, much of this guide is applicable 

to signalized intersections of all volume levels. 

The guide takes a holistic approach to signalized intersections and considers the safety and 

operational implications of a particular treatment on all system users (motorists, pedestrians, 

bicyclists, transit users). 

Practitioners will find the tools and information necessary to make insightful intersection 

assessments and to understand the tradeoffs of potential improvement measures. The 

information here is based on the latest research available and includes examples of novel 

treatments as well as best practices in use by jurisdictions across the United States. Additional 

resources and references are highlighted for the practitioner who wishes to learn more about a 

particular subject. 

This guide is not intended to replicate or replace traditional traffic engineering documents 

such as the Manual on Uniform Traffic Control Devices (MUTCD),

(1) the Highway Capacity 

Manual (HCM) 2000,

(2) or the American Association of State Highway and Transportation 

Officials’ (AASHTO) A Policy on Geometric Design of Highways and Streets,

(3) nor is it intended 

to serve as a standard or policy document. Rather, it provides a synthesis of the best practices 

and novel treatments intended to help practitioners make informed, thoughtful decisions. 

1.1 BACKGROUND 

Traffic signals are a common form of traffic control used by State and local agencies to 

address roadway operations. They allow the shared use of road space by separating conflicting 

movements in time and allocating delay. They can also be used to enhance the mobility of some 

movements as, for example, along a major arterial. 

Traffic signals play a prominent role in achieving safer performance at intersections. 

Research has shown that, under the right circumstances, the installation of traffic signals will 

reduce the number and severity of crashes. But inappropriately designed and/or located signals 

can have an adverse effect on traffic safety, so care in their placement, design, and operation is 

essential. Table 1 shows that in 2002, 21 percent of all crashes and 24 percent of all fatalities 

and injury collisions occurred at signalized intersections. 

Table 1. Summary of motor vehicle crashes related to junction and severity 

in the United States during 2002. 

Total Crashes Fatalities/Injuries 

 Number Percent Number Percent

Non-Intersection Crashes 3,599,000 57 1,022,549 52 

Signalized Intersection Crashes 1,299,000 21 462,766 24 

Non-Signalized Intersection Crashes 1,418,000 22 481,994 25 

Total 6,316,000 100 1,967,309 100 

Source: Adapted from table 28 of Traffic Safety Facts 2002.(4)
4 Federal Highway Administration 

In some cases, the dual objectives of mobility and safety conflict. To meet increasing and 

changing demands, one element may need to be sacrificed to some degree to achieve 

improvements in another. In all cases, it is important to understand the degree to which traffic 

signals are providing mobility and safety for each of transportation. 

Assuring the efficient operation of the traffic signal is becoming an increasingly important 

issue as agencies attempt to maximize vehicle roadway capacity to serve the growing demand for 

travel. “Quick fixes” and low-cost treatments are increasingly limited. 

Grade separation has traditionally been viewed as the next logical step beyond a signalized 

intersection. In some cases, grade separation may be the most appropriate choice, and the 

practitioner needs guidance on when and how to make the transition to an interchange. However, 

given the construction costs, availability of right-of-way, and social and environmental constraints 

associated with a grade-separated improvement, alternative traffic control and geometric design 

forms are sometimes preferable if they can be shown to be feasible and adequate from 

operational, safety, and design perspectives. 

A variety of alternative traffic control forms can be found around the country, many of which 

have seen widespread application in only limited geographic areas. For example, New Jersey has 

long had a practice of using jughandle left turns to improve the operation of signalized 

intersections. Michigan has used median U-turns to eliminate movements at critical intersections. 

Maryland and New York have constructed versions of a continuous flow intersection. 

Reducing crashes should always be one of the objectives whenever the design or operational 

characteristics of a signalized intersection are modified. As described by the Federal Highway 

Administration (FHWA), the “mission is not simply to improve mobility and productivity, but to 

ensure that improved mobility and productivity come with improved safety.”(5)

1.2 SCOPE OF GUIDE 

This guide covers all aspects of signalized intersections, with some emphasis on signalized 

intersections with traffic volumes typically exceeding 40,000 entering vehicles per day where all 

approaches are heavily used. These are intersections well beyond MUTCD volume thresholds for 

signal warrants. This is intended to cover arterial/arterial level facilities and higher. Intersections 

of this size typically include a minimum of five lanes on the major street and three lanes on the 

minor street. Intersections considered for grade separation are within the scope of the guide. 

The intersection forms considered here include signalized at-grade intersections and 

intersections with the potential for grade separation. Intersections that include alternative or 

unconventional turn treatments such as median U-turns and jughandles are within the scope of 

these guidelines to the extent that they have been implemented and accepted by some U.S. 

jurisdictions. Roundabouts are not addressed in this document; for more information, please refer 

to FHWA’s Roundabouts: An Informational Guide.(6)

The guide addresses safety and operation for all users of signalized intersections including 

motorists, pedestrians, bicyclists, and transit riders. This guide addresses Americans with 

Disabilities Act (ADA) requirements and provides guidelines for considering older drivers. 
Signalized Intersections: Informational Guide 5

Introduction

1.3 AUDIENCE FOR THIS GUIDE 

This guide is intended for planners, designers, and operations analysts who perform, or want 

to perform, one or more of the following functions as they pertain to signalized intersections: 

• Evaluate substantive safety performance experienced by users of the system. 

• Evaluate operational performance experienced by users of the system. 

• Identify treatments that could address a particular operational or safety deficiency. 

• Understand fundamental user needs, geometric design elements, or signal timing and 

traffic design elements. 

• Understand the impacts and tradeoffs of a particular intersection treatment. 

It is envisioned that this guide will be used by engineers, planners, and decisionmakers who: 

• Are involved with the planning, design, and operation of signalized intersections, 

particularly those with high volumes. 

• Are involved with the identification of potential treatments. 

• Make decisions regarding the implementation of treatments at those intersections. 

1.4 ORGANIZATION OF THE GUIDELINES 

This guide is arranged in three parts: 

• Part I: Fundamentals. 

• Part II: Project Process and Analysis Methods. 

• Part III: Treatments. 

The chapters on fundamentals (chapters 2-4) in part I provide key background information on 

three topic areas: user needs, geometric design, and traffic design and illumination. These 

chapters provide a foundation of knowledge of signalized intersections that is useful as a learning 

tool for entry-level engineers and as a refresher for more experienced engineers. The information 

contained in these chapters is referenced in parts II and III. 

The chapters on project process and analysis methods (chapters 5-7) in part II outline the 

steps that should be carried out in a project involving the evaluation and assessment of a 

signalized intersection. Part II also provides tools practitioners can use to evaluate the safety and 

operational performance of an intersection and determine geometric needs. 

Part III provides a description of treatments that can be applied to mitigate a known safety or 

operational deficiency. The treatments are organized in chapters 8-12 based on the intersection 

element (system, approach, movement, etc.). Within each chapter, the treatments are grouped by 

a particular user type (e.g., pedestrian treatments) or are grouped to reflect a particular condition 

(e.g., signal head visibility). 

Table 2 depicts the organization of the guide. 
6 Federal Highway Administration 

Table 2. Organization of the guide. 

Part Chapter Title 

 1 Introduction 

 

Part I: Fundamentals 2 User Needs 

 3 Geometric Design 

 4 Traffic Design and Illumination 

 

5 Project Process 

6 Safety Analysis Methods 

Part II: Project 

Process and Analysis 

Methods 7 Operational Analysis Methods 

 

Part III: Treatments 8 System-Wide Treatments 

 • Access Management 

 • Signal Coordination 

 

 9 Intersection-Wide Treatments 

 • Pedestrian Facilities and Design 

 • Bicycle Facilities and Design 

 • Transit Facilities and Design 

 • Traffic Control 

 • Illumination 

 

 10 Alternative Intersection Treatments 

 • Indirect Left-Turn Movements 

 • Intersection Reconfiguration 

 • Grade Separation 

 

 11 Approach Treatments 

 • Signal Head Placement and Visibility 

 • Signing and Speed Control 

 • Pavement/Cross Section 

 • Sight Distance 

 

 12 Individual Movement Treatments 

 • Left-Turn Movements 

 • Through Movements 

 • Right-Turn Movements 

 • Variable Lane Use 
Signalized Intersections: Informational Guide 7

Introduction

Table 3 provides a list of the treatments discussed in part III. Each treatment includes a 

description, a photo or diagram where available, and a summary of the treatment’s applicability. 

In addition, these sections identify key design elements; operational and safety impacts; impacts 

on other modes; socioeconomic and physical impacts; and education, enforcement, and 

maintenance issues. The treatments in table 3 represent some, but not all, possible treatments. 

Table 3. List of intersection treatments discussed in this document. 

Treatment Type Treatments 

System-Wide 

Treatments 

(Chapter 8) 

• Provide median 

• Access management 

• Provide signal coordination 

• Provide signal preemption/priority 

Intersection-Wide 

Treatments 

(Chapter 9) 

• Reduce curb radius 

• Provide curb extensions 

• Provide advance stop bars 

• Improve pedestrian signal 

display 

• Modify pedestrian signal 

phasing 

• Separate pedestrian 

movements 

• Provide bicycle box 

• Provide bike lanes 

• Relocate transit stop 

• Convert from pre-timed to actuated 

operation 

• Modify clearance interval 

• Modify cycle length 

• Remove late night/early morning flash 

• Provide/upgrade illumination 

Alternative 

Intersection 

Treatments 

(Chapter 10) 

• Jughandle 

• Median U-turn 

• Continuous-flow 

intersection 

• Remove skew 

• Remove deflection in 

through path 

• Improve horizontal/vertical 

alignment 

• Split intersection 

• Quadrant roadway intersection 

• Super-street median crossover 

• Convert four-leg intersection to two T 

intersections 

• Convert two T intersections to four-leg 

intersection 

• Close intersection leg 

• Convert to diamond interchange 

Approach Treatments 

(Chapter 11) 

• Convert to mast arm or 

span wire 

• Add near-side polemounted signal heads 

• Increase size of signal 

heads 

• Use two red signal sections 

• Increase number of signal 

heads 

• Provide backplates 

• Improve signing 

• Provide advance warning 

• Reduce operating speed 

• Improve pavement surface 

• Provide rumble strips 

• Improve cross section 

• Remove obstacles from clear zone 

• Improve sight lines 

Individual Movement 

Treatments 

(Chapter 12) 

• Add single left-turn lane 

• Add multiple left-turn lane 

• Prohibit turn movements 

• Provide auxiliary through 

lane 

• Add single right-turn lane 

• Provide double right-turn lanes 

• Provide channelized right-turn lane 

• Delineate path 

• Provide reversible lane 

• Provide variable lane use 

Signalized Intersections: Informational Guide 9

Part I—Fundamentals 

Part I 

Fundamentals 

Part I discusses the fundamentals of signalized intersections as they relate to User Needs (chapter 

2), Geometric Design (chapter 3), and Traffic Design and Illumination (chapter 4). These chapters are 

intended for use by entry-level engineers and other users of the guide who seek broad-level information 

on the technical aspects of signalized intersections. The information provides a background for the 

chapters in part II and part III. 

Signalized Intersections: Informational Guide 11

Road User Needs 

CHAPTER 2 

ROAD USER NEEDS 

TABLE OF CONTENTS 

2.0 ROAD USER NEEDS ...........................................................................................................13 

 2.1 Overview of Human Factors .......................................................................................13 

 2.1.1 Positive Guidance ..........................................................................................14 

 2.1.2 Roadway Safety.............................................................................................15 

 2.2 Intersection Users .......................................................................................................16 

 2.2.1 Human Factors Common to All Road Users..................................................16 

 2.2.2 Motorists.........................................................................................................20 

 2.2.3 Bicyclists ........................................................................................................23 

 2.2.4 Pedestrians ....................................................................................................27 

 2.3 Applying Human Factors.............................................................................................32 

LIST OF FIGURES 

Figure Page

1 Traffic controls such as official signs need to be close to the road, distinctive from 

other information presentations, brief, and explicit. This photo provides an example 

of signs that are close to the road but may be confused with background information ....17 

2 In terms of both official signs and advertising displays, too many displays may have the 

effect of causing drivers to “tune out,” and recall will be poor. This photo shows an 

example of sign clutter where the regulatory sign is difficult to isolate from the 

background advertising signs............................................................................................17 

3 Enforcement cameras, as shown in the photo above, are used at signalized intersections 

to identify red light runners ................................................................................................23

4 Typical dimensions of a bicyclist...........................................................................................25 

5 Bicyclist conflicts at signalized intersections ........................................................................27 

6 Examples of pedestrians of various abilities preparing to cross an intersection ..................28 

7 Typical dimensions for a turning wheelchair.........................................................................29 

8 Crosswalks are used by a variety of users with different speed characteristics. 

Pedestrian walking speeds generally range between 0.8 to 1.8 m/s (2.5 to 6.0 ft/s)........30 

9 Pedestrian conflicts at signalized intersections ....................................................................31 

LIST OF TABLES

Table Page

4 Estimated number of registered vehicles by type, 2002.......................................................20 

5 Fatalities and injuries by mode, 2001 ...................................................................................21 

6 Total motor vehicle crashes and injury/fatal collisions at signalized intersections by total 

ADT entering the intersection............................................................................................21 

7 Proportion of crashes by collision type at signalized intersections.......................................22 

8 Typical dimensions for a sample of types of pedestrians.....................................................29 
 
Signalized Intersections: Informational Guide 13

Road User Needs

2. ROAD USER NEEDS 

The purpose of this chapter is to describe road user needs. The description is based on three 

assumptions: 

• Practitioners want to adopt an integrated, systems view founded on human factors 

principles of the interactions among intersection design, traffic control, environmental 

factors, and road users. 

• The road user—motorist, bicyclist, and pedestrian—is the operative element in the 

system; decisions affecting user performance taken at any point in the roadway life 

cycle often involve tradeoffs. 

• Practitioners need to fully understand and quantify intersection operations and safety 

performance in the pursuit of informed and balanced decisionmaking. 

A discussion of user needs requires an understanding of human factors principles for all 

intersection users. This chapter begins with an overview of human factors research and is 

followed by a description of user needs for motorists, pedestrians, and bicyclists. The chapter 

concludes with a discussion of applying human factors principles to the planning, design, and 

operation of signalized intersections. 

Documents marked with an asterisk in the reference list provide additional coverage of user 

needs and human factors and helpful background reading. 

2.1 OVERVIEW OF HUMAN FACTORS 

Human factors research deals with human physical, perceptual, and cognitive abilities and 

characteristics and how they affect our interactions with tools, machines, and workplaces. The 

goal of human factors analysis in road transportation is to: 

• Explain, as fully as is possible, the information needs, abilities and characteristics of 

road users. 

• Study the human-machine-situational interactions that occur. 

• Capitalize on this knowledge through improvements in engineering design. 

At signalized intersections, the application of human factors principles to the problems of 

safety and efficiency requires an approach that is both systems oriented and human-centered. A 

systems approach recognizes the interaction between the road user and road/roadway 

environment. This acknowledges that no one element can be analyzed and understood in 

isolation. A human-centered approach recognizes road users as the operative element within the 

system—the decisionmakers—and focuses the engineering effort on optimizing their 

performance. 

Human factors analysis, particularly as it relates to any element of the transportation system 

(including signalized intersections), includes the following tasks: 

• Ensuring road users are presented with tasks that are within their capabilities under a 

broad range of circumstances. 

• Designing facilities that are accessible to and usable by all road users. 

• Anticipating how road users may react to specific situations to ensure a predictable, 

timely, accurate and correct response, thus avoiding situations that violate road users’ 

expectations. 

• Designing and applying appropriate traffic control devices so they are conspicuous, 

legible, comprehensible, credible, and provide sufficient time to respond in an 

appropriate manner. 
14 Federal Highway Administration 

• Understanding how geometric design properties of width, enclosure, slope, and 

deflection affect users and contribute to behaviors such as speeding, yielding, and gap 

acceptance. 

Signalized intersections serve a variety of road users, chiefly motorists, bicyclists, and 

pedestrians. Within each road user group, there are multiple user types. For example, motorists 

include passenger car and commercial truck drivers. Bicyclists include recreational and 

commuting bicyclists, as well as a wide range of ages and abilities. Pedestrians include all age 

groups (children, adults, elderly), some of whom have cognitive, mobility, or vision impairments. 

Each road user has unique abilities and characteristics, all of which need to be considered in the 

design of an intersection. 

The basic function of signalized intersections is to sequence right-of-way between 

intersecting streams of users. These intersections thus serve multiple functions: they allow 

motorists to access new streets and change directions in travel; they are junctions for bike routes; 

and they provide a primary connection to and from activity centers for pedestrians. Intersections 

also serve as public right-of-way and include space for public utilities such as power and 

communication lines; water, sanitary sewer, and storm drainage pipes; and traffic signs and 

signal equipment. 

Each road user has specific needs traversing an intersection. Motorists and cyclists must 

detect the intersection on approach, assess its relevance from a navigational perspective, 

respond to the applicable traffic controls, and negotiate the intersection. In a similar manner, 

pedestrians must identify the crossing location, maneuver to and position themselves accordingly 

at the crossing, activate a crossing device, and respond appropriately to the traffic controls. All 

users must remain vigilant for potential conflicts with other road users. 

Under ADA, all people, including those with disabilities, have the right to equal access to 

transportation.(7) Designing facilities that cannot be used by people with disabilities constitutes 

illegal discrimination under the ADA. Designing safe and usable facilities demands an 

understanding that persons with disabilities have varying abilities, use a variety of adaptive 

devices, and may have multiple impairments. 

Road users are limited in the amount of information they can process. For vehicle drivers and 

bicyclists, the pace at which information is encountered increases with travel speed. The number 

of choices facing drivers and bicyclists at any one time should be minimized, and information 

presented should be concise, complete, explicit, and located sufficiently in advance of the choice 

point to allow for a comfortable response. 

2.1.1 Positive Guidance 

In the 1980s, FHWA’s Office of Human Factors brought forth a series of documents 

advocating the explicit application of human factors-based knowledge in the design of roadways 

and in the design, selection and application of information presentations targeted at vehicle 

users.(8)

Termed positive guidance, the concept focuses on understanding and making allowances for 

how road users—primarily motorists—acquire, interpret, and apply information in the driving task. 

Key concepts are those of driver expectation, expectancy violation, primacy, and road user error. 

Positive guidance places the driving task within the framework of a road environment viewed 

as an information system, where the driver is the operative element. The roadway, with its formal 

and informal sources of information, becomes the input. The vehicle, controlled by the driver, 

becomes the conduit for output. The driving task itself is subdivided into three performance levels: 

control, guidance, and navigation, each oriented in decreasing order of primacy and increasing 

order of complexity. 

Positive guidance is founded on a simple concept: if drivers are provided with all of the 

information they need, in a format they can readily read, interpret and apply, and in sufficient time 

to react appropriately, then the chances of driver error will be reduced, and relative safety will be 
Signalized Intersections: Informational Guide 15

Road User Needs

improved. Uniformity in the design and context of application of information presentations is a key 

component of positive guidance. Information presentations must work within the roadway 

information system to reinforce driver expectations that are correct and restructure those that are 

not. They must provide the information necessary to support rapid decisionmaking while 

minimizing the potential for driver error. 

Strict interpretation of the positive guidance concept implies telling the driver what he or she 

needs to know and nothing else. In practical application, positive guidance suggests that 

competition for driver attention, the presence of information irrelevant to driving-related tasks, as 

well as exceeding the information-processing limitations of drivers, may have a negative impact 

on relative safety. 

This road user-based approach to information presentation is the foundation of state-of-theart information presentation policies, standards and guidelines, including FHWA’s MUTCD.(1) 

However, a growing body of research is suggesting that redundancy in message delivery systems 

may in fact improve the efficiency, safety, and/or usability of a facility. For example, pedestrians 

tend to begin their crossing more quickly if an audible prompt accompanies the visible pedestrian 

signal indication. There is always a risk that some users will miss or be unable to receive 

information that relies on only one sense (e.g., sight). 

2.1.2 Roadway Safety 

In the past, roads were considered to be “safe” if they were designed, built, operated, and 

maintained in accordance with nominal standards. These standards were usually based on 

empirical data or long-standing practice. Collisions were viewed as an unavoidable outcome of 

the need for mobility and the inevitability of human error. When human errors resulted in 

collisions, the fault was perceived to lie with the road user, rather than with the road. 

The approach to roadway safety has since evolved. In the explicit consideration of roadway 

safety, safety itself is now recognized to be a relative measure, with no road open to traffic being 

considered completely “safe”—only “more safe” or “less safe” relative to a particular benchmark, 

as defined by one or more safety measures. While the concept of “road user error” remains, it is 

now understood that errors and the collisions that result don’t just “happen,” they are “caused,” 

and that the roadway environment often plays a role in that causation. 

In the Institute for Transportation Engineers (ITE) Traffic Safety Toolbox: A Primer on Traffic 

Safety, Hauer refers to nominal safety as compliance with standards, warrants, guidelines and 

sanctioned design procedures, and substantive safety as the expected crash frequency and 

severity for a highway or roadway.(9)

The concept of the “forgiving” roadway—one that minimizes the consequences of road user 

error by designing out or shielding hazards—has more recently given way to the “caring” 

roadway. The caring roadway combines all of the forgiving features of its predecessor (crash 

cushions, clear zones, etc.) with elements that respond to driver capabilities, limitations, 

expectations, and information needs. The caring roadway seeks to create an operating 

environment that is user-friendly and simplifies the information presented to the driver, a roadway 

that is conducive to rapid, error-free performance by the road user. 

By attacking the environmental and situational elements that contribute to the occurrence of 

driver error, the caring roadway seeks to break the chain of causation between the erroneous 

decisions and/or actions, and their undesirable outcomes (e.g., crashes). 

The caring roadway concept is largely information driven. It is predicated on meeting the 

expectations of road users—motorists, bicyclists, and pedestrians—and assuring that they get 

needed information, when it is required, in an explicit and usable format, in sufficient time to react. 

Implicit in the caring roadway approach is that the information-processing capabilities of users 

must at no time be overtaxed, by either an overabundance of potentially relevant information, or 

by the additive presence of information not immediately relevant to the task of negotiating the 

roadway. 
16 Federal Highway Administration 

2.2 INTERSECTION USERS 

Knowing the performance capabilities and behavioral characteristics of road users is 

essential for designing and operating safe and efficient signalized intersections. All road users 

have the same human factors, no matter how they use the road. For example, older drivers, older 

pedestrians, and people with visual disabilities all frequently share the characteristic of longer 

reaction times. The following section discusses human factor issues common to all road users, 

followed by a discussion of issues specific to motorists, bicyclists, and pedestrians. 

2.2.1 Human Factors Common to All Road Users 

The task of traveling on the roadway system, whether by motor vehicle, bicycle, or foot, 

primarily involves searching for, finding, understanding, and applying information, as well as 

reacting to the appearance of unanticipated information. Once found and understood, the 

relevance of this information must be assessed, and decisions and actions taken in response. 

This activity is cyclic, often occurring many times per second in complex, demanding 

environments. The capabilities of human vision, information processing, and memory all affect a 

road user’s ability to use an intersection, and these may affect the likelihood of user error. Age 

plays a role in all of these factors. The following sections discuss each of these factors. 

Human Vision 

Road users receive most of their information visually. The human visual field is large; 

however, the area of accurate vision is quite small. Drivers, for example, tend to scan a fairly 

narrow visual field ahead of them. Drivers do not dwell on any target for long; studies indicate that 

most drivers become uncomfortable if they cannot look back at the roadway at least every two 

seconds.(10) This means that information searches and the reading of long messages is carried 

out during a series of glances rather than with one long look. Complex or cluttered backgrounds, 

such as that shown in figures 1 and 2, make individual pieces of information more difficult to 

identify and can make the driving task more difficult. Looking at irrelevant information when it is 

not appropriate to do so may cause drivers to overlook relevant information, or fail to accurately 

monitor a control or guidance task. This is of particular concern in areas of high workload, at 

decision points, and at locations where there is a high potential for conflict (e.g., intersections and 

crosswalks). 
Signalized Intersections: Informational Guide 17

Road User Needs

Figure 1. Traffic controls such as official signs need to be close to the road, distinctive from other 

information presentations, brief, and explicit. This photo provides an example of signs that are 

close to the road but may be confused with background information. 

Figure 2. In terms of both official signs and advertising displays, too many displays may have the 

effect of causing drivers to “tune out,” and recall will be poor. This photo shows an example of 

sign clutter where the regulatory sign is difficult to isolate from the background advertising signs. 
18 Federal Highway Administration 

Information Processing 

Road users perform best under moderate levels of demand. Overload or underload tends to 

degrade performance. Consider the example of driving. The presentation of information in 

circumstances of low driving-task demand is commonly assumed to avert boredom; however, this 

assumption is untested. During periods of high task demand, however, it is known that the 

duration of drivers’ glances at signs become shorter, as more time is needed to accommodate 

control and guidance tasks, and less is available for reading signs. Extra effort should be made to 

limit information presentations to those immediately relevant to the driving task where 

circumstances of high workload are apt to occur. 

Road users are adept at recognizing patterns—clues as to what is upcoming—and using 

those clues, along with expectations, to anticipate and prepare for situations similar to those 

experienced before. When things turn out as expected, performance is often rapid and error-free. 

When expectations are violated, surprise results, and new information must be gathered so the 

user can rethink a response. Adherence to uniform principles of information presentation in the 

design and application of traffic control devices—and managing the overall information load 

placed on road users—is vital to ensure that the users get the information they need, when they 

need it, in a form that they can recognize and understand, in time to perceive and react to it in an 

appropriate manner. 

Memory 

Humans have a limited short-term memory. Only a small percentage of what they see is 

actually remembered, including information presentations viewed while driving, cycling, or 

walking. Long-term memory is made up of experiences that have been ingrained through 

repetition. These are the source of our expectations. Expectations play a strong role in the 

performance of all road users. Information about an upcoming condition or hazard should be 

proximate to its location, or repeated at intervals for emphasis. 

User Error 

There is a common belief that the risk of user error is increased when needed information: 

• Is missing or incomplete. 

• Is difficult to locate, read or interpret. 

• Lacks credibility. 

• Leads to false expectations. 

• Provides insufficient time for decision and appropriate action. 

Information presentations must be conspicuous, legible, readable at a glance, and explicit as 

to their meaning. Uniformity and consistency are paramount. For example, drivers must receive 

the same clues and information in similar situations so that their expectations will be consistent 

with reality, or their expectations will be restructured accordingly. The presentations must be 

located in advance, to provide time to react, and they must be spaced—both from each other and 

from other competing sources of information—so as not to confuse or overload the road user. 

Drivers in particular often have difficulties in following through the sequence of driving tasks, 

which leads to driving errors. The most common driving errors include improper lookout (faulty 

visual surveillance), inattention, false assumption, excessive speed, improper maneuvers, 

improper evasive action, and internal distraction.(11) Cyclists can also have similar difficulties. 

These errors often result from: 

• Inadequate input for the task at hand (e.g., night time travel, poor sight distance, 

inconspicuous traffic control devices, complex intersection layouts, insufficient 

advance signing). 

• Uncommon events (violations by other road users, emergency vehicles traveling 

through red light). 
Signalized Intersections: Informational Guide 19

Road User Needs

• Inappropriate inputs (extraneous or conflicting signage). 

• The shedding of important information when overloaded. 

• Stress, frustration, inexperience, fatigue, intoxication. 

• Imperfect decisionmaking. 

In summary, the engineer should be aware of road users and their needs and limitations with 

regard to signalized intersections. Information displayed in advance of and at the intersection 

needs to be consistent, timely, legible, and relevant. Awareness of how human factors play a role 

in the task of using the intersection will go a long way toward reducing error and the collisions this 

may cause. 

Age 

Age and experience have a significant effect on the ability of drivers, cyclists, and pedestrians 

to use an intersection. For example, young drivers have a quicker perception and reaction time 

yet often lack the judgment to perceive something as being hazardous, something only 

experience can teach a driver. In contrast, older drivers have the experience yet may lack the 

perception and reaction time.(12) 

According to the FHWA Highway Design Handbook for Older Drivers and Pedestrians, half of 

fatal crashes involving drivers 80 or older took place at intersections.(12) This document also 

points to a large body of evidence showing higher crash involvement among older drivers, 

particularly with crash types that require complex speed-distance judgment under time 

constraints, such as a left-turn against oncoming traffic. 

As one ages, specific functions related to the driving task may deteriorate, such as vision, 

hearing, sensation, and cognitive and motor abilities. Peripheral vision and a decreased range of 

motion in an older person’s neck may limit their ability to attend to a traffic signal while searching 

for a gap in traffic when making a left turn. Sorting out visual distractions at intersections can be 

difficult. Cognitive changes require that older drivers need more time to recognize hazards and 

respond. It would also appear that driving situations involving complex speed-distance judgments 

under time constraints as found at many signalized intersections are problematic for older drivers 

and pedestrians. 

The following specific tasks were reported as being problematic for older road users: 

• Reading street signs. 

• Driving through an intersection. 

• Finding the beginning of a left-turn lane at an intersection. 

• Judging a gap in oncoming traffic to make a left turn or cross the street (both driving 

and on foot). 

• Following pavement markings. 

• Responding to traffic signals. 

Little research has been done on the performance and needs of young and inexperienced 

drivers at signalized intersections. Young drivers aged 16 to 24 have a higher risk (2.5 times) of 

being involved in a collision compared to other drivers. Young pedestrians (i.e., pedestrians under 

the age of 12) also have a higher risk of being in a collision. These users may: 

• Have difficulty in judging speed, distance, and reaction time. 

• Tend to concentrate on near objects and other vehicles. 

• Miss important information. 

• Have a poor perception of how hazardous a situation can become 
20 Federal Highway Administration 

• Fix their eyes on an object for longer periods. 

• Have difficulty integrating information. 

• Be easily distracted by unrelated events (i.e. conversations between passengers and 

adjusting the stereo). 

• Underestimate their risk of being in a collision. 

• Make less effective driving and crossing decisions. 

2.2.2 Motorists 

Motorists account for by far the most number of trips taken on roads. There are more than 

225 million licensed vehicles in the United States.(13) Traffic engineers have traditionally sought to 

design and operate intersections with the typical driver in mind, trying to best accommodate their 

needs in terms of their ability to perceive, react, and safely navigate through an intersection. This 

being so, bicyclists and pedestrians are often at a disadvantage at many intersections. 

Road users—drivers, bicyclists, and pedestrians—are not homogeneous in their 

characteristics, and traffic engineers must be conscious of the need to design for a range of 

human characteristics and responses. Specific subgroups of drivers may have an elevated risk of 

being involved in a collision (e.g., teenaged drivers, older drivers, and aggressive drivers). 

Most drivers traveling through signalized intersections will be operating passenger vehicles. 

These may be cars, but in ever-increasing numbers they are minivans, pickups and sports utility 

vehicles. More than 22,000 fatal collisions in the United States each year involve passenger 

vehicles.(14) However, commercial vehicles (tractor-trailers, single-unit trucks, and cargo vans) 

account for more than their share of fatal collisions, based on fatal crash rates per mile.(15) These 

vehicles need to be properly accommodated at intersections. Vehicle acceleration from a 

stationary position, braking distances required, safe execution of a left or right turn, and provision 

of adequate storage in turning lanes are important items that should be considered. 

Table 4 identifies general characteristics of vehicle types, and table 5 shows the frequency of 

fatalities and injuries by mode. 

Table 4. Estimated number of registered vehicles by type, 2002. 

Vehicle Type Number of Registered Vehicles 

Percent of 

Total 

Passenger car 

(convertibles, sedans, station wagons)

133.6 million 59 

Other 2-axle, 4-tire vehicles 

(pick-up trucks, vans, sport utility 

vehicles) 

79.1 million 35 

Motorcycles 4.3 million 2 

Truck, single unit 5.9 million 3 

Truck, combination 2.1 million 1 

Bus 0.8 million < 1 

Total 225.8 million 

Source: Bureau of Transportation Statistics, 2002.(16)
Signalized Intersections: Informational Guide 21

Road User Needs

Table 5. Fatalities and injuries by mode, 2001. 

Mode Fatalities 

Percent of 

Total Injuries 

Percent of 

Total 

Passenger car occupants 

(all types) 20,233 48 1,926,625 64 

Truck occupants1 12,381 29 889,951 29 

Motorcyclists 3,181 8 60,236 2 

Bus occupants 34 < 1 15,427 1 

Pedestrians 4,882 12 77,619 3 

Bicyclists 728 2 45,277 1 

Other 677 1 17,536 1 

Total 42,116 3,032,672 

1

 Includes single-unit trucks, truck tractors, pickups, vans, truck-based station wagons, and utility 

vehicles. 

Source: Bureau of Transportation Statistics, 2001(17)

Crash data from the Highway Safety and Information System (HSIS) database for the State 

of California were summarized to identify the proportion of crashes by ranges of Average Daily 

Traffic (ADT) for movements entering the intersection and the proportion of crashes by collision 

type. The HSIS data includes all reported crashes at signalized intersections for the period 

between 1994 and 1998. Table 6 presents a summary of total and injury/fatal crashes by volume, 

and table 7 presents the results and identifies the proportion of crashes by collision type for 

signalized intersection based on the California HSIS data. 

Table 6. Total motor vehicle crashes and injury/fatal collisions at signalized intersections by total 

ADT entering the intersection. 

ADT 

Intersections 

(percent of total)

Total Crashes 

(percent of total) 

Injury/Fatal Crashes 

(percent of total) 

<20000 16 8 7 

20,000-40,000 45 40 38 

40,000-60,000 29 36 37 

60,000-80,000 8 13 14 

80,000 and more 2 3 4 

TOTAL 100 100 100 

Source: HSIS California database, 1994-1998(18)

As shown in table 6, the 20,000 to 40,000 ADT and 40,000 to 60,000 ADT ranges represent 

the greatest percentage of signalized intersections from the database and have the highest 

percentage of total crashes and injury/fatal crashes. The percentage of total and injury/fatal 

crashes that occurred in the 40,000-60,000 ADT range is similar; however, the proportion of 

intersections in this range is much smaller. 
22 Federal Highway Administration 

Table 7. Proportion of crashes by collision type at signalized intersections.(18)

Collision Type Percent 

Head on 3 

Sideswipe 12 

Rear end 42 

Broadside 28 

Fixed object 6 

Overturned 0 

Pedestrian 3 

Other 6 

TOTAL 100 

As shown in table 7, the most frequently occurring collision is a rear-end crash, which 

represents 42 percent of all reported intersection crashes in the database. 

Vehicle Dimensions 

Motor vehicle needs at a signalized intersection are governed by the dimensions of the 

design vehicle, which is the largest vehicle reasonably expected to use the intersection. 

Commonly, WB-15 (WB-50) vehicles, or truck/trailer combinations with a wheelbase of 15 m (50 

ft), are the largest vehicles along many arterials. However, many signalized intersections are 

located on State highways where the design vehicle is an interstate vehicle such as a WB-20 

(WB-67), or a truck/trailer combination with a wheelbase of 20 m (67 ft). Specific information on 

the dimensions for these and other design vehicles can be found in standard references.(3)

Design vehicles need to be carefully considered wherever they are expected to make a 

turning movement through the intersection. Affected elements include corner radii, channelization 

islands, median noses, and stop bar locations. In accommodating the design vehicle, however, 

tradeoffs for other users need to be acknowledged, such as the increase in pedestrian crossing 

distance or the accommodation of cyclists around channelization islands. 

Red Light Running 

One primary cause of collisions at signalized intersections is when a motorist enters an 

intersection when the red signal is displayed, and as a consequence collides with another 

motorist, pedestrian, or bicyclist who is legally within the intersection. It is estimated that 

approximately 750 fatalities and 150,000 injuries occur on a yearly basis due to red light running. 

A study of HSIS data determined that red light runners cause 16 to 20 percent of all collisions at 

signalized intersections.(19)

Red light running may occur due to poor engineering, distraction, inattention, or willful 

disregard. Those who deliberately violate red lights tend to be younger, male, less likely to use 

seat belts, have poorer driving records, and drive smaller and older vehicles. 

Countermeasures proposed to address red light running are removal of unwarranted traffic 

signals, changing the signal timing, improving the visibility of the traffic signal, or enforcement. An 

example of red light running enforcement cameras is given in figure 3. 
Signalized Intersections: Informational Guide 23

Road User Needs

Figure 3. Enforcement cameras, as shown in the photo above, are used at signalized 

intersections to identify red light runners. 

Driver Distraction 

Despite the complexity of the driving task, it is not uncommon to see drivers engaging in 

other tasks while operating a motor vehicle. While these tasks may seem trivial, they take the 

attention of the driver away from the task of driving. One report estimated that 13 percent of all 

collisions occur due to driver distraction. Drivers involved in collisions at intersections were more 

likely to report that they “looked but didn’t see.” Drivers involved in intersection collisions as 

opposed to other driving situations reported that they were more likely to be distracted by:(20)

• An outside person, object, or event. 

• Another occupant in the vehicle. 

• Vehicle and climate controls. 

• Eating food. 

• Using or dialing a cell phone. 

2.2.3 Bicyclists 

Bicycle travel is an important component of any multimodal transportation system. Bicycle 

travel is healthy, cost effective, energy efficient, and environmentally friendly. Traditionally, the 

most popular form of bicycle travel is recreational cycling. Given the increases in traffic 

congestion over the past few decades, particularly in urban areas, the number of people that use 

bicycles to commute to work is on the rise.(21) 

Bicyclists have unique needs at signalized intersections. Bicyclists are particularly vulnerable 

because they share the roadway with motorists and follow the same rules of the road, yet they do 

not possess nearly the same attributes in size, speed, and ability to accelerate as their motor 

vehicle counterparts. Consequently, roadway characteristics such as grades, lane widths, 

intersection widths, and lighting conditions influence the safety and operations of bicyclists to a 

larger degree than they do for vehicles. External conditions such as inclement weather also 

significantly affect bicyclists’ performance. 

Providing safe, convenient, and well-designed facilities is essential to encourage bicycle 

use.(21) To accomplish this, planning for bicycle use, whether existing or potential, should be 

integrated into the overall transportation planning process. 
24 Federal Highway Administration 

Providing a safe and attractive environment for bicyclists requires special attention to the 

types of bicycle users, their characteristics and needs, and factors that influence bicyclist safety. 

Bicycle Users 

Bicyclists range widely in terms of skills, experience, and preferences. A 1994 report by 

FHWA defined the following general categories (A, B, and C) of bicycle user types:(22) 

• “Advanced or experienced riders are generally using their bicycles as they would a 

motor vehicle. They are riding for convenience and speed and want direct access to 

destinations with a minimum of detour or delay. They are typically comfortable riding 

with motor vehicle traffic; however, they need sufficient operating space on the 

traveled way or shoulder to eliminate the need for either [them] or a passing motor 

vehicle to shift position. 

• “Basic or less confident adult riders may also be using their bicycles for transportation 

purposes, e.g., to get to the store or to visit friends, but prefer to avoid roads with fast 

and busy motor vehicle traffic unless there is ample roadway width to allow easy 

overtaking by faster motor vehicles. Thus, basic riders are comfortable riding on 

neighborhood streets and shared use paths and prefer designated facilities such as 

bike lanes or wide shoulder lanes on busier streets. 

• “Children, riding on their own or with their parents, may not travel as fast as their adult 

counterparts but still require access to key destinations in their community, such as 

schools, convenience stores and recreational facilities. Residential streets with low 

motor vehicle speeds, linked with shared use paths and busier streets with welldefined pavement markings between bicycle and motor vehicle, can accommodate 

children without encouraging them to ride in the travel lane of major arterials” (cited on 

p. 6, reference 22). 

Bicyclist Dimensions 

Bicyclists require at least 1.0 m (40 inches) of operating space, with an operating space of 

1.2 m (4 ft) as the minimum width for bike lanes or other facilities designed for exclusive one-way 

or preferential use by bicyclists (see figure 4). For facilities where motor vehicle volumes, motor 

vehicle or bicyclist speed, and the mix of truck and bus traffic increase, such as most high-volume 

signalized intersections, a more comfortable operating space of 1.5 m (5 ft) or more is 

desirable.(22) In addition, because most bicyclists ride a distance of 0.8 to 1.0 m (32 to 40 inches) 

from a curb face, this area should be clear of drain inlets, utility covers, and other items that may 

cause the bicyclist to swerve.(22) Where drain inlets are unavoidable, their drainage slots should 

not run parallel to the direction of travel, as these can cause a bicyclist to lose control. 

Bicycle User Needs 

The general objectives for bicycle travel are similar to those for other modes: to get from point 

“A” to point “B” as efficiently as possible on a route that is safe and enjoyable. At the same time, 

the mode of travel must integrate with other forms of transportation that use the roadway network 

and not adversely affect other modes or uses. 
Signalized Intersections: Informational Guide 25

Road User Needs

Figure 4. Typical dimensions of a bicyclist. 

• Width—1.2 m (4 ft) design minimum for exclusive bicycle lanes; 1.5 m (5 ft) design 

minimum where motor vehicle traffic volumes, motor vehicle or bicyclist speed, and/or 

the mix of truck and bus traffic increase; bicycle lane width is the affected intersection 

feature. 

• Length—1.8 m (5.9 ft), median island width at crosswalk is the affected intersection 

feature. 

• Lateral clearance on each side—0.6 m (2.0 ft); 1.0 m (3.3 ft) to obstructions; shared 

bicycle-pedestrian path width is the affected intersection feature. 

Sources: (22); (6), as adapted from (23) 
26 Federal Highway Administration 

The Danish Road Directorate identifies key elements to incorporate in the planning of cycling 

facilities: 

• Accessible and coherent. The cycle network should run directly from residential 

areas to the most important destinations such as schools, workplaces, and shopping 

and entertainment centers. 

• Direct and easy. If the cycle network is not direct, logical, and easy to use, some 

cyclists will choose roads not planned for bicycle traffic.

• Safe and secure. Adequate visibility and curve radii should make it possible for 

cyclists to travel safely at a minimum of 25 km/h (15 mph). Parked cars, vegetation, 

barriers, etc. can result in poor or reduced visibility. Awareness of presence of 

bicyclists can be heightened by signing and road marking.

• Self-explanatory design. Edge lines, bicycle symbols, colored tracks and lanes, and 

channelization of traffic make it easy to understand where cyclists should place 

themselves. Uniformity over long stretches is an important component. 

Other elements that should be considered in the planning and design of bicycle facilities 

include bike lanes, pavement surface conditions, drainage inlet grates, refuge, and lighting.(24) 

Bicycle Safety 

In 2001, the National Highway Traffic Safety Administration (NHTSA) reported that 728 

bicyclists were killed and 45,000 injured in motor vehicle crashes.(25) However, many bicycle 

crashes either do not involve a motor vehicle or go unreported. A study of records at eight 

hospitals in three States found that 55 percent of bicycle injury events in a roadway did not 

involve a motor vehicle.(26) In addition, the study found that 40-60 percent of bicycle-motor 

vehicle crashes were not reported to the official State files. 

Bicycle-motor vehicle crashes are a concern at intersections. An FHWA report identified four 

common crash types, three of which occur at intersections:(27)

• Motorist left turn facing the bicyclist. 

• Bicyclist left turn in front of traffic. 

• Motorist drive-out from a driveway or alley. 

• Bicyclist ride-out from a stop sign or flashing red signal. 

Figure 5 presents the typical conflicts for bicyclists at a signalized intersection. As the exhibit 

shows, bicyclists going straight through a signalized intersection encounter the same conflicts as 

a motor vehicle (shown in the exhibit as open circles) but also encounter conflicts from motor 

vehicles turning right from the same direction. 

Left turns for bicyclists are even more complex and depend on the type of bicyclists. For 

small- to medium-sized signalized intersections, Category A and some Category B cyclists will 

generally choose to take the lane as a motor vehicle, as it is the fastest way through the 

intersection; the remainder will likely feel more comfortable traveling as a pedestrian, as shown in 

figure 5. As the size of the intersection increases, the difficulty for cyclists to weave to the left turn 

lane can be daunting for Category B and even some Category A cyclists. 
Signalized Intersections: Informational Guide 27

Road User Needs

Figure 5. Bicyclist conflicts at signalized intersections. 

Research confirms that the conflicts described above result in high risk for bicyclists at 

signalized intersections. Geary examined nearly 4,000 bicycle fatalities recorded on American 

roads during the period 1994-1998 with the use of the Fatality Analysis Reporting System 

database maintained by NHTSA.(28) The research indicated that intersections are far more 

involved in the injury-producing bicyclist crashes (73 percent) than in the fatal crashes (37 

percent). Intersection-related fatalities are far more common on urban rather than rural roads, and 

during daylight instead of after dark. Recent trends suggest that adults are becoming more 

involved in collisions involving bicycles, while children are becoming less involved. 

An analysis of police-reported collisions between bicyclists and motorists that occurred in 

Toronto, Canada, indicated that 17 percent of bicycle collisions occur at signalized 

intersections.(29) In just over half of these crashes, the cyclist was struck while crossing the 

intersection within the pedestrian crosswalk. 

A Vancouver study found that the risk for collision while cycling is approximately three times 

higher than for driving a motor vehicle over the same distance.(30) The ratio varies between 2:1 

and 6:1 in other British Columbia jurisdictions. Right-angle collisions were the most frequent 

collision type (28 percent of all collisions). Collisions that occur at signalized intersections 

accounted for 17 percent of all collisions. 

2.2.4 Pedestrians 

Walking is the oldest and most basic form of transportation. Nearly every trip includes a 

walking element. According to the 2001 Nationwide Personal Transportation Survey, 8.6 percent 

of all daily trips occurred via the walk mode.(31) People walk for a variety of reasons: social and 

recreational activities, trips to school or church, shopping, commuting to and from work, and 

connecting to or from other modes of transportation. Activities often concentrate on the corners of 

intersections where pedestrian streams converge, people interact and socialize, and people wait 

for crossing opportunities. 

The variety of pedestrian users includes persons of all ages, with and without disabilities, 

persons in wheelchairs, and persons with strollers, freight dollies, luggage, etc; an example is 

given in figure 6. The design of intersection facilities should accommodate all types of 

pedestrians, because the user cannot be anticipated. 
28 Federal Highway Administration 

Figure 6. Examples of pedestrians of various abilities preparing to cross an intersection. 

Pedestrian Dimensions 

Research has shown that the ambulatory human body encompasses an ellipse of 45 by 60 

cm (18 by 24 inches).(32) This dimension, however, does not account for a variety of scenarios, 

including pedestrians walking side by side; persons using canes, walkers, dog guides, or 

wheelchairs; persons with shopping carts or baby carriages, and so on. Table 8 shows 

dimensions for various types of pedestrians. 

The Americans with Disabilities Act Accessibility Guidelines (ADAAG), specifies a 1.525-m 

(60-inch) square area to allow a wheelchair user to make a 180-degree turn (figure 7).(33) For 

parallel approaches, ADAAG specifies a minimum low-side reach of 0.23 m (9 inches) and a 

maximum high-side reach of 1.37 m (54 inches). For a forward approach, ADAAG specifies a 

minimum low-reach point of 0.38 m (15 inches) and a maximum high-reach point of 1.22 m (48 

inches). 
Signalized Intersections: Informational Guide 29

Road User Needs

Table 8. Typical dimensions for a sample of types of pedestrians. 

User and Characteristic Dimension Affected Intersection 

Features 

Pedestrian (walking) 

 Width 0.5 m (1.6 ft) Sidewalk width, crosswalk 

width 

Wheelchair 

 Minimum width 

 Operating width 

0.75 m (2.5 ft) 

0.90 m (3.0 ft) 

Sidewalk width, crosswalk 

width, ramp landing areas 

Person pushing stroller 

 Length 1.70 m (5.6 ft) Median island width at 

crosswalk 

Skaters 

 Typical operating width 1.8 m (6 ft) Sidewalk width 

Source: (6), as adapted from (23). 

 Source: (Reference 33, figure 3a) 

Figure 7. Typical dimensions for a turning wheelchair. 

Pedestrian Characteristics 

Pedestrian walking speeds generally range between 0.8 to 1.8 m/s (2.5 to 6.0 ft/s).(3) The 

MUTCD uses a walk speed of 1.2 m/s (4.0 ft/s) for determining crossing times.(1) However, 

FHWA pedestrian design guidance recommends a lower speed of 1.1 m/s (3.5 ft/s) in general to 

accommodate users who require additional time to cross the roadway, and in particular a lower 

speed in areas where there are concentrations of children and or elderly persons.(34,35) The HCM 

2000 indicates that if elderly persons constitute more than 20 percent of the total pedestrians, the 

average walking speed decreases to 0.9 m/s (3.0 ft/s).(2)
30 Federal Highway Administration 

Figure 8. Crosswalks are used by a variety of users with different speed characteristics. 

Pedestrian walking speeds generally range between 0.8 to 1.8 m/s (2.5 to 6.0 ft/s). 

A general rule of thumb indicates that pedestrians at crossings are willing to wait only 30 

seconds, at which point they will begin to look for opportunities to cross, regardless of the walk 

indication and the crossing location (reference 7, chapter 18 of HCM 2000).

(2) Shorter cycle 

lengths benefit pedestrians, particularly where pedestrians often need to cross two streets at a 

time to travel in a diagonal direction, as well as drivers, who experience generally shorter delays. 

Pedestrian Conflicts 

Figure 9 presents the typical conflicts between pedestrians and motor vehicles at a signalized 

intersection. 

• Vehicles turning right on red. Where allowed by law, this conflict occurs most often 

when the driver of a vehicle turning right on red is looking to the left and does not 

perform an adequate search for pedestrians approaching from the right and crossing 

perpendicularly to the vehicle. In addition, the sound of vehicles turning right on red 

masks audible cues used by blind pedestrians to determine the beginning of the 

crossing phase. 

• Vehicles turning right on green. This conflict occurs when vehicles do not yield to a 

pedestrian crossing in the parallel crosswalk. 

• Vehicles turning left on green. This conflict occurs at intersections with permissive left 

turns where vehicles may be focused on selecting an acceptable gap in oncoming 

vehicular traffic and do not see and/or yield to a pedestrian in the conflicting 

crosswalk. 

• Vehicles running the red light. This conflict is the most severe due to the high 

vehicular speeds often involved. 
Signalized Intersections: Informational Guide 31

Road User Needs

Figure 9. Pedestrian conflicts at signalized intersections. 

In addition, large signalized intersections with multiple lanes on each approach present the 

pedestrian with the possibility of having a vehicle in one lane yield but having a vehicle in the 

adjacent lane continue without yielding. The vehicle that has yielded may block the pedestrian’s 

and other motorist’s view of each other, thus putting the pedestrian at greater risk. This type of 

conflict may be present at signalized intersections in the following situations: 

• Double right-turn movements. These may be in the form of either two exclusive rightturn lanes or one exclusive right-turn lane and a shared through-right lane. 

• Permissive double left-turn movements. These are not common but are used in some 

jurisdictions, either with permissive-only phasing or with protected-permissive phasing. 

Pedestrian Safety 

The safety of pedestrians must be a particular concern at signalized intersections, particularly 

those with a high volume of motorized vehicles. Pedestrians are vulnerable in an environment 

surrounded by large, powerful, and fast-moving vehicles. Data from the Bureau of Transportation 

Statistics shows that in 2001, there were a total of 4,882 pedestrian fatalities involved in motor 

vehicle crashes; this represents 12 percent of all the 42,116 motorist collisions. More than 77,000 

pedestrians were injured in motor vehicle collisions during this time.(17)

Of all crashes between single vehicles and pedestrians in 2001, 940 (22 percent) occurred at 

intersections (both signalized and unsignalized).(36) Speed plays a major role in motoristpedestrian collisions, particularly fatalities; a pedestrian struck at 65 km/h (40 mph) has an 85-

percent chance of being killed, at 48 km/h (30 mph) the probability of fatality is 45 percent, and at 

30 km/h (20 mph) the probability of fatality drops to 5 percent.(37) Compounding the problem, 

motorists rarely stop to yield to a pedestrian when their speeds are greater than 70 km/h (45 

mph); they are likely to stop when their speeds are less than 30 km/h (20 mph).(38)
32 Federal Highway Administration 

From the driver’s perspective, the mind goes through five psychological steps to “see” an 

object such as a pedestrian: selection, detection, recognition, location, and prediction. The speed 

of the vehicle and the experience of the driver play critical roles in the driver’s ability to detect 

pedestrians and react appropriately. Research shows that difficulties in information processing 

and driver perception contribute to approximately 40 percent of all traffic crashes involving human 

error.(38)

The time required for a driver to detect a pedestrian, decelerate, and come to a complete 

stop is oftentimes underestimated, or worse yet, not even considered as part of the geometric 

design of an intersection. AASHTO’s A Policy on Geometric Design of Highways and Streets

recommends a brake reaction time of 2.5 s for determining stopping sight distance.(3) Additional 

research has suggested that the value of 2.5 s has limitations and represents nearly ideal 

conditions with younger, alert drivers.(39) Research conducted by Hooper and McGee suggests 

that a perception-reaction time of 3.2 s is more reasonable.(40) Even then, the reaction time 

assumes an expected or routine condition such as a vehicle turning into or out of a driveway ⎯

more time is needed to account for an unexpected condition, such as a child darting into the 

street. A conservative perception-reaction time estimate for a “surprise” condition is 4.8 s.(38) 

Many things can impact the sight distance that allows the driver and pedestrian to see each other: 

landscaping, parked vehicles, traffic control devices, street furniture, etc. The practitioner must be 

mindful of these elements, particularly given that two-dimensional plans do not necessarily reflect 

the three-dimensional field of vision from the pedestrian and driver vantage points. 

The combination of vehicle speed and visibility (or lack thereof) is a critical reason that the 

majority of motorists involved in pedestrian collisions claim that they “did not see them until it was 

too late.”(38)

Accessibility for pedestrians is also a key element. The ADA of 1990 mandates, among other 

things, that transportation facilities be accessible for all persons.(7) This requires that new or 

altered facilities be designed to allow pedestrians of all abilities to identify the crossing location, 

access the pushbutton, know when to cross, and know where to cross. The Americans with 

Disabilities Act Accessibility Guidelines published by the U.S. Access Board in 1991 identify 

minimum design standards that must be applied to all new construction or alteration projects to 

adequately accommodate persons with disabilities.(33) The accommodation of all users needs to 

be included into the construction cost of an improvement. Note that facilities that are designed 

above the minimum standards generally improve the safety and accessibility for all pedestrians. 

2.3 APPLYING HUMAN FACTORS 

To achieve error-free road user performance at signalized intersections, the information 

necessary to permit relatively safe performance in an inherently hazardous environment must be 

effectively communicated. The design of the roadway network, including the intersections, should 

inherently convey what to expect to the various users. Road users must receive information in a 

form they can read, understand, and react to in a timely fashion. This information must reinforce 

common road user expectations, or if uncommon elements are present, emphatically 

communicate alternative information with sufficient time to react. 

Failure to fully and adequately communicate the circumstances to be encountered by the 

road user increases the risk of hesitation, erroneous decisionmaking and incorrect action. Road 

users will rely on experience rather than their perceptions (however incomplete) of the situation at 

hand when their expectations are not met. 

A fundamental premise of human factors is that insufficient, conflicting, or surprising 

information reduces both the speed and accuracy of human response. The following bullet items 

offer key information regarding the application of human factors principles in the analysis and 

design of a signalized intersection: 

• All road users must first recognize signalized intersections before they can respond. 
Signalized Intersections: Informational Guide 33

Road User Needs

• All road users must have a clear presentation of the intersection on approach, or be 

appropriately forewarned by traffic control devices. 

• Adequate illumination for nighttime operations is required. 

• Navigational information must be available sufficiently in advance to allow for speed 

and path adjustments such as slowing to execute turns and lane changes. 

• Signal indications must be visible from a sufficient approach distance for the user to 

perceive and react to changes in the assignment of right-of-way and the presence of 

queued traffic in a safe manner, according to table 4D-1 of the MUTCD.(1)

• Phasing and clearance intervals for both vehicles and pedestrians must be suited to 

the characteristics and mix of road users using the intersection. 

• The geometric aspects of the intersection, such as the presence of medians, curb 

radius, lane width, and channelization, and the implications of lane choices, must be 

clear. 

• Points of potential conflict, particularly those involving vulnerable road users, must be 

evident and offer the approaching driver and pedestrian a clear view of each other. 

• The route through the intersection itself must be explicit, to avoid vehicles encroaching 

on each other. 

Signalized Intersections: Informational Guide 35

Geometric Design 

CHAPTER 3 

GEOMETRIC DESIGN 

TABLE OF CONTENTS 

3.0 GEOMETRIC DESIGN .........................................................................................................37

3.1 Channelization ............................................................................................................37 

3.2 Number of Intersection Legs.......................................................................................44 

3.3 Intersection Angle .......................................................................................................45

3.4 Horizontal and Vertical Alignment...............................................................................46 

3.5 Corner Radius and Curb Ramp Design ......................................................................46 

 3.5.1 Corner Radius................................................................................................47 

 3.5.2 Curb Ramp Design ........................................................................................47 

 3.5.3 Detectable Warnings......................................................................................51 

3.6 Sight Distance.............................................................................................................53 

 3.6.1 Stopping Sight Distance.................................................................................53 

 3.6.2 Decision Sight Distance.................................................................................53 

 3.6.3 Intersection Sight Distance ............................................................................54 

3.7 Pedestrian Facilities....................................................................................................54

3.8 Bicycle Facilities..........................................................................................................55 

LIST OF FIGURES 

Figure Page

10 The photograph shows a raised median that restricts left-turn egress movements from a 

driveway located between two signalized intersections ....................................................38 

11 Pavement markings can be used to delineate travel lanes within wide intersections as 

shown in the photograph ...................................................................................................39 

12 Various right-turn treatments may be used, depending on the speed environment.............40 

13 Providing a dedicated left-turn lane reduces potential collisions between left-turning 

and through vehicles, increasing the capacity of the approach for both left and 

through traffic.....................................................................................................................41 

14 The photo shows how double left-turn and double right-turn lanes can be used to 

accommodate high-priority movements ............................................................................42 

15 Intersection skew increases both the intersection width and pedestrian crossing distance.43 

16 The photograph illustrates a multileg intersection ................................................................44 

17 Potential conflicts at intersections with three and four legs..................................................45 

18 Curb ramp components ........................................................................................................48 

19 Examples of preferred designs.............................................................................................50

20 Examples of acceptable curb ramp designs.........................................................................50 

21 Examples of inaccessible designs........................................................................................50 

22 This crosswalk design incorporates the use of detectable warning surfaces into the curb 

ramps to facilitate navigation by a visually impaired pedestrian .......................................51 

LIST OF TABLES

Table Page

9 Summary of best practices for curb ramp design and associated rationale.........................49 

10 Requirements for detectable warning surfaces ....................................................................52 

11 Design values for stopping sight distance ............................................................................53 

12 Design values for decision sight distance for selected avoidance maneuvers ....................54 

Signalized Intersections: Informational Guide 37

Geometric Design 

3. GEOMETRIC DESIGN 

This chapter presents geometric design guidelines for signalized intersections based on a 

review of technical literature and current design policy in the United States. 

Geometric design of a signalized intersection involves the functional layout of travel lanes, 

curb ramps, crosswalks, bike lanes, and transit stops in both the horizontal and vertical 

dimensions. Geometric design has a profound influence on roadway safety; it shapes road user 

expectations and defines how to proceed through an intersection where many conflicts exist. 

In addition to safety, geometric design influences the operational performance for all road 

users. Minimizing impedances, eliminating the need for lane changes and merge maneuvers, and 

minimizing the required distance to traverse an intersection all help improve the operational 

efficiency of an intersection. 

The needs of all possible road users (see chapter 2) must be considered to achieve optimal 

safety and operational levels at an intersection. At times, design objectives may conflict between 

road user groups; the practitioner must carefully examine the needs of each user, identify the 

tradeoffs associated with each element of geometric design, and make decisions with all road 

user groups in mind. 

This chapter addresses the following topics: 

• Principles of channelization. 

• Number of intersection approaches. 

• Intersection angle. 

• Horizontal and vertical alignment. 

• Corner radius and curb ramp design 

• Detectable warnings. 

• Access control. 

• Sight distance. 

• Pedestrian facilities. 

• Bicycle facilities. 

3.1 CHANNELIZATION 

A primary goal of intersection design is to limit or reduce the severity of potential road user 

conflicts. Basic principles of intersection channelization that can be applied to reduce conflicts are 

described below.(41) 

1. Discourage undesirable movements. Designers can utilize corner radii, raised 

medians, or traffic islands to prevent undesirable or wrong-way movements. Examples 

include: 

• Preventing left turns from driveways or minor streets based on safety or operational 

concerns. 

• Designing channelization to prevent wrong way movements onto freeway ramps, oneway streets, or divided roadways. 

• Designing approach alignment to discourage undesirable movements. 

Figure 10 shows how a raised median can be used to restrict undesirable turn movements 

within the influence of signalized intersections. 
38 Federal Highway Administration 

Figure 10. The photograph shows a raised median that restricts left-turn egress movements from 

a driveway located between two signalized intersections. 

2. Define desirable paths for vehicles. The approach alignment to an intersection as well 

as the intersection itself should present the roadway user with a clear definition of the proper 

vehicle path. This is especially important at locations with “unusual” geometry or traffic 

patterns such as highly skewed intersections, multileg intersections, offset-T intersections 

and intersections with very high turn volumes. Clear definition of vehicle paths can minimize 

lane changing and avoid “trapping” vehicles in the incorrect lane. Avoiding these undesirable 

effects can improve both the safety and capacity at an intersection. Figure 11 shows how 

pavement markings can be applied to delineate travel paths. 
Signalized Intersections: Informational Guide 39

Geometric Design 

Figure 11. Pavement markings can be used to delineate travel lanes within wide intersections as 

shown in the photograph. 

3. Encourage safe speeds through design. An effective intersection design promotes 

desirable speeds to optimize intersection safety. The appropriate speed will vary based on 

the use, type, and location of the intersection. On high-speed roadways with no pedestrians, 

it may be desirable to promote higher speeds for turning vehicles to remove turning vehicles 

from the through traffic stream as quickly and safely as possible. This can be accomplished 

with longer, smooth tapers and larger curb radii. On low-speed roadways or in areas with 

pedestrians, promotion of lower turning speeds is appropriate. This can be accomplished with 

smaller turning radii, narrower lanes, and/or channelization features. These are illustrated in 

figure 12. 
40 Federal Highway Administration 

(a) Higher speed design 

(b) Lower speed design 

Figure 12. Various right-turn treatments may be used, depending on the speed environment. 

4. Separate points of conflict where possible. Separation of conflict points can ease the 

driving task while improving both the capacity and safety at an intersection. The use of 

exclusive turn lanes, channelized right turns, and raised medians as part of an access control 

strategy are all effective ways to separate vehicle conflicts. Figure 13 illustrates how the 

addition of a left-turn lane can reduce conflicts with through vehicles traveling in the same 

direction. 
Signalized Intersections: Informational Guide 41

Geometric Design 

(a) Major street with shared left-through lane causes through vehicles to queue behind left-turning vehicles. 

(b) Major street with dedicated left-turn lane removes left-turning vehicles from the paths of through vehicles. 

Figure 13. Providing a dedicated left-turn lane reduces potential collisions between left-turning 

and through vehicles, increasing the capacity of the approach for both left and through traffic. 

5. Facilitate the movement of high-priority traffic flows. Accommodating high-priority 

movements at intersections addresses both driver’s expectations and intersection capacity. 

The highest volume movements at an intersection typically define the intersection’s highpriority movements, although route designations and functional classification of intersecting 

roadways may also be considered. In low-density suburban and rural areas, it may be 

appropriate to give priority to motor vehicle movements; however, in some urban locations, 

pedestrians and bicyclists at times may be the highest priority users of the road system. 

Figure 14 shows an intersection where double left and right turn lanes are used to facilitate 

high-volume turning movements. 
42 Federal Highway Administration 

Photograph Credit and Copyright: www.portlandmaps.com, 2004 

Figure 14. The photo shows how double left-turn and double right-turn lanes can be used to 

accommodate high-priority movements. 

6. Design approaches to intersect at near right angles and merge at flat angles.

Roadway alignments that cross as close to 90 degrees as practical can minimize the 

exposure of vehicles to potential conflicts and reduce the severity of a conflict. Skewed 

crossings produce awkward sight angles for drivers, which can be especially difficult for older 

drivers. Skewed crossings also result in additional distance for vehicles to traverse the 

intersections. This additional distance should be considered when developing the timing for a 

signal, as it may require the need for additional all-red clearance time. Figure 15 shows how 

a skewed intersection approach can increase the distance to clear the intersection for 

pedestrians and vehicles. 
Signalized Intersections: Informational Guide 43

Geometric Design 

(a) Intersection skew at 90 degrees. 

(b) Intersection skew at 75 degrees. 

(c) Intersection skew at 60 degrees. 

Figure 15. Intersection skew increases both the intersection width and pedestrian crossing 

distance. 

7. Facilitate the desired scheme of traffic control. The design of a signalized intersection 

should attempt to maximize traffic safety and operations while providing operational flexibility. 

Lane arrangements, location of channelization islands, and medians should be established to 

facilitate pedestrian access and the placement of signs, signals, and markings. Consideration 

of these “downstream” issues as part of design can optimize the operation of an intersection. 

Providing exclusive left-turn bays that can accommodate left-turn movements can improve 

operations and safety while providing flexibility to accommodate varying traffic patterns. 

Positive offset left-turn lanes can improve sight distance for left-turning movements but may 
44 Federal Highway Administration 

prohibit U-turns if insufficient width is available. Reversible lanes may be appropriate for 

arterials that experience heavy directional peaks in traffic volumes during commuter periods. 

8. Accommodate decelerating, slow, or stopped vehicles outside higher speed 

through traffic lanes. Speed differentials between vehicles in the traffic stream are a 

primary cause of traffic crashes. Speed differentials at intersections are inherent as vehicles 

decelerate to facilitate a turning maneuver. The provision of exclusive left- and right-turn 

lanes can improve safety by removing slower moving turning vehicles from the higher speed 

through traffic stream and reducing potential rear-end conflicts. In addition, through 

movements will experience lower delay and fewer queues. 

9. Provide safe refuge and wayfinding for bicyclists and pedestrians. Intersection 

design must consider the needs of roadway users other than motorists. Intersection 

channelization can provide refuge and/or reduce the exposure distance for pedestrians and 

bicyclists within an intersection without limiting vehicle movement. The use of raised 

medians, traffic islands, and other pedestrian-friendly treatments should be considered as 

part of the design process. Wayfinding may also be an issue, particularly at intersections with 

complicated configurations. 

3.2 NUMBER OF INTERSECTION LEGS 

While the geometry of various types of intersections may vary, the complexity of an 

intersection increases with an increasing number of approach legs to the intersections, as shown 

in figures 16 and 17. The latter shows the number and type of conflicts that occur at intersections 

with three and four legs, respectively. The number of potential conflicts for all users increases 

substantially at intersections with more than four legs. Note that many potential conflicts, 

including crossing and merging conflicts, can be managed (but not eliminated) at a signalized 

intersection by separating conflicts in time. 

Photograph Credit and Copyright: www.portlandmaps.com, 2004 

Figure 16. The photograph illustrates a multileg intersection. 
Signalized Intersections: Informational Guide 45

Geometric Design 

(a) Three-leg intersection. 

(b) Four-leg intersection. 

Figure 17. Potential conflicts at intersections with three and four legs. 

3.3 INTERSECTION ANGLE 

The angle of intersection of two roadways can influence both the safety and operational 

characteristics of an intersection. Heavily skewed intersections not only affect the nature of 

conflicts, but they produce larger, open pavement areas that can be difficult for drivers to navigate 

and pedestrians to cross. Such large intersections can also be more costly to build and maintain. 

Undesirable operational and safety characteristics of skewed intersections include: 

• Difficulty in accommodating large vehicle turns. Additional pavement, channelization, 

and right-of-way may be required. The increase in pavement area poses potential 

drainage problems and gives smaller vehicles more opportunity to “wander” from the 

proper path. 
46 Federal Highway Administration 

• Vehicles crossing the intersection are more exposed to conflicts. This requires longer 

clearance intervals and increased lost time, which reduces the capacity of the 

intersection. 

• Pedestrians and bicyclists are exposed to vehicular traffic longer. Longer pedestrian 

intervals may be required, which may have a negative impact on the intersection’s 

capacity. 

• Pedestrians with visual disabilities may have difficulty finding their way to the other 

side of the street when crossing. 

• Driver confusion may result at skewed crossings. Woodson, Tillman, and Tillman 

found that drivers are more positive in their sense of direction when roadways are at 

right angles to each other.(42) Conversely, drivers become more confused as they 

traverse curved or angled streets. 

Skewed intersections are generally related to right-angle type crashes that can be associated 

with poor sight distance. AASHTO policy and many State design standards permit skewed 

intersections of up to 60 degrees.(3) Gattis and Low conducted research to identify constraints on 

the angle of a left-skewed intersection as it is affected by the vehicle body’s limiting a driver lineof-sight to the right.(43) Their findings suggest that if roadway engineers are to consider the 

limitations created by vehicle design, a minimum intersection angle of 70 to 75 degrees will offer 

an improved line of sight. FHWA’s Highway Design Handbook for Older Drivers and Pedestrians

recommends intersection angles of 90 degrees for new intersections where right-of-way is not a 

constraint, and angles of not less than 75 degrees for new facilities or redesigns of existing 

facilities where right-of-way is restricted.(12)

3.4 HORIZONTAL AND VERTICAL ALIGNMENT 

The approach to a signalized intersection should promote awareness of an intersection by 

providing the required stopping sight distance in advance of the intersection. This area is critical 

as the approaching driver or bicyclist begins to focus on the tasks associated with navigating the 

intersection. 

To meet the driver’s or cyclist’s expectations on approaches to an intersection, the following 

guidelines are suggested: 

• Avoid approach grades to an intersection of greater than 6 percent. On higher design 

speed facilities (80 km/h (50 mph) and greater), a maximum grade of 3 percent should 

be considered. 

• Avoid locating intersections along a horizontal curve of the intersecting road. 

• Strive for an intersection platform (including sidewalks) with cross slope not exceeding 

2 percent, as needed for accessibility. 

3.5 CORNER RADIUS AND CURB RAMP DESIGN 

Intersection corners that are designed appropriately accommodate all users. The selection of 

corner radius and curb ramp design should be guided by pedestrian crossing and design vehicle 

needs at the intersection. In general, it is recommended to provide a pedestrian crossing that is 

as near to perpendicular to the flow of traffic as practical with no intermediate angle points. This 

keeps pedestrian crossing time and exposure to a minimum, which may allow more efficient 

operation of the signal. It also aids visually impaired pedestrians in their wayfinding task by 

eliminating changes in direction that may not be detectable. 

Corner radii should also be designed to accommodate the turning path of a design vehicle to 

avoid encroachment on pedestrian facilities and opposing lanes of travel. 
Signalized Intersections: Informational Guide 47

Geometric Design 

3.5.1 Corner Radius 

The corner radii of an intersection should be designed to facilitate the turning and tracking 

requirements of the selected design vehicle. Other considerations when designing a corner radius 

include location of traffic control devices (signal poles, controller, signs, etc.), the need to provide 

channelizing islands, and available right-of-way. The corner radii should be compatible with other 

intersection features and the speed environment. For example, larger radii are more compatible 

with high-speed facilities with few pedestrians, whereas smaller radii are more compatible with 

low-speed facilities with many pedestrians.(41)

Factors that influence the selection of appropriate corner radii include the following: 

• Design vehicle. Selection of a design vehicle should be based on the largest vehicle 

type that will regularly use an intersection. Often, a design vehicle is mandated by 

agency policy, regardless of vehicle mix. In certain instances, more than one design 

vehicle may be appropriate depending on traffic patterns. 

• Angle of intersection. Large intersection skew angles make turning maneuvers more 

difficult, particularly for larger vehicles. This has the potential to increase the overall 

size of the intersection, making drainage difficult and increasing signal clearance 

intervals to clear the intersection. 

• Pedestrians and bicyclists. In areas of high pedestrian and bike use, smaller radii 

are desirable to reduce turning speeds and decrease the distance for pedestrians and 

bikes to cross the street. 

• Constraints. Multicentered curves or simple curves with tangent offsets can be used 

to better match the turn path of the design vehicle and reduce required right-of-way. 

3.5.2 Curb Ramp Design 

Curb ramps provide access for people who use wheelchairs and scooters. Curb ramps also 

aid people with strollers, luggage, bicycles, and other wheeled objects in negotiating the 

intersection. The basic components of a curb ramp, including ramp, landing, detectable warning, 

flare, and approach, are diagrammed in figure 18. The ADAAG require that curb ramps be 

provided wherever an accessible route crosses a curb, which includes all designated crosswalks 

at new and retrofitted signalized intersections.(33) While curb ramps increase access for mobilityimpaired pedestrians, they can decrease access for visually impaired pedestrians by removing 

the vertical curb face that provides an important tactile cue. This tactile cue is instead provided by 

a detectable warning surface placed at the bottom of the ramp, which provides information on the 

boundary between the sidewalk and roadway. 
48 Federal Highway Administration 

Figure 18. Curb ramp components. 

Table 9, adapted from FHWA’s Designing Sidewalks and Trails for Access, Part 2: Best 

Practices Design Guide, provides a summary of recommended fundamental practices for curb 

ramp design, along with the rationale behind each practice.(34) A designer can apply these 

principles in designing intersections in a wide variety of circumstances. 

Figures 19-21 provides examples of three categories of typical curb ramp treatments used at 

signalized intersections: those that should be implemented wherever possible (“preferred 

designs”), those that meet minimum accessibility requirements but are not as effective as the 

preferred treatments (“acceptable designs”), and those that are inaccessible and therefore should 

not be used in new or retrofit designs (“inaccessible designs”). Additional guidance and design 

details can be found in the source document.(34)
Signalized Intersections: Informational Guide 49

Geometric Design 

Table 9. Summary of best practices for curb ramp design and associated rationale. 

Best Practice Rationale 

Provide a level maneuvering area or 

landing at the top of the curb ramp. 

Landings are critical to allow wheelchair users space to maneuver on or off 

the ramp. Furthermore, people who are continuing on the sidewalk will not 

have to negotiate a surface with a changing grade or cross slope. 

Clearly identify the boundary between the 

bottom of the curb ramp and the street 

with a detectable warning. 

Without a detectable warning, people with visual impairments may not be 

able to identify the boundary between the sidewalk and the street. (Note 

that detectable warnings are a requirement of ADA as of July 2001.) 

Design ramp grades that are 

perpendicular to the curb. 

Assistive devices for mobility are unusable if one side of the device is lower 

than the other or if the full base of support (e.g., all four wheels on a 

wheelchair) is not in contact with the surface. This commonly occurs when 

the bottom of a curb ramp is not perpendicular to the curb. 

Place the curb ramp within the marked 

crosswalk area. 

Pedestrians outside of the marked crosswalk are less likely to be seen by 

drivers because they are not in an expected location. 

Avoid changes of grade that exceed 11 

percent over a 610 mm (24 inch) interval. 

Severe or sudden grade changes may not provide sufficient clearance for 

the frame of the wheelchair, causing the user to tip forward or backward. 

Design the ramp so that it does not require 

turning or maneuvering on the ramp 

surface. 

Maneuvering on a steep grade can be very hazardous for people with 

mobility impairments. 

Provide a curb ramp grade that can be 

easily distinguished from surrounding 

terrain; otherwise, use detectable 

warnings. 

Gradual slopes make it difficult for people with visual impairments to detect 

the presence of a curb ramp. 

Design the ramp with a grade of 7.1 ±1.2 

percent. Do not exceed 8.33 percent 

(1:12). 

Shallow grades are difficult for people with vision impairments to detect, but 

steep grades are difficult for those using assistive devices for mobility. 

Design the ramp and gutter with a cross 

slope of 2.0 percent. 

Ramps should have minimal cross slope so users do not have to negotiate 

a steep grade and cross slope simultaneously. 

Provide adequate drainage to prevent the 

accumulation of water or debris on or at 

the bottom of the ramp. 

Water, ice, or debris accumulation will decrease the slip resistance of the 

curb ramp surface. 

Provide transitions from ramps to gutter 

and streets that are flush and free of level 

changes. 

Maneuvering over any vertical rise such as lips and defects can cause 

wheelchair users to propel forward when wheels hit this barrier. 

Align the curb ramp with the crosswalk so 

there is a straight path of travel from the 

top of the ramp to the center of the 

roadway to the curb ramp on the other 

side. 

Where curb ramps can be seen in advance, people using wheelchairs often 

build up momentum in the crosswalk in order to get up the curb ramp grade 

(i.e., they “take a run at it”). This alignment may be useful for people with 

vision impairments. 

Provide clearly defined and easily 

identified edges or transitions on both 

sides of the ramp to contrast with the 

sidewalk. 

Clearly defined edges assist users with vision impairments to identify the 

presence of the ramp when it is approached from the side. 

Source: Adapted from reference 34, table 7-1. 
50 Federal Highway Administration 

(a) (b) (c) (d) (e) (f) 

a. Perpendicular curb ramps with flares and a level landing. 

b. Perpendicular curb ramps with returned curbs and a level landing. 

c. Two parallel curb ramps on a wide turning radius. 

d. Two parallel curb ramps with a lowered curb. 

e. Two combination curb ramps on a corner with a wide turning radius. 

f. A curb extension with two perpendicular curb ramps with returned curbs and level landings. 

Figure 19. Examples of preferred designs. 

(a) (b) (c) (d) (e) (f) 

a. Perpendicular curb ramps, oriented perpendicular to the curb, on a corner with a wide turning radius. 

b. Diagonal curb ramp with flares and a level landing, in addition to at least 1.22 m (48 inch) of clear space. 

c. Diagonal curb ramp with returned curbs, a level landing, and sufficient clear space in the crosswalk. 

d. Single parallel curb ramp with at least 1.22 m (48 inch) clear space. 

e. Two built-up curb ramps. 

f. Partially built-up curb ramps. 

Figure 20. Examples of acceptable curb ramp designs. 

(a) (b) (c) (d) 

a. Perpendicular curb ramps without a landing. 

b. On a corner with a wide turning radius, curb ramps are aligned parallel with the crosswalk. 

c. Diagonal curb ramp with no clear space or no level area at the bottom of the curb ramp. 

d. Diagonal curb ramps without a level landing. 

Figure 21. Examples of inaccessible designs.

Source: Reproduced from reference 34, table 7-2 
Signalized Intersections: Informational Guide 51

Geometric Design 

3.5.3 Detectable Warnings 

The ADAAG require that a detectable warning surface be applied to the surface of the curb 

ramps and within the refuge of any medians and islands (defined in the ADAAG as “hazardous 

vehicle areas”) to provide tactile cues to individuals with visual impairments.(33) Detectible 

warnings consist of a surface of truncated domes built in or applied to walking surfaces; the 

domes provide a distinctive surface detectable by cane or underfoot. This surface alerts visually 

impaired pedestrians of the presence of the vehicular travel way, and provides physical cues to 

assist pedestrians in detecting the boundary from sidewalk to street where curb ramps and 

blended transitions are devoid of other tactile cues typically provided by a curb face. 

At the face of a curb ramp and within the refuge area of any median island, a detectable 

warning surface should be applied as shown in figure 22. The detectable warning surface begins 

at the curb line and extends into the ramp or pedestrian refuge area a distance of 610 mm (24 

inches). For a median island, this creates a minimum clear space of 610 mm (24 inches) between 

the detectable warning surfaces for a minimum median island width of 1.8 m (6 ft) at the 

pedestrian crossing. This is a deviation from the requirements of the ADAAG (§4.29.5), which 

requires a surface width of 915 mm (36 inches). However, this deviation is necessary to enable 

visually impaired pedestrians to distinguish where the refuge begins and ends from the adjacent 

roadway where the minimum 1.8 m (6 ft) refuge width is provided. 

Table 10 summarizes ADAAG requirements for detectable warning surfaces. 

Photograph Credit: Lee Rodegerdts, 2003 

Figure 22. This crosswalk design incorporates the use of detectable warning surfaces into the 

curb ramps to facilitate navigation by a visually impaired pedestrian. 
52 Federal Highway Administration 

Table 10. Requirements for detectable warning surfaces. 

Legislation 

Americans with Disabilities Act 

Accessibility Guidelines(33)

Draft Guidelines on 

Accessible Public Rights-of-Way(44)

Applicability Required under existing regulations. These guidelines are in the rulemaking 

process and are therefore not 

enforceable. They will be incorporated 

into the ADAAG; however, the 

recommendations listed below are 

subject to revision prior to the issuance of 

a final rule. 

Type Raised truncated domes. Raised truncated domes aligned in a 

square grid pattern. 

Dome Size Nominal diameter: 23 mm (0.9 inches). 

Nominal height: 5 mm (0.2 inches). 

Base diameter: 23 mm (0.9 inches) 

minimum, 36 mm (1.4 inches) maximum. 

Ratio of top diameter to base diameter: 

50% minimum, 65% maximum. 

Height: 5 mm (0.2 inches). 

Dome Spacing Nominal center-to-center spacing: 60 mm 

(2.35 inches). 

Center-to-center spacing: 41 mm (1.6 

inches) minimum, 61 mm (2.4 inches) 

maximum. 

Base-to-base spacing: 16 mm (0.65 

inches) minimum, measured between the 

most adjacent domes on square grid. 

Contrast Detectable warning surfaces must contrast 

visually with adjacent walking surfaces 

either light-on-dark, or dark-on-light. 

The material used to provide contrast must 

be an integral part of the walking surface. 

Detectable warning surfaces must 

contrast visually with adjacent walking 

surfaces either light-on-dark, or dark-onlight. 

At curb ramps: The detectable warning must 

extend the full width and depth of the curb 

ramp. 

At curb ramps, landings, or blended 

transitions connecting to a crosswalk: 

Detectable warning surfaces must extend 

610 mm (24 inches) minimum in the 

direction of travel and the full width of the 

curb ramp, landing, or blended transition. 

The detectable warning surface must be 

located so that the edge nearest the curb 

line is 150 mm (6 inches) minimum and 

205 mm (8 inches) maximum from the 

curb line. 

Size 

Within median islands, the boundary 

between the curbs must be defined by a 

continuous detectable warning 915 mm (36 

inches) wide, beginning at the curb line. 

Within median islands, the detectable 

warning surface must begin at the curb 

line and extend into the pedestrian refuge 

a minimum of 610 mm (24 inches). 

Detectable warnings must be separated 

by a minimum length of walkway of 610 

mm (24 inches) without detectable 

warnings. 

The Draft Guidelines on Accessible Public Rights-of-Way, developed by the U.S. Access 

Board, issued a similar recommendation for use of a 610-mm (24-inch) width for detectable 

warning surfaces.(44) This is consistent with the existing ADAAG requirements for truncated dome 

detectable warning surfaces at transit platforms. The draft public right-of-way guidelines are 

based upon the recommendations of the Public Rights of Way Access Advisory Committee as 

published in the report Building a True Community.

(45) For detectable warning surfaces, both the 

U.S. Access Board and FHWA are encouraging the use of the new (recommended) design 

pattern and application over the original ADAAG requirements.(33)
Signalized Intersections: Informational Guide 53

Geometric Design 

3.6 SIGHT DISTANCE 

A driver’s ability to see the road ahead and other intersection users is critical to safe and 

efficient use of all roadway facilities, especially signalized intersections. Stopping sight distance, 

decision sight distance, and intersection sight distance are particularly important at signalized 

intersections. 

3.6.1 Stopping Sight Distance 

Stopping sight distance is the distance along a roadway required for a driver to perceive and 

react to an object in the roadway and to brake to a complete stop before reaching that object. 

Stopping sight distance should be provided throughout the intersection and on each entering and 

exiting approach. Table 11 gives recommended stopping sight distances for design, as computed 

from the equations provided in the AASHTO policy.(3)

Table 11. Design values for stopping sight distance. 

Speed 

(km/h) 

Computed 

Distance* 

(m) 

Design 

Distance 

(m) 

Speed 

(mph) 

Computed 

Distance* 

(ft) 

Design 

Distance 

(ft) 

 20 18.5 20 15 76.7 80 

 30 31.2 35 20 111.9 115 

 40 46.2 50 25 151.9 155 

 50 63.5 65 30 196.7 200 

 60 83.0 85 35 246.2 250 

 70 104.9 105 40 300.6 305 

 80 129.0 130 45 359.8 360 

 90 155.5 160 50 423.8 425 

100 184.2 185 55 492.4 495 

110 215.3 220 60 566.0 570 

120 248.6 250 65 644.4 645 

* Assumes 2.5 s perception-braking time, 3.4 m/s2

 (11.2 ft/s2) driver deceleration 

Source: Reference 3, exhibit 3-1. 

Stopping sight distance should be measured using an assumed height of driver’s eye of 

1,080 mm (3.5 ft) and an assumed height of object of 600 mm (2.0 ft).(3)

3.6.2 Decision Sight Distance 

Decision sight distance is “the distance needed for a driver to detect an unexpected or 

otherwise difficult-to-perceive information source or condition in a roadway environment that may 

be visually cluttered, recognize the condition or its potential threat, select an appropriate speed 

and path, and initiate and complete the maneuver safely and efficiently.”(3, p. 115) Decision sight 

distance at intersections is applicable for situations where vehicles must maneuver into a 

particular lane in advance of the intersection (e.g., alternative intersection designs using indirect 

left turns). 

Decision sight distance varies depending on whether the driver is to come to a complete stop 

or make some kind of speed, path, or direction change. Decision sight distance also varies 

depending on the environment—urban, suburban, or rural. Table 12 gives recommended values 

for decision sight distance, as computed from equations in the AASHTO policy.(3)
54 Federal Highway Administration 

Table 12. Design values for decision sight distance for selected avoidance maneuvers. 

Metric (m) U.S. Customary (ft) 

Speed 

(km/h) A B C D E 

Speed

(mph) A B C D E 

 50 70 155 145 170 195 30 220 490 450 535 620

 60 95 195 170 205 235 35 275 590 525 625 720

 70 115 235 200 235 275 40 330 690 600 715 825

 80 140 280 230 270 315 45 395 800 675 800 930

 90 170 325 270 315 360 50 465 910 750 890 1030

100 200 370 315 355 400 55 535 1030 865 980 1135

110 235 420 330 380 430 60 610 1150 990 1125 1280

120 265 470 360 415 470 65 695 1275 1050 1220 1365

Avoidance Maneuver A: Stop on rural road, time (t) = 3.0 s. 

Avoidance Maneuver B: Stop on urban road, t = 9.1 s. 

Avoidance Maneuver C: Speed/path/direction change on rural road, t = 10.2 s to 11.2 s. 

Avoidance Maneuver D: Speed/path/direction change on suburban road, t = 12.1 s to 12.9 s. 

Avoidance Maneuver E: Speed/path/direction change on urban road, t = 14.0 s to 14.5 s. 

Source: Reference 3, exhibit 3-3. 

3.6.3 Intersection Sight Distance 

Intersection sight distance is the distance required for a driver without the right of way to 

perceive and react to the presence of conflicting vehicles and pedestrians. 

Intersection sight distance is traditionally measured through the determination of a sight 

triangle. This triangle is bounded by a length of roadway defining a limit away from the 

intersection on each of the two conflicting approaches and by a line connecting those two limits. 

Intersection sight distance should be measured using an assumed height of driver’s eye of 1,080 

mm (3.5 ft) and an assumed height of object of 1,080 mm (3.5 ft).(3) The area within the triangle is 

referred to as the clear zone and should remain free from obstacles. 

The reader is encouraged to refer to the AASHTO policy, pp. 654-680, for a complete 

discussion of intersection sight distance requirements.(3) Intersection sight distance at signalized 

intersections is generally simpler than for stop-controlled intersections. The following criteria 

should be met: 

• The first vehicle stopped on an approach should be visible to the first driver stopped 

on each of the other approaches. 

• Vehicles making permissive movements (e.g., permissive left turns, right turns on red, 

etc.) should have sufficient sight distance to select gaps in oncoming traffic. 

• Permissive left turns should satisfy the case for left turns from the major road (Case F, 

reference 3). 

• Right turns on red should satisfy the case for a stop-controlled right turn from the 

minor road (Case B2, reference 3). 

For signalized intersections where two-way flashing operation is planned (i.e., flashing yellow 

on the major street and flashing red on the minor street), departure sight triangles for Case B 

should be provided for the minor-street approaches.(3)

3.7 PEDESTRIAN FACILITIES 

Pedestrian facilities should be provided at all intersections in urban and suburban areas. In 

general, design of the pedestrian facilities of an intersection with the most challenged users in 

mind—pedestrians with mobility or visual impairments—should be done. The resulting design will 

serve all pedestrians well. In addition, the ADA requires that new and altered facilities constructed 
Signalized Intersections: Informational Guide 55

Geometric Design 

by, on behalf of, or for the use of State and local government entities be designed and 

constructed to be readily accessible to and usable by individuals with disabilities.(33) Therefore, it 

is not only good practice to design for all pedestrian types, but it is also a legal requirement. 

Pedestrians are faced with a number of disincentives to walking, including centers and 

services located far apart, physical barriers and interruptions along pedestrian routes, a 

perception that routes are unsafe due to motor vehicle conflicts and crime, and routes that are 

esthetically unpleasing.(46)

Key elements that affect a pedestrian facility that practitioners should incorporate into their 

design are listed below:(47)

• Keep corners free of obstructions to provide enough room for pedestrians waiting to 

cross. 

• Maintain adequate lines of sight between drivers and pedestrians on the intersection 

corner and in the crosswalk. 

• Ensure curb ramps, transit stops (where applicable), pushbuttons, etc. are easily 

accessible and meet ADAAG design standards. 

• Clearly indicate the actions pedestrians are expected to take at crossing locations. 

• Design corner radii to ensure vehicles do not drive over the pedestrian area yet are 

able to maintain appropriate turning speeds. 

• Ensure crosswalks clearly indicate where crossings should occur and are in desirable 

locations. 

• Provide appropriate intervals for crossings and minimize wait time. 

• Limit exposure to conflicting traffic, and provide refuges where necessary. 

• Ensure the crosswalk is a direct continuation of the pedestrian’s travel path. 

• Ensure the crossing is free of barriers, obstacles, and hazards. 

3.8 BICYCLE FACILITIES 

Some intersections have on-street bicycle lanes or off-street bicycle paths entering the 

intersection. When this occurs, intersection design should accommodate the needs of cyclists in 

safely navigating such a large and often complicated intersection. Some geometric features that 

should be considered include: 

• Bike lanes and bike lane transitions between through lanes and right turn lanes. 

• Left turn bike lanes. 

• Median refuges with a width to accommodate a bicycle: 2.0 m (6 ft) = poor; 

2.5 m (8 ft) = satisfactory; 3.0 m (10 ft) = good.(21, p. 52)

• Separate facilities if no safe routes can be provided through the intersection itself. 

The interaction between motor vehicles and bicyclists at interchanges with merge and 

diverge areas is especially complex, and some signalized intersections also have merge and 

diverge areas due to free right turns or diverted movements (see chapter 10). AASHTO 

recommends that “[i]f a bike lane or route must traverse an interchange area, these intersection 

or conflict points should be designed to limit the conflict areas or to eliminate unnecessary 

uncontrolled ramp connections to urban roadways.”(21, p. 62)

Signalized Intersections: Informational Guide 57

Traffic Design and Illumination

CHAPTER 4 

TRAFFIC DESIGN AND ILLUMINATION 

TABLE OF CONTENTS 

4.0 TRAFFIC DESIGN AND ILLUMINATION.............................................................................59 

4.1 Traffic Signal Control Type .........................................................................................59 

4.2 Traffic Signal Phasing .................................................................................................59 

 4.2.1 “Permissive-Only” Left-Turn Phasing.............................................................60 

 4.2.2 “Protected-Only” Left-Turn Phasing...............................................................62 

 4.2.3 Protected-Permissive Left-Turn Phasing .......................................................63 

 4.2.4 Split Phasing ..................................................................................................67 

 4.2.5 Prohibited Left-Turn Phasing .........................................................................70 

 4.2.6 Right-Turn Phasing ........................................................................................70 

4.3 Vehicle and Pedestrian Displays ................................................................................72 

 4.3.1 Vehicle Displays.............................................................................................72 

 4.3.2 Pedestrian Displays .......................................................................................76 

4.4 Traffic Signal Pole Layout ...........................................................................................77 

4.5 Traffic Signal Controller ..............................................................................................78 

4.6 Detection Devices .......................................................................................................79 

 4.6.1 Vehicle Detection ...........................................................................................79 

 4.6.2 Pedestrian Detection......................................................................................83 

4.7 Basic Signal Timing Parameters.................................................................................83 

 4.7.1 Pedestrian Timing ..........................................................................................84 

 4.7.2 Vehicle Timing—Green Interval.....................................................................84 

 4.7.3 Vehicle Timing—Detector Timing ..................................................................85 

 4.7.4 Vehicle Timing—Vehicle Clearance...............................................................85 

 4.7.5 Vehicle Timing—Cycle Length.......................................................................86 

4.8 Signing and Pavement Marking Design......................................................................86 

4.9 Illumination Design......................................................................................................90

 4.9.1 Illuminance.....................................................................................................91 

 4.9.2 Veiling Illuminance .........................................................................................92 

LIST OF FIGURES 

Figure Page

23 Standard NEMA ring-and-barrier structure...........................................................................60 

24 Typical phasing diagram for “permissive-only” left-turn phasing..........................................61 

25 Possible signal head arrangements for “permissive-only” left-turn phasing.........................62 

26 Typical phasing diagram for “protected-only” left-turn phasing ............................................63 

27 Possible signal head arrangements for “protected-only” left-turn phasing...........................63 

28 Typical phasing diagram for protected-permissive left-turn phasing....................................64 

29 Possible signal head and signing arrangement for protected-permissive left-turn phasing.64 

30 Illustration of the yellow trap .................................................................................................66 

31 The protected-permissive left-turn display known as “Dallas display” uses louvers to 

restrict visibility of the left-turn display to adjacent lanes ..................................................67 

32 Typical phasing diagrams for split phasing...........................................................................69

33 Common signal head arrangement for split phasing............................................................70 

34 Typical phasing diagram illustrating a right-turn overlap ......................................................71 

35 Common signal head and signing arrangement for right-turn-overlap phasing ...................72 

36 Examples showing five optional signal head locations.........................................................74 
58 Federal Highway Administration 

CHAPTER 4 FIGURES, CONTINUED 

Figure Page

37 Pedestrian signal indicators..................................................................................................76 

38 Example of advance street name sign for upcoming intersection........................................87 

39 Example of advance street name sign for two closely spaced intersections .......................88 

40 Example of signing for a left-hand land trap .........................................................................88 

41 Example of advance overhead signs indicating lane use for various destinations ..............89 

42 Example of pavement legends indicating destination route numbers 

(“horizontal signage”).........................................................................................................90 

LIST OF TABLES 

Table Page

13 Advantages and disadvantages of various configurations for displaying vehicle signal 

indications..........................................................................................................................77 

14 Traffic signal controller advantages and disadvantages.......................................................79 

15 Strengths and weaknesses of commercially available detector technologies......................81 

16 Location of advanced vehicle detectors ...............................................................................83 

17 Recommended illuminance for the intersection of continuously lighted urban streets.........92 

18 RP-8-00 guidance for roadway and pedestrian/area classification for purposes of 

determining intersection illumination levels.......................................................................93 
Signalized Intersections: Informational Guide 59

Traffic Design and Illumination

4. TRAFFIC DESIGN AND ILLUMINATION 

This chapter deals with the traffic signal hardware and software—the infrastructure that 

controls the assignment of vehicular and pedestrian right-of-way at locations where conflicts or 

hazardous conditions exist. The proper application and design of the traffic signal is a key 

component in improving the safety and efficiency of the intersection. 

This chapter presents an overview of the fundamental principles of traffic design and 

illumination as they apply to signalized intersections. The topics discussed include: 

• Traffic signal control types. 

• Traffic signal phasing. 

• Vehicle and pedestrian detection. 

• Traffic signal pole layout. 

• Traffic signal controllers. 

• Basic signal timing parameters. 

• Signing and pavement marking. 

• Illumination. 

4.1 TRAFFIC SIGNAL CONTROL TYPE 

Traffic signals operate in either pre-timed or actuated mode. Pre-timed signals operate with 

fixed cycle lengths and green splits. Actuated signals vary the amount of green time allocated to 

each phase based on traffic demand. Either type may be used in isolated (independent) or 

coordinated operation. Most pre-timed controls feature multiple timing plans, with different cycle, 

split, and offset values for different periods of the day. 

Actuated control does not rely on a fixed cycle length unless the intersection is in a 

coordinated system or under adaptive control. Actuated control provides variable lengths of green 

timing for phases that are equipped with detectors. The time for each movement depends on the 

characteristics of the intersection and timing parameters (which are based on demand at the 

intersection). 

4.2 TRAFFIC SIGNAL PHASING 

The MUTCD defines a signal phase as the right-of-way, yellow change, and red clearance 

intervals in a cycle that are assigned to an independent traffic movement or combination of traffic 

movements.(1) Signal phasing is the sequence of individual signal phases or combinations of 

signal phases within a cycle that define the order in which various pedestrian and vehicular 

movements are assigned the right-of-way. The MUTCD provides rules for determining controller 

phasing, selecting allowable signal indication combinations for displays on an approach to a 

traffic control signal, and determining the order in which signal indications can be displayed. 

Signal phasing at most intersections in the United States makes use of a standard National 

Electrical Manufacturers Association (NEMA) ring-and-barrier structure, shown in figure 23. This 

structure organizes phases to prohibit conflicting movements (e.g., eastbound and southbound 

through movements) from timing concurrently while allowing nonconflicting movements (e.g., 

northbound and southbound through movements) to time together. Most signal phasing patterns 

in use in the United States can be achieved through the selective assignment of phases to the 

standard NEMA ring-and-barrier structure. 
60 Federal Highway Administration 

Figure 23. Standard NEMA ring-and-barrier structure. 

Depending on the complexity of the intersection, 2 to 8 phases are typically used, although 

some controllers can provide up to 40 phases to serve complex intersections or sets of 

intersections. Pedestrian movements are typically assigned to parallel vehicle movements. 

Developing an appropriate phasing plan begins with determining the left-turn phase type at 

the intersection. The most basic form of control for a four-legged intersection is “permissive only” 

control, which allows drivers to make left turns after yielding to conflicting traffic or pedestrians 

and provides no special protected interval for left turns. As a general rule, the number of phases 

should be kept to a minimum because each additional phase in the signal cycle reduces the time 

available to other phases. 

Provision of a separate left-turn lane may alleviate the problems somewhat by providing 

storage space where vehicles can await an adequate gap without blocking other traffic 

movements at the intersection. In most cases, the development of a signal phasing plan should 

involve an analytical analysis of the intersection. Several software packages are suitable for 

selecting an optimal phasing plan for a given set of geometric and traffic conditions for both 

individual intersections and for system optimization. 

Pedestrian movements must be considered during the development of a phasing plan. For 

example, on wide roadways pedestrian timing may require timing longer than what is required for 

vehicular traffic, which may have an effect on the operation analysis. 

4.2.1 “Permissive-Only” Left-Turn Phasing 

“Permissive-only” (also known as “permitted-only”) phasing allows two opposing approaches 

to time concurrently, with left turns allowed after yielding to conflicting traffic and pedestrians. One 

possible implementation of this phasing pattern is illustrated in figure 24. Note that the two 

opposing movements could be run in concurrent phases using two rings; for example, the 

eastbound and westbound through movements shown in figure 24 could be assigned as phase 2 

and phase 6, respectively. 
Signalized Intersections: Informational Guide 61

Traffic Design and Illumination

Figure 24. Typical phasing diagram for “permissive-only” left-turn phasing. 

For most high-volume intersections, “permissive-only” left-turn phasing is generally not 

practical for major street movements given the high volume of the intersections. Minor side street 

movements, however, may function acceptably using “permissive-only” left-turn phasing, provided 

that traffic volumes are low enough to operate adequately and safely without additional left-turn 

protection. 

“Permissive-only” displays are signified by a green ball indication. In this case, no regulatory 

sign is required, but the MUTCD (sections 2B.45 and 4D.06) allows the option of using the R10-

12 regulatory sign (“LEFT TURN YIELD ON GREEN (symbolic green ball)”).(1) As traffic volumes 

increase at the intersection, the number of adequate gaps to accommodate left-turning vehicles 

on the permissive indication may result in safety concerns at the intersection. Common signal 

head arrangements that implement “permissive only” phasing are shown in figure 25; refer to the 

MUTCD for other configurations. 
62 Federal Highway Administration 

(a) Permissive left-turn phasing using three-section signal heads over the through lanes only. 

(b) Permissive left-turn phasing using three-section signal heads over the through lanes and a three-section 

signal head and accompanying sign over the left turn lane. 

Figure 25. Possible signal head arrangements for “permissive-only” left-turn phasing. 

4.2.2 “Protected-Only” Left-Turn Phasing 

“Protected-only” phasing consists of providing a separate phase for left-turning traffic and 

allowing left turns to be made only on a green left arrow signal indication, with no pedestrian 

movement or vehicular traffic conflicting with the left turn. As a result, left-turn movements with 

“protected-only” phasing have a higher capacity than those with “permissive-only” phasing due to 

fewer conflicts. This phasing pattern is illustrated in figure 26. Typical signal head and associated 

signing arrangements that implement “protected-only” phasing are shown in figure 27; refer to the 

MUTCD for other configurations. Chapter 12 of this document provides guidance on determining 

the need for protected left turns. 
Signalized Intersections: Informational Guide 63

Traffic Design and Illumination

Figure 26. Typical phasing diagram for “protected-only” left-turn phasing. 

(a) Protected left-turn phasing using a three-section signal head with red, yellow, and green arrows. 

(b) Protected left-turn phasing using a three-section signal head with red ball, yellow arrow, and green arrow 

and an accompanying sign. 

Figure 27. Possible signal head arrangements for “protected-only” left-turn phasing. 

4.2.3 Protected-Permissive Left-Turn Phasing 

A combination of protected and permissive left-turn phasing is referred to as protectedpermissive left-turn (PPLT) operation. This phasing pattern is illustrated in figure 28. A typical 

signal head and associated signing arrangement that implements protected-permissive phasing is 

shown in figure 29; refer to the MUTCD for other configurations. 
64 Federal Highway Administration 

Figure 28. Typical phasing diagram for protected-permissive left-turn phasing. 

(a) Protected-permissive left-turn phasing using a five-section head located directly above the lane line that 

separates the exclusive through and exclusive left-turn lane, along with an accompanying sign. 

(b) Protected-permissive left-turn phasing using a five-section signal head located directly above the 

exclusive left-turn lane. 

Figure 29. Possible signal head and signing arrangement for protected-permissive 

left-turn phasing. 

Observed improvements in signal progression and efficiency combined with driver 

acceptance have led to expanded usage of PPLT over the years. PPLT signals offer numerous 

advantages when compared to “protected-only” operation. These advantages are associated with 
Signalized Intersections: Informational Guide 65

Traffic Design and Illumination

both protected-permissive and lead-lag operation. They include the following (adapted with 

additions by the authors):(48)

• Average delay per left-turn vehicle is reduced. 

• Protected green arrow time is reduced. 

• There is potential to omit a protected left-turn phase. 

• Arterial progression can be improved, particularly when special signal head treatments 

are used to allow lead-lag phasing. 

Some disadvantages include the following: 

• The permissive phase increases the potential for vehicle-vehicle and vehiclepedestrian conflicts. 

• There is a limited ability to use lead-lag phase sequences unless special signal head 

treatments are used (see below). 

The controller phasing for protected-permissive mode is the most complicated phasing 

because of the safety implications created by the potential of what is known as the “yellow trap.” 

In a permissive-mode operation, the left-turning driver must obey the green display for the 

adjacent through movement, which also gives permission for the permissive left turn. When the 

yellow display for the adjacent through movement appears, the left-turning driver ordinarily 

expects the opposing through display to be yellow as well. The driver may now mistakenly believe 

that the left turn can be completed on the yellow display or immediately thereafter when the 

opposing through display will be red. 

For ordinary lead-lead operation where both protected left-turn phases precede the 

permissive phases, this is not a concern, as both permissive phases end concurrently. However, 

this problem can occur when a permissive left turn is opposed by a lagging protected left turn. In 

this type of operation (known as lag-permissive), the yellow display seen by a left-turning driver is 

not indicative of the display seen by the opposing through driver. The opposing through display 

may be yellow or may remain green. A driver who turns left believing that the opposing driver has 

a yellow or red display when the opposing driver has a green display may be making an unsafe 

movement. This yellow trap is illustrated in figure 30. 

Drivers who encounter this trap are those that attempt to make a permissive left-turn after a 

protected leading left-turn phase. Typically they have entered the intersection on a permissive 

green waiting to make a left turn when sufficient gaps occur in opposing through traffic. If the 

absence of gaps in opposing through traffic requires them to make their turn during the left-turn 

clearance interval, they may be “stranded" in the intersection because of the absence of gaps 

and because the opposing through movement remains green. More importantly, they may 

incorrectly presume that the opposing through traffic is being cleared at the same time that the 

adjacent through movement is being terminated. Therefore, they may complete their turn 

believing that opposing vehicles are slowing to a stop when in fact the opposing vehicles are 

proceeding into the intersection with a green ball signal indication. 

There are two ways to eliminate the yellow trap. First, the phase sequence at the intersection 

can be restricted to simultaneous leading (lead-lead) or lagging (lag-lag) left-turn phasing. 

Second, the signal display can be altered to allow the left-turn signal head to display a permissive 

left turn independently of the adjacent through movements, which allows the through movements 

to terminate but allow a permissive left turn to continue during the opposite approach’s lagging 

protected left-turn phase. Some agencies have experimented with signal displays (e.g., “Dallas 

Display,” flashing circular red, flashing red arrow, flashing circular yellow, and flashing yellow 

arrow) that allow this type of operation. Of these, the “Dallas Display” optically restricts the 

visibility of the permissive movement using louvers; it is fully compliant with the MUTCD and is 

shown in figure 31. 
66 Federal Highway Administration 

Figure 30. Illustration of the yellow trap.(3)
Signalized Intersections: Informational Guide 67

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Figure 31. The protected-permissive left-turn display known as “Dallas display” uses louvers to 

restrict visibility of the left-turn display to adjacent lanes.(49)

A national NCHRP study, has examined the operational advantages and safety aspects of 

various PPLT control devices and signal arrangements. The study determined that a flashing 

yellow arrow PPLT display was consistently found to be equal or superior to existing PPLT 

displays both in a laboratory environment and in cities where the display was experimentally 

implemented in the field.(49) The flashing yellow arrow display for PPLT is still considered 

experimental by the MUTCD and is undergoing further field testing. 

4.2.4 Split Phasing 

Split phasing consists of having two opposing approaches time consecutively rather than 

concurrently (i.e., all movements originating from the west followed by all movements from the 

east). Split phase can be implemented in a variety of ways depending on signal controller 

capabilities and how pedestrian movements are treated. Three basic variations, shown in figure 

32, are described as follows: 

• Method A: Consecutive pedestrian phases using one ring. This method 

associates each pedestrian phase with its adjacent vehicle phase. This places 

pedestrians at potential conflict with right-turning traffic only. However, this may result 

in potentially consecutive pedestrian phases if pedestrian calls are present on both 

phases. For large intersections, the minimum time needed to serve these consecutive 

movements may result in excessively long cycle lengths. Implementation uses two 

consecutive phases in the same ring (e.g., phases 3 and 4), with pedestrian phases 

assigned to each. 

• Method B: Consecutive pedestrian phases using “exclusive” settings in 

controller. This method is functionally identical to method A. Implementation differs 

from method A in that a setting in the controller is needed to force the phases to time 

in an “exclusive” mode (e.g., the phase must not time with any other phases). 

• Method C: Concurrent pedestrian phases using two rings. This method, used by 

some agencies in certain situations, associates pedestrian movements with a single 

phase in one ring that, when actuated, operates concurrently with two consecutively 

timing vehicle phases in the second ring. Details of implementation of this method can 

be found in Wainwright.(50) This method can provide a considerably more efficient 

operation of the intersection, particularly where pedestrian crossing demands are 

large enough to warrant pedestrian signals but are relatively infrequent (not every 

cycle) during most or all of the day. In most cycles, no pedestrian actuation occurs, 

so: 

– The split vehicular phases operate without any pedestrian timing considerations. 
68 Federal Highway Administration 

– The sequential vehicular phase green times are directly related to their 

respective vehicular demands. 

– The green left arrow signal indication is displayed to each of the sequential 

vehicle phases to encourage efficient nonyielding movement. 

Method C is advantageous under some conditions, but should not be applied 

indiscriminately because it does have some potential liabilities as compared to the 

other two methods. Firstly, during the cycles when the pedestrian phase is actuated, 

left-turning vehicles can sometimes be placed in an awkward situation of not being 

able to clear the intersection when the vehicle phase terminates because conflicting 

pedestrians have not yet finished crossing. Secondly, pedestrians could face both 

left-turning and right-turning conflicting vehicles. Thirdly, if for some reason the timing 

parameters for the two crosswalks are different, then this method might be 

disadvantageous because placing both crosswalks on a single phase requires 

identical timing parameters for both crosswalks. 

Split phasing is used infrequently at signalized intersections because a more efficient 

conventional phasing plan can usually be found. The following conditions could indicate that split 

phasing might be an appropriate design choice: 

• There is a need to accommodate multiple turn lanes on an approach, but sufficient 

width is not available to provide separate lanes. Therefore, a shared through/left lane 

is required. An operational analysis should be performed to ensure this option is 

superior compared to a single turn lane option under various phasing scenarios. 

• The left-turn lane volumes on two opposing approaches are approximately equal to 

the through traffic lane volumes and the total approach volumes are significantly 

different on the two approaches. Under these somewhat unusual conditions, split 

phasing may prove to be more efficient than conventional phasing. 

• A pair of opposing approaches is physically offset such that the opposing left turns 

could not proceed simultaneously or a permissive left turn could not be expected to 

yield to the opposing through movement. 

• The angle of the intersection is such that the paths of opposing left turns would not be 

forgiving of errant behavior by turning motorists. 

• The safety experience indicates an unusual number of crashes (usually sideswipes or 

head-on collisions) involving opposing left turns. This may be a result of unusual 

geometric conditions that impede visibility of opposing traffic. 

• A pair of opposing approaches each has only a single lane available to accommodate 

all movements and the left turns are heavy enough to require a protected phase. 

• One of the two opposing approaches has heavy demand and the other has minimal 

demand. Under this condition, the signal phase for the minimal approach would be 

skipped frequently and the heavy approach would function essentially as the stem of a 

T intersection. 
Signalized Intersections: Informational Guide 69

Traffic Design and Illumination

(a) Method A: Consecutive pedestrian phases using one ring. 

(b) Method B: Consecutive pedestrian phases using “exclusive” settings in controller. 

Note: Separate “exclusive” setting must be used for phases 4 and 8; otherwise, operation results in 

simultaneous display of phases 4 and 8. 

(c). Method C: Concurrent pedestrian phases using two rings. 

Figure 32. Typical phasing diagrams for split phasing. 
70 Federal Highway Administration 

No standard method is provided in the MUTCD for indicating split phasing at an intersection, 

and the methods vary considerably depending on what type of phasing sequence has been used. 

A common way to implement method A or B described above involves using a four-section head 

displaying both a green ball and a green left-turn arrow simultaneously, as shown in figure 33. 

This method does not require the use of additional signs. Note that additional measures are 

needed with method C, as the protected left-turn arrow conflicts with the concurrent pedestrian 

phase, as follows:(50)

• A special logic package can be used to suppress the green arrow display whenever 

the pedestrian phase is being served. 

• A static sign indicating “LEFT TURN YIELD TO PEDS ON GREEN (symbolic green 

ball)” can be located next to the leftmost signal head for emphasis. 

• A blankout sign indicating “LEFT TURN YIELD TO PEDS” can be activated when the 

conflicting vehicular and pedestrian phases are running concurrently. 

Figure 33. Common signal head arrangement for split phasing. 

4.2.5 Prohibited Left-Turn Phasing 

An alternative to providing a left-turn phase is to prohibit left-turn movements at the subject 

intersection. Under this scenario, left-turning drivers would be required to divert to another facility 

or turn in advance or beyond the intersection via a geometric treatment such as a jughandle or 

median U-turn. Left-turns can be prohibited on a full- or part-time basis. The amount of traffic 

diverted, effects on transit routes, the adequacy of the routes likely to be used, and community 

impacts are all important issues to consider when investigating a turn prohibition. A variety of 

treatments that redirect left turns are discussed in chapter 10. 

4.2.6 Right-Turn Phasing 

Right-turn phasing may be controlled in a permissive or protected manner with different 

configurations depending on the presence of pedestrians and lane configuration at the 

intersections. 

Right turns have been operated on overlap phases to increase efficiency for the traffic signal. 

An overlap is a set of outputs associated with two or more phase combinations. As described 

earlier, various movements can be assigned to a particular phase. In some instances, right-turn 

movements operating in exclusive lanes can be assigned to more than one phase that is not 

conflicting. In this instance, a right turn is operated at the same time as the left turn, as shown in 

figure 34. The overlap forms a separate movement that derives its operation from its assigned 

phases (also called parent phases); for example, overlap A (OL A) is typically assigned to phase 

2 (the adjacent through phase) and phase 3 (the nonconflicting left-turn phase from the cross 

street). During a transition between two parent phases, the overlap will remain green. To 
Signalized Intersections: Informational Guide 71

Traffic Design and Illumination

implement this type of true overlap, a three-section head with limited visibility must be used, as 

the right-turn display may be different from the adjacent through phase. 

Figure 34. Typical phasing diagram illustrating a right-turn overlap. 

More commonly, a five-section head with a combination of circular and arrow indications is 

used. Note that the MUTCD requires the display of a yellow change interval between the display 

of a green right-turn arrow and a following circular green display that applies to the continuing 

right-turn movement on a permissive basis. This yellow change interval is necessary to convey 

the change in right-of-way from fully protected during the green arrow to requiring a yield to 

pedestrians and other vehicles during the circular green. This can be implemented by assigning 

the right-turn arrows to the same phase as the nonconflicting left-turn phase on the cross street 

and the circular indications to the same phase as the adjacent through movement. A typical fivesection signal head that implements protected-permissive right-turn phasing is shown in figure 35; 

refer to the MUTCD for other configurations. 
72 Federal Highway Administration 

(a) Right-turn overlap phasing using a five-section head located directly above the lane line that separates 

the exclusive through and exclusive right-turn lane. 

(b) Right-turn overlap phasing using a five-section signal head centered above the right-turn lane. 

Figure 35. Common signal head and signing arrangements for right-turn-overlap phasing. 

This type of operation increases efficiency by providing more green time to this right-turn 

movement but may compromise the intersection’s usability for visually impaired pedestrians. The 

transition from the protected right-turn movement on the green arrow to the permissive right-turn 

movement on the green ball masks the sound of the adjacent through vehicles. This makes it 

difficult for visually impaired pedestrians to hear when the adjacent through vehicles begin to 

move, which is used as an audible cue for crossing the street. Therefore, the use of accessible 

pedestrian signals to provide an audible indication of the start of the pedestrian phase may be 

needed to restore this cue. 

4.3 VEHICLE AND PEDESTRIAN DISPLAYS 

Signal displays can be generally categorized into those for vehicles and for pedestrians. The 

following sections discuss each type. 

4.3.1 Vehicle Displays 

The location of signal heads should be evaluated based on visibility requirements and type of 

signal display. While signal head placement is governed by MUTCD requirements for signal 

displays (discussed earlier in this chapter), the specific placement of signal heads is typically 

determined by local policies. When designing the placement of signal heads, the following should 

be considered in addition to the minimum requirements described in the MUTCD: 

• Consistency with other intersections in the area. 

• A geometric design issue that could confuse a driver. 
Signalized Intersections: Informational Guide 73

Traffic Design and Illumination

• A large percentage of vehicles on one or more approaches that block lines of sight 

including trucks and vans. 

• The width of the intersection. 

• The turning paths of the vehicles. 

At large signalized intersections, the safety and operation of the intersection may be 

enhanced through the use of additional signal heads, some of which are standard in some States. 

Figure 36 shows a typical intersection design with five types of optional heads: 

Optional Head #1: This is a near-right-side side head that can be used to provide an 

advanced head at wide intersections as well as provide a supplemental head for vehicles that are 

unable to see the signal heads over the lanes due to their position behind large vehicles (trucks, 

etc.). 

Optional Head #2: This is an extra through head that can be used to supplement the 

overhead signal heads. This head provides an indication for vehicles that might be behind large 

vehicles and may be more visible than the overhead signal head when the sun is near the 

horizon. 

Optional Head #3: This is an extra left-turn head that can be used to guide left-turning 

vehicles across a wide intersection as they make their turn. It also helps visibility for vehicles 

behind large vehicles and for times of day when the sun is near the horizon. 

Optional Head #4: This is a near-left-side head that can be used to provide an advance 

indication if visibility is hampered by a curve in the road upstream of the intersection. 

Optional Head #5: This is a head that can be used to provide a display in direct view of a 

right-turn lane and can also be used to provide a right-turn overlap phase in conjunction with the 

nonconflicting left-turn phase on the cross street. The head should contain either three circular 

balls or be a five-section head with three balls and two right-turn arrows due to the concurrent 

pedestrian crossing. 
74 Federal Highway Administration 

(a) Optional Head #1: Near-side head for through vehicles. 

(b) Optional Head #2: Far-side supplemental head for through vehicles. 

(c) Optional Head #3: Far-side supplemental head for left-turning vehicles. 

Figure 36. Examples showing five optional signal head locations. 
Signalized Intersections: Informational Guide 75

Traffic Design and Illumination

(d) Optional Head #4: Near-side head on curving approach. 

(e) Optional Head #5: Far-side head for right-turning vehicles. 

Figure 36. Examples showing five optional signal head locations, continued. 
76 Federal Highway Administration 

4.3.2 Pedestrian Displays 

According to section 4E.03 of the 2003 MUTCD, pedestrian signal heads must be used in 

conjunction with vehicular traffic control signals under any of the following conditions:(1)

• If a traffic control signal is justified by an engineering study and meets either Warrant 

4, Pedestrian Volume, or Warrant 5, School Crossing (see MUTCD chapter 4C). 

• If an exclusive signal phase is provided or made available for pedestrian movements 

in one or more directions, with all conflicting vehicular movements being stopped. 

• At an established school crossing at any signalized location. 

• Where engineering judgment determines that multiphase signal indications (as with 

split-phase timing) would tend to confuse or cause conflicts with pedestrians using a 

crosswalk guided only by vehicular signal indications. 

Pedestrian signals should be used under the following conditions: 

• If it is necessary to assist pedestrians in making a reasonably safe crossing or if 

engineering judgment determines that pedestrian signal heads are justified to 

minimize vehicle-pedestrian conflicts. 

• If pedestrians are permitted to cross a portion of a street, such as to or from a median 

of sufficient width for pedestrians to wait, during a particular interval but are not 

permitted to cross the remainder of the street during any part of the same interval. 

• If no vehicular signal indications are visible to pedestrians, or if the vehicular signal 

indications that are visible to pedestrians starting or continuing a crossing provide 

insufficient guidance for them to decide when it is reasonably safe to cross, such as 

on one-way streets, at T-intersections, or at multiphase signal operations. 

The MUTCD provides specific guidance on the type and size of pedestrian signal indications 

(section 4E.04). As noted in the MUTCD, all new pedestrian signals should use the UPRAISED 

HAND (symbolizing DON’T WALK) and WALKING PERSON (symbolizing WALK) indications, 

shown in figure 37. The pedestrian displays must be mounted so that the bottom of the 

pedestrian signal display housing (including mounting brackets) is no less than 2.1 m (7 ft) and no 

more than 3 m (10 ft) above sidewalk level.(1)

Figure 37. Pedestrian signal indications. 
Signalized Intersections: Informational Guide 77

Traffic Design and Illumination

Some signalized intersections have factors that may make them difficult for pedestrians who 

have visual disabilities to cross safely and effectively. As noted in the MUTCD (section 4E.06), 

these factors include:(1)

• Increasingly quiet cars. 

• Right turn on red (which masks the sound of the beginning of the through phase). 

• Continuous right-turn movements. 

• Complex signal operations (e.g., protected-permissive phasing, lead-lag phasing, or 

atypical phasing sequences). 

• Wide streets. 

To address these challenges, accessible pedestrian signals have been developed to provide 

information to the pedestrian in a nonvisual format, such as audible tones, verbal messages, 

and/or vibrating surfaces. Detail on these treatments can be found in the MUTCD(1) and in several 

references sponsored by the U.S. Access Board and the National Cooperative Highway 

Research Program (NCHRP).(51,52,53)

4.4 TRAFFIC SIGNAL POLE LAYOUT 

Three primary types of signal configurations display vehicle signal indications: 

• Pedestal or post-mounted signal displays. 

• Span-wire configurations. 

• Mast arms. 

Table 13 identifies the advantages and disadvantages of each configuration. 

Table 13. Advantages and disadvantages of various configurations for displaying vehicle signal 

indications. 

Advantages Disadvantages 

Pedestal (post-mounted) vehicle signal 

• Low cost 

• Less impact on view corridors 

• Lower maintenance costs 

• Esthetics 

• Difficult to meet MUTCD visibility requirements, 

particularly at large signalized intersections 

Span wire vehicle signal 

• Can accommodate large intersections 

• Flexibility in signal head placement 

• Lower cost than mast arms 

• Higher maintenance costs 

• Wind and ice can cause problems 

• May be considered aesthetically unpleasing 

Mast arm vehicle signal 

• Provides good signal head placement 

• Lower maintenance costs 

• Many pole esthetic design options 

• More costly than span wire 

• Mast arm lengths can limit use and be extremely 

costly for some large intersections 

In addition to providing support for the optimal location of vehicle and pedestrian signal 

indications, signal poles need to be located carefully to address the following issues: 

• Pedestrian walkway and ramp locations. 

• Pedestrian pushbutton locations, unless separate pushbutton pedestals are provided. 

• Clearance from the travel way. 

• Available right-of-way and/or public easements. 
78 Federal Highway Administration 

• Overhead utility conflicts, as most power utilities require at least 3.0 m (10 ft) 

clearance to power lines. 

• Underground utilities, as most underground utilities are costly to relocate and therefore 

will impact the location of signal pole foundations. 

The MUTCD,(1) the ADAAG,(33) and the AASHTO Roadside Design Guide(54) all contain 

guidance regarding the lateral placement of signal supports and cabinets. Generally, signal poles 

should be placed as far away from the curb as possible, not conflict with the pedestrian walking 

paths, and be located for easy access to the pushbuttons by disabled pedestrians. In some 

circumstances, it may be difficult or undesirable to locate a single pole that adequately serves 

both pedestrian ramps and provides adequate clearances. In these cases, one or more 

pedestals with the pedestrian signal heads and/or pushbuttons should be considered to ensure 

visibility of the pedestrian signal heads and accessibility to the pushbuttons. 

4.5 TRAFFIC SIGNAL CONTROLLER 

The traffic controller is the brain of the intersection. There are two general categories of 

traffic signal controllers: pre-timed and actuated. In the past two decades, most electromechanical and early solid-state controllers have been replaced with NEMA, 170, and advanced 

traffic controllers (ATC), even in locations where the signal is operated in a pre-timed mode. 

Although most modern controllers can perform the functions needed at typical signalized 

intersections, some may not be able to handle: more complicated configurations (e.g., 

intersections with more than four legs or two closely spaced intersections); communications with 

other controllers of dissimilar brands; or accommodation of priority treatments (e.g., transit 

priority). Therefore, the choice of controller may play a significant role in the types of treatments 

that can be considered at a signalized intersection. 

Traffic controllers can be generally classified into three types: 

1. NEMA. 

2. Type 170. 

3. ATC. 

Some advantages and disadvantages of each type are described in table 14. 
Signalized Intersections: Informational Guide 79

Traffic Design and Illumination

Table 14. Traffic signal controller advantages and disadvantages. 

Advantages Disadvantages 

NEMA Controller 

• Specific vendor software 

• Reduced software/hardware problems 

• Cabinets are not standardized 

• Proprietary software 

• Proprietary features may not be 

interchangeable with other NEMA 

controllers 

• Typically require larger cabinets 

• May require extra spare parts if different 

models exist within one jurisdiction 

Type 170 Controller 

• Standard layout and design 

• Many software choices 

• More easily adapted to special applications 

(i.e., ramp metering and Intelligent 

Transportation Systems (ITS)). 

• Reduced spare parts inventory 

• Software and hardware compatibility 

problems 

• Software can be expensive 

• Liability can be greater with separate 

software/hardware vendors 

Advanced Traffic Controllers (ATC and 2070) 

• Compatible with the National Transportation 

Communications for ITS Protocol (NTCIP) 

• Much faster processing speeds 

• Additional phase inputs 

• Flexibility for ITS applications 

• Lack of proven software 

• Expensive 

• Current variations may not be 

interchangeable 

In locating the controller cabinet, consider the following: 

• It should not interfere with sight lines for pedestrians or right-turning vehicles. 

• It should be in a location that is less likely to be struck by an errant vehicle and where 

it does not impede pedestrian circulation, including wheelchairs and other devices that 

assist mobility. 

• A technician at the cabinet should be able to see the signal indications for two 

approaches while standing at the cabinet. 

• The cabinet should be located near the power source. 

• The cabinet location should afford ready access by operations and maintenance 

personnel, including consideration for where personnel would park their vehicle. 

4.6 DETECTION DEVICES 

The detectors (or sensors) at an intersection inform the signal controller that a vehicle, 

pedestrian, or bicycle is present at a defined location within the intersection or signal system. 

The controller then uses this information to determine the amount of green time and the signal 

phases to serve. 

4.6.1 Vehicle Detection 

Table 15, excerpted from the final draft of the Traffic Detector Handbook, 2003 edition, 

presents an overview of the strengths and weaknesses of commercially available detector 

technology.(55) The good performance of in-roadway detectors such as inductive loops, magnetic, 

and magnetometer detectors is based, in part, on their close location to the vehicle, which makes 

them insensitive to inclement weather due to a high signal-to-noise ratio. Their main 

disadvantage is their in-roadway installation, necessitating physical changes in the roadway as 

part of the installation process. In addition, in-roadway detectors may be damaged or disrupted 

by utility cuts, pavement milling operations for resurfacing, and movement of pavement joints and 

cracks. Over-roadway detectors often provide data not available from in-roadway sensors, and 
80 Federal Highway Administration 

some can monitor multiple lanes with one unit. The reader is encouraged to refer to the Traffic 

Detector Handbook for further discussion on detector technology. 

Vehicle detectors provide advanced detection, left-turn lane presence detection, and stop-bar 

presence detection. Advanced detection extends a green signal to get an approaching vehicle 

through the signal. Left-turn lane presence detection detects left-turning vehicles that are waiting. 

Stop-bar presence detection will pick up any vehicles that may have entered to roadway from 

driveways and vehicles that might not have made it though the intersection on the previous 

green. 

A fourth detector function is as a system detector. On many large streets with coordinated 

signal systems, system detectors are used to collect midblock vehicle volume and occupancy 

data, which is analyzed by a master signal controller or central system to determine whether 

signal timing changes are needed. The location of the system detectors varies based on the 

signal system and software being used, but typically they are located downstream of the 

intersection on the major roadway. 

The location of the advanced detectors is often based on the dilemma zone boundary. The 

dilemma zone is that portion of the approach where a driver suddenly facing a yellow indication 

must make a decision whether to stop safely or to proceed through the intersection. As a result, 

the dilemma zone boundary is typically dictated by the minimum stopping distance. The actual 

distances vary by jurisdictional policies and should be reviewed before the traffic signal is 

designed. The typical location for advance detectors based on stopping sight distance is shown in 

table 16. 
Signalized Intersections: Informational Guide 81

Traffic Design and Illumination

Table 15. Strengths and weaknesses of commercially available detector technologies.

Technology Strengths Weaknesses 

Inductive Loop • Flexible design to satisfy large 

variety of applications 

• Mature, well understood technology 

• Large experience base 

• Provides basic traffic parameters 

(e.g., volume, presence, occupancy, 

speed, headway, and gap) 

• Insensitive to inclement weather 

such as rain, fog, and snow 

• Provides best accuracy for count 

data as compared with other 

commonly used techniques 

• Common standard for obtaining 

accurate occupancy measurements 

• High frequency excitation models 

provide classification data 

• Installation requires pavement 

cut 

• Improper installation decreases 

pavement life 

• Installation and maintenance 

require lane closure 

• Wire loops subject to stresses 

of traffic and temperature 

• Multiple detectors usually 

required to monitor a location 

• Detection accuracy may 

decrease when design requires 

detection of a large variety of 

vehicle classes 

• Destroyed by utility cuts or 

pavement milling operations 

Magnetometer 

(two-axis 

fluxgate 

magnetometer) 

• Less susceptible than loops to 

stresses of traffic 

• Insensitive to inclement weather 

such as snow, rain, and fog. 

• Some models transmit data over 

wireless radio frequency (RF) link 

• Installation requires pavement 

cut 

• Improper installation decreases 

pavement life 

• Installation and maintenance 

require lane closure 

• Models with small detection 

zones require multiple units for 

full lane detection 

Magnetic 

(induction or 

search coil 

magnetometer) 

• Can be used where loops are not 

feasible (e.g., bridge decks) 

• Some models are installed under 

roadway without need for pavement 

cuts, but boring under roadway is 

required 

• Insensitive to inclement weather 

such as snow, rain, and fog. 

• Less susceptible than loops to 

stresses of traffic 

• Installation requires pavement 

cut or tunneling under roadway 

• Cannot detect stopped 

vehicles unless special sensor 

layouts and signal processing 

software are used 

Microwave 

Radar 

• Typically insensitive to inclement 

weather at the relatively short 

ranges encountered in traffic 

management applications 

• Direct measurement of speed 

• Multiple lane operation available 

• Continuous Wave (CW) 

doppler sensors cannot detect 

stopped vehicles 

Source: Adapted from reference 55. 
82 Federal Highway Administration 

Table 15. Strengths and weaknesses of commercially available sensor technologies, continued. 

Technology Strengths Weaknesses 

Active Infrared 

(laser radar) 

• Transmits multiple beams for 

accurate measurement of 

vehicle position, speed, and 

class 

• Multiple-lane operation 

available 

• Operation may be affected by fog when 

visibility is less than ~6 m (20 ft) or 

blowing snow is present 

• Installation and maintenance, including 

periodic lens cleaning, require lane 

closure 

Passive Infrared • Multizone passive sensors 

measure speed 

• Passive sensor may have reduced 

vehicle sensitivity in heavy rain, snow, 

and dense fog 

• Some models not recommended for 

presence detection 

Ultrasonic • Multiple-lane operation 

available 

• Capable of overheight vehicle 

detection 

• Large Japanese experience 

base 

• Environmental conditions such as 

temperature change and extreme air 

turbulence can affect performance; 

temperature compensation is built into 

some models 

• Large pulse repetition periods may 

degrade occupancy measurement on 

freeways with vehicles traveling at 

moderate to high speeds 

Acoustic • Passive detection 

• Insensitive to precipitation 

• Multiple lane operation 

available in some models 

• Cold temperatures may affect vehicle 

count accuracy 

• Specific models are not recommended 

with slow moving vehicles in stop-andgo traffic 

Video Image 

Processor 

• Monitors multiple lanes and 

multiple detection zones/lanes 

• Easy to add and modify 

detection zones 

• Rich array of data available 

• Provides wide-area detection 

when information gathered at 

one camera location can be 

linked to another 

• Installation and maintenance, including 

periodic lens cleaning, require lane 

closure when camera is mounted over 

roadway (lane closure may not be 

required when camera is mounted at 

side of roadway) 

• Performance affected by inclement 

weather such as fog, rain, and snow; 

vehicle shadows; vehicle projection into 

adjacent lanes; occlusion; day-to-night 

transition; vehicle/road contrast; and 

water, salt grime, icicles, and cobwebs 

on camera lens 

• Requires 15- to 21-m (50- to 70-ft) 

camera mounting height (in a sidemounting configuration) for optimum 

presence detection and speed 

measurement 

• Some models susceptible to camera 

motion caused by strong winds or 

vibration of camera mounting structure 

• Generally cost-effective when many 

detection zones within the camera fieldof-view or specialized data are required 

Source: Adapted from reference 55. 
Signalized Intersections: Informational Guide 83

Traffic Design and Illumination

Table 16. Location of advanced vehicle detectors. 

Multiple Detector Setback 

Speed 

Calculated Stopping 

Distance 

Single 

Detector 

Setback 

10% 

Probability of 

Stopping 

90% 

Probability of 

Stopping 

33 km/h (20 mph) 22.0 m (72.2 ft) 21 m (70 ft) — — 

40 km/h (25 mph) 31.8 m (104.4 ft) 32 m (105 ft) — — 

48 km/h (30 mph) 42.9 m (140.8 ft) 43 m (140 ft) — — 

56 km/h (35 mph) 55.7 m (182.9 ft) 56 m (185 ft) 31 m (102 ft) 77 m (254 ft) 

64 km/h (40 mph) 70.4 m (231.0 ft) 70 m (230 ft) 37 m (122 ft) 87 m (284 ft) 

72 km/h (45 mph) 86.5 m (283.8 ft) * 46 m (152 ft) 100 m (327 ft) 

80 km/h (50 mph) 104.2 m (341.9 ft) * 52 m (172 ft) 108 m (353 ft) 

88 km/h (55 mph) 123.8 m (406.3 ft) * 71 m (234 ft) 118 m (386 ft) 

* Use multiple detectors or volume-density modules. 

Source: (Reference 56 (table 7-1); reference 57 (table 4-3); metric values converted from U.S. 

customary provided in sources)

As shown in table 16, the stopping distance can be computed for both the average stopping 

condition as well as the probability ranges for stopping. For most large intersections, a multipleloop design should be used to account for the higher speeds and probabilities of stopping. More 

detailed information on detector placement, including the results of several calculation methods, 

can be found in the Manual of Traffic Detector Design.(58)

4.6.2 Pedestrian Detection 

Pedestrian detection at actuated signals is typically accomplished through the use of 

pedestrian push buttons. Accessible pedestrian signal detectors, or devices to help pedestrians 

with visual or mobility impairments activate the pedestrian phase, may be pushbuttons or other 

passive detection devices. For pushbuttons to be accessible, they should be placed in 

accordance with the guidance in the MUTCD and located as follows (sections 4E.08 and 

4E.09):(1)

• Adjacent to a level all-weather surface to provide access from a wheelchair with a 

wheelchair-accessible route to the ramp. 

• Within 1.5 m (5 ft) of the crosswalk extended. 

• Within 3 m (10 ft) of the edge of the curb, shoulder, or pavement. 

• Parallel to the crosswalk to be used. 

• Separated from other pushbuttons by a distance of at least 3 m (10 ft). 

• Mounted at a height of approximately 1.1 m (3.5 ft) above the sidewalk. 

Alternative methods of pedestrian detection, including infrared and microwave detectors, are 

emerging. Additional information on these devices can be found in FHWA’s Pedestrian Facilities 

User Guide—Providing Safety and Mobility.(35)

4.7 BASIC SIGNAL TIMING PARAMETERS 

Signal operation and timing have a significant impact on intersection performance. 

Controllers have a vast array of inputs that permit tailoring of controller operation to the specific 

intersection. This section provides guidance for the determination of basic timing parameters. 

The development of a signal timing plan should address all user needs at a particular location 

including pedestrians, bicyclists, transit vehicles, emergency vehicles, automobiles, and trucks. 

For the purposes of this section, signal timing is divided into two elements: pedestrian timing and 

vehicle timing. 
84 Federal Highway Administration 

4.7.1 Pedestrian Timing 

Pedestrian timing requirements include a WALK interval and a flashing DON’T WALK 

interval. The WALK interval varies based upon local agency policy. The MUTCD recommends a 

minimum WALK time of 7 s, although WALK times as low as 4 s may be used if pedestrian 

volumes and characteristics do not require an interval of 7 s (section 4E.10).(1) The WALK interval 

gives pedestrians adequate time to perceive the WALK indication and depart the curb before the 

clearance interval (flashing DON’T WALK) begins. 

In downtown areas, longer WALK times are often appropriate to promote walking and serve 

pedestrian demand. School zones and areas with large numbers of elderly pedestrians also 

warrant consideration and the display of WALK time in excess of the minimum WALK time. 

The MUTCD states that the pedestrian clearance time should allow a pedestrian crossing in 

the crosswalk to leave the curb and travel to at least the far side of the traveled way or to a 

median of sufficient width for pedestrians to wait before opposing vehicles receive a green 

indication. The MUTCD uses a walk speed of 1.2 m/s (4.0 ft/s) for determining crossing times.(1)

However, the Pedestrian Facilities Users Guide recommends a lower speed of 1.1 m/s (3.5 ft/s); 

see chapter 2 for further discussion.(35) Pedestrian clearance time is calculated using equation 1: 

Walking Speed

CrossingDistance Pedestrian Clearance Time = (1) 

where: Pedestrian Clearance Time is in seconds 

 Crossing Distance is measured from the near curb to at least the far side 

of the traveled way or to a median; and 

 Walking Speed is typically 1.2 m/s (4 ft/s) or 1.1 m/s (3.5 ft/s) as indicated 

above. 

Pedestrian clearance time is accommodated during either a combination of flashing DON’T 

WALK time and yellow clearance time or by flashing DON’T WALK time alone. The 

recommended practice is for the pedestrian clearance time to be accommodated completely 

within the flashing DON’T WALK time. However, at high-volume locations, it may be necessary as 

a tradeoff for vehicular capacity to use the yellow change interval as part of satisfying the 

calculated pedestrian clearance time. 

4.7.2 Vehicle Timing—Green Interval 

Ideally, the length of the green display should be sufficient to serve the demand present at 

the start of the green phase for each movement and should be able to move groups of vehicles, 

or platoons, in a coordinated system. At an actuated intersection, the length of the green interval 

varies based on inputs received from the detectors. Minimum and maximum green times for 

each phase are assigned to a controller to provide a range of allowable green times. Detectors 

are used to measure the amount of traffic and determine the required time for each movement 

within the allowable range. 

The minimum green time is the amount of time allocated to each phase so that vehicles in 

queue at the stop bar are able to start and clear the intersection. The minimum initial green time 

is established by determining the time needed to clear the vehicles located between the stop bar 

and the detector nearest the stop bar. Where presence detection is installed at the stop bar, a 

minimum interval may be set to a value that is less than 1.0 s. 

Consider an intersection with the following properties: average vehicle spacing is 7.5 m (25 ft) 

per vehicle, initial start-up time is 2 s, and vehicle headway is 2 s per vehicle. For an approach 

with a detector located 30 m (100 ft) from the stop bar, the minimum green time is 2 + (30 m/7.5 

m x 2) = 2 + (100 ft/25 ft x 2) = 10 s. 

The maximum green time is the maximum limit to which the green time can be extended for a 

phase in the presence of a call from a conflicting phase. The maximum green time begins when a 
Signalized Intersections: Informational Guide 85

Traffic Design and Illumination

call is placed on a conflicting phase. The phase is allowed to "max-out" if the maximum green 

time is reached even if actuations have been received that would typically extend the phase. 

4.7.3 Vehicle Timing—Detector Timing 

One advantage of actuated control is that it can adjust timing parameters based on vehicle or 

pedestrian demand. The detectors and the timing parameters allow the signal to respond to 

varied flow throughout the day. For pedestrians, detectors are located for convenient access; for 

vehicles, detector spacing is a function of travel speed and the characteristics of the street. The 

operation of the signal is highly dependent on detector timing. More information about detector 

timing, including settings for various detector configurations, is found in the FHWA Traffic 

Detector Handbook.(55)

One type of detector timing, known as volume-density timing, uses gap timers to reduce the 

allowable gap time the longer the signal is green. This type of timing makes the signal less likely 

to extend the green phase the longer the signal is green. A typical setting for a volume-density 

controller is to have the passage gap set to twice the calculated gap time to ensure the phase 

does not gap out too early. The minimum gap time might be set to less than the calculated gap 

time on multiple lane approaches, depending on the characteristics of the intersection. 

Signal timing parameters may provide an opportunity to maximize the efficiency of the 

intersection. Signal timing parameters control how quickly the phase ends once traffic demand is 

no longer present. The one phase that is the exception is the coordinated phase, which receives 

the unused or additional time. 

4.7.4 Vehicle Timing—Vehicle Clearance 

The vehicle clearance interval consists of the yellow change and red clearance intervals. The 

recommended practice for computing the vehicle clearance interval is the ITE formula (reference 

56, equation 11-4), given in equation 2 (to use with metric inputs, use 1 m = 0.3048 ft): 

V

W L

a g

V CP t+

+

+ = +2 64.4 (U.S. Customary) (2) 

where: CP = change period (s) 

t = perception-reaction time of the motorist (s); typically 1 

V = speed of the approaching vehicle (ft/s) 

a = comfortable deceleration rate of the vehicle (ft/s2

); typically 10 ft/s2 

W = width of the intersection, curb to curb (ft) 

L = length of vehicle (ft); typically 20 ft 

g = grade of the intersection approach (%); positive for upgrade, negative 

for downgrade 

For change periods longer than 5 s, a red clearance interval is typically used. Some agencies 

use the value of the third term as a red clearance interval. The MUTCD does not require specific 

yellow or red intervals but provides guidance that the yellow change interval should be 

approximately 3 s to 6 s and that the red clearance interval should not exceed 6 s (section 

4D.10).(1) Note that because high-volume signalized intersections tend to be large and frequently 

on higher speed facilities, their clearance intervals are typically on the high end of the range. 

These longer clearance intervals increase loss time at the intersection and thus reduce capacity. 

The topic of yellow and red clearance intervals has been much debated in the traffic 

engineering profession. At some locations, the yellow clearance interval is either too short or set 

improperly due to changes in posted speed limits or 85th-percentile speeds. This is a common 

problem and frequently causes drivers to brake hard or to run through the intersection during the 

red phase. Because not all States follow the same law with regard to what is defined as "being in 

the intersection on the red phase," local practice for defining the yellow interval varies 
86 Federal Highway Administration 

considerably. For this reason, red light photo enforcement should not be used during the period of 

red clearance required by the ITE formula. 

Current thought is that longer clearance intervals will cause drivers to enter the intersection 

later and will breed disrespect for the traffic signal. Wortman and Fox conducted a study that 

showed that the time of entry of vehicles into the intersection increased due to a longer yellow 

interval.(59) Additional research is needed to examine the effect of lengthening the yellow interval 

on driver behavior. 

4.7.5 Vehicle Timing—Cycle Length 

For isolated, actuated intersections, cycle length varies from cycle to cycle based on traffic 

demand and signal timing parameters. For coordinated intersections, a background cycle length 

is used to achieve consistent operation between consecutive intersections. In general, shorter 

cycle lengths are preferable to longer ones because they result in less delay and shorter queues. 

However, the need to accommodate multiple pedestrian movements across wide roadways, 

coupled with complex signal phasing and minimum green requirements to accommodate signal 

progression in multiple directions, may sometimes require the use of even longer cycle lengths. 

Wherever possible, such use should be limited to peak traffic periods only. 

In general, it is preferred that the cycle lengths for conventional, four-legged intersections not 

exceed 120 s, although larger intersections may require longer cycle lengths. Longer cycle 

lengths generally result in increased delay and queues to all users, particularly minor movements. 

There may also be a connection between longer cycle lengths and increased incidence of redlight running, although this has not been documented in research. Although longer cycle lengths 

result in fewer change periods per hour and thus fewer opportunities for red-light running, more 

drivers may be tempted to run the red light to avoid the extra delay caused by the longer cycle 

length.(60)

4.8 SIGNING AND PAVEMENT MARKING DESIGN 

Signs and pavement markings are important elements of the design of an intersection. 

Because of the complexity of driver decisions, particularly at large signalized intersections, 

special attention to signing and pavement markings can maximize the safety and efficiency of the 

intersection. At signalized intersections, these traffic control devices serve several key functions, 

including: 

• Advance notice of the intersection. 

• Directional route guidance. 

• Lane use control, including indications of permissive or prohibited turning movements. 

• Regulatory control of channelized right turn movements (e.g., through the use of 

YIELD signs). 

• Delineation and warning of pedestrian crossing locations. 

• Delineation and warning of bicycle lane locations. 

The FHWA’s MUTCD(1) is the primary reference for use in the design and placement of signs 

and pavement markings. Additional resources include State supplements to the MUTCD and 

reference materials such as ITE’s Traffic Control Devices Handbook (TCDH)(61) and Traffic 

Signing Handbook.(62)

Designing effective signing and pavement marking at high-volume signalized intersections in 

particular often requires thinking beyond standard drawings of typical sign and pavement marking 

layouts at intersections. High-volume signalized intersections typically have more lanes than most 

intersections. They may have redirected or restricted turning movements. They often join two or 

more designated routes (e.g., State highways) that require directional guidance to the user. They 

are also frequently in urban areas where other intersections, driveways, and urban land use 
Signalized Intersections: Informational Guide 87

Traffic Design and Illumination

create visibility conflicts. The following questions, adapted from the ITE Traffic Signing 

Handbook(62), represent a basic thought process that is recommended for engineers to follow 

when developing a sign layout at an intersection: 

1. From a given lateral and longitudinal position on the roadway, what information does 

the user need, both in advance and at the intersection? At signalized intersections, is 

information on lane use at the intersection provided? Is advance street name information 

(“XX Street, Next Signal,” etc.) and (if appropriate) route number directional signage provided 

in advance of the intersection? Figure 38 gives an example of a simple advance street name 

sign on approach to an intersection, and figure 39 gives an example of an advance sign that 

provides street names for the next two signalized intersections. 

Figure 38. Example of advance street name sign for upcoming intersection. 
88 Federal Highway Administration 

Figure 39. Example of advance street name sign for two closely spaced intersections. 

2. Are there any on- or off-road conditions that would violate driver expectancy? Lane 

drops, trap lanes, and right-hand exits for left turns are all examples where driver expectancy 

is violated and should be addressed by signing. Figure 40 shows an example of signage 

used to advise motorists of a trap lane. 

Figure 40. Example of signing for a left-hand lane trap. 
Signalized Intersections: Informational Guide 89

Traffic Design and Illumination

3. Is a specific action required by a road user? If the road user needs to be in an appropriate 

lane in advance of an intersection to make a movement at the intersection, signage is needed 

to convey this message to the user. Figure 41 provides an example of an overhead signs 

used to assist drivers in selecting the proper lane on approach to a signalized intersection. 

Figure 41. Example of advance overhead signs indicating lane use for various destinations. 

4. Are signs located so that the road user will be able to see, comprehend, and attend to 

the intended message? Signs must be simple enough to be easily comprehended and 

attended to before the driver receives the next message. This requires adequate sign size, 

sign spacing, and attention to the number of elements on each sign. This may, for example, 

lend itself to the use of overhead signs in advance of large intersections, as well as large 

retroreflectorized or internally illuminated overhead signs (including street name signs) at 

intersections. 

5. For what part of the driver population is the sign being designed? Have the needs of 

older drivers or nonlocal drivers been accommodated? This may require the use of larger 

lettering or sign illumination. 

6. Does the sign “fit in” as part of the overall sign system? Signing at an intersection needs 

to be consistent with the overall sign layout of the connecting road system. For example, the 

consistent use of guide signs is helpful to freeway users in identifying the appropriate exit. 

Similar consistency is needed on arterial streets with signalized intersections. 

Pavement markings also convey important guidance, warning, and regulatory lane-use 

information to users at signalized intersections. In addition to delineating lanes and lane use, 

pavement markings clearly identify pedestrian crossing areas, bike lanes, and other areas where 

driver attention is especially important. Where in-pavement detection is installed for bicycles and 

motorcycles, appropriate markings should be painted to guide these vehicles over the portion of 

the loop that will best detect them. 

Several supplemental pavement markings are particularly useful at large signalized 

intersections. For example, the use of lane line extensions into the intersection can be a helpful 

tool where the intersection is so large that the alignment of through or turning lanes between 
90 Federal Highway Administration 

entering the intersection and exiting the intersection could be confused. This can occur, for 

example, where multiple turn lanes are provided, where the through lane alignments make a 

curve through the intersection, or where the receiving lanes at an intersection are offset laterally 

from the approach lanes. In addition, pavement legends indicating route numbers and/or 

destinations in advance of the intersection (i.e., “horizontal signage”) may be used to supplement 

signing for this purpose, as shown in figure 42. 

Figure 42. Example of pavement legends indicating destination route numbers (“horizontal 

signage”) 

4.9 ILLUMINATION DESIGN 

As noted in American National Standard Practice for Roadway Lighting (RP-8-00), “[t]he 

principal purpose of roadway lighting is to produce quick, accurate, and comfortable visibility at 

night. These qualities of visibility may safeguard, facilitate, and encourage vehicular and 

pedestrian traffic...[T]he proper use of roadway lighting as an operative tool provides economic 

and social benefits to the public including: 

(a) Reduction in night accidents, attendant human misery, and economic loss. 

(b) Aid to police protection and enhanced sense of personal security. 

(c) Facilitation of traffic flow. 

(d) Promotion of business and the use of public facilities during the night hours.”(63, p.1)

Specifically with respect to intersections, the document notes that “[s]everal studies have 

identified that the primary benefits produced by lighting of intersections along major streets is the 

reduction in night pedestrian, bicycle and fixed object accidents.” (section 3.6.2)(63) With respect 

to signalized intersections, roadway lighting can play an important role in enabling the intersection 

to operate at its best efficiency and safety. The highest traffic flows of the day (typically the 

evening peak period) may occur during dusk or night conditions where lighting is critically 

important, particularly in winter for North American cities in northern latitudes. 

The document includes three different criteria for roadway lighting: illuminance, luminance, 

and small target visibility (STV). These are described as follows: 
Signalized Intersections: Informational Guide 91

Traffic Design and Illumination

• Illuminance is the amount of light incident on the pavement surface from the lighting 

source. 

• Luminance is the amount of light reflected from the pavement toward the driver’s eyes. 

The luminance criterion requires more extensive evaluation. Because the reflectivity 

of the pavement surfaces constantly changes over time, it is difficult to accurately 

estimate this criterion. 

• Small target visibility is the level of visibility of an array of targets on the roadway. The 

STV value is determined by the average of three components: the luminance of the 

targets and background, the adaptation level of adjacent surroundings, and the 

disability glare. 

4.9.1 Illuminance 

The two principal measures used in the illuminance method are light level and uniformity 

ratio. Light level represents the intensity of light output on the pavement surface and is reported in 

units of lux (metric) or footcandles (U.S. Customary). Uniformity represents the ratio of either the 

average-to-minimum light level (Eavg/Emin) or the maximum-to-minimum light level (Emax/Emin) on 

the pavement surface. The light level and uniformity requirements are dependent on the roadway 

classification and the level of pedestrian night activity. 

The basic principle behind the lighting of intersections is that the amount of light on the 

intersection should be proportional to the classification of the intersecting streets and equal to the 

sum of the values used for each separate street. For example, if Street A is illuminated at a level 

of x and Street B is illuminated at a level of y, the intersection of the two streets should be 

illuminated at a level of x+y. RP-8-00 also specifies that if an intersecting roadway is illuminated 

above the recommended value, then the intersection illuminance value should be proportionately 

increased. If the intersection streets are not continuously lighted, a partial lighting system can be 

used. RP-8-00 and its annexes should be reviewed for more specific guidance on partial lighting, 

the specific calculation methods for determining illuminance, and guidance on the luminance and 

STV methods.(63)

Table 17 presents the recommended illuminance for the intersections within the scope of this 

document located on continuously illuminated streets. Separate values have been provided for 

portland cement concrete road surfaces (RP-8-00 Road Surface Classification R1) and typical 

asphalt concrete road surfaces (RP-8-00 Road Surface Classification R2/R3). 

Table 18 presents the roadway and pedestrian area classifications used for determining the 

appropriate illuminance levels in table 17. RP-8-00 clarifies that although the definitions given in 

table 18 may be used and defined differently by other documents, zoning bylaws, and agencies, 

the area or roadway used for illumination calculations should best fit the descriptions contained in 

table 18 (section 2.0, p. 3).(63)

4.9.2 Veiling Luminance 

Veiling luminance is produced by stray light from light sources within the field of view. This 

stray light is superimposed in the eye on top of the retinal image of the object of interest, which 

alters the apparent brightness of that object and the background in which it is viewed. This glare, 

known as disability glare, reduces a person’s visual performance and thus must be considered in 

the design of illumination on a roadway or intersection (annex C).(63) Table 17 shows the 

maximum veiling luminance required for good intersection lighting design. 
92 Federal Highway Administration 

Table 17. Recommended illuminance for the intersection of continuously lighted urban streets. 

Average Maintained Illuminance at 

Pavement1

Pedestrian/Area Classification 

Pavement 

Classification2

Roadway 

Classification 

High 

(lux (fc)) 

Medium 

(lux (fc)) 

Low 

(lux (fc)) 

Uniformity Ratio 

(Eavg/Emin)3 

Veiling Luminance 

Ratio 

(Lvmax/Lavg)4 

Major/Major 24.0 (2.4) 18.0 (1.8) 12.0 (1.2) 3.0 0.3 

Major/Collector 20.0 (2.0) 15.0 (1.5) 10.0 (1.0) 3.0 0.3 

Major/Local 18.0 (1.8) 14.0 (1.4) 9.0 (0.9) 3.0 0.3 

Collector/Collector 16.0 (1.6) 12.0 (1.2) 8.0 (0.8) 4.0 0.4 

Collector/Local 14.0 (1.4) 11.0 (1.1) 7.0 (0.7) 4.0 0.4 

R1 

Local/Local 12.0 (1.2) 10.0 (1.0) 6.0 (0.6) 6.0 0.4 

Major/Major 34.0 (3.4) 26.0 (2.6) 18.0 (1.8) 3.0 0.3 

Major/Collector 29.0 (2.9) 22.0 (2.2) 15.0 (1.5) 3.0 0.3 

Major/Local 26.0 (2.6) 20.0 (2.0) 13.0 (1.3) 3.0 0.3 

Collector/Collector 24.0 (2.4) 18.0 (1.8) 12.0 (1.2) 4.0 0.4 

Collector/Local 21.0 (2.1) 16.0 (1.6) 10.0 (1.0) 4.0 0.4 

R2/R3 

Local/Local 18.0 (1.8) 14.0 (1.4) 8.0 (0.8) 6.0 0.4 

Notes: 1

 fc = footcandles 

 2

 R1 is typical for portland cement concrete surface; R2/R3 is typical for asphalt surface. 

 3

 Eavg/Emin = Average illuminance divided by minimum illuminance 

 4

 Lvmax/Lavg = Maximum veiling luminance divided by average luminance. 

Source: Reference 63, table 9 (for R2/R3 values); R1 values adapted from table 2. 
Signalized Intersections: Informational Guide 93

Traffic Design and Illumination

Table 18. RP-8-00 guidance for roadway and pedestrian/area classification for purposes of 

determining intersection illumination levels. 

Roadway 

Classification Description 

Average Daily 

Vehicular Traffic 

Volumes (ADT)1

Major That part of the roadway system that serves as the 

principal network for through-traffic flow. The routes 

connect areas of principal traffic generation and important 

rural roadways leaving the city. Also often known as 

“arterials,” thoroughfares,” or “preferentials.” 

More than 

3,500 

Collector Roadways servicing traffic between major and local 

streets. These are streets used mainly for traffic 

movements within residential, commercial, and industrial 

areas. They do not handle long, through trips. 

1,500 to 3,500 

Local Local streets are used primarily for direct access to 

residential, commercial, industrial, or other abutting 

property. 

100 to 1,500 

 

Pedestrian 

Conflict Area 

Classification Description 

Possible Guidance 

on Pedestrian 

Traffic Volumes2

High Areas with significant numbers of pedestrians expected to 

be on the sidewalks or crossing the streets during 

darkness. Examples are downtown retail areas, near 

theaters, concert halls, stadiums, and transit terminals. 

More than 100 

pedestrians/hour 

Medium Areas where lesser numbers of pedestrians use the 

streets at night. Typical are downtown office areas, blocks 

with libraries, apartments, neighborhood shopping, 

industrial, older city areas, and streets with transit lines. 

11 to 100 

pedestrians/hour 

Low Areas with very low volumes of night pedestrian usage. 

These can occur in any of the cited roadway 

classifications but may be typified by suburban single 

family streets, very low density residential developments, 

and rural or semirural areas. 

10 or fewer 

pedestrians/hour 

Notes: 1

 For purposes of intersection lighting levels only. 

 2

 Pedestrian volumes during the average annual first hour of darkness (typically 18:00-19:00), representing the total 

number of pedestrians walking on both sides of the street plus those crossing the street at non-intersection locations in 

a typical block or 200 m (656 ft) section. RP-8-00 clearly specifies that the pedestrian volume thresholds presented 

here are a local option and should not be construed as a fixed warrant. 

Source: Reference 63, sections 2.1, 2.2, and 3.6 

Signalized Intersections: Informational Guide 95

Part II—Project Process and Analysis Methods

Part II 

Project Process and 

Analysis Methods

Part II describes the key elements of a typical project process (chapter 5) from project initiation to 

implementation and monitoring. Part II also includes a description of safety analysis methods (chapter 

6) and operational analysis methods (chapter 7) that can be used in the evaluation of a signalized 

intersection. The chapters in part II provide the reader with the tools needed to determine deficiencies 

of a signalized intersection and areas for improvement and mitigation. The findings from part II should 

be used to identify applicable treatments in part III. 

Signalized Intersections: Informational Guide 97

Project Process 

CHAPTER 5 

PROJECT PROCESS 

TABLE OF CONTENTS 

5.0 PROJECT PROCESS ..........................................................................................................99

5.1 Project Initiation...........................................................................................................99 

5.2 Identify Stakeholder Interests and Objectives ............................................................99 

 5.2.1 Intersection Users ........................................................................................100 

 5.2.2 Adjacent Property/Business Owners ...........................................................100 

 5.2.3 Facility Managers.........................................................................................100 

 5.2.4 Other Decisionmakers .................................................................................100 

5.3 Data Collection..........................................................................................................101 

 5.3.1 Office Review...............................................................................................101 

 5.3.2 Field Investigation ........................................................................................101 

5.4 Problem Identification................................................................................................102 

 5.4.1 Establish Performance Measures and Criteria ............................................105 

 5.4.2 Summarize Operational and Safety Conditions...........................................107 

 5.4.3 Develop Problem Statement........................................................................107 

5.5 Identify Problem Cause.............................................................................................108 

5.6 Treatment Selection..................................................................................................109 

 5.6.1 Identify Range of Treatments.......................................................................109 

 5.6.2 Evaluate Treatments....................................................................................110 

 5.6.3 Assess Potential To Introduce Undesirable Effects.....................................110 

 5.6.4 Determine Costs and Implementation Issues..............................................110 

5.7 In-Service Assessments ...........................................................................................111 

 5.7.1 Followup Plan...............................................................................................111 

 5.7.2 Monitoring Program .....................................................................................111 

LIST OF TABLES 

Table Page

19 Example stakeholder interests and objectives ...................................................................101 

20 User characteristics ............................................................................................................103 

21 Operational characteristics .................................................................................................103 

22 Safety characteristics..........................................................................................................104 

23 Geometric, traffic signal control, and land use characteristics ...........................................104 

24 Policy and background information.....................................................................................105 

25 Common concerns raised by stakeholders ........................................................................105 

26 Example performance measures and criteria.....................................................................106 

27 Possible causes of intersection problems ..........................................................................109 

 
 
Signalized Intersections: Informational Guide 99

Project Process

5. PROJECT PROCESS 

This chapter describes a standard process for conducting an intersection design/redesign 

project. During the initial stages of a project, stakeholders are identified, the scope of analysis is 

determined, data are collected, and key issues of concern are identified. From this information, a 

problem statement is developed and potential countermeasures or treatments are identified. In 

the alternatives evaluation stage, potential treatments are evaluated for feasibility and 

effectiveness. After a treatment is chosen, the improvement is implemented and monitored over 

time. This chapter describes a general thought process to guide readers to issues to consider and 

questions to ask. 

5.1 PROJECT INITIATION 

An intersection project typically begins with notification to a lead engineer. The engineer 

could be a city, county, or State traffic engineer responding to a concern raised by the public, a 

supervisor, a planning commission, or a city council. In other cases, the lead engineer may be a 

consultant responding to a request for proposal for a particular intersection design project. During 

this process, the lead engineer should gather initial information that will lead to identification of 

problems. Information should be gathered through stakeholder interviews, review of existing data, 

and field visits as described in the following sections. 

Two questions that should be asked at the outset of the process are: 

1. Does the project involve a new or existing intersection? 

2. Does the intersection experience system-wide effects? 

New intersections typically afford greater flexibility for design and the selection of treatments 

than do existing ones. Existing intersections are often constrained by utility placement, presence 

of development surrounding the intersection, and issues related to construction and to 

maintenance of traffic. The effect of a treatment at an existing location must take into account the 

effect on user expectancy. Changes to way-finding, lane geometry, and traffic control may result 

in confusion and, in turn, create a safety deficiency. 

Determining whether an intersection condition is part of a system problem is an important 

consideration when evaluating intersection treatments. For certain cases, a capacity improvement 

to an intersection may provide little benefit if the constraining point on the system is located 

upstream or downstream of the intersection. Likewise, implementing an improvement such as a 

turn movement restriction may solve an operational or safety problem at the subject intersection, 

but may result in the migration of the problem to a new location. These system effects must be 

considered at each step in the treatment evaluation and selection process. 

5.2 IDENTIFY STAKEHOLDER INTERESTS AND OBJECTIVES 

Each project should begin by identifying the affected stakeholders and conducting 

stakeholder interviews to define interests, goals, and objectives. Stakeholders include any person 

or group affected by a project: users of the facility (motorists, pedestrians, bicyclists, etc.); 

adjacent property owners and residents; jurisdictional owners and managers of the facility; and 

decisionmakers who have influence over making improvements to the facility. 

The interest range of stakeholders is widespread: A local business owner may be solely 

concerned with maintaining access for his/her business; a neighborhood group may want 

pedestrian treatments to improve the safety for a pedestrian crossing; and a traffic engineer may 

want to maximize throughput on the mainline facility. A planning commission may recommend yet 

another treatment based on concerns raised from its constituents. 

It is important to highlight the interests of all stakeholders and clearly define their goals and 

objectives early in the process. This includes defining jurisdictional policies and standards 

regarding the safety and operations of the intersection. Stakeholders’ goals and objectives need 
100 Federal Highway Administration 

to be considered carefully and acknowledged at each step of the process, and should be tied to 

performance measures to provide a means for evaluation. 

The following sections identify usual stakeholders and provide direction to readers for 

highlighting the interests, goals, and objectives for each. 

5.2.1 Intersection Users 

Intersection users include motorists, pedestrians, bicyclists, and transit riders (see chapter 2 

for a more complete discussion of user types). These users may be categorized in subgroups 

with similar concerns and issues (e.g., citizens from a neighborhood group, disabled persons, 

truck drivers). 

It is important to understand how the goals and objectives of each user group relate to each 

other, and the tradeoffs that exist between them. For example, lane-widening improvements that 

are implemented to solve an operational deficiency for motorists may reduce the safety and 

quality of service for pedestrians due to the number of conflicts added and the increased crossing 

distance. In some cases, the benefits experienced by one user group may be offset by the 

negative impacts imposed on another. 

5.2.2 Adjacent Property/Business Owners 

The access and circulation needs for adjacent properties and business owners should be 

addressed based on an evaluation of the land use, traffic demand, and access needs of each 

site. Air quality and noise impacts to adjacent properties and businesses are also important 

consideration when evaluating improvement alternatives. 

5.2.3 Facility Managers 

Stakeholders include the owners and managers of the facility such as State departments of 

transportation engineers and city and county planning and public works staff. Facility managers 

typically are expected to meet an adopted standard or policy for the facility. As part of the 

stakeholder identification process, relevant and adopted documents such as State highway plans, 

comprehensive plans, and transportation system plans should be reviewed to identify the 

transportation standards and policies in place that may affect the study intersection. In addition, 

jurisdiction officials should be contacted and interviewed to identify plans for system improvement 

that may affect the characteristics or demand patterns at an intersection. 

5.2.4 Other Decisionmakers 

It is also important to consider other decisionmakers in addition to local jurisdiction officials, 

including technical advisory committee members, steering committee members, planning 

commissioners, city councilors, and other government officials. It is important to gain an 

understanding of the criteria that each of these decisionmakers uses in evaluating 

recommendations and making decisions. Driving forces may include local policy, local politics, 

agencies/organizations represented, and level of ownership and commitment to the project. 

A summary of the key concerns and issues of each stakeholder should be prepared and 

circulated to relevant project team members to ensure that everyone has a clear understanding of 

the constraining factors of a project. Table 19 provides an example of cataloging stakeholder 

interests and objectives. 
Signalized Intersections: Informational Guide 101

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Table 19. Example stakeholder interests and objectives. 

Stakeholder Primary Interest Objectives 

Motorist Mobility, ease of commute Coordinated signal system–limited 

stop-and-go conditions 

Pedestrian Mobility and safety Fewer conflicts, reduced crossing 

distance, direct connections, adequate 

facilities 

Bicyclist Mobility and safety Provision of bike lane, minimized 

conflicts with motor vehicles, extended 

clearance interval 

State Traffic Engineer Mobility on State highway Maximize throughput on mainline 

City Planner Long-term operations Obtain necessary right-of-way and 

funding to construct improvements 

sufficient through a 20-year horizon to 

accommodate all modes 

City Engineer Safety Minimize severity and frequency of 

crashes 

Neighborhood Group Pedestrian/bicycle access Provide bike/pedestrian connections 

linking residential area with shopping 

district 

Business Owner Access Maintain full-access turn movements at 

driveways 

Planning Commissioner Compliance with local 

standards and policies 

Ensure intersection meets operations 

standards and intent of policy for 

safety, accessibility, and 

pedestrian/bicyclist/transit usability 

5.3 DATA COLLECTION 

Data acquisition and field investigation provides an understanding of the physical and 

operational characteristics of the study intersection and identify factors that contribute to its 

deficiencies. All information required for analysis and evaluation should be obtained in this step. 

The amount and type of data required for analysis is dependent upon the analysis method 

selected. Additional site visits may be required after the initial visit to obtain supplementary data. 

A description of the analysis methods available for safety and operational evaluation, along with 

specific data requirements, are described in chapters 6 and 7. The following sections describe the 

data that should be collected and obtained for an office review and field investigation. 

5.3.1 Office Review 

Office reviews include obtaining relevant safety, operations, and design data from available 

resources (e.g., local public works and planning departments, State department of transportation 

offices, and Internet sites). As-built drawings and aerial photography should be obtained for this 

effort. Past studies conducted within the study area should also be obtained. In general, the office 

review should make use of all data that can be obtained without extraordinary expenditures. 

5.3.2 Field Investigation 

Field investigations should be performed to observe safety and operating conditions. 

Everyone involved with evaluating and recommending improvements to an intersection should 

visit the site. Three perspectives should be considered. 
102 Federal Highway Administration 

1. User perspective: visibility, ability to process information, decisionmaking, level of 

service, and conflicts for all user types. 

2. Intersection perspective: operations and safety performance, geometric 

characteristics, movements operating with high delay/overcapacity, safety conflicts, 

signal timing, signing, and pavement markings. 

3. System perspective: impacts of upstream/downstream intersections, influence of 

adjacent driveways, location relative to other facility types. 

The site visit should occur during peak-hour traffic conditions. Additional field visits may be 

appropriate for the following conditions: 

• Off-peak periods. 

• Night. 

• Inclement weather. 

• Special events. 

Observations of events and physical characteristics should be noted. Photographs and video 

should be made for reference and use in presentations and reports. 

During the observation, vehicle queues and travel patterns through the intersection should be 

examined and noted if they interfere with upstream driveways and/or intersections. Likewise, 

arrival patterns, modal distribution, operations, and closely spaced downstream traffic signals 

should be observed to determine if they affect, or are affected by, operations at the subject 

intersection. Special conditions such as nearby pedestrian/bicyclist generators, transit transfer 

points, and populations with special needs should be noted. The type and operating 

characteristics of nearby commercial establishments and institutions may have an important 

effect on the intersection and should also be noted. The intersection’s relationship to other 

important system components (e.g., freeways, principal arterials, and even sensitive 

neighborhoods) must be recognized. To assess the system-wide impacts of a potential 

improvement, it is necessary to understand how the study intersection interacts with its 

surrounding facilities. 

The following tables provide a description of the data items that should be collected as part of 

the office review and field investigation stages. Table 20 identifies user characteristics, table 21 

identifies operational characteristics, and table 22 identifies safety characteristics. Table 23 

identifies physical characteristics such as geometry, traffic signal control, and land use, and table 

24 lists key policy and background information that should be obtained. 

5.4 PROBLEM IDENTIFICATION 

Problems at an intersection are identified through a synthesis of stakeholder interviews, office 

reviews, field investigations, and preliminary operational and safety analysis. To determine 

whether a problem exists, this information needs to be evaluated against defined goals or 

standards. A problem statement can be defined after a review of the established operational and 

safety criteria against the known characteristics of an intersection. In some cases, additional data 

may need to be collected to confirm that a problem exists. 

The steps for identifying problems as described in this chapter are: (1) establish performance 

measures and criteria; (2) summarize operational and safety conditions; and (3) develop a 

problem statement. 
Signalized Intersections: Informational Guide 103

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Table 20. User characteristics. 

Data Item Description Determines 

Motor vehicle 

traffic volumes 

Includes ADT volumes for a roadway 

segment and peak-hour turning-movement 

volumes for existing and future year 

conditions 

Travel patterns, high-demand (critical) 

movements, appropriate number of lanes 

for a roadway approach 

Origindestination 

information 

Detailed description of vehicle movements 

classified by start and end points 

Expected lane utilization, whether a 

weaving condition is expected, impact a 

turn movement restriction may have on 

surrounding area 

Heavy vehicle 

data 

Identification of number and type of trucks, 

percentage of trucks by movement 

Appropriate design vehicle for geometric 

evaluation, whether special consideration 

is warranted to account for heavy vehicle 

movements 

Pedestrian and 

bicyclist 

demand 

Volume and/or demand and location of 

pedestrian and bicyclist movements as well 

as location of nearby generators and 

attractors 

The level of activity that needs to be 

accounted for in the design and signal 

timing of an intersection 

Table 21. Operational characteristics. 

Data Item Description Determines 

Capacity 

analysis 

Evaluation of traffic operations for either a 

planning level, macroscopic, or microscopic 

level analysis (see chapter 7 for details on 

performing an operational analysis) 

Critical movements, volume-to-capacity 

ratio, average intersection delay, level of 

service, vehicle queues, pedestrian 

capacity and level of service, bicycle 

capacity and level of service 

Delay study Measure time each vehicle (car, truck, 

transit, or bicycle) enters and discharges 

from queue; measure time each pedestrian 

arrives and departs; measure available 

gaps in the traffic stream for pedestrians to 

cross 

Average delay per vehicle by approach, 

average pedestrian delay, average bicycle 

delay, average transit delay 

Saturation flow 

study 

Measure time headway for vehicles 

discharging from a stopped position 

Average saturation headway and loss time 

per approach 

Queue 

observations 

Identify location of maximum back of queue 

and number of vehicles in queue 

Required storage lengths, whether queues 

interfere with upstream driveways or 

intersections 

Vehicle speeds Identification of 85th percentile speeds and 

posted speeds for all approaches 

Whether a speeding condition exists, signal 

design parameters 
104 Federal Highway Administration 

Table 22. Safety characteristics. 

Data Item Description Determines 

Crash history Includes summary of reported crashes for 

past 3 to 5 years 

Whether excessive crashes are occurring 

when compared to crash data for similar 

facilities 

Conflict study Identification of conflicts and near-collisions Potential for collisions 

Collision 

diagram 

Diagram illustrating location, type, and 

severity of reported collisions 

Whether a pattern in crashes exists 

Interview with 

local police and 

jurisdiction 

officials 

Identification of anecdotal evidence 

regarding crash history of intersection 

History and background of an intersection’s 

safety condition 

Table 23. Geometric, traffic signal control, and land use characteristics. 

Data Item Description Determines 

Lane 

configuration 

Number of lanes on approach, lane use 

type (shared vs. exclusive), presence of 

add/drop lanes, free-flow movements, 

storage lengths for turn bays, and distance 

to nearby driveways and intersections 

Presence of weaving sections, adjacent 

driveways/ intersections within influence of 

intersection, presence of short lanes 

Pedestrian 

facilities 

Location and configuration of crosswalks, 

ramps, accessible treatments, pedestrian 

signal equipment, and network connectivity 

Pedestrian crossing distance, compliance 

with ADA requirements, traffic signal needs 

Bicycle facilities Location and configuration of bicycle lanes, 

detection equipment, and network 

connectivity 

Bicycle facility needs, traffic signal needs 

Roadway/ 

intersection 

geometric data 

Cross slopes, channelization features, 

posted and prevailing speeds, lane widths, 

right-of-way locations, median type, 

horizontal and vertical curve data, corner 

radii, presence of bicycle/pedestrian/transit 

facilities, sight distance, and presence of 

offsets/skews 

Whether physical constraints exist; right-ofway available to accommodate 

improvements; presence of horizontal or 

vertical curves that may affect sight 

distance and speeds 

Illumination 

drawings 

Location, type, and wattage of street 

lighting 

Whether lighting is adequate 

Roadside 

features 

Location and type of roadside elements 

including drainage ditches, trees, shrubs, 

buildings, signs, street lights, signal poles, 

etc. 

Whether roadside elements may be 

leading to fixed-object crashes, sight 

distance deficiencies, or driver confusion 

Traffic signal 

phasing and 

timing plans 

Type of signal control (actuated or pretimed), coordinated/noncoordinated 

operations, cycle length, left-turn phasing 

type, phase order, and timing parameters 

(loss time, clearance intervals, min/max 

greens, unit extension, etc.) 

Whether intersection is located in a 

coordinated system; whether left-turn 

phasing treatments such as permissive or 

protected-permissive may be a cause of 

collisions 

Adjacent land 

uses 

Size and type of use, location and type of 

driveways, circulation patterns, design 

vehicles 

Access needs for local land uses 
Signalized Intersections: Informational Guide 105

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Table 24. Policy and background information. 

Data Item Description Determines 

Planned developments 

and transportation 

improvements in the 

area 

Location, site, type, and completion date of 

planned and approved developments; 

description of improvement project, limits of 

project, and scheduled construction dates 

Additional traffic volumes that may 

affect facility; impacts to travel 

patterns that can be expected from 

an improvement project 

Functional 

classification of 

roadways 

Description of facility type for intersecting 

roadways 

System-wide function of 

intersecting roadways 

Design standards Standards for lane widths, medians, curb 

radii, sidewalks, bike lanes, curb ramps, 

signal timing, etc. 

Requirements for intersection 

design; may indicate that design 

modifications are needed 

Applicable plans and 

studies 

All applicable access management plans, 

corridor studies, transportation system plans, 

traffic impact studies, bicycle and pedestrian 

plans, ADA transition plan, etc. 

Existing and projected future 

safety/operational characteristics of 

intersection 

5.4.1 Establish Performance Measures and Criteria 

The selection of performance measures should be made on a case-by-case basis; the 

measures should address concerns raised by stakeholders and issues identified during the office 

review and field investigation. Table 25 lists common concerns of motorists, pedestrians, transit 

riders, bicyclists, and facility managers. 

Table 25. Common concerns raised by stakeholders. 

Motorists Pedestrians 

Transit 

Riders/Operators Bicyclists Facility Managers 

• Takes more 

than one signal 

cycle to get 

through 

intersection 

• High delays 

• Queue spillback 

• Too many stops 

• Inefficient signal 

timing 

• Too many 

crashes 

• High severity of 

crashes 

• Poor sight 

distance 

• Vehicle speeds 

too high 

• Confusing 

signing 

• Inadequate 

facilities 

• Wait time too 

long 

• Crossing 

distance too far 

• Vehicle speeds 

too fast 

• Ramps and/or 

pushbuttons 

poorly located 

• Too many 

conflicts 

• Inability to 

identify when to 

begin crossing 

• Bus stop 

inaccessible 

• Bus stop impedes 

vehicle movement 

• Bus stop poorly 

located for 

pedestrians to use 

• Difficult for bus to 

merge into traffic 

stream 

• Facilities not 

adequate 

• Clearance 

interval too 

short 

• Lane striping 

ineffective 

• Unsafe/too 

many conflicts 

with vehicles 

• Local/Statewide 

policy not met 

• Not in 

compliance 

with 

comprehensive 

plan, 

transportation 

system plan, 

corridor plan, 

etc. 

• Construction 

impacts and 

maintenance of 

traffic during 

construction 

• Fiscal, land 

use, and rightof-way 

constraints 

Ideally, performance measures are quantitative and can be measured for a future-year 

condition to evaluate the long-term effects of potential treatments. Certain cases, however, may 

require selection of qualitative performance measures, particularly when evaluating 

characteristics such as driver expectations and pedestrian/bicyclist comfort. 

Once performance measures are defined that adequately address the scope of the issues, 

desired performance levels should be established for each measure. This process should take 
106 Federal Highway Administration 

into account local policy and standards, driver expectations, operational and safety levels at 

similar facilities, and research findings. All decisionmakers on a project should agree on the 

performance levels established. 

Desired levels of performance should be defined for all study periods and years. For 

operational evaluations, the typical weekday peak hour(s) should be included in the evaluation. 

Other conditions may be included as deemed necessary. Operational performance levels should 

be established for year of opening and long-term (20 to 25 years) conditions. For safety 

evaluations, performance levels are generally established on an annual basis and evaluated over 

a period of 3 to 5 years. 

The desired performance level may vary based on time of day and year. For an operational 

issue, a degraded level of performance may be tolerated for certain periods of the day while more 

stringent standards are applied for the remaining periods. Similarly, a worsened operating 

condition may be tolerated better under long-term conditions than near-term conditions. 

In some cases, particularly for multimodal aspects, it may be difficult to establish quantifiable 

performance levels. Performance levels for these cases may be based on a design element (e.g., 

sidewalk width, buffer, distance to transit stop). Efforts should be made to establish quantifiable 

levels to effectively assess the impact of various treatments. 

A list of example performance measures and criteria is provided in table 26. Numerical values 

in the performance level column were developed for a hypothetical example. 

Table 26. Example performance measures and criteria. 

Performance Measure Concerns Addressed 

Desired Performance Level 

(What is acceptable?) 

Critical Movement 

Volume-to-Capacity 

Ratio 

Motorist operations 0.90 (peak 15 minute period for 5-year 

condition); 1.00 (peak hourly period for 20-year 

condition) 

Average Vehicle Delay Motorist operations 55 seconds or less per vehicle (to achieve level 

of service (LOS) D or better) 

Vehicle Queues Motorist operations and safety Eliminate queue spillback 

Total Intersection 

Crashes 

Motorist safety Reduce existing crashes by 20% 

Crash Severity Motorist safety Reduce fatal and injury crashes by 20% 

Approach Speeds Motorist, bicyclist, and pedestrian 

safety 

Reduce 85th percentile prevailing speed by 16 

km/h (10 mph) 

Pedestrian Delay Pedestrian operations 40 seconds or less per pedestrian (to achieve 

LOS D or better) 

Pedestrian Accessibility Pedestrian usability Compliance with ADA standards 

Total Bicycle Conflicts Bicycle safety Reduce number of bicycle-motor vehicle 

conflict points by 25% 

Transit Delay Transit operations Reduce transit vehicle delay by 10% 

Way-Finding Motorist, bicyclist, and pedestrian 

operations and safety 

Reduce intersection clutter, increase 

conspicuity of key road signs and signal heads, 

provide accessible routes for pedestrians 
Signalized Intersections: Informational Guide 107

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As shown in table 26, certain performance measures are readily quantifiable (critical 

movement volume-to-capacity ratio, average vehicle delay, queues), while others have a higher 

level of uncertainty for prediction (total intersection crashes, approach speeds) or require a 

qualitative assessment (multimodal impacts and way-finding). While some measures are not 

easily quantifiable, it is important that they be recognized and considered in the evaluation and 

selection of intersection treatments. 

5.4.2 Summarize Operational and Safety Conditions 

Problems at an intersection usually are related to a safety or operational deficiency. Defining 

a problem generally requires an assessment of performance from the perspective of all users of 

the intersection, regardless of mode of travel. At this stage in the project, a primary problem may 

have already been defined and be the cause for initiating the project. In these instances, the 

operations and safety conditions should be reviewed to confirm the problem exists and determine 

whether other problems exist or likely will exist in the future. 

The level of effort required for determining operational and safety conditions at this stage 

varies from intersection to intersection. The information gathered through the stakeholder 

interviews and office review/field investigation may be sufficient in some cases, while other 

situations may require more extensive operational and safety evaluations. 

Common questions that should be answered in evaluating intersection safety and operations 

are: 

• Is sight distance adequate? 

• Are red light running violations occurring? 

• Does the intersection have enough capacity under existing and future conditions? 

• Are pedestrian and bicycle facilities available, adequate, and supportive of existing or 

potential use? 

• Is adequate queue storage available to accommodate all turn movements? 

• Do signs and pavement markings clearly and accurately communicate the intended 

message? 

• Do upstream or downstream intersections interfere with operations at the subject 

intersection? 

• Are nearby driveways interfering with intersection operations? 

• Is there a pattern of collision type or location? 

• Are crashes occurring under inclement weather or nighttime conditions? 

A complete description of analysis procedures that can be applied to estimate safety and 

operations conditions for signalized intersections and answer the above questions is provided in 

chapters 6 and 7. 

5.4.3 Develop Problem Statement 

After comparing the operational and safety conditions of an intersection against the 

established performance measures, problems and deficiencies should begin to emerge. 

Deficiencies should be expressed in terms of the user group (motorist, pedestrian, bicyclist, etc.) 

and reference the specific movement that initiates the problem as well as the time and duration 

during which the problem occurs. For example, a safety condition could be expressed as: an 

excessive number of rear-end collisions involve vehicles traveling on the northbound approach 

during wet-weather conditions. An operational problem could be stated as: an eastbound left-turn 

movement operates over capacity during the weekday p.m. and Saturday peak periods. 
108 Federal Highway Administration 

Problems should be stated in terms of the performance measures defined earlier in this 

chapter. Example problem statements follow. 

• Excessive conflict for one or more movements. 

• Excessive number of collisions or type of collision. 

• Excessive number of injury/fatal collisions. 

• Inadequate capacity for one or more movements. 

• Excessive vehicle delay for one or more movements. 

• Excessive vehicle queuing for one or more movements. 

• Inaccessible pedestrian facilities. 

• Excessive pedestrian crossing delay. 

• Excessive transit delay. 

• Excessive number of bicycle-motor vehicle conflicts. 

5.5 IDENTIFY PROBLEM CAUSE 

Once the problems at an intersection have been identified, initiative should be taken to 

determine the cause of each. The previous section explained that the effect of a problem is often 

a deficient safety or operational performance measure. The cause of the problem, in many cases, 

is attributable to a design element. As an example, a safety problem with an effect of a high 

occurrence of sideswipe collisions on an approach with dual left-turn lanes may be caused by 

inadequate lane width and a lack of delineation for the left-turn lanes. 

Aerial photography and as-built drawings should be used to assist in the determination of 

problem cause. Results from the office review, field investigation, and preliminary analysis should 

also be used to determine possible causes. Detailed review of all elements of a signalized 

intersection, as described in previous chapters, are required to determine the cause of a problem. 

Table 27 provides lists possible causes related to common operational and safety 

deficiencies. This list should be applied to specific movements and approaches where an 

operational or safety deficiency may be occurring. 
Signalized Intersections: Informational Guide 109

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Table 27. Possible causes of intersection problems. 

Potential Cause Delays Queues Collisions 

Injury/Fatality 

Collisions 

Effects from nearby intersections √ √ √ √

Insufficient number of through lanes √ √ √ √

Insufficient design or lack of turn lanes √ √ √ √

Insufficient pedestrian crosswalk, ramps, landing 

area, and accessible facilities 

√ √ √ √

Insufficient bicycle detection √ − √ √

Speed differential − − √ √

Poor pavement conditions − − √ √

Turning movements from adjacent driveways (poor 

access management) 

√ √ √ √

Poor sight distance − − √ √

Poor signal visibility − − √ √

Inadequate signal phasing and/or timing (including 

vehicle and pedestrian clearance intervals) 

√ √ √ √

Poor dilemma zone protection − − √ √

Inadequate roadway lighting − − √ √

Inadequate roadway signing − − √ √

Inadequate pavement marking − − √ √

Bicycle conflicts √ − √ √

Pedestrian conflicts √ − √ √

Bus conflicts √ √ √ √

5.6 TREATMENT SELECTION 

Treatments should be selected that address the specific areas for safety and operational 

improvement identified in the preceding stages of the intersection evaluation process. The 

primary objectives of the treatment selection stage are to (1) identify the range of treatments; (2) 

evaluate treatments; (3) assess potential for undesirable effects; and (4) determine costs and 

implementation issues. 

5.6.1 Identify Range of Treatments 

What treatments are likely to influence the areas for safety and operations improvement? The 

range of treatments provided in this guide are categorized into the following chapters: 

• System-wide treatments (chapter 8). 

• Intersection-wide treatments (chapter 9). 

• Alternative intersection treatments (chapter 10). 

• Approach treatments (chapter 11). 

• Individual movement treatments (chapter 12). 

A list of identified treatments is provided in chapter 1. A complete discussion of the safety, 

operational, and design characteristics of each treatment is provided in part III of this guide, which 
110 Federal Highway Administration 

also discusses the applicability of each treatment and identifies the problem and cause the 

treatment addresses. The level of detail provided for each treatment varies based on the amount 

of research and field evaluation available. It should be noted that treatments listed in this guide by 

no means represent the full extent of treatment possibilities. 

5.6.2 Evaluate Treatments 

Once possible treatments have been listed that could address the identified problems, it is 

necessary to evaluate the possible countermeasures to determine the potential for improvement 

to safety and operations. Treatment descriptions in part III describe the impact each treatment 

has on safety and operations. Where available, crash modification factors are provided to 

estimate the possible reduction in crashes. Operational benefits can be determined based on 

performing an analysis described in chapter 7. 

5.6.3 Assess Potential To Introduce Undesirable Effects 

In addition to considering the potential safety and operational improvements that 

countermeasures can offer, consideration needs to be given to the possibility that 

countermeasures can have negative effects. Efforts should be made to assess the likelihood of 

introducing undesirable safety or operational consequences through the implementation of 

recommended countermeasures. These undesirable effects include the potential for a treatment 

to result in: 

• Out-of-direction travel. 

• Increased speed. 

• Cut-through traffic. 

• Illegal maneuvers. 

• Driver confusion. 

• False expectations. 

• Adverse impacts to pedestrians, cyclists, and transit users. 

• Migration of a safety or operational condition to another location. 

5.6.4 Determine Costs and Implementation Issues 

Costs are usually assessed in three categories: capital costs, operating costs, and 

maintenance costs. Other issues that should be considered include right-of-way needs, ADA 

compliance, environmental impacts, constructability, and maintenance of traffic. 

• Capital costs are normally associated with initial construction and implementation. The 

installation of traffic signals, for example, involves design, materials, construction, and 

installation costs normally paid for out of a capital program fund. This is normally a 

one-time cost. Where the capital investment is projected to occur some time in the 

future (e.g., grade separation 10 years from now), these costs must be discounted 

back to present value to enable a fair comparison with other alternatives. 

• Operating costs are usually associated with consumables. In the case of traffic 

signals, the principle operating expense is electrical power for signal operation and 

illumination. 

• Maintenance costs are periodic, recurring costs of keeping an initial investment 

productive. For traffic signals this may include the time and materials associated with 

monitoring, periodic retiming, replacing lamps, repairing malfunctions in timing and 

operation, and repairing and replacing damaged equipment. 
Signalized Intersections: Informational Guide 111

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• The amount of right-of-way required and the ability of the local agency to acquire 

needed property may influence the decision to implement a treatment. 

• Treatments must also be evaluated to determine their potential impact on drainage, 

wetlands, historic landmarks, and archaeological features. 

• The construction of a treatment may have a significant impact on the existing flow of 

vehicular and pedestrian traffic. Constructability issues and maintenance of traffic for 

each mode should be considered in the treatment evaluation stage. 

The final decision to implement treatments should incorporate a wide range of parameters 

that decisionmakers deem appropriate. While operational benefits, safety benefits, and cost are 

key criteria, they are not the only elements that must be considered. Other criteria, such as 

coordination with other projects, special funding, and ADA transition plan requirements, may 

dictate the implementation and timing of a project. 

5.7 IN-SERVICE ASSESSMENTS 

5.7.1 Followup Plan 

Identifying and documenting the physical and operational hazards determined during the 

safety assessment should be coupled with a followup plan. The plan should identify what 

measures will be taken by whom and when, and it should effectively communicate these 

decisions to each of the stakeholder groups identified above. 

The objective of a followup plan is to ensure that the: 

• Department, jurisdiction and/or agency responsible for implementing the proposed 

countermeasures is properly notified of the action required. 

• Period to implement these countermeasures is properly conveyed, including urgency. 

• Remedial measures, when completed, are done in accord with best practices, have 

addressed the hazard, and have not created unforeseen negative impacts on traffic 

operations or safety at the location. 

Where the action of others is required to achieve the implementation of a recommendation, 

an appropriate followup system should be implemented. The system should endeavor to do more 

than simply monitor the status of other activities. If recommendations involve the need for design, 

those involved in the intersection evaluation process can use the followup process to comment on 

design and installation details before the remedial measures and countermeasures are ultimately 

installed. Staff familiar with the original intent of these measures should also ensure that the 

proposed measure was installed as directed. 

5.7.2 Monitoring Program 

A monitoring program should be developed to evaluate the impacts of countermeasures that 

are selected and implemented. The scope of the monitoring program will be a function of the 

nature of the countermeasures and their likely effects on operations and safety at and adjacent to 

the study location. Ideally, data would be collected prior to construction of a treatment to provide 

a benchmark for future comparisons. The objectives of the monitoring program are to: 

• Focus on the dominant collision types to determine whether the recommended 

countermeasure has improved the performance at the specific location by causing a 

decline in the dominant collision types. 

• Focus on the dominant operational deficiency to determine whether the recommended 

countermeasure has improved the performance at the specific location by reducing 

the delay and queuing experienced by motorists. 

• Identify effects on all users. 
112 Federal Highway Administration 

• Ensure that the recommended treatment does not adversely affect safety or 

operations on the road network. 

• Improve techniques and practices for identifying existing or potential operational 

concerns. 

• Provide data that can be used in establishing quantitative safety measures, such as 

crash modification factors, for the road authority. 

• Justify improvements to the road authority’s transportation-related standards, policies, 

and procedures that are applied in all areas from transportation planning to roadway 

and right-of-way maintenance. 

The monitoring program should have a clearly understood monitoring frequency, duration, 

and objectives, as appropriate for the measure installed. The need to advise stakeholders of the 

monitoring program should be considered, but may not always be necessary. However, should 

the monitoring program result in a modification or removal of the originally proposed 

countermeasures, further notification to the stakeholders is required. 

A key goal of the program is to be able to continually improve the road system, constantly 

seeking to reduce the number of collisions that occur on roads within the jurisdiction and improve 

the operational efficiency. 
Signalized Intersections: Informational Guide 113

Safety Analysis Methods 

CHAPTER 6 

SAFETY ANALYSIS METHODS 

TABLE OF CONTENTS 

6.0 SAFETY ANALYSIS METHODS ........................................................................................115 

6.1 Balancing Safety and Mobility...................................................................................115 

6.2 Selection of an Intersection.......................................................................................116 

 6.2.1 Collision Frequency .....................................................................................119 

 6.2.2 Collision Rate...............................................................................................119 

 6.2.3 Combined Collision Frequency and Rate Method .......................................120 

 6.2.4 Collision Severity Method ............................................................................120 

 6.2.5 Critical Collision Rate...................................................................................121 

 6.2.6 Risk Analysis Methods.................................................................................121 

 6.2.7 Safety Performance Functions.....................................................................122 

 6.2.8 Empirical Bayes Method ..............................................................................122 

 6.2.9 Conclusions..................................................................................................123 

6.3 Identification of Potential Problems...........................................................................125 

 6.3.1 Safety Diagnosis ..........................................................................................125 

 6.3.2 Assemble Collision Data..............................................................................126 

 6.3.3 Analyze/Diagnose Collision Data.................................................................128 

 6.3.4 Determine Overrepresentation.....................................................................129 

 6.3.5 Conduct Site Visit(s) ....................................................................................132 

 6.3.6 Deciding on Further Analysis .......................................................................134 

 6.3.7 Conducting Further Studies .........................................................................134 

 6.3.8 Defining the Problem Statement..................................................................135 

6.4 Identification of Possible Treatments........................................................................136 

 6.4.1 List Possible Treatments..............................................................................136 

 6.4.2 Screen Treatments ......................................................................................138 

 6.4.3 Selecting a Collision Modification Factor or Study Finding..........................139 

 6.4.4 Quantify Safety Benefit ................................................................................140 

 6.4.5 Selected Treatment(s) .................................................................................142 

6.5 Improvement Plan Development...............................................................................142 

LIST OF FIGURES 

Figure Page

43 Exclusion of property-damage-only collisions (such as this one from an analysis) may 

mask valuable information...............................................................................................117 

44 The potential for error in coding the location of a collision should be understood .............118 

45 Selecting a candidate intersection using a combined collision frequency/collision rate 

method, where each diamond represents an intersection ..............................................120 

46 Example of SPF curve ........................................................................................................122 

47 Identification of potential problems .....................................................................................126

48 The original police collision report may contain valuable information regarding collisions 

that have occurred at the intersection .............................................................................127 

49 Possible taxonomy for collision type classification .............................................................131 

50 Conducting a site visit.........................................................................................................133 

51 Examples of problem statements .......................................................................................135 

52 Identification of possible treatments .................................................................................. 136 

 
114 Federal Highway Administration 

LIST OF TABLES 

Table Page

28 Suggested weighting for collision severity method.............................................................121 

29 Common methods of assessing safety at a location ..........................................................124 

30 Chi-square test values and corresponding confidence levels ............................................129 

31 Collision types commonly identified, possible causes, and associated treatments ...........138 

32 Example calculation of safety benefit of adding a right-turn lane.......................................141 
Signalized Intersections: Informational Guide 115

Safety Analysis Methods 

6. SAFETY ANALYSIS METHODS 

Decisions made at each step in the roadway life cycle are no longer dominated solely by 

mobility considerations; they must now be made in a context-sensitive manner and must address 

accessibility. At the planning stage, the need for and purpose of the project are examined. 

Safety, mobility, cost, and the preservation of resources must all be carefully considered in the 

design, operation, management, and rehabilitation phases of a roadway project. Quantifying the 

impacts of tradeoffs made at each step in the process is an essential element of the contextsensitive, flexible design process. 

The explicit consideration of safety and the development of quantifiable safety information 

have greatly enhanced the flexible design process. The availability of quantifiable safety tools 

has helped elevate the role of safety in the design decision process, such that it may be 

considered on a par with competing demands such as mobility, sustainability, aesthetics, 

environmental impact, and cost. 

Efforts to eliminate unnecessary cost while preserving needed functionality in the delivery of 

road infrastructure have led to the application of value analysis techniques to road designs. A 

key aspect in assessing the true societal value of a road infrastructure investment, over its entire 

useful life, is its safety performance. Safety performance has begun to take its place alongside 

operational performance (level of service), environmental, and financial performance. 

An increased focus on the societal costs of road trauma has drawn attention to the proportion 

of injuries and fatalities attributable to designs in-service that, while perhaps conforming to 

prevailing minimum standards, are less than optimally safe. This recognition has led, in turn, to 

the concepts of design domain, road safety audit, and an explicit consideration of road safety at 

each step in the roadway life cycle⎯in other words, in planning, functional design, detail design, 

construction, operations, management, maintenance, and rehabilitation. Further, it has 

sharpened the focus of applied research and has highlighted the need for advances in the road 

safety body of knowledge to be considered in setting road transportation policy, and in 

maintaining the currency of standards. 

A key outcome of this increasingly holistic view of road safety is the growing recognition that 

the safety implications of each step in the roadway life cycle are inextricably linked to those that 

preceded it and those that follow. Decisions taken at one stage in the process are constrained by 

those made previously, and those taken at subsequent stages are likely to pose constraints 

and/or have substantive impacts in the future. 

6.1 BALANCING SAFETY AND MOBILITY 

Some countermeasures to improve safety at a signalized intersection do so at the expense of 

mobility. In certain cases, the operational disbenefits may be too great. The traffic engineer needs 

to understand the tradeoff between safety and mobility. 

Furthermore, mobility means more than just the movement of motor vehicles. It includes 

providing mobility for bicyclists, transit, and pedestrians of all abilities. Some mobility measures 

fall outside the range of tradeoffs. For example, ADA improvements required by law are not 

subject to traditional constraints of volume of use, cost, and warranting criteria. However, these 

improvements should be folded into the considerations in the evaluation and selection of 

improvements. 

Access management is another example of the tradeoff between safety and mobility. Many 

intersections in commercial areas allow access via driveways within the functional area of the 

intersection, leading to unnecessary conflict. Closure or relocation of these driveways, the 

addition of medians, and the prohibition of certain turns can all improve safety at the expense of 

overall mobility. In older intersections, residential or commercial driveway access often remains 

within the intersection, once of little concern in the past, but now a major source of conflict due to 

the amount of traffic passing through. 
116 Federal Highway Administration 

Consideration of the competing goals of safety and mobility are needed for operations and 

safety of a signalized intersection. A typical problem traffic engineers face is the need to 

accommodate turning vehicles while recognizing when a particular movement may be too 

dangerous to allow or may have a significant impact on overall intersection operations. Using 

multiphase signal operation instead of one with only permissive left turns aids drivers in safely 

making left turns at the expense of lengthening the overall signal phase. Right turns may be 

allowed during the red phase at the expense of increasing pedestrian and bicycle collisions. 

Some means of providing for turning traffic may do so without sacrificing mobility. Exclusive 

turn lanes, offset lanes, and channelization remove turning traffic from through lanes. Other 

solutions for accommodating left-turning vehicles may be signal coordination through the 

provision of gaps in oncoming traffic. At some intersections, the safety record, the operations, or 

the accessibility of the intersection to pedestrians and bicyclists may be so poor that an 

intersection redesign may be considered. This may mean realigning an approach, closing a leg, 

reducing curb radii or lane widths, using an innovative intersection design that allows for left turns 

at another location, or total grade separation. 

The following sections will detail the four-part process for a safety evaluation of a signalized 

intersection. 

• Selection of an intersection: The intersection is chosen using a selection tool. 

• Identification of potential problems: Potential problems at the intersection are 

diagnosed using a detailed collision analysis, a site visit, and, if necessary, additional 

field studies. The end product is a set of problem statements that clearly shows 

cause and effect. 

• Identification of possible treatments: Potential treatments are selected either 

through using part III of this guide as a reference or through other sources. 

Treatment are evaluated using either a quantitative or qualitative method of 

assessment. 

• Improvement plan development: A plan is developed identifying the treatments, a 

schedule detailing their implementation, and the final plan for making the 

improvements. 

6.2 SELECTION OF AN INTERSECTION 

In selecting an intersection for a detailed safety analysis, the key questions are: 

• What is the safety performance of the location in comparison with other similar 

locations? 

• Is the safety performance at the location acceptable or not acceptable? 

Based on what is observed at the intersection in terms of its overall safety experience, the 

traffic engineer can make a decision to proceed with a more detailed causal evaluation of the 

safety performance, as detailed later. If it appears that safety concerns are present, operational 

and design problems will likely also exist, given the relationships among poor level of service, 

design deficiencies, and a poor safety record. This section will discuss various statistical 

techniques for determining the relative safety of an individual location as compared to other 

locations and highlight the merits of each. 

The collision history of a signalized intersection is the key indicator of its safety performance, 

and is the focus of the remainder of this section. Statistical techniques for evaluating the collision 

performance vary from the most basic to the complex. They may compare the safety performance 

of a single signalized intersection to another group of similar intersections, or serve as a 

screening tool for sifting through a large group of sites and determining which site has the most 

promise for improvement. 
Signalized Intersections: Informational Guide 117

Safety Analysis Methods 

Many jurisdictions carrying out a review of safety at a signalized intersection will usually have 

a collision database which provides information on the location, time, severity, and other 

circumstances surrounding each collision reported by police or the parties involved. Collision data 

in this form can provide the traffic engineer with a quick assessment of safety at a location. 

However, the traffic engineer should keep the following in mind in the analysis of safety using 

collision data. 

First, the engineer needs to be aware of what constitutes a collision in the available data. 

Collisions can be classified as reportable or nonreportable. Nonreportable collisions always 

involve no injury and usually involve vehicle damage below a certain threshold. Collisions may 

also be considered nonreportable if they take place on private property, as in a shopping mall 

parking lot or on a driveway. In other instances, they may involve a vehicle striking another 

parked vehicle and leaving the scene of the accident. The traffic engineer needs to be aware that 

nonreportable collisions may not show up in the collision database. If they are not recorded, their 

absence may possibly mask an underlying safety concern (figure 43). 

The definition of a reportable collision varies from jurisdiction to jurisdiction. Usually, all 

collisions involving personal injury and those with damage exceeding a selected threshold may 

be classified as reportable. Occasionally the threshold dollar value used to classify propertydamage-only collisions changes, and this may be a problem if the review period crosses through 

such a change and if property-damage-only collisions are being included in an analysis. This is 

one reason some jurisdictions will only consider injury and fatal collisions in their safety 

assessments. However, by doing so, they will have excluded a majority of collisions that actually 

occurred at a site, masking valuable information that may be useful at the diagnosis stage. 

Photograph Credit: Synectics Transportation Consultants, Inc. 

Figure 43. Exclusion of property-damage-only collisions (such as this one from an analysis) may 

mask valuable information. 

Second, in some instances, a collision may be self-reported. In some jurisdictions, when the 

collision is property damage only, the police will not investigate, and the parties involved are 

required to report the collision on their own. Because information is self-reported and no 

information is collected on-scene by police, collisions may contain inaccurate or erroneous 

information. Because of the increased potential for low-quality information, detailed analysis 

involving self-reported collision information needs to be treated with caution. 

Last, users of collision data should be aware of how the location of a collision is recorded. 

Adjacent intersections can be a convenient reference point for coding collisions. It is not 

uncommon to code a collision as occurring at an intersection when it actually occurred at a 

location nearby, such as an adjacent parking lot, a driveway, or immediately upstream or 
118 Federal Highway Administration 

downstream of the intersection (figure 44). The potential for error in coding the location of a 

collision should be understood. The traffic engineer should be aware of the procedures for 

coding locations and be satisfied that sufficient error checking of data has been done. 

Photograph Credit: Synectics Transportation Consultants, Inc. 

Figure 44. The potential for error in coding the location of a collision should be understood. 

Once data are available, the most common method of assessing safety at a location is 

through comparing its collision history to other similar sites. If the traffic engineer is comparing the 

safety performance of a location to another set of locations, these need to be carefully thought 

through. At the very least, the other locations should also be signalized and have the same 

number of approaches as the site being examined; sites with different traffic control devices and 

layouts can be expected to have differing levels of safety. Surrounding land use will also have a 

significant effect on collision frequency, with intersections in urban areas having a different 

collision profile than intersections in rural areas. Finally, comparisons with sites that are located in 

other jurisdictions may be tainted by differing collision-reporting thresholds, enforcement, 

predominant land use, vehicle mix, road users, climatic conditions, or other unknown factors; 

results of such a comparison should be tempered with caution. 

With these in mind, different methods of using collision data to assess safety are discussed in 

the following sections, highlighting their benefits and drawbacks. The different methods to be 

discussed are: 

• Collision frequency. 

• Collision rate. 

• Combined collision frequency and rate. 
Signalized Intersections: Informational Guide 119

Safety Analysis Methods 

• Equivalent property damage only method. 

• Critical collision rate. 

• Risk analysis methods. 

• Safety performance functions. 

• Empirical Bayes method. 

6.2.1 Collision Frequency 

Traditionally, traffic engineers used (and many still use) a frequency-based method of 

identifying and evaluating the safety of a site.(64) Past observed collision frequencies at a site may 

be used to compare and rank the site with collision frequencies at a group of similar locations. 

Many jurisdictions produce a top-10 list of the intersections producing the highest collision 

frequency in their jurisdictions and concentrate all of their efforts at reducing collisions at these 

sites. Recently, one insurance company released a list of the “worst” intersections in the United 

States, according to internal insurance data.(65)

Collision frequency may also be used to screen candidate sites for improvements. The 

collision frequency at the site may be compared to the average collision frequency for a reference 

population to calculate a potential for improvement. However, relatively short periods of time, 

such as one year of collision data, should never be used as the basis for a safety intervention. 

Because collisions are relatively rare events, a high collision frequency in any given year at a 

particular intersection may be simply a random fluctuation around a much lower long-term 

average at the site. In the next year or series of years, the collision frequency may drop, without 

any safety intervention at all. This phenomenon is referred to as regression to the mean. 

Regression to the mean may be minimized by using data collected over a longer period of time, 

such as 3 years or more, when evaluating the site. Site selection based on multiple years of 

collision data will provide a truer picture of the collision profile of the intersection and avoid errors 

that can result from looking at collision history over a short period. 

Apart from regression to the mean, there are several other disadvantages to using collision 

frequency as the sole means of evaluating safety at a location. First, a high collision frequency 

may not necessarily mean that a site is truly in need of safety improvement. It is known that sites 

with higher volumes will have a higher collision frequency than sites with lower volumes. 

Therefore, sites ranked simply by collision frequency will invariably end up with higher volume 

sites at the top of the list. Second, the method does not address the severity of collisions at the 

site. Failing to consider severity may result in the identification of sites with high numbers of minor 

collisions, while ignoring sites with fewer but more severe collisions. The approach results in a 

failure to identify sites at which the public has greater risk of injury or death. 

6.2.2 Collision Rate 

Collision rates are an improvement over measuring just collision frequency: They allow a 

measure of the risk road users face because rates consider exposure. Collision rates are 

calculated by dividing the collision frequency for a period of time by the estimated average annual 

daily traffic (AADT) of vehicles entering for all approaches in that time period. Collision rate 

provides an improved yardstick for comparison to other sites. As with collision frequency, a 

collision rate for a location undergoing a safety assessment may be compared to similar 

intersections (signalized, same number of legs, same range in AADT). The intersection may be 

ranked to produce a top-10 list, or a threshold value may be used above which a detailed safety 

analysis is warranted. Using a collision rate will account for the effect that volume has on collision 

frequency. 

However, using a simple collision rate to screen locations has several disadvantages. First, 

using a collision rate to rank sites that have different volumes requires the assumption that 

collision frequency and volume have a linear relationship, but research suggests that this is not 

the case. Lower volume sites tend to experience a higher collision rate. Ignoring this fact means 
120 Federal Highway Administration 

that low volume sites may appear less safe than their higher volume counterparts. Second, 

collision rates, as with collision frequency, do not consider collision severity. Sites with a high 

collision rate may have relatively few casualty (fatal and injury) collisions. Last, as collision rates 

are calculated from collision frequency, which fluctuate around a long-term average and 

experience regression to the mean, a site might be ranked high on a list due to a recent period 

with an unusually higher number of collisions. If collision rates are being used to screen out 

candidate sites for safety improvements, it is recommended that a collision rate be calculated for 

a longer time period (3 to 5 years). 

6.2.3 Combined Collision Frequency and Rate Method 

Weaknesses in the collision frequency and collision rate methods of selecting candidate 

intersections for further collision analysis may be somewhat overcome by an approach that 

combines both methods. In this approach, intersections with both a high collision frequency and a 

high collision rate may be candidates for a more detailed safety diagnosis. 

An example of this is presented in figure 45. The collision rate (per million entering vehicles) 

and the 5-year average collision frequency for 10 sites were plotted. Threshold values were 

selected to separate out the sites with the highest combined collision frequency and rates. Sites 

to be considered for further safety analysis were those with an average yearly collision frequency 

of greater than 30 collisions/year and a collision rate of 1.50 collisions per million vehicles 

entering the intersection. Based on this, one candidate intersection was selected. In the above 

example, the threshold values were arbitrarily chosen. The traffic engineer may also consider 

using a value that is twice the average collision frequency and rate as the threshold. 

Figure 45. Selecting a candidate intersection using a combined collision frequency/collision rate 

method, where each diamond represents an intersection. 

6.2.4 Collision Severity Method 

In the above discussion, sites were considered for further analysis if the collision frequency, 

rate, or a combination of the two was particularly high. As identified, a weakness with these 

methods is that they do not consider the severity of the collisions involved. The collision severity 

method considers the distribution of collision severity for each site under consideration. A typical 

approach is through use of the Equivalent Property Damage Only (EPDO) index. It attaches 

greater importance, or weight, to collisions resulting in a serious injury or a fatality, lesser 

importance to collisions resulting in a moderate or slight injury, and the least importance to 

property-damage-only collisions. A weighting factor suggested in the 1999 ITE publication 

Statistical Evaluation in Traffic Safety Studies suggests the following severity breakdown (table 
Signalized Intersections: Informational Guide 121

Safety Analysis Methods 

28), based on values used by the U.S Department of Transportation and the American 

Association of Motor Vehicle Administrators.(64)

Table 28. Suggested weighting for collision severity method. 

Severity Weighting 

Fatal collisions 9.5 

Incapacitating injury (Type A Injury)–Any nonfatal injury that prevents the victim from 

walking, driving, or other normal activity 

9.5 

Non-incapacitating injury (Type B Injury)–Any evident injury that is not fatal or incapacitating 3.5 

Possible injury (Type C Injury)–No visible injuries, but complaint of pain 3.5 

PDO collision–Property damage only 1.0 

Depending on local considerations, the above weighting system may be modified to reflect 

actual values in terms of cost, such as property damage, lost earnings, lost household production, 

medical costs, and workplace costs. A comparison with similar intersections (signalized, same 

number of legs, same range of AADT) may be done by calculating the EPDO index for similar 

sites to the one being considered. The EPDO index will explicitly consider the severity 

breakdown of collisions, providing greater weight to fatal and injury collisions over propertydamage-only collisions. The traffic engineer should be aware, however, that because the severity 

of a collision is associated with higher speeds, signalized intersections on roads with a higher 

operating speed, such as in a rural location, will likely have a higher EPDO index than in an urban 

area. This may result in a bias that emphasizes higher speed locations. In addition, as with 

rankings based on collision frequency and rate, regression to the mean will be an issue if the 

study period chosen is short. 

6.2.5 Critical Collision Rate 

The critical collision rate method has been widely used among traffic engineers. It represents 

the expected collision rate of locations with similar characteristics (in this case, the same traffic 

control device). The critical rate is calculated based on the system-wide average collision rates 

for intersection or road sections of a similar characteristic. If the actual collision rate is greater 

than the critical rate, the deviation is probably not due to chance, but to the unfavorable 

characteristics of the intersection or road section. The method considers the collision rate of a 

location, allows for comparison with other similar sites, and incorporates a simple statistical test to 

determine whether the collision rate is significantly higher than expected. The statistical test is 

based on the assumption that collisions have a Poisson distribution. 

The critical collision rate method is more robust than using collision frequency or collision rate 

alone, as it provides a means of statistically testing how different the collision rate is at a site 

when compared to a group of similar sites. The desired level of confidence may be varied 

depending on the preference of the user. 

Disadvantages of using this method are that it still does not consider the severity of the 

collisions and assumes that traffic volume and collisions have a linear relationship. In addition, 

this approach does not consider regression to the mean. 

6.2.6 Risk Analysis Methods 

The concept of risk analysis involves the determination of collision risk using collision and 

volume data. Existing safety levels are evaluated at defined roadway locations within the 

jurisdiction. The collision risk is calculated at each specific site (local risk), across all sites of a 

specific group (area risk), and across the entire jurisdiction (global risk). Collisions of different 

severities (property damage only, injury, and fatal) are weighted according to the EPDO index. By 
122 Federal Highway Administration 

combining the results of the local, area, and global risk calculation, locations can be compared 

and ranked according to their relative risk and the potential for collision mitigation. Sites with the 

highest risk score would be candidate locations for further safety diagnostics. 

Risk analysis methods are robust in that they consider the exposure (volume) and severity of 

the collisions occurring at the site. The local risk, area risk (risk among locations of a similar 

nature), and global risk (across the entire jurisdiction) are considered. However, they still assume 

that the relationship between collision frequency and volume is linear, and they do not consider 

regression to the mean. 

6.2.7 Safety Performance Functions 

A safety performance function (SPF) is an equation that presents the mathematical 

relationship between collision frequency and volume based on a group of intersections with 

similar characteristics (e.g., signalized, same number of legs). When collision frequency and 

volume are plotted, an equation can be developed that is represented by a line that is the best fit 

possible through the various points. Generally, SPFs demonstrate that the expected number of 

collisions increases as traffic volume increases, and an SPF is curvilinear rather than a straight 

line. Because the line that plots an SPF is curved, the rate (rise/run) varies continuously along the 

curve. An SPF typically shows that higher volume sites have a lower collision rate than do lower 

volume sites. 

A simple example of an SPF is illustrated in figure 46. The blue points represent individual 

intersections with their respective average yearly collision frequency and AADTs. A curve can be 

drawn through the points representing the best fit. The green point above the curve represents an 

intersection that is performing worse than predicted. 

Figure 46. Example of SPF curve. 

Advantages of using such a method are that the potential for safety improvement is more 

accurately calculated, and that it acknowledges that the relationship between collision frequency 

and volume is not a straightforward linear one. Disadvantages are that this method is relatively 

complex and still does not acknowledge the random variation of collisions. 

6.2.8 Empirical Bayes Method 

Each of the above methods only considers past collision history by either ranking and 

selecting a candidate location for further collision analysis, or determining whether a particular 
Signalized Intersections: Informational Guide 123

Safety Analysis Methods 

intersection under study has a collision problem. Using collision history alone is flawed, because 

the frequency of collisions from year to year will randomly fluctuate about a long-term average 

(regression to the mean). Improved methods have evolved that identify high-risk sites that may 

benefit from remedial treatment(s), particularly the empirical Bayes (EB) method. Many 

jurisdictions are already employing the EB method. 

The EB method calculates expected collision frequencies through a combination of observed 

and estimated collision frequencies. The estimated collision frequencies are derived through the 

development of an SPF curve. The SPF relates the level of safety of an intersection to traffic 

volume and other relevant geometric factors. The function estimates the expected number of 

collisions based on traffic volume and other characteristics; it is expressed in collisions/year for 

intersections. 

The pivotal concept upon which contemporary methods for conducting proper road safety 

evaluations depend is the EB method. It is superior to traditional methods because it: 

• Considers regression to the mean. 

• Produces more stable and precise estimates of safety. 

• Allows for estimates over time of expected collisions. 

Although the development of SPFs is a relatively new area of road safety research, they have 

been implemented successfully for measuring the safety of road locations. Sites can be ranked to 

determine which is experiencing the highest number of collisions based on actual collision counts, 

and to determine its expected collision performance. 

6.2.9 Conclusions 

The above section has detailed various methods of assessing the safety of a location through 

consideration of its collision history and comparison with other similar sites. Care must be taken 

to ensure that the site is being compared with sites that should have a similar level of safety (i.e., 

sites with a traffic signal and the same number of legs). Simpler methods such as collision 

frequency and rate may provide a simple and quick way of diagnosing a potential safety problem, 

but should be used with caution. The traffic engineer may consider using the critical collision rate 

method or the collision severity method as these provide a more balanced assessment of safety. 

Developing an SPF, either on its own or for use in applying to the EB method, is a much more 

sophisticated method of evaluating safety at a location. A summary of the relative merits and 

drawbacks of each method is presented below in table 29. 
124 Federal Highway Administration 

Table 29. Common methods of assessing safety at a location. 

Method Advantages Disadvantages 

Collision frequency • Simple to use 

• Easy for the public to 

understand 

• Biased toward high-volume 

sites 

• Does not consider exposure 

• Severity not considered 

• Regression to the mean not 

addressed 

Collision rates • Simple to use 

• Considers exposure 

• Biased toward low-volume 

sites 

• Requires volume data 

• Assumes collisions and 

volume have linear 

relationship 

• Severity not considered 

• Regression to the mean not 

addressed 

Critical collision rate • Relatively simple 

• Considers exposure 

• Applies a recognized statistical 

method 

• Requires volume data 

• Assumes collisions and 

volume have linear 

relationship 

• Severity not considered 

• Regression to the mean not 

addressed 

Collision severity method • Relatively simple 

• Considers exposure 

• Biased toward high-speed 

sites 

• Assumes collisions and 

volume have linear 

relationship 

• Regression to the mean not 

addressed 

Risk analysis methods • Accurate 

• Considers exposure and 

severity 

• Considers varying safety levels 

but locally, among a group of 

similar locations and across an 

entire jurisdiction 

• Requires volume data 

• Assumes collisions and 

volume have linear 

relationship 

• Regression to the mean not 

addressed 

Safety performance functions • More accurate 

• Considers exposure 

• Acknowledges that collisions 

and volume have a nonlinear 

relationship 

• Requires volume data 

• Regression to the mean not 

addressed 

• Labor intensive 

• Difficult for public to 

conceptualize 

EB method • Most accurate 

• Considers exposure 

• Acknowledges that collisions 

and volume have a nonlinear 

relationship 

• Addresses regression to the 

mean 

• Requires volume data 

• Difficult for public to 

conceptualize 
Signalized Intersections: Informational Guide 125

Safety Analysis Methods 

6.3 IDENTIFICATION OF POTENTIAL PROBLEMS 

The previous section discussed different tools that may be used to select a candidate 

intersection for a safety evaluation. At a certain point, the traffic engineer will conclude, based on 

past collision history, that there is a safety concern and a significant potential for safety 

improvement at the location in question. It should be noted that some traffic engineers may have 

completely bypassed the entire first step of this process (in determining a candidate intersection 

for safety improvements), because they have been asked to carry out a safety analysis of an 

intersection due to: 

• Safety complaints or concerns raised by others (other departments, local politicians, 

the public). 

• Planned reconstruction that would make it worthwhile to carry out a safety evaluation 

and improvements. 

• Identified operational deficiencies. 

This section will discuss how the traffic engineer may correctly diagnose what types of safety 

problems/issue may be present at a location. Diagnosis of a particular safety concern can then 

lead to appropriate treatment, as discussed in part III. 

6.3.1 Safety Diagnosis 

In conducting a safety diagnosis at a signalized intersection, the traffic engineer seeks to 

understand and identify causal factors of collisions within the functional boundaries of the 

intersection. All information gathered needs to be thoroughly reviewed and analyzed with the 

objective of identifying whether there exists one or more opportunities to improve safety at the 

location. The stages in carrying out a safety diagnosis are: 

• Assemble collision data. 

• Carry out a collision diagnostic analysis. 

• Determine overrepresentation. 

• Conduct a site visit. 

• Conduct further studies, if necessary. 

• Define problem statement(s). 

Figure 47 shows the process described in this section. 
126 Federal Highway Administration 

Figure 47. Identification of potential problems. 

6.3.2 Assemble Collision Data 

Collision data used for diagnosing safety at a signalized intersection should represent at least 

3 years of collision data. It should include all collisions reported as occurring at or within the 

intersection’s sphere of influence. If available, the original police reports should be used to gather 

anecdotal comments written by police officers at the collision scene and firsthand accounts of the 

collisions based on involved parties and eyewitnesses (figure 48). Using either the original police 

reports or collision data taken from a database, a collision diagram should be prepared, providing 

a pictorial representation of the collision types, severity, movements, and involved approaches. 
Signalized Intersections: Informational Guide 127

Safety Analysis Methods 

Photograph Credit: Synectics Transportation Consultants, Inc. 

Figure 48. The original police collision report may contain valuable information regarding 

collisions that have occurred at the intersection. 

All collisions occurring within the intersection should be included in the analysis, as well as 

those occurring immediately upstream and downstream. Collisions occurring further upstream 

may be included in the analysis, if it is found that operations at the intersection in question 

contributed to the collision. Rear-end collisions commonly occur well upstream of a signalized 

intersection due to vehicle queuing. Queuing may occur because of an operational deficiency at 

the signalized intersection. 

The collision diagram will help the traffic engineer quickly ascertain: 

• Whether the collisions are predominantly occurring on a particular approach or are 

systemic to the entire intersection. 

• What movements appear to be the most problematic. 

• Where and what type of injury and fatal collisions are occurring. 

As highlighted earlier, the accuracy of safety diagnosis detailed in this chapter will depend on 

the quality of the collision data. Collision reporting systems may contain incorrect or missing 

information because: 

• Collisions are not reported. 

• Collisions are self-reported. 

• Collisions are coded incorrectly. 

Before beginning a detailed collision analysis, the traffic engineer should be aware of the 

strengths and weaknesses of collision data collected in the jurisdiction. Questions to consider are: 

• Is there a reason not to trust information contained in any field of interest? 
128 Federal Highway Administration 

• Is information in this field collected consistently? 

• What quality control is used on the information inputted? 

• Is the information double-keyed to detect mistakes? 

• Are logic checks built into the computer database (i.e., ensuring that snow is not 

reported in July, or an angle collision involving two vehicles traveling in the same 

direction)? 

The above demonstrates the need to supplement any analysis of collisions in the office with 

field observations. 

6.3.3 Analyze/Diagnose Collision Data 

To correctly diagnose safety issues at an intersection, a detailed collision analysis is required, 

cataloguing the different characteristics of collisions at the intersection. The purpose of this 

analysis is to determine if any collision characteristics (e.g., collision type) at the study location 

are “abnormal” compared to these expected for signalized intersections having the same number 

of approaches elsewhere in the jurisdiction in question. By finding a collision characteristic that is 

abnormally elevated for a location, the traffic engineer can begin to pinpoint the cause of a 

collision. 

The standard police collision report includes a number of collision descriptors that are 

collected by police and maintained in a database. These range from information on the driver, the 

vehicle, the road, and the environment. Many of these characteristics could help in determining 

causal factors; however, an exhaustive diagnosis of every collision descriptor may not be 

warranted to establish probable causes. As a primary review, collision characteristics that the 

traffic engineer should consider analyzing are: 

• Collision distribution by season, day of week, and time of day. 

• Collision severity. 

• Collision type. 

• Weather, light, and road surface conditions. 

It is recommended that the traffic engineer prepare a table or set of tables that shows the 

typical collision profile of signalized intersection that is representative of the jurisdiction for each 

of the above-listed characteristics. 

A number of statistical tests are available to determine whether the proportion of a 

characteristic found at a specific site is the same as that found in a group of similar sites. 

Identification of abnormal trends can lead toward possible solutions. To ensure that the 

determination of overrepresentation is valid, appropriate statistical techniques should be 

employed. The chi-square method is suggested. 

Chi-Square Test 

The chi-square test is a measure of the differences between measured and expected 

frequencies at location. The collision data at the subject location provide the measured frequency; 

the aggregate collision data from a large number of similar intersections provide the expected 

frequency. If the subject intersection displays a measured frequency that is greater than the 

expected frequency, then use of the chi-square test and reference to standard statistical tables 

will allow the analyst to determine whether the difference is likely a random variation or a real 

difference. Real differences, also called statistically significant differences, are an indication that 

the subject location has a site-specific deficiency that may be causing this trend. 

The chi-square test can be calculated using equation 3. 
Signalized Intersections: Informational Guide 129

Safety Analysis Methods 

(1 )

( ) [( ) (1 )] 2 2

2

n p

n x n p

pn

x pn

−

− − − + − χ = (3) 

Where: χ2

 = Chi-square test value 

p = The average ratio for the collision type being investigated (i.e., 75 

 percent of collisions occurred during clear conditions) 

x = The frequency of the collision type being investigated 

n = The total number of collisions at the site 

The chi-square test is not reliable when the expected frequency is less than 5. The expected 

frequency is determined by multiplying p and n. If p*n is less than 5, then another statistical test 

is required. Confidence levels for the chi-square test are shown in table 30. 

Table 30. Chi-square test values and corresponding confidence levels.

Chi-square Value Confidence Level 

> 7.88 99.5% confidence 

> 6.63 99.0% confidence 

> 5.02 97.5% confidence 

> 3.84 95.0% confidence 

An example of how the chi-square test may be used to determine overrepresentation is 

provided in the following example. A chi-square analysis was carried out to test whether 

collisions during wet road surface conditions are over-represented at a signalized intersection. 

Given: 

x = Wet road surface collisions at site (18) 

n = Total collisions at site (50) 

p = Percent of wet road surface collisions (25.4 percent) typically found at signalized 

intersections in the municipality. 

Therefore: 

2.96

50(1 0.254)

[(50 18) 50(1 0.254)]

0.254(50)

(18 (0.254)50)

2 2

2 = −

− − − + − χ = (4) 

Chi-square values above 3.84 indicate a 95.0 percent confidence level in the result. In the 

example above, the chi-square value is 2.96, which is less than 3.84. Therefore, there is not 

enough evidence to suggest that wet road surface collisions are over-represented at the site. 

6.3.4 Determine Overrepresentation 

The traffic engineer may determine overrepresentation using either the chi-square or 

expected values method. The collision characteristics should be reviewed for over representation, 

through comparison with collision characteristic information representing the typical experience of 

a signalized intersection. Possible patterns the traffic engineer may encounter are highlighted 

below. 

An examination of collision distribution by season, day of week, or time of day may be helpful 

in finding patterns that relate to the general travel patterns of road users passing through the 

intersection. Seasonal patterns, indicating a higher-than-expected proportion of collisions 

occurring during a particular time of year, may coincide with an influx of unfamiliar drivers to an 

area—as may be the case in resort areas and/or areas with a significant number of tourist 
130 Federal Highway Administration 

attractions. Day of week and time of day patterns should be examined. Morning/afternoon 

weekday overrepresentation may suggest collision patterns related to commuting traffic 

(coinciding with the morning and afternoon rush hours). A late night/early morning/weekend 

overrepresentation may suggest problems with drunk drivers. 

Overrepresentation in collision severity will highlight a location that has an unusually high 

proportion of fatal and/or injury collisions. A higher proportion of fatal and/or injury collisions may 

suggest a problem with higher operating speeds. 

Collision type, together with a collision diagram, can greatly aid the traffic engineer in 

diagnosis. A cluster of rear-end collisions on a particular approach may suggest a slippery 

pavement surface, a large turning volume inadequately serviced by existing lanes, or poor 

visibility of signals. Unfortunately, most collision reporting systems provide a very basic 

classification of collision type. For diagnosis purposes, this may not be especially helpful. For 

instance, one jurisdiction may group all collisions involving a turning movement together, whereas 

collisions involving left-turning vehicles being struck by an opposing vehicle may be of particular 

interest to the traffic engineer. The traffic engineer may wish to consider using more finely 

developed subcategories of collision types, such as detailed in figure 49, to aid in diagnosis. As 

well, the collision diagram will be an invaluable tool for isolating the combination of movements 

and/or approaches involved in the abnormal collision type. 

Further analysis of such characteristics as vehicle type, driver/pedestrian condition, and/or 

apparent driver action may be required to provide further symptoms of the collision occurrences. 

The end product of the above analysis will be a set of characteristics that is identified as 

being over-represented. A collision diagram, as discussed previously, may narrow the problem to 

a particular approach, and should at the very least assist in searching for the causes of the 

collisions and identifying patterns. 

In some instances, however, no specific statistically significant overrepresentation will be 

found. This does not mean that the location is free of any safety concern. In these cases, the 

predominant collision type should be the focus of the problem statement (as confirmed through 

field observations). 
Signalized Intersections: Informational Guide 131

Safety Analysis Methods 

Figure 49. Possible taxonomy for collision type classification. 
132 Federal Highway Administration 

6.3.5 Conduct Site Visit(s) 

To supplement the analysis and diagnosis using collision data, a site visit or series of site 

visits should be undertaken. Before initiating site visit(s), the study team should be aware of: 

• Whether certain collision characteristics were overrepresented based on the analysis 

of collision overrepresentation. 

• Which areas within the intersection’s sphere of influence are showing unusual clusters 

of collisions. 

• If available, what operational problems have been identified as part of the operational 

analysis. 

The purpose of the site visit is to gather additional information that can aid in pinpointing 

potential underlying cause or causes of the abnormal collision patterns (figure 50). The site visit 

should be undertaken to: 

• Observe driver/road user behavior during the following conditions: 

o Peak and off-peak periods. 

o Evening/night (as necessary). 

o Wet weather (as necessary). 

o Weekend and special events (as necessary). 

• Photograph relevant features. Consideration may be given to using video recording 

to capture each intersection approach from the driver’s perspective. 

• Review the site from the perspective of all users, including motorists, pedestrians, 

and bicyclists. This includes observing motorist, bicyclist, and pedestrian circulation 

and identifying origins and destinations in the vicinity. 

• Check for physical evidence of collisions or near-collisions, such as vehicle damage 

to street furniture, signs and other objects near the roadway, skid marks on the 

intersection approaches, tire marks on the shoulder or ground adjacent to the 

roadway. 

• Conduct a conformance/consistency check: an assessment of signs and traffic 

control, markings, delineation, geometry and street furniture to ensure standard 

application and consistency and that all traffic control devices are in conformance 

with local, State, and Federal standards. 

One of the key tasks the study team will wish to conduct during the site visit is a positive 

guidance review.(8) A positive guidance review uses an indepth knowledge of human factors and 

the driving task to screen roadways for: 

• Information deficiencies. 

• Expectancy violations. 

• Workload issues. 
Signalized Intersections: Informational Guide 133

Safety Analysis Methods 

Photograph Credit: Synectics Transportation Consultants, Inc. 

Figure 50. Conducting a site visit. 

Each of the above may contribute to the occurrence of driver error and collisions. 

Information deficiencies occur when information that the driver needs to carry out the driving 

task safely is missing. An example may be inadequate signage/pavement marking for a 

designated right-turn lane that traps drivers intending to proceed straight. Attempts to move over 

to the through lane can cause queuing and possible rear-end and sideswipe conflicts. 

Expectancy violations occur when a driver encounters a traffic control or roadway design that 

conflicts with his or her expectations. The traffic engineer should structure expectancies about 

treatments at similar locations.(66) The key to effective expectancy structuring is uniformity and 

standardization. Standard devices that are inconsistently applied can create expectancy problems 

for drivers. A prime example of this is the use of a left-hand exit amidst a series of right-hand 

exits. Positive guidance seeks to address this expectancy violation through clearly 

communicating to the driver that a left-hand exit is ahead. 

Workload issues occur when the driver is bombarded with too much information, increasing 

the likelihood of error. This may occur at an intersection with an abundance of signage, pavement 

markings, traffic signals, and pedestrian and bicycle activity. All of the above may be further 

complicated if the operating speed on the approaches is high, giving the driver even less time to 

sort through and comprehend what to do to get safely through the intersection and on to the 

intended destination. The traffic engineer should seek to reduce the complexity of the information 

the driver receives at the intersection or spread information by using advance signs. 

Although positive guidance techniques are generally applied to the driving task, these 

concepts and tools can easily be considered from the perspective of all road users. Positive 

guidance is a holistic approach that treats the roadway, the vehicle, and the driver as a single, 
134 Federal Highway Administration 

integrated system. It recognizes drivers as the information gatherers and decisionmakers within 

the system and focuses attention on assuring that they get the information they need, when they 

need it, in a form they can understand, in time to make rapid, error-free decisions and take 

appropriate actions. When this occurs, the system functions most effectively, and the driving task 

is successfully accomplished. Creating and sustaining a supportive information environment on 

the roadway is the goal of positive guidance. 

In conducting a positive guidance review, the analyst attempts to view the roadway through 

the eyes of an average driver, postulating what the driver’s perceptions, interpretations, 

expectations, and actions might be. This is done to formulate theories and possible explanations 

regarding the cause or causes of previous or potential conflicts and/or collisions. 

Positive guidance normally focuses on low-cost, information-oriented improvements that can 

be implemented quickly, either as solutions in and of themselves, or as interim improvements 

until a more definitive solution can be achieved. It may also identify the need for additional 

investigation, in the form of conventional engineering analysis, to support theories regarding the 

contributory causes of collisions, and to justify mitigation measures. 

6.3.6 Deciding on Further Analysis 

The outcome of the site visit, including a positive guidance review, should be a clear 

understanding of the safety problem occurring at the locations in terms of its underlying causes 

(field observations that explain the reason for that particular problem) and its link to any 

subsequent effects (an unusual pattern/high incidence of a specific collision group). 

If the underlying cause of the safety problem is not entirely clear to the study team, 

treatments should not selected until further field studies are carried out. 

6.3.7 Conducting Further Studies 

Further studies should provide a better understanding of the level of safety experienced by 

various users passing through the intersection by means of direct observational methods. The 

study team will need to spend an extended period on site observing traffic patterns and the 

interaction between the roadway/roadside elements and the drivers, pedestrians, and bicyclists. 

The study team may choose to a traffic conflict analysis that will provide a generic overview 

of driver, pedestrian, and bicyclist interactions over the course of a few days.(67) The traffic conflict 

analysis technique involves the systematic observation and reporting of traffic conflicts, or “near 

collisions,” and an assessment of the degree of severity for each conflict. When two or more road 

users approach the same point in time and space, one or both must take evasive action to avoid 

a collision. At this point, one of two events may occur. If the evasive action is unsuccessful, then 

a collision occurs. If the evasive action is successful, a traffic conflict occurs. In general, the 

presence of a significant number of traffic conflicts indicates operational deficiencies and, 

possibly, collision potential. 

The severity of the traffic conflict is measured by the summation of two scores assigned by 

the observer: the time-to-collision score and the risk-of-collision score. The time-to-collision score 

is a measure of the time before a collision would have occurred had no evasive action been 

taken, and is a function of the travel speeds, trajectories, and separation of the vehicles involved. 

The risk-of-collision score is a subjective measure of the collision potential and depends on the 

perceived control that the motorist had over the traffic conflict event. Factors such as 

maneuvering space and severity of the evasive action taken are considered in the assignment of 

the risk-of-collision score. 

Upon completion of the traffic conflict analysis study, the various conflicts are drawn onto a 

diagram of the intersection, as with the collision diagram. Questions the traffic engineer may want 

to investigate are: 

• Where in the intersection are the conflicts occurring? 
Signalized Intersections: Informational Guide 135

Safety Analysis Methods 

• What movements appear to generate the most conflicts? 

• Which movements appear to have the highest severity score? 

• Are there any repeated patterns of driver making errors or disobeying/disregarding 

traffic control devices? 

A full traffic conflict analysis for all movements at the intersection may not be necessary if a 

specific behavior is suspected as being a problem based on the site visit and/or collision analysis. 

Engineers may choose to study a specific behavior such as red light running, lane 

encroachments, failing to check blind spots while turning, failing to yield, stopping beyond the 

stop bar, blocking the crosswalk, blocking the intersection, illegal parking, or disobeying turn 

prohibitions. 

The end result of the safety diagnosis (including the analysis of collision data, the site visits, 

and further studies, if necessary), will be a clear understanding of any abnormal collision patterns 

occurring at the site, along with the underlying and probable cause for these patterns. 

6.3.8 Defining the Problem Statement 

A set of one or more clear problem statements should be developed. The problem 

statement(s) are developed on the basis of the collision analysis (i.e. evidence of over 

representation among a collision subgrouping) and should be supported through the site visit and 

any further analysis. It should clearly state a probable “cause” and observed “effect.” 

The problem statement helps clearly define safety concerns at the location. Circumstances 

associated with these safety concerns may be mentioned along with possible causal factors. The 

problem statement may be multifaceted and encompass the physical and/or operational attributes 

of the intersection, road user behavior and/or actions, environment and/or temporal conditions, as 

well as transitory or peripheral events. In many instances, the study team will identify several 

problems or issues. 

Examples of problem statements are given in figure 51. 

Problem Statement #1

Rear-end collisions and collisions occurring between 3 and 6 p.m. are overrepresented. The 

collision diagram shows that almost all of these occur on the westbound approach. Based on the 

site visit, the initial problem statement is that these are occurring due to: 

• Lack of traffic signal visibility for westbound drivers. 

• Movement into and out of a commercial driveway on the near side of the intersection. 

• A polished pavement surface on this approach.

• Glare from the afternoon sun. 

Problem Statement #2

Fatal and injury collisions were overrepresented, and four fatal or injury collisions involved 

pedestrians. The collision diagram indicates that all occurred on the southwest corner of the 

intersection and are related to the right-turn lane channelization. Based on the site visit and 

subsequent further analysis, the initial problem statement is that these are occurring due to: 

• The design of the right-turn channelization operating under YIELD control, which contributes to 

excessive driver speed. 

• Drivers failing to yield to pedestrians. 

• The presence of a bus shelter that partially blocks the view of the crosswalk. 

Figure 51. Examples of problem statements. 
136 Federal Highway Administration 

6.4 IDENTIFICATION OF POSSIBLE TREATMENTS 

The process described below and shown in figure 52 shows how possible treatments are 

initially identified, screened, and evaluated. 

Figure 52. Identification of possible treatments. 

6.4.1 List Possible Treatments 

Using the problem statement(s) developed by the study team, possible treatments may now 

be identified. Possible treatments will be all measures listed that are likely to decrease the 

frequency or severity of collisions identified as exhibiting an abnormal pattern 

(overrepresentation). 

In part III of this guide, the reader will find treatments organized into five broad groups: 

• System-wide treatments (chapter 8). 

• Intersection-wide treatments (chapter 9). 

• Alternative intersection treatments (chapter 10). 

• Approach treatments (chapter 11). 

• Individual movement treatments (chapter 12). 

For each treatment, there are references to possible collision groups that are likely to be 

positively affected through a treatment’s implementation. At signalized intersections, the four 

collisions groups most commonly identified as a cause for concern are: 

• Rear-end collisions. 
Signalized Intersections: Informational Guide 137

Safety Analysis Methods 

• Angle collisions. 

• Left-turn collisions. 

• Collisions involving pedestrians and bicyclists. 

Table 31 presents possible causes and treatments for each of these types, along with the 

appropriate chapter. Note that treatments involving enforcement and education are not discussed 

in part III of this report. 

The material presented here by no means represents the limitation of possible treatments. It 

gives some indication of the range of options that could be selected, but is not fully 

comprehensive. It is not possible to develop a complete list of all potential collision treatments, 

because new tools and techniques for improvement traffic safety are constantly being developed 

and adopted. It is important that the study team not limit itself to existing lists or tables of 

treatments. The team should consider a wide range of treatments (including those based on local 

practice) that may be beneficial, particularly when the collision pattern identified represents a 

unique situation. 

Over the course of the above collision diagnostic analysis, site visits, and field analysis, the 

traffic engineer may have identified treatments that are of little cost and without question 

beneficial to improving safety at the intersection. Such treatments may relate to repairing 

sidewalks, removing sight obstructions, reapplying faded pavement markings, and relocating or 

adding new signs. These may be implemented without going through the process described 

below.
138 Federal Highway Administration 

Table 31. Collision types commonly identified, possible causes, and associated treatments. 

Collision 

Type Possible Cause 

Possible Treatment Group 

(Chapter) 

• Sudden and unexpected slowing or stopping when 

motorists make left turns in and out of driveways 

along corridor 

• Median improvements 

(chapter 8) 

• Sudden and unexpected slowing or stopping when 

motorists make right turns in and out of driveways 

along corridor 

• Access management 

(chapter 8) 

• Too much slowing and stopping along corridor due to 

turbulent traffic flow 

• Signal spacing and 

coordination improvement 

(chapter 9) 

• Too much slowing and stopping along intersection 

approaches due to traffic-control issues 

• Drivers caught in intersection during red phase due 

to inadequate traffic control or inadequate clearance 

interval 

• Traffic signal not conspicuous or visible to 

approaching drivers, causing sudden and 

unexpected slowing or stopping movements 

• Traffic control improvement 

(chapter 9) 

• Enforcement of red light 

running and aggressive 

driving 

• Drivers unable to stop in time due to road surface • Pavement / crosswalk 

improvements (chapter 9) 

Rear-end 

collisions 

• Sudden and unexpected slowing or stopping due to 

inadequate intersection capacity 

• Individual movement 

treatments (chapter 12) 

• Enforcement of aggressive 

driving 

Angle 

collisions 

• Drivers caught in intersection during red phase due 

to inadequate traffic control or inadequate clearance 

interval 

• Traffic signal not conspicuous or visible to 

approaching drivers, causing drivers to get caught in 

intersection during red phase 

• Drivers caught in intersection during red phase due 

to inadequate warning/inability to stop 

• Traffic control improvement 

(chapter 9) 

• Approach improvement 

(chapter 11) 

• Enforcement of red light 

running and aggressive 

driving 

Left-turn 

collisions 

• Intersection cannot accommodate left-turn 

movements safely 

• Alternative intersection 

treatments (chapter 10) 

• Individual movement 

treatments (chapter 12) 

Collisions or 

conflicts 

involving 

bicyclists and 

pedestrians 

• Either the intersection cannot safely accommodate 

the pedestrians and/or bicyclists, or motorists are 

failing to see or yield to their movements 

• Pedestrian, bicycle, and/or 

transit improvements 

(chapter 9) 

• Enforcement of aggressive 

driving 

6.4.2 Screen Treatments 

The study team likely will generate a long list of treatments that may have been identified in 

this guide, based on local practice or representative of a unique situation identified at the 

intersection through the collision analysis, site visits, and subsequent studies carried out in the 

field. To narrow the options, the study team may consider screening the treatments. One method 

of screening proposed treatments is to develop a matrix where each treatment is given a score 

within different categories, based on the consensus among study team members. The individual 

score categories may be as follows: 
Signalized Intersections: Informational Guide 139

Safety Analysis Methods 

• Overall Feasibility: How feasible would it be to implement the treatment? Would it 

involve a significant amount of work, time and/or coordination with police, 

maintenance staff, transportation planners, or the public? Straightforward treatments 

get positive scores. Difficult-to-implement treatments get negative scores.

• Installation Cost: What would be the significance of the cost of implementing the 

treatment? Treatment involving little or no capital costs score positive. Treatments 

involving a significant investment in capital costs score negative. 

• Maintenance Cost: What would be the significant of the cost of the upkeep of the 

treatment? Treatments that would decrease maintenance requirements/efforts score 

positive. Treatments that would increase maintenance requirements/efforts score 

negative.

• Reduction in Collision Frequency: Is the treatment expected to bring about a 

reduction in collision of the particular type identified? Treatments that would reduce 

such collision frequency score positive. Treatments that would increase that collision 

frequency score negative.

• Reduction in Collision Severity: Is the treatment expected to bring about a 

reduction in severity in the collision type identified? Treatments that would reduce 

severity score positive. Treatments that would increase severity score negative.

• Impact on Traffic Operations: Is the treatment expected to improve the flow of 

traffic within the intersection influence area? Treatments that would improve traffic 

operations score positive. Treatments that would degrade traffic operations score 

negative.

• Consistency with Local Practice: Is the treatment consistent with local practice? 

Treatments that are familiar to the public and have known benefits score positive. 

Treatments that are unfamiliar and are largely untested score negative. 

Scoring each treatment allows the study team to quickly determine which treatments are 

expected to have a positive or negative effect on the intersection. The long list of potential 

treatments then can be reduced to a short list of viable treatments. Based on a threshold score 

decided upon among the study team, the treatments may then be screened and those scoring 

poorly may be discarded. 

The ability to evaluate the safety impacts of a treatment is paramount to implementing an 

intersection improvement plan. Information is needed on whether the treatment under 

consideration is effective in reducing collisions. Most treatments proposed in part III of this guide 

have some published material that provides a quantitative estimate of effectiveness. For other 

treatments in part III, no research was found that provided any quantifiable estimate of safety 

benefits. Before any further consideration as to be applicability of a treatment can occur, the 

study team will need to decide whether they have a quantifiable estimate of the expected results 

of a treatment available. If they do, they can proceed with the steps described below. If not, they 

should carefully consider whether the treatment should be implemented. 

6.4.3 Selecting a Collision Modification Factor or Study Finding 

Generally speaking, quantitative estimates of the effectiveness of a treatment may be 

developed from: 

• Collision (or crash) modification factors (CMF). 

• Study findings. 

CMF is a term that is widely used in road safety engineering. It may also be referred to as an 

accident modification factor (AMF). A CMF is the ratio of expected collision frequency at a 

location with a treatment divided by the expected collision frequency at the location without the 
140 Federal Highway Administration 

treatment. If the expected collision frequency with a treatment is 9 and the expected collision 

frequency without the treatment is 12, then the CMF is 9/12 = 0.75. 

Traffic engineers should be careful not to confuse the term CMF with CRF, which stands for 

collision reduction factors. A CRF is the portion of collisions that will be reduced if a treatment is 

applied. The CRF is easily determined, being 1 minus the CMF value. Using the above example, 

if the CMF is 0.75, then the CRF is 1 – 0.75 = 0.25. The expected reduction in collisions that 

would come from application of the treatment would be 0.25 x 12 = 3. 

Many State jurisdictions have developed reference lists of CMFs to help them choose an 

appropriate treatment for an intersection improvement plan. In some cases, very little or no 

documentation exists showing how these CMFs were derived. Some State authorities are 

currently using CMFs developed from in-house projects; others use CMFs developed by other 

transportation authorities or based on published research. 

Part III of this guide reports study findings taken from a variety of sources. These findings 

either reported a change in collision frequency or rate as part of a cross-sectional study, a beforeafter study, or by more sophisticated methods. Each study finding was reviewed in terms of: 

• The reasonableness of the values presented. 

• The year of the study. 

• The general integrity of the study in terms of collision data used, methodology, and 

sample size. 

• The country of origin. 

In general, findings were discarded that appeared unreasonable, were outdated, used overly 

simplistic methods, or were based on research carried out outside of North America, unless no 

other finding was available for the treatment in question. The results are presented as the 

expected change in collision frequency (and are expressed as a percentage). A study finding of 

50 percent means that there is expected to be a reduction of 50 percent in the number of 

collisions occurring after the application of the treatment the study finding describes. Each CMF 

or study finding in part III of this guide is referenced. In applying a CMF or finding was to 

determine the expected outcome of implementing a treatment, the user is urged to review the 

source material from which the CMF or study finding was derived, to determine its applicability to 

his or her specific project. Readers may wish to use their own CMFs or the results of another 

study finding known to them, should they believe that it is more accurate or better reflects 

conditions occurring at the location in question. 

6.4.4 Quantify Safety Benefit 

The target benefit of any treatment is a reduction in the frequency or severity of collisions. 

Assumptions regarding potential benefit of a treatment must be realistic. The collision frequency 

(or collision frequency of a specific group of collisions) cannot be driven below zero. To quantify 

the safety benefit of implementing a treatment, the estimated collision reduction that will be 

connected with the implementation of the treatment must be determined. If a treatment is 

successful in eliminating or reducing the severity of collisions that would have been expected 

without the treatment, then the benefits can be attributed to the treatment. 

When two treatments are considered and each has a quantifiable safety benefit, a common 

way to express the combined safety benefit is to multiply both values. For example, treatment A 

might have a CMF of 0.90, and treatment B might have a CMF of 0.80. Combined, the two 

treatments should have an expected benefit of (CMF A (0.90) x CMF B (0.80)) of 0.72. 

Usually, treatments can only be expected to be successful when applied to a particular target 

group of collisions. For example, the installation of protected left-turn phasing on one approach 

should substantially reduce left-turn collisions involving that particular approach, but cannot be 

expected to affect left-turn collisions on any other approach. 
Signalized Intersections: Informational Guide 141

Safety Analysis Methods 

Treatments can also have undesirable effects that need to be considered in evaluating their 

overall benefit. For example, the installation of right-turn channelization may reduce collisions 

involving right-turning vehicles and possibly rear-end collisions on a particular approach, but may 

increase collisions involving pedestrians. If the treatment is to be applied, both positive and 

negative consequences need to be considered. 

The potential collision reduction from a treatment is determined by multiplying the expected 

number of collisions by the percentage reduction that the treatment is expected to have. The 

expected number of collisions (total or by severity) may be assumed to be the same as in the 

period before the treatment, but a much more refined method would be to develop an estimate of 

the expected number of collisions based on SPF curves or the EB method. 

Placing an economic value on collisions, by severity, is a common practice in quantifying the 

safety benefits of a treatment. There are several ways of arriving at societal cost (such figures are 

available from FHWA and various State transportation agencies). 

Calculating the safety benefit of a treatment means multiplying the expected collision 

reduction by severity (property damage, injury, and fatal) by applicable society cost figures. A 

means of expressing the calculation of the safety benefit of the treatment is as follows: 

Safety Benefit ($) = ∆nPDO x CPDO + ∆nI x CI + ∆nF x CF (5) 

Where: ∆nPDO = Expected reduction in property-damage-only collisions 

CPDO = Societal costs of property-damage-only collisions 

∆nI = Expected reduction in injury collisions 

CI = Societal costs of injury collisions 

∆nF = Expected reduction in fatal collisions 

CF = Societal costs of fatal collisions 

 

The end result of the above calculations will be a list of treatments with associated societal 

benefits. 

As an example: A multilane signalized intersection has been diagnosed as having a safety 

problem associated with a particular approach. Adding a right-turn lane is being considered as a 

possible treatment. Calculation of the safety benefit involves determining the product of the yearly 

average number of collisions, the societal benefit, and the estimated reduction in collisions 

grouped by collision type (table 32). The total societal benefit is calculated to be $66,000. 

Table 32. Example calculation of safety benefit of adding a right-turn lane. 

Collision 

Type 

5-Year Total 

Before 

Treatment 

Yearly 

Average 

Before 

Treatment 

Estimated 

Reduction 

Due to 

Treatment 

Estimated 

Yearly 

Average 

After 

Treatment 

Unit 

Societal 

Benefit 

Estimated 

Yearly 

Benefit of 

Treatment 

Fatal 0 0.00 40% 0.00 $3,500,000 $0 

Injury 8 1.60 40% 0.64 $100,000 $64,000 

PDO 25 5.00 10% 0.50 $4,000 $2,000 

Total $66,000 

Source for estimated reductions: (68) 

In certain situations, no CMF or study findings will be available for a particular treatment. A 

qualitative assessment of safety risk at the considered treatment may be undertaken. Safety risk 

is used to determine the relative severity of each issue or problem, and is a function of the 

exposure of the different road users; the probability of a crash occurring under the geometric, 

environmental, and traffic characteristics; and the likely consequences of a crash. This concept is 

further explored in a 2002 paper by de Leur and Sayed.(69)
142 Federal Highway Administration 

Exposure. Exposure typically is measured in terms of traffic volume, including passenger 

vehicles, trucks, pedestrians, and bicyclists. Exposure is also expressed in distance traveled or 

in time spent on the roadway. With increased exposure, the more a person is involved in road 

traffic, the more likely it is that the person will be involved in a collision. 

Probability. The probability of a crash measures the degree of certainty that a particular 

event would occur. Probability is dependent upon design parameters, traffic operations, time 

periods, environmental conditions, and traffic characteristics. 

Consequence. The consequence refers to the severity of an injury sustained by a person 

involved in an accident. Severity is measured in terms of property damage collisions, injuries, or 

fatalities. 

Using the approach described above, consideration may be given to treatments having no 

quantifiable safety benefit. Such treatments should be considered with caution, however, as 

described below. 

6.4.5 Selected Treatment(s) 

As a result of the above, the traffic engineer will have selected a set of treatments, some 

having an associated dollar value indicating the societal benefit in terms of collision avoided. 

These treatments should all be carried forward for the improvement plan development discussed 

in the next section. 

6.5 IMPROVEMENT PLAN DEVELOPMENT 

The stages in the improvement plan development are: 

• Creating an implementation schedule. 

• Producing a final plan. 

Findings from the safety analysis should be carried forward in coordination with the findings 

of the operational analysis; the two components together can be carried forward into an 

improvement plan. 

Treatments that have quantifiable safety benefits, based on the results of the numerical 

analysis, may be considered with some degree of confidence using a cost-benefit analysis. The 

cost of implementing the treatment should be considered in terms of construction, operating, and 

maintenance costs, if applicable, and then compared to the benefits in terms of the societal cost 

of collisions avoided. 

A treatment with no quantifiable safety benefit also can be evaluated in a cost-benefit 

analysis, but the results should be treated with caution. The study team should recognize the 

reduced confidence in a treatment’s ability to effect an improvement in safety. The following 

questions may help the team decide whether to implement such a treatment: 

• Does the study team believe that the treatment would be associated with a significant 

improvement in safety? 

• Can the treatment be implemented with relatively few (or no) construction, 

maintenance, and operating costs? 

• Would the treatment significantly benefit vulnerable road users? 

• Do other incidental benefits result from implementing the treatment? 

In developing an improvement plan, the study team will need to refer to the findings of the 

operational analysis. The operational analysis provides recommendations that address the 

identified operational problems occurring at the intersection. These recommendations may be in 

agreement with the recommended treatments of the safety analysis. 
Signalized Intersections: Informational Guide 143

Operational Analysis Methods 

CHAPTER 7 

OPERATIONAL ANALYSIS METHODS 

TABLE OF CONTENTS 

7.0 OPERATIONAL ANALYSIS METHODS ............................................................................145 

7.1 Operational Measures of Effectiveness ....................................................................146 

 7.1.1 Motor Vehicle Capacity and Volume-to-Capacity Ratio...............................147 

 7.1.2 Motor Vehicle Delay and Level of Service ...................................................148 

 7.1.3 Motor Vehicle Queue ...................................................................................148 

 7.1.4 Transit Level of Service ...............................................................................149 

 7.1.5 Bicycle Level of Service...............................................................................149 

 7.1.6 Pedestrian Level of Service .........................................................................150 

7.2 Traffic Operations Elements .....................................................................................151 

 7.2.1 Traffic Volume Characteristics.....................................................................151 

 7.2.2 Intersection Geometry..................................................................................152 

 7.2.3 Signal Timing ...............................................................................................152 

7.3 Rules of Thumb for Sizing an Intersection................................................................153 

7.4 Critical Movement Analysis.......................................................................................154 

7.5 HCM Operational Procedure for Signalized Intersections ........................................157 

7.6 Arterial and Network Signal Timing Models..............................................................157 

7.7 Microscopic Simulation Models.................................................................................158 

LIST OF FIGURES 

Figure Page

53 Still reproduction of a graphic from an animated traffic operations model .........................146 

54 Overview of intersection traffic analysis models.................................................................147 

55 Pedestrian LOS based on cycle length and minimum effective pedestrian green time .....151 

56 Graphical summary of the Quick Estimation Method .........................................................155 

LIST OF TABLES 

Table Page

33 Motor vehicle LOS thresholds at signalized intersections ..................................................148 

34 Bicycle LOS thresholds at signalized intersections ............................................................150 

35 Pedestrian LOS thresholds at signalized intersections ......................................................150 

36 Planning-level guidelines for sizing an intersection............................................................153 

37 V/C ratio threshold descriptions for the Quick Estimation Method .....................................156 

Signalized Intersections: Informational Guide 145

Operational Analysis Methods

7. OPERATIONAL ANALYSIS METHODS 

Chapter 6 described tools that can be used to assess the safety performance at a signalized 

intersection. Evaluating a candidate treatment usually requires that its performance also be 

assessed from the perspective of traffic operations. This chapter will, therefore, focus on 

measures for assessing operational performance and computational procedures used to 

determine specific values for those measures. 

The relationships between safety performance and operational performance are difficult to 

define in general terms. Some intersection treatments that would improve safety might also 

improve operational performance, but others might diminish operational performance. 

Furthermore, the nature of safety and operational measures makes them difficult to combine in a 

way that would represent both perspectives. 

Operational performance measures tend to be fewer in number and more easily related to 

site-specific conditions than are safety performance measures. The computations themselves 

are more amenable to deterministic models, and a wide variety of such models, mostly software 

based, is available. Selecting a model for a specific purpose is generally based on the tradeoff 

between the difficulty of applying the model and the required degree of accuracy and confidence 

in the results. The degree of application difficulty is reflected in the required amount of sitespecific data as well as the level of personnel time and training needed to apply the model and to 

interpret the results. 

Recent user interface enhancements in the more advanced traffic model software products 

have made the products much easier to apply; some can generate animated graphics displays 

depicting the movement of individual vehicles and pedestrians in an intersection (an example is in 

figure 53). An increasing trend toward the use and acceptance of advanced traffic modeling 

techniques has occurred as a result of these enhancements. 

While the range of operational performance models is more or less continuous, it will be 

categorized into the following four analysis levels for purposes of this discussion: 

• Rules of thumb for intersection sizing. 

• Critical movement analysis. 

• The HCM 2000 operational analysis procedure.(2)

• Arterial signal timing design and evaluation models. 

• Microscopic simulation models. 

These levels are listed in order of complexity and application difficulty, from least to greatest. 

They are summarized in figure 54 in terms of their inputs, outputs and the data that may flow 

between them. Each analysis levels will be discussed separately. 

The process for evaluating the operational performance of an intersection remains 

unchanged regardless of the analysis level and the issues at hand. The analysis should begin at 

the highest level and should continue to the next level of detail until the key operations-related 

issues and concerns have been addressed in sufficient detail. 
146 Federal Highway Administration

Figure 53. Still reproduction of a graphic from an animated traffic operations model. 

The ability to measure, evaluate, and forecast traffic operations is a fundamental element of 

effectively diagnosing problems and selecting appropriate treatments for signalized intersections. 

A traffic operations analysis should describe how well an intersection accommodates demand for 

all user groups. Traffic operations analysis can be used at a high level to size a facility and at a 

refined level to develop signal timing plans. This section describes key elements of signalized 

intersection operations and provides guidance for evaluating results. 

7.1 OPERATIONAL MEASURES OF EFFECTIVENESS 

Three measures of effectiveness are commonly used to evaluate signalized intersection 

operations: 

• Capacity and volume-to-capacity ratio. 

• Delay. 

• Queue. 

The HCM 2000 estimates measures of effectiveness by lane group.(2) A lane group includes 

a movement or movements that share a common stop bar. Exclusive turn lanes are generally 

treated as individual lane groups (i.e., right-turn-only lane). Shared movements (such as one or 

more through lanes that are also serving right turns) are represented as a single lane group. 

Lane group results can be aggregated by approach and for an entire intersection. 
Signalized Intersections: Informational Guide 147

Operational Analysis Methods

Other international capacity analysis procedures, including the Australian-based SIDRA 

software analysis package,(70) the Canadian capacity guide,(71) and the Swedish capacity 

guide,(72) provide methods for estimating performance measures at the individual lane level. 

These procedures implicitly assume an equal volume-to-capacity (v/c) ratio across “choice lanes” 

(i.e., a through and a through/right-turn lane). 

Figure 54. Overview of intersection traffic analysis models.

7.1.1 Motor Vehicle Capacity and Volume-to-Capacity Ratio 

Capacity is defined as the maximum rate at which vehicles can pass through a given point in 

an hour under prevailing conditions; it is often estimated based on assumed values for saturation 

flow. Capacity accounts for roadway conditions such as the number and width of lanes, grades, 

and lane use allocations, as well as signalization conditions. Under the HCM 2000 procedure, 

intersection capacity is measured for critical lane groups (those lane groups that requires the 

most amount of green time). Intersection volume-to-capacity ratios are based on critical lane 
148 Federal Highway Administration

groups; noncritical lane groups do not constrain the operations of a traffic signal. Rules for 

determining critical lane groups are further explained in HCM 2000. 

Research conducted as part of the 1985 HCM showed that the capacity for the critical lanes 

at a signalized intersection was approximately 1,400 vehicles per hour.(73) This capacity is a 

planning-level estimate that incorporates the effects of loss time and typical saturation flow rates. 

Studies conducted in the State of Maryland have shown that signalized intersections in urbanized 

areas have critical lane volumes upwards of 1,800 vehicles per hour.(74)

The v/c ratio, also referred to as degree of saturation, represents the sufficiency of an 

intersection to accommodate the vehicular demand. A v/c ratio less than 0.85 generally indicates 

that adequate capacity is available and vehicles are not expected to experience significant 

queues and delays. As the v/c ratio approaches 1.0, traffic flow may become unstable, and delay 

and queuing conditions may occur. Once the demand exceeds the capacity (a v/c ratio greater 

than 1.0), traffic flow is unstable and excessive delay and queuing is expected. Under these 

conditions, vehicles may require more than one signal cycle to pass through the intersection 

(known as a cycle failure). For design purposes, a v/c ratio between 0.85 and 0.95 generally is 

used for the peak hour of the horizon year (generally 20 years out). Overdesigning for an 

intersection should be avoided due to negative impacts to pedestrians associated with wider 

street crossings, the potential for speeding, land use impacts, and cost. 

7.1.2 Motor Vehicle Delay and Level of Service 

Delay is defined in HCM 2000 as “the additional travel time experienced by a driver, 

passenger, or pedestrian.”(2) The signalized intersection chapter (chapter 16) of the HCM 

provides equations for calculating control delay, the delay a motorist experiences that is 

attributable to the presence of the traffic signal and conflicting traffic. This includes time spent 

decelerating, in queue, and accelerating. 

The control delay equation comprises three elements: uniform delay, incremental delay, and 

initial queue delay. The primary factors that affect control delay are lane group volume, lane 

group capacity, cycle length, and effective green time. Factors are provided that account for 

various conditions and elements, including signal controller type, upstream metering, and delay 

and queue effects from oversaturated conditions. 

Control delay is used as the basis for determining LOS. Intersection control delay is 

generally computed as a weighted average of the average control delay for all lane groups based 

on the amount of volume within each lane group. Caution should be exercised when evaluating 

an intersection based on a single value of control delay because this is likely to over- or 

underrepresent operations for individual lane groups. Delay thresholds for the various LOS are 

given in table 33. 

Table 33. Motor vehicle LOS thresholds at signalized intersections.(2)

LOS 

Control Delay per Vehicle 

(seconds per vehicle) 

A ≤ 10 

B > 10-20 

C > 20-35 

D > 35-55 

E > 55-80 

F > 80 

7.1.3 Motor Vehicle Queue 

Vehicle queuing is an important measure of effectiveness that should be evaluated as part of 

all analyses of signalized intersections. Estimates of vehicle queues are needed to determine the 
Signalized Intersections: Informational Guide 149

Operational Analysis Methods

amount of storage required for turn lanes and to determine whether spillover occurs at upstream 

facilities (driveways, unsignalized intersections, signalized intersections, etc.). Approaches that 

experience extensive queues also are likely to experience an overrepresentation of rear-end 

collisions. 

Vehicle queues for design purposes are typically estimated based on the 95th percentile 

queue that is expected during the design period. Appendix G to chapter 16 of the HCM 2000

provides procedures for calculating back of queue. In addition, all known simulation models 

provide ways of obtaining queue estimates. 

7.1.4 Transit Level of Service 

The assessment of transit capacity and quality of service is the subject of its own reference 

document, the Transit Capacity and Quality of Service Manual.(75) In addition, on-street elements 

from that document are presented in the HCM 2000 in chapters 14 and 27.(2) Space does not 

permit the reproduction of these elements in this document; therefore the reader is encouraged to 

review these references for more information on the variety of quality-of-service measures and 

capacity estimation techniques available. 

7.1.5 Bicycle Level of Service 

The HCM 2000 provides an analysis procedure for assessing the LOS for bicycles at 

signalized intersections where there is a designated on-street bicycle lane on at least one 

approach. This section replicates the procedure from chapter 19 of the HCM 2000. 

Many countries have reported a wide range of capacities and saturation flow rates for bicycle 

lanes at signalized intersections. The HCM 2000 recommends the use of a saturation flow rate of 

2,000 bicycles per hour as an average value achievable at most intersections. This rate assumes 

that right-turning motor vehicles yield the right-of-way to through bicyclists. Where aggressive 

right-turning traffic exists, this rate may not be achievable, and local observations are 

recommended to determine an appropriate saturation flow rate. 

Using the default saturation flow rate of 2,000 bicycles per hour, the capacity of the bicycle 

lane at a signalized intersection may be computed using equation 6: 

C

g

C

g c s b = b = 2000 (6) 

Where: cb = capacity of bicycle lane (bicycles/hour) 

 sb = saturation flow rate of bicycle lane (bicycles/hour) 

 g = effective green time for bicycle lane in seconds (s) 

 C = signal cycle length (s) 

At most signalized intersections, the only delay to bicycles is caused by the signal itself 

because bicycles have right-of-way over turning motor vehicles. Where bicycles are forced to 

weave with motor vehicle traffic or where bicycle right-of-way is disrupted due to turning traffic, 

additional delay may be incurred. Control delay is estimated using the first term of the delay 

equation for motor vehicles at signalized intersections, which assumes that there is no overflow 

delay. This is reasonable in most cases, as bicyclists will not normally tolerate an overflow 

situation and will use other routes. This control delay is estimated using equation 7: 

⎥

⎦

⎤ ⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ −

⎟

⎠

⎞ ⎜

⎝

⎛ −

=

1 min ,1.0

0.5 1

2

b

b

b

c

v

C

g

C

g C

d (7) 
150 Federal Highway Administration

Where: db = control delay (s/bicycle) 

g = effective green time for bicycle lane (s) 

 C = signal cycle length (s) 

 vb = flow rate of bicycles in the bicycle lane (one direction) (bicycles/h)

 cb = capacity of bicycle lane (bicycles/h) 

Table 34 indicates LOS criteria for bicycles at signalized intersections on the basis of control 

delay. 

Table 34. Bicycle LOS thresholds at signalized intersections.(2)

LOS Control Delay per Bicycle (s/bicycle) 

A ≤ 10 

B > 10-20 

C > 20-30 

D > 30-40 

E > 40-60 

F > 60 

7.1.6 Pedestrian Level of Service 

In the HCM 2000 (chapter 18), pedestrian LOS is determined based on the average delay per 

pedestrian (i.e., wait time). Pedestrian delay is calculated using two parameters: cycle length and 

effective green time for pedestrians. In the absence of field data, the HCM 2000 recommends 

estimating effective green time for pedestrians by taking the walk interval and adding 4 seconds 

of the flashing DON’T WALK interval to account for pedestrians who depart the curb after the 

start of flashing DON’T WALK. Equation 8 shows the equation for calculating pedestrian delay 

based on equation 18-5 of the HCM 2000: 

( )

C

C g d p

2 .5 − = (8) 

Where: dp = average pedestrian delay (s) 

 C = cycle length (s) 

 g = effective green time for pedestrians (s) 

Table 35 indicates the LOS thresholds for pedestrian crossings at signalized intersections. 

Table 35. Pedestrian LOS thresholds at signalized intersections.(2)

LOS Pedestrian Delay (sec/ped) Likelihood of Noncompliance 

A < 10 Low 

B ≥ 10-20 

C > 20-30 Moderate 

D > 30-40 

E > 40-60 High 

F > 60 Very High 

Figure 55 illustrates the amount of effective green time required for pedestrians to achieve 

each LOS threshold based on a specified cycle length. As shown in the figure, the amount of 

green time required for pedestrian crossings to meet a LOS D standard increases with longer 
Signalized Intersections: Informational Guide 151

Operational Analysis Methods

cycle lengths. For cycle lengths in excess of 150 seconds, a minimum pedestrian effective green 

time of 40 seconds is required to maintain LOS D. 

Note: FDW = Flashing “DON’T WALK” 

Figure 55. Pedestrian LOS based on cycle length and minimum effective pedestrian green time.(2)

7.2 TRAFFIC OPERATIONS ELEMENTS 

Signalized intersection operations are a function of three elements described in the following 

sections along with a discussion on their effect on operations. 

• Traffic volume characteristics. 

• Roadway geometry. 

• Signal timing. 

7.2.1 Traffic Volume Characteristics 

The traffic characteristics used in an analysis can play a critical role in determining 

intersection treatments. Overconservative judgment may result in economic inefficiencies due to 

the construction of unnecessary treatments, while the failure to account for certain conditions 

(such as a peak recreational season) may result in facilities that are inadequate and experience 

failing conditions during certain periods of the year. 

An important element of developing an appropriate traffic profile is distinguishing between 

traffic demand and traffic volume. For an intersection, traffic demand represents the arrival 

pattern of vehicles, while traffic volume is generally measured based on vehicles’ departure rate. 

For the case of overcapacity or constrained situations, the traffic volume may not reflect the true 
152 Federal Highway Administration

demand on an intersection. In these cases, the user should develop a demand profile. This can 

be achieved by measuring vehicle arrivals upstream of the overcapacity or constrained approach. 

The difference between arrivals and departures represents the vehicle demand that does not get 

served by the traffic signal. This volume should be accounted for in the traffic operations 

analysis. 

Traffic volume at an intersection may also be less than the traffic demand due to an 

overcapacity condition at an upstream or downstream signal. When this occurs, the upstream or 

downstream facilities “starve” demand at the subject intersection. This effect is often best 

accounted for using a microsimulation analysis tool. 

7.2.2 Intersection Geometry 

The geometric features of an intersection influence the service volume or amount of traffic an 

intersection can process. A key measure used to establish the supply of an intersection is 

saturation flow, which is similar to capacity in that it represents the number of vehicles that 

traverse a point per hour; however, saturation flow is reported assuming the traffic signal is green 

the entire hour. By knowing the saturation flow and signal timing for an intersection, one can 

calculate the capacity (capacity = saturation flow times the ratio of green time to cycle length). 

Saturation headway is determined by measuring the average time headway between vehicles 

that discharge from a standing queue at the start of green, beginning with the fourth vehicle.(2)

Saturation headway is expressed in time (seconds) per vehicle. 

Saturation flow rate is simply determined by dividing the average saturation headway into the 

number of seconds in an hour, 3,600, to yield units of vehicles per hour. The HCM 2000 uses a 

default ideal saturation flow rate of 1,900 vehicles per hour. Ideal saturation flow assumes 3.6-m 

(12-ft)-wide travel lanes, through movements only, and no curbside impedances, 

pedestrians/bicyclists, grades, or central business district influences. The HCM 2000 provides 

adjustment factors for nonideal conditions to estimate the prevailing saturation flow rate. 

Saturation flow rate can vary in time and location. Saturation flow rates have been observed to 

range between 1,500 and 2,000 passenger cars per hour per lane.(2) Given the variation that 

exists in saturation flow rates, local data should be collected where possible to increase the 

accuracy of the analysis. 

Existing or planned intersection geometry should be evaluated to determine features that 

may impact operations and that require special consideration. 

7.2.3 Signal Timing 

The signal timing of an intersection also plays an important role in its operational 

performance. Key factors include: 

• Effective green time. Effective green time represents the amount of usable time 

available to serve vehicular movements during a phase of a cycle. It is equal to the 

displayed green time minus startup loss time plus end gain. The effective green time 

for each phase is generally determined based on the proportion of volume in the 

critical lane for that phase relative to the total critical volume of the intersection. If not 

enough green time is provided, vehicle queues will not be able to clear the 

intersection, and cycle failures will occur. If too much green time is provided, portions 

of the cycle will be unused resulting in inefficient operations and frustration for drivers 

on the adjacent approaches. 

• Clearance interval. The clearance interval represents the amount of time needed for 

vehicles to safely clear the intersection and includes the yellow change and red 

clearance intervals. The capacity effect of the clearance interval is dependent upon 

the loss time.

• Loss time. Loss time represents the unused portion of a vehicle phase. Loss time 

occurs twice during a phase: at the beginning when vehicles are accelerating from a 
Signalized Intersections: Informational Guide 153

Operational Analysis Methods

stopped position, and at the end when vehicles decelerate in anticipation of the red 

indication. Longer loss times reduce the amount of effective green time available and 

thus reduce the capacity of the intersection. Wide intersections and intersections with 

skewed approaches or unusual geometrics typically experience greater loss times 

than conventional intersections. 

• Cycle length. Cycle length determines how frequently during the hour each 

movement is served. It is either a direct input, in the case of pre-timed or coordinated 

signal systems running a common cycle length, or an output of vehicle actuations, 

minimum and maximum green settings, and clearance intervals. Cycle lengths that 

are too short do not provide adequate green time for all phases and result in cycle 

failures. Longer cycle lengths result in increased delay and queues for all users. 

• Progression. Progression is the movement of vehicle platoons from one signalized 

intersection to the next. A well-progressed or well-coordinated system moves 

platoons of vehicles so that they arrive during the green phase of the downstream 

intersection. When this occurs, fewer vehicles arrive on red, and vehicle delay and 

queues are minimized. A poorly coordinated system moves platoons such that 

vehicles arrive on red, which increases the delay and queues for those movements 

beyond what would be experienced if random arrivals occurred. 

7.3 RULES OF THUMB FOR SIZING AN INTERSECTION 

This is the first level of analysis. It is the only level that does not use formal models or 

procedures. Instead, it relies on the collective experience of past practice. As such, it offers only 

a very coarse approximation of a final answer. 

In spite of its obvious limitations, this approach can be used to size an intersection and 

determine appropriate lane configurations. The literature provides guidelines, shown in table 36, 

for determining intersection geometry at the planning level. 

Table 36. Planning-level guidelines for sizing an intersection. 

Geometric Property Comment 

Number of lanes(2) As a general suggestion, enough roadway lanes should be provided to prevent a lane from 

exceeding 450 vehicles per hour. Mainline facilities that are allocated the majority of green 

time may accommodate higher volumes. 

Other elements that should be considered in the sizing of a facility include the number of 

upstream/downstream lanes, lane balance, signal design elements, pedestrian/bicycle 

effects, right-of-way constraints, and safety implications. 

Exclusive left-turn lanes(2) The decision to provide an exclusive left-turn lane should generally be based on the volume 

of left-turning and opposing traffic, intersection design, and safety implications. Exclusive 

left-turn lanes should be investigated when a left-turn volume exceeds 100 vehicles per 

hour. Dual left-turn lanes could be considered when the left-turn volume exceeds 300 

vehicles per hour. On some facilities, left-turn lanes may be desirable at all locations 

regardless of volume. 

Exclusive right-turn lanes(2) The provision of right-turn lanes reduces impedances between lower speed right-turning 

vehicles and higher speed left-turning vehicles. Separating right turns also reduces the 

green time required for a through lane. Safety implications associated with pedestrians and 

bicyclists should be considered. In general, a right-turn lane at a signalized intersection 

should be considered when the right-turn volume and adjacent through lane volume each 

exceeds 300 vehicles per hour. 

Left-turn storage bay length(41) Storage bays should accommodate twice the average number of left-turn arrivals during a 

cycle. 
154 Federal Highway Administration

7.4 CRITICAL MOVEMENT ANALYSIS 

Critical movement analysis (CMA) is usually applied at the planning stage; represents the 

highest of the 4 levels of operational performance models. Various versions of CMA procedures 

have been widely used over the past 20 years, including: 

• Transportation Research Board (TRB) Circular 212,(76) which presented interim capacity 

materials that preceded the release of the 1985 HCM.(73)

• The Intersection Capacity Utilization (ICU) method, which is popular in parts of California. 

• The HCM Planning Method, as set forth in the 1985, 1994, and 1997 versions of the 

HCM.(73,77,78)

• The Quick-Estimation Method (QEM), which now appears in the HCM 2000 as a 

refinement of the planning method found in previous HCM editions.(2)

Most agencies would consider the QEM to be the most current, and therefore the preferred, 

procedure for conducting critical movement analyses; thus it will be described in detail here. 

The QEM procedures can be carried out by hand, although software implementation is much 

more productive. The computations themselves are somewhat complex, but the minimal 

requirement for site-specific field data (traffic volumes and number of lanes) is what puts the QEM 

into the category of a simple procedure. While the level of output detail is simplified in 

comparison to more data-intensive analysis procedures, the QEM provides a useful description of 

the operational performance by answering the following questions: 

• What are the critical movements at the intersection? 

• Is the intersection operating below, near, at, or above capacity? 

• Where are capacity improvements needed? 

The requirement for site-specific data is minimized through the use of assumed values for 

most of the operating parameters and by a set of steps that synthesizes a “reasonable and 

effective” operating plan for the signal. Figure 56 illustrates the various steps involved in 

conducting a QEM analysis, and table 37 identifies the various thresholds for v/c ratio. 
Signalized Intersections: Informational Guide 155

Operational Analysis Methods

Figure 56. Graphical summary of the Quick Estimation Method. 

Step 1—Identify movements to be served and assign hourly traffic volumes per lane. This is the 

only site-specific data that must be provided. The hourly traffic volumes are usually adjusted to 

represent the peak 15-minute period. The number of lanes must be known to compute the hourly 

volumes per lane. 

Step 2—Arrange the movements into the desired signal phasing plan. The phasing plan is based 

on the treatment of each left turn (protected, permitted, etc.). The actual left-turn treatment may 

be used, if known. Otherwise, the likelihood of needing left-turn protection on each approach will 

be established from the left-turn volume and the opposing through traffic volume. 

Step 3—Determine the critical volume per lane that must be accommodated on each phase. 

Each phase typically accommodates two nonconflicting movements. This step determines which 

movements are critical. The critical movement volume determines the amount of time that must 

be assigned to the phase on each signal cycle. 

Step 4—Sum the critical phase volumes to determine the overall critical volume that must be 

accommodated by the intersection. This is a simple mathematical step that produces an estimate 

of how much traffic the intersection needs to accommodate. 

Step 5—Determine the maximum critical volume that the intersection can accommodate: This 

represents the overall intersection capacity. The HCM QEM suggests 1,710 vph for most 

purposes. 

Step 6—Determine the critical volume-to-capacity ratio, which is computed by dividing the overall 

critical volume by the overall intersection capacity, after adjusting the intersection capacity to 

account for time lost due to starting and stopping traffic on each cycle. The lost time will be a 

function of the cycle length and the number of protected left turns. 

Step 7—Determine the intersection status from the critical volume-to-capacity ratio. The status 

thresholds are given in table 37. 
156 Federal Highway Administration

Table 37. V/C ratio threshold descriptions for the Quick Estimation Method.(2)

Critical Volume-to-Capacity 

Ratio Assessment 

< 0.85 Intersection is operating under capacity. Excessive delays are not 

experienced. 

0.85-0.95 Intersection is operating near its capacity. Higher delays may be 

expected, but continuously increasing queues should not occur. 

0.95-1.0 Unstable flow results in a wide range of delay. Intersection 

improvements will be required soon to avoid excessive delays. 

> 1.0 The demand exceeds the available capacity of the intersection. 

Excessive delays and queuing are anticipated. 

Understanding the critical movements and critical volumes of a signalized intersection is a 

fundamental element of any capacity analysis. A CMA should be performed for all intersections 

considered for capacity improvement. The usefulness and effectiveness of this step should not 

be overlooked, even for cases where more detailed levels of analysis are required. The CMA 

procedure gives a quick assessment of the overall sufficiency of an intersection. For this reason, 

it is useful as a screening tool for quickly evaluating the feasibility of a capacity improvement and 

discarding those that are clearly not viable. 

Some limitations of CMA procedures in general, and the QEM in particular: 

• No provision exists for the situation of when the timing requirements for a concurrent 

pedestrian phase (such as for crossing a wide street) exceed the timing requirements 

for the parallel vehicular phase. As a result, the CMA procedure may underestimate 

the green time requirements for a particular phase. 

• A fixed value is assumed for the overall intersection capacity per lane. Adjustment 

factors are not provided to account for differing conditions among various sites and 

there is no provision for the use of field data to override the fixed assumption. 

• Complex phasing schemes such as lagging left-turn phases, right-turn overlap with a 

left-turn movement, exclusive pedestrian phases, leading/lagging pedestrian intervals, 

etc., are not considered. Significant operational and/or safety benefits can sometimes 

be achieved by the use of complex phasing. 

• Loss time is not directly accounted for in the CMA procedures. Therefore, the effect of 

longer change and clearance intervals cannot be directly accommodated with this 

procedure. 

• The synthesized operating plan for the signal does not take minimum green times into 

account, and therefore may not be readily implemented as a part of an intersection 

design. The HCM specifically warns against the use of the QEM for signal timing 

design. 

• Performance measures (e.g., control delay, LOS, and back of queue) are not 

provided. 

For these reasons, it frequently will be necessary to examine the intersection using a more 

detailed level of operational performance modeling. 
Signalized Intersections: Informational Guide 157

Operational Analysis Methods

7.5 HCM OPERATIONAL PROCEDURE FOR SIGNALIZED INTERSECTIONS 

For many applications, performance measures such as vehicle delay, LOS, and queues are 

desired. These measures are not reported by the CMA procedures, but are provided by 

macroscopic-level procedures such as the HCM operational analysis methodology for signalized 

intersections. This procedure is represented as the second analysis level in figure 54. 

Macroscopic-level analyses provide results over multiple cycle lengths based on hourly vehicle 

demand and service rates. HCM analyses are commonly performed for 15-minute periods to 

accommodate the heaviest part of the peak hour. 

The HCM analysis procedures provide estimates of saturation flow, capacity, delay, LOS, and 

back of queue by lane group for each approach. Exclusive turn lanes are considered as separate 

lane groups. Lanes with movements that are shared are considered a single lane group. Lane 

group results can be aggregated to estimate average control delay per vehicle at the intersection 

level. 

The increased output detail compared to the CMA procedure is obtained at the expense of 

additional input data requirements. A complete description of intersection geometrics and 

operating parameters must be provided. Several factors that influence the saturation flow rates 

(e.g., lane width, grade, parking, pedestrians) must be specified. A complete signal operating 

plan, including phasing, cycle length, and green times, must be developed externally. As 

indicated in figure 54, an initial signal operating plan may be obtained from the QEM, or a more 

detailed and implementable plan may be established using a signal timing model that represents 

the next level of analysis. Existing signal timing may also be obtained from the field. 

In addition to the signalized intersection procedure, the HCM also includes procedures to 

estimate the LOS for bicyclists, pedestrians, and transit users at signalized intersections. These 

have been discussed previously in this chapter. 

Known limitations of the HCM analysis procedures for signalized intersections exist under the 

following conditions: 

• Available software products that perform HCM analyses generally do not 

accommodate intersections with more than four approaches. 

• The analysis may not be appropriate for alternative intersection designs. 

• The effect of queues that exceed the available storage bay length is not treated in 

sufficient detail, nor is the backup of queues that block a stop line during a portion of 

the green time. 

• Driveways located within the influence area of signalized intersections are not 

recognized. 

• The effect of arterial progression in coordinated systems is recognized, but only in 

terms of a coarse approximation. 

• Heterogeneous effects on individual lanes within multilane lane groups (e.g., 

downstream taper, freeway on-ramp, driveways) are not recognized. 

If any of these conditions exist, it may be necessary to proceed to the next level of analysis. 

7.6 ARTERIAL AND NETWORK SIGNAL TIMING MODELS 

As with the HCM procedures, arterial and network signal timing models are also macroscopic 

in nature. They do, however, deal with a higher level of detail, and are more oriented to 

operational design than is the HCM. The effect of traffic progression between intersections is 

treated explicitly, either as a simple time-space diagram or a more complex platoon propagation 

phenomenon. In addition, these models can explicitly account for pedestrian actuations at 

intersections and their effect on green time for affected phases. 
158 Federal Highway Administration

These models attempt to optimize some aspect of the system performance as a part of the 

design process. The two most common optimization criteria are quality of progression as 

perceived by the driver, and overall system performance, using measures such as stops, delay, 

and fuel consumption. As indicated in figure 54, the optimized signal timing plan may be passed 

back to the HCM analysis or forward to the next level of analysis, which involves microscopic 

simulation. 

While the signal timing models are more detailed than the HCM procedures in most respects, 

they are less detailed when it comes to determining the saturation flow rates. The HCM provides 

the computational structure for determining saturation flow rates as a function of geometric and 

operational parameters. On the other hand, saturation flow rates are generally treated as input 

data by signal timing models. The transfer of saturation flow rate data between the HCM and the 

signal timing models is therefore indicated on figure 54 as a part of the data flow between the 

various analysis levels. 

The additional detail present in the signal timing models overcomes many of the limitations of 

the HCM for purposes of operational analysis of signalized intersections. It will not generally be 

necessary to proceed to the final analysis level, which involves microscopic simulation, unless 

complex interactions take place between movements or additional outputs, such as animated 

graphics, are considered desirable. 

7.7 MICROSCOPIC SIMULATION MODELS 

For cases where individual cycle operations and/or individual vehicle operations are desired, 

a microscopic-level analysis should be considered to supplement the aggregate results provided 

by the less detailed analysis levels. Microscopic analyses are performed using one or more of 

several simulation software products. Microsimulation analysis tools are based on a set of rules 

used to propagate the position of vehicles from one second to the next. Rules such as car 

following, yielding, response to signals, etc., are an intrinsic part of each simulation software 

package. The rules are generally stochastic in nature, in other words there is a random variability 

associated with each aspect of the operation. Some simulation tools produce animated graphical 

outputs to illustrate the operating conditions on a vehicle-by-vehicle and second-by-second basis 

for a given time period. Some simulation models can explicitly model pedestrians, enabling the 

analyst to study the impedance effects of vehicles on pedestrians and vice versa. However, the 

pedestrian modeling ability of most simulation programs is quite simplistic and does not capture 

the full range of pedestrian activity and ability. 

Microscopic models produce nominally the same measures of effectiveness as their 

macroscopic counterparts, although minor differences exist in the definition of some measures. 

Pollutant discharge measures are typically included in microscopic results. Interestingly, one of 

the most important measures, capacity, is notably absent from simulation results because the 

nature of simulation models does not lend itself to capacity computations 

Microscopic simulation tools can be particularly effective for cases where intersections are 

located within the influence area of adjacent signalized intersections and are affected by 

upstream and/or downstream operations. In addition, graphical simulation output may be desired 

to verify field observations and/or provide a visual description of traffic operations for an 

audience. Microscopic simulation tools also can be used to identify the length of time that a 

condition occurs, and can account for the capacity and delay effects associated with known 

system-wide travel patterns. 

The level of effort involved with developing a microscopic simulation network is considerably 

greater than that of a macroscopic analysis, and enormously greater than a critical movement 

analysis. Like the HCM operational procedure, microscopic simulation tools require a fully 

specified signal-timing plan that must be generated externally. Unlike the HCM, however, an 

extensive calibration effort using field data is essential to the production of credible results. For 

this reason, the decision of whether to use a microscopic simulation tool should be made on a 

case-by-case basis, considering the resources available for acquisition of the software and for 

collecting the necessary data for calibrating the model to the intersection being studied. 
Signalized Intersections: Informational Guide 159

Part III—Treatments

Part III 

Treatments 

Part III includes a description of treatments that can be applied to signalized intersections to 

mitigate an operational and/or safety deficiency. The treatments are organized as follows: SystemWide Treatments (chapter 8), Intersection-Wide Treatments (chapter 9), Alternative Intersection 

Treatments (chapter 10), Approach Treatments (chapter 11), and Individual Movement Treatments 

(chapter 12). It is assumed that before readers begin to examine treatments in part III, they will already 

have familiarized themselves with the fundamental elements described in part I and the project process 

and analysis methods described in part II. 

Signalized Intersections: Informational Guide 161

System-Wide Treatments

CHAPTER 8 

SYSTEM-WIDE TREATMENTS 

TABLE OF CONTENTS 

8.0 SYSTEM-WIDE TREATMENTS.........................................................................................163 

 8.1 Median Treatments ...................................................................................................163 

 8.1.1 Description ...................................................................................................163 

 8.1.2 Applicability ..................................................................................................163 

 8.1.3 Key Design Features ...................................................................................163 

 8.1.4 Safety Performance .....................................................................................169 

 8.1.5 Operational Performance.............................................................................169 

 8.1.6 Multimodal Impacts ......................................................................................169 

 8.1.7 Physical Impacts ..........................................................................................170 

 8.1.8 Socioeconomic Impacts ...............................................................................170 

 8.1.9 Enforcement, Education, and Maintenance.................................................170 

 8.1.10 Summary......................................................................................................170 

 8.2 Access Management.................................................................................................171 

 8.2.1 Description ...................................................................................................171 

 8.2.2 Applicability ..................................................................................................172 

 8.2.3 Design Features...........................................................................................172 

 8.2.4 Safety Performance .....................................................................................177 

 8.2.5 Operational Performance.............................................................................177 

 8.2.6 Multimodal Impacts ......................................................................................178 

 8.2.7 Physical Impacts ..........................................................................................178 

 8.2.8 Socioeconomic Impacts ...............................................................................178 

 8.2.9 Enforcement, Education, and Maintenance.................................................178 

 8.2.10 Summary......................................................................................................178 

 8.3 Signal Coordination...................................................................................................179 

 8.3.1 Description ...................................................................................................179 

 8.3.2 Applicability ..................................................................................................179 

 8.3.3 Safety Performance .....................................................................................180 

 8.3.4 Operational Performance.............................................................................180 

 8.3.5 Multimodal Impacts ......................................................................................181 

 8.3.6 Physical Impacts ..........................................................................................181 

 8.3.7 Socioeconomic Impacts ...............................................................................181 

 8.3.8 Enforcement, Education, and Maintenance.................................................181 

 8.3.9 Summary......................................................................................................181 

 8.4 Signal Preemption and/or Priority .............................................................................181 

 8.4.1 Description ...................................................................................................181 

 8.4.2 Emergency Vehicle Preemption...................................................................182 

 8.4.3 Applicability ..................................................................................................182 

 8.4.4 Safety Performance .....................................................................................183 

 8.4.5 Operational Performance.............................................................................183 

 8.4.6 Multimodal Impacts ......................................................................................183 

 8.4.7 Physical Impacts ..........................................................................................183 

 8.4.8 Socioeconomic Impacts ...............................................................................183 

 8.4.9 Enforcement, Education, and Maintenance.................................................183 

 8.4.10 Summary......................................................................................................183 
162 Federal Highway Administration

LIST OF FIGURES 

Figure Page

57 Issues associated with intersections with a narrow median ...............................................164 

58 Issues associated with intersections with a wide median...................................................165 

59 Median pedestrian treatments ............................................................................................167 

60 Median pedestrian signal treatments..................................................................................168 

61 This refuge island enables two-stage pedestrian crossings...............................................169 

62 Comparison of physical and functional areas of an intersection ........................................172 

63 Diagram of the upstream functional area of an intersection...............................................173 

64 Access points near signalized intersections .......................................................................175 

65 Access management requiring U-turns at a downstream signalized intersection..............176 

66 Access management requiring U-turns at an unsignalized, directional median opening...176 

LIST OF TABLES 

Table Page

38 Summary of issues for providing median treatments .........................................................171 

39 Relative crash rates for unsignalized intersection access spacing ....................................177 

40 Summary of issues for providing access management......................................................179 

41 Selected findings of safety benefits associated with signal coordination or progression...180 

42 Summary of issues for providing signal coordination .........................................................181 

43 Summary of issues for providing signal preemption and/or priority....................................184 
Signalized Intersections: Informational Guide 163

System-Wide Treatments

8. SYSTEM-WIDE TREATMENTS 

Treatments in this chapter apply to roadway segments located within the influence of 

signalized intersections and intersections affected by the flow of traffic along a corridor. They 

primarily address safety deficiencies associated with rear-end collisions due to sudden 

accelerating/decelerating; turbulence involved with midblock turning movements from driveways 

or unsignalized intersections; and coordination deficiencies associated with the progression of 

traffic from one location to another. Four specific treatments are examined: 

• Median treatments. 

• Access management. 

• Signal coordination. 

• Signal preemption and/or priority. 

8.1 MEDIAN TREATMENTS 

The median of a divided roadway is used for left turns, pedestrian refuge, access to 

properties on the other side of the road, and separation of opposing directions of travel. These 

purposes can conflict, and each use should be considered when design changes are proposed. 

8.1.1 Description 

Median design contributes to safe and efficient operation of intersections, especially left-turn 

movements. Specifically, width and type are key factors in median design. The median provides a 

location for vehicles to wait for a gap in opposing traffic through which to turn; it also separates 

opposing directions of travel. Inappropriate median design may contribute to operational or safety 

problems related to vehicles turning left from the major road and vehicles proceeding through or 

turning left from the minor road. 

8.1.2 Applicability 

Operational or safety issues that provide evidence that median design changes may be 

appropriate include spillover of left-turn lanes into the through traffic stream, rear-end or sideswipe crashes involving left-turning vehicles, inappropriate use of the median, and pedestrian 

crashes. Medians may also form an integral part of an overall access management plan, as 

discussed later. 

8.1.3 Key Design Features 

Width, channelization, end type, and pedestrian treatments are key features of a median 

design. The elements combine to provide storage for left-turning vehicles, guide turning vehicles 

through the intersection, and help pedestrians cross the street. 

Median Width 

Medians physically separate opposing directions of travel, and provide a safety benefit by 

helping reduce occurrence of head-on collisions. It is possible that a median can be so narrow or 

so wide that its safety benefit is canceled by operational or safety problems created by an 

inappropriate width, as shown in figures 57 and 58. 

• Narrow medians: Many of the problems associated with medians that are too narrow 

relate to unsignalized intersections upstream or downstream of the signalized 

intersection in question. These include vehicles stopping in the median at an angle 

instead of perpendicular to the major road, or long vehicles stopping in the median 

and encroaching on major road through lanes. However, pedestrians can have 

difficulty at signalized intersections with medians that are too narrow. At large 

intersections with medians, it is common to allow pedestrians to cross the street in two 
164 Federal Highway Administration

stages. If the median width is too narrow, there may be insufficient room for 

pedestrians to wait safely and comfortably. In addition, there may be insufficient room 

to provide adequate ADA-compliant detectable warning surfaces and, in some cases, 

curb ramps. 

• Wide medians: Just as medians that are too narrow can pose difficulties, overly wide 

medians also can be problematic. At signalized intersections, large medians increase 

motor vehicle and bicycle clearance time, thus adding loss time and delay to the 

intersection. If pedestrians are expected to cross both directions of traffic in one 

crossing, overly wide medians result in very long pedestrian clearance times, which 

often lead to excessively long cycle lengths. Wide medians also can create visibility 

problems for signal displays, which often results in the use of two sets of signal 

indications: one mid-intersection, and one on the far side. This increases the cost of 

construction and operation of the intersection. 

Figure 57. Issues associated with intersections with a narrow median. 
Signalized Intersections: Informational Guide 165

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Figure 58. Issues associated with intersections with a wide median. 

Median Channelization 

The appropriateness of the use of raised or flush medians depends on conditions at a given 

intersection. Raised (curbed) medians should provide guidance in the intersection area but 

should not present a significant obstruction to vehicles. The design should be balanced between 

the desire for it to be cost effective to construct and maintain and for it to provide safe 

channelization. Raised medians should be delineated (such as with reflectors) if lighting is not 

provided at the intersection, since they are sometimes difficult to see at night. AASHTO 

recommends that flush medians are appropriate for intersections with:(3)

• Relatively high approach speeds. 

• No lighting. 

• Little development where access management will not be considered. 

• No sign, signal, or luminaire supports in the median. 

• Little/infrequent snowplowing operations. 

• A need for left-turn storage space. 

• Little or no pedestrian traffic. 
166 Federal Highway Administration

Where left-turn lanes are provided in the median, curbed dividers should be used to separate 

left-turn and opposing through traffic on medians 4.8 m (16 ft) wide or less. These dividers should 

be 1.2 m (4 ft) wide. Medians 5.4 m (18 ft) wide or more should have a painted or physical divider 

that delineates the movements. It is also recommended that the left-turn lane be offset to provide 

improved visibility with opposing through traffic. This treatment is discussed in more detail in 

chapter 12. 

Median End Type 

AASHTO provides the following guidance for median ends:(3, p. 701)

• Semicircular medians and bullet nose median ends perform the same for medians 

approximately 1.2 m (4 ft) wide. 

• Bullet-nose median ends are preferred for medians 3.0 m (10 ft) or more wide. 

A semicircle is an appropriate shape for the end of a narrow median. An alternative design is 

a bullet nose, which is based on the turning radius of the design vehicle. This design better 

guides a left-turning driver through the intersection, because the shape of the bullet nose reflects 

the path of the inner rear wheel. The bullet nose, being elongated, better serves as a pedestrian 

refuge than does a semicircular median end. 

Medians greater than 4.2 m (14 ft) wide with a control radius of 12 m (40 ft) (based on the 

design vehicle) should have the shape of flattened or squared bullets to provide channelization, 

though the length of the median opening will be controlled by the need to provide for cross traffic. 

The median end controls the turning radius for left-turning vehicles. It can affect movement of 

vehicles using that leg of the intersection both to turn left from the approach and to depart from 

the intersection on that leg after turning left from the cross street. A median nose that does not 

significantly limit the turning radius will help turning vehicles proceed through the intersection at 

higher speeds. This could contribute to efficient vehicular operations but could also create 

additional safety issues for pedestrians. 

Median Pedestrian Treatments 

Careful attention should be given to pedestrian treatments at signalized intersections with 

medians, as these intersections tend to be larger than most. Two key treatments are discussed 

here: the design of the pedestrian passage through the median, and the design of the pedestrian 

signalization. 

Pedestrian treatments at medians can be accommodated in two basic ways: a cut-through 

median, where the pedestrian path is at the same grade as the adjacent roadway; and a ramped 

median, where the pedestrian path is raised to the grade of the top of curb. Figure 59 shows the 

basic features and dimensions for each treatment. Note that if the median is too narrow to 

accommodate a raised landing of minimum width, a ramped median design cannot be used. If the 

median is so narrow that a pedestrian refuge cannot be accommodated, then the crosswalk 

should be located outside the median. Per ADAAG, all curb ramps, including those at median 

crossings, must have detectable warnings. Further discussion of pedestrian treatments at 

medians can be found in FHWA’s Designing Sidewalks and Trails for Access: Part II.

(34)
Signalized Intersections: Informational Guide 167

System-Wide Treatments

Figure 59. Median pedestrian treatments.(34)

Pedestrian signal treatments also depend on the width of the median and are summarized in 

figure 60. 

• For narrow crossings where no refuge is provided, a one-stage crossing is required 

using a single set of pedestrian signal displays and detectors. For this option, 

pedestrian clearance time needs to accommodate crossing the entire roadway. 

• For wide medians where there is ample room for pedestrians to wait in the median 

and where it is advantageous to all users to cross in two stages, separate pedestrian 

signal displays and detectors can be provided for each half of the roadway. Pedestrian 

clearance times are set independently for each half of the roadway. An example of this 

is also shown in figure 61. 

• A third option is for crossings where part of the pedestrian population can be 

reasonably expected to cross in one stage, but others need two stages. For this 

option, pedestrian clearance time is set to accommodate crossing the entire roadway, 

but a supplemental pedestrian detector is placed in the median to accommodate 

pedestrians needing to cross in two stages. 
168 Federal Highway Administration

(a) One-stage pedestrian crossing. 

(b) Two-stage pedestrian crossing. 

(c) One-stage pedestrian crossing with optional two-stage crossing. 

Figure 60. Median pedestrian signal treatments. 
Signalized Intersections: Informational Guide 169

System-Wide Treatments

Photograph Credit: Synectics Transportation Consultants, Inc.

Figure 61. This refuge island enables two-stage pedestrian crossings. 

8.1.4 Safety Performance 

Provision of medians at intersections provides safety benefits similar to medians between 

intersections. One report has shown that at urban and suburban intersections, multiple-vehicle 

crash frequency increases as median width increases for widths between 4.2 m (14 ft) and 24 m 

(80 ft), unlike in rural areas where multiple-vehicle crash rates tend to be lower for wider 

medians.(79) The report also provided a summary of a study that found no statistically significant 

effect of median width on traffic delays and conflicts on medians between 9 m (30 ft) and 18 m 

(60 ft) wide.(80)

One study found decreasing crash rates with increasing median widths.(81) A Michigan State 

University study found that Michigan’s boulevard roadways experience a crash rate half that of 

roadways with continuous center left-turn lanes.(82) A median width of 9.15 m (30 ft) to 18.30 m 

(60 ft) was found to be the most effective in providing a safe method for turning left. 

8.1.5 Operational Performance 

Simulation of signalized directional crossovers showed they operate better than other designs 

(specifically, an undivided cross section with a continuous center left-turn lane and a boulevard 

with bidirectional crossovers). The undivided cross section has larger delays for left-turning 

vehicles than do boulevard roadways, even for low turn volumes. The width of the median affects 

the storage capacity of the crossover, of course, so a crossover in a narrow median may not 

function as well as a left-turn lane. The signalized crossovers functioned more efficiently (i.e., with 

less time to make a left-turn) than did stop-controlled crossovers.(83)

8.1.6 Multimodal Impacts 

As noted previously, the width of the median (and the roadway in general) has a direct 

relationship with the amount of time needed for pedestrians and bicycles to cross the roadway. 

Large intersections that have no median or a median too narrow to provide a refuge force 

pedestrians to cross the entire street in one stage. Therefore, the provision of a median with at 

least enough width to accommodate a pedestrian can provide pedestrians with the option of 

crossing in one stage or two. This can be a significant benefit to elderly and disabled pedestrians 

who cross at speeds less than the typical 1.2 m/s (4 ft/s) or 1.1 m/s (3.5 ft/s) used to time 

pedestrian clearance intervals. 
170 Federal Highway Administration

If the median is so wide that pedestrian crossings are operated in two stages, the sequence 

of the stages may increase crossing time significantly. For example, if the vehicle phases running 

parallel to the pedestrian crossing in question are split-phased and the sequence of the vehicle 

phases is in the same direction as the pedestrian, crossing time is similar to that of a single-stage 

crossing. On the other hand, the reverse direction will result in additional delay to the pedestrian 

in the median area as the signal cycles through all conflicting phases. 

8.1.7 Physical Impacts 

Improvements made in the median should not have an effect on the footprint of an 

intersection unless a roadway is widened to provide the median to use for left-turn lanes, 

pedestrian refuges, and so on. Use of a curbed median or separator between left and opposing 

through traffic would add a vertical component to the intersection that should accommodate the 

necessary curb cuts. 

8.1.8 Socioeconomic Impacts 

The primary socioeconomic impact of medians at signalized intersections relates more to 

their effect on overall access within the corridor, which is discussed in section 8.2. However, 

landscaping can play an important aesthetic role at the intersection itself. The appropriate use of 

landscaping can visually enhance a road and its surroundings. Landscaping may act as a buffer 

between pedestrians and motorists, and reduce the visual width of a roadway, serving to reduce 

traffic speeds and providing a more pleasant environment. 

Landscaping must be carefully considered at signalized intersections, otherwise it will prevent 

motorists from making left and right turns safely because of inadequate sight distances. Care 

should be taken to ensure that traffic signs, pedestrian crossings, nearby railroad crossings, and 

school zones are not obstructed. Median planting of trees or shrubs greater than 0.6 m (2 ft) in 

height should be well away from the intersection (more than 15 m (50 ft)). No plantings having 

foliage between 0.6 m (2 ft) and 2.4 m (8 ft) in height should be present within sight distance 

triangles. 

Low shrubs or plants not exceeding a height of 0.6 m (2 ft) are appropriate on the 

approaches to a signalized intersection, either on the median, or along the edge of the roadway. 

These should not be allowed to overhang the curb onto the pavement nor interfere with the 

movement of pedestrians. All planting should have an adequate watering and drainage system, 

or should be drought resistant. FHWA’s report Vegetation Control for Safety provides additional 

guidelines and insight.(84)

8.1.9 Enforcement, Education, and Maintenance 

Medians introduce little in the way of unique enforcement or education issues for motor 

vehicles. Pedestrians may need assistance through the use of signs or other methods to make 

them aware of one-stage versus two-stage crossings, particularly in communities that have both 

types of crossings at their signalized intersections. 

Typical maintenance procedures will apply to medians. Landscaping should be maintained 

so as not to obstruct sight distance. 

8.1.10 Summary 

Table 38 summarizes issues associated with providing median treatments. 
Signalized Intersections: Informational Guide 171

System-Wide Treatments

Table 38. Summary of issues for providing median treatments. 

Characteristic Potential Benefits Potential Liabilities 

Safety Safety results are mixed with 

respect to median width. 

Operations Signalized directional crossovers 

can operate more efficiently than 

unsignalized directional 

crossovers. 

Narrow medians may create 

storage problems. 

Multimodal Medians of moderate width can 

allow pedestrians to cross in one 

or two stages, depending on 

ability. 

Overly wide medians may 

require all pedestrians to cross 

in two stages, significantly 

increasing pedestrian delay. 

Narrow medians may require 

long one-stage crossings. 

Physical Changes to median width may 

have a substantial physical 

impact upstream and 

downstream of the 

intersection. 

Socioeconomic Access control upstream or 

downstream of the intersection 

may create challenges. 

Enforcement, 

Education, and 

Maintenance 

 Education on the use of 

pedestrian push buttons in the 

median may be considered. 

Landscaping in the median 

may require maintenance. 

8.2 ACCESS MANAGEMENT 

Practical experience and recent research indicate that controlling access on a roadway can 

have a positive impact on both traffic operation and safety. Access management is a key issue in 

planning and designing roadways so they perform according to their functional classification. 

The topic of access management is growing and exceeds the space that this guide can 

provide. More information on access management can be found in a number of references, 

including AASHTO’s A Policy on Geometric Design of Highways and Streets;(3) NCHRP 420: 

Impacts of Access Management Techniques;(85) ITE’s Transportation and Land Development;(86)

and TRB’s Access Management Manual.(87) Several States, including Colorado and Florida, also 

have extensive guidance on access management. This section focuses on the operational and 

safety effects of unsignalized intersections (both public streets and private driveways) located 

within the vicinity of signalized intersections. 

8.2.1 Description 

Access management plays an important role in the operation and safety of arterial streets 

where both mobility of through traffic and access to adjacent properties are needed. Studies have 

repeatedly shown that improvements in access management improve safety and capacity, and 

also that roadways with poor access management have safety and operations records worse 

than those with better control of access. Treatments to improve access management near 

intersections (within 75 m (250 ft) upstream or downstream) include changes in geometry or 

signing to close or combine driveways, provide turn lanes, or prohibit turn movements. 

AASHTO presents a number of principles that define access management techniques:(3)

• Classify the road system by the primary function of each roadway. 
172 Federal Highway Administration

• Limit direct access to roads that have higher functional classifications. 

• Locate traffic signals to emphasize through movements. 

• Locate driveways and major entrances to minimize interference with traffic operations. 

• Use curbed medians and locate median openings to manage access movements and 

minimize conflicts. 

Access management works best when combined with land use and zoning policies. Parking 

lot placement behind urban and suburban shopping and community attractions can minimize the 

need to mitigate traffic movements. 

8.2.2 Applicability 

Intersection problems that indicate an improvement in access management may be desirable 

include delay to through vehicles caused by vehicles turning left or right into driveways, and rearend or angle crashes involving vehicles entering or leaving driveways. 

8.2.3 Design Features 

To understand the effects of a signalized intersection on access management upstream and 

downstream of the intersection, the functional area of the signalized intersection, shown in figure 

62, needs to be determined. The functional area is larger than the physical area of the 

intersection because it includes several items, as shown in figure 63:(87)

• Distance d1: Distance traveled during perception-reaction time as a driver approaches 

the intersection, assuming 1.5 s for urban and suburban conditions and 2.5 s for rural 

conditions. 

• Distance d2: Deceleration distance while the driver maneuvers to a stop upstream of 

the intersection. 

• Distance d3: Queue storage at the intersection. 

• Distance immediately downstream of the intersection so that a driver can completely 

clear the intersection before needing to react to something downstream (stopping 

sight distance is often used for this). 

Figure 62. Comparison of physical and functional areas of an intersection.(87)
Signalized Intersections: Informational Guide 173

System-Wide Treatments

Figure 63. Diagram of the upstream functional area of an intersection.(87)

When two signalized intersections are in proximity to each other, their overlapping functional 

areas may result in varying levels of access that might be considered between the two 

intersections, as shown in figure 64. As the figure demonstrates, the functional areas of nearby 

signalized intersections affects the location and extent of feasible access. Ideally, driveways with 

full access should be located in the area clear of the functional areas of both signalized 

intersections. However, signalized intersections are often located close enough to each other that 

the upstream functional area of one intersection partially or completely overlaps with the 

upstream functional area of the other. In these cases, there is no clear area between the two 

intersections where a driveway can operate without infringing upon the functional area of one of 

the signalized intersections. As such, it is important to apply sound engineering judgment to 

determine where and if driveway access should be allowed. Some important considerations in the 

evaluation would include the volume of traffic using the driveway, the type of turning maneuvers 

that will be most prominent, the type of median present, potential conflicts with and proximity to 

other driveways, and the volume of traffic on the major street. 

Access points that are clear of only one of the two signalized intersections would likely 

perform best from a safety perspective if restricted to right-in, right-out operation. However, in 

urban areas, this may not always be practical or may create other problems at downstream 

intersections, so again it is important to apply sound engineering judgment. In some cases, the 

two signalized intersections may be so close together that any access would encroach within the 

functional area of the intersection. These situations are likely to be candidates for either partial or 

full access restriction. It is important to note that driveways should not be simply eliminated 

based on simple guidelines but rather should be evaluated on a case-by-case basis with 

consideration of the broader system effects. When driveways are closed without any regard to 

the system effects, there is a high potential that the problem will be transferred to another 

location. Finally, as a general guideline, the functional area of an intersection is more critical 

along corridors with high speeds (70 km/h (45 mph) or greater) and whose primary purpose is 

mobility. 

Improvements to the current access to properties adjacent to an intersection area can be 

implemented by: 

• Closing, relocating, or combining driveways. 
174 Federal Highway Administration

• Restricting turning movements through median treatments, using driveway treatments, 

and/or using signing. 

As discussed previously, where access is restricted, the redirection of driveway traffic needs 

to be considered. Two of the more typical options are: 

• Require drivers to make a U-turn at a downstream, signalized intersection (figure 65). 

This requires adequate cross-section width to allow the U-turn and sufficient distance 

to weave across the through travel lanes. In addition to increasing the traffic volumes 

at the signalized intersection, U-turns also decrease the saturation flow rate of the leftturn movement. These combined effects potentially decrease the available capacity at 

the signalized intersection if the affected left-turn movement is a critical movement at 

the intersection. 

• Create a midblock opportunity for drivers to make an unsignalized U-turn maneuver 

via a directional median opening (figure 66). A study in Florida evaluated the safety 

effect of these directional median openings on six-lane divided arterials with large 

traffic volumes, high speeds, and high driveway/side-street access volumes.(88)

 This 

study found a statistically significant reduction in the total crash rate of 26.4 percent as 

compared with direct left turns. 
Signalized Intersections: Informational Guide 175

System-Wide Treatments

(a) Minimal amount of potential adverse effects due to adjacent signalized intersections. 

(b) Moderate amount of potential adverse effects due to adjacent signalized intersections. 

(c) Substantial amount of potential adverse effects due to adjacent signalized intersections. 

Figure 64. Access points near signalized intersections.(adapted from 87, figure 8-15)
176 Federal Highway Administration

Figure 65. Access management requiring U-turns at a downstream signalized intersection. 

Figure 66. Access management requiring U-turns at an unsignalized, directional median opening. 

Note that the conversion of an existing full-access point to right-in/right-out operation has 

both advantages and disadvantages. The advantages of right-in/right-out operation include: 

• Removal of movements from the functional area of the signalized intersection. This 

reduces conflicts near the signalized intersection and improves capacity by minimizing 

turbulence. 

• Better operation for the driveway. Eliminating left turns out of the driveway generally 

reduces delays for the driveway movements. 

Disadvantages include: 

• Increase in U-turn movements at signalized intersections or at other unsignalized 

locations. This may reduce the available capacity at the intersection and increase 

delay. This may also increase the potential for left-turn crashes at the location of the 

U-turn. 
Signalized Intersections: Informational Guide 177

System-Wide Treatments

• Increase in arterial weaving. This may happen as the driveway movement attempts to 

get into position to make the U-turn. 

• Potential for increased demand for left turns at other driveways serving the same 

property. 

As with other access management treatments, involvement of property owners in the 

decisionmaking and design process is key to the success of the project. 

8.2.4 Safety Performance 

In general, an increase in the number of access points along a roadway correlates with 

higher crash rates. Specific relationships vary based on specific roadway geometry (lane width, 

presence or absence of turn lanes, etc.) and traffic characteristics. 

Table 39 presents a summary of the relative crash rates for a range of unsignalized 

intersection access spacing. As can be seen, doubling access frequency from 6 to 12 access 

points per km (10 to 20 access points per mi) increases crash rates by about 40 percent. An 

increase from 6 to 37 access points per km (10 to 60 access points per mi) would be expected to 

increase crash rates by approximately 200 percent. Generally, each additional access point per 

mile along a four-lane roadway increases the crash rate by about 4 percent (see also references 

89 and 90). 

Table 39. Relative crash rates for unsignalized intersection access spacing.* 

Unsignalized Access Points Spacing** Average Spacing*** Relative Crash Rate****

6 per km (10 per mi) 322 m (1056 ft) 1.0 

12 per km (20 per mi) 161 m (528 ft) 1.4 

19 per km (30 per mi) 107 m (352 ft) 1.8 

25 per km (40 per mi) 80 m (264 ft) 2.1 

31 per km (50 per mi) 64 m (211 ft) 2.4 

37 per km (60 per mi) 54 m (176 ft) 3.0 

44 per km (70 per mi) 46 m (151 ft) 3.5 

*Source: Reference 87, as adapted from 85. 

**Total access connections on both sides of the roadway. 

*** Average spacing between access connections on the same side of the roadway; one-half of the connections on each 

side of the roadway. 

**** Relative to the crash rate for 6.2 access points per km (10 access points per mi). 

8.2.5 Operational Performance 

The reduction of access along an arterial street has the potential to improve traffic operations. 

For example, urban arterials with a high degree of access control function 30 to 50 percent better 

than the same facility with no control.(91) Improved access management also has been shown to 

improve LOS.(92)

Access points close to a signalized intersection can reduce the saturation flow rate of the 

signalized intersection. Research has determined that the amount of reduction depends on the 

corner clearance of the driveway, the proportions of curb-lane volume that enter and exit the 

driveway, and the design of the driveway itself.(93)

However, as indicated earlier, it is important to evaluate the impact of access control on the 

upstream and downstream intersections, which may experience a significant increase in U-turns 

or other types of turning movements. For example, if there is adequate capacity to accommodate 

the turning movements at midblock access driveways and no safety problems have been 

identified, eliminating the left-turn movements and converting them to U-turns at signalized 

intersections would likely degrade the operational performance of the arterial because less green 

time will be available for through traffic. 
178 Federal Highway Administration

8.2.6 Multimodal Impacts 

Access treatments that reduce the number of driveways or restrict turning movements at 

driveways also reduce the number of potential conflicts for pedestrians and bicycles near a 

signalized intersection. In addition, a median treatment used as part of an overall access 

management strategy may also provide the opportunity for a midblock signalized or unsignalized 

pedestrian crossing. It would be important to evaluate whether the access treatments being 

considered would result in a significant increase in operating speed on the facility, as increases in 

speed have a negative impact on both pedestrians and bicyclists that should be considered in the 

evaluation. 

8.2.7 Physical Impacts 

Addition of turn lanes for property access will increase the footprint of the intersection area. 

Turn restrictions should not have any effect on the physical size of an area, but may add a 

vertical element to the intersection (if, for example, a raised curb or flexible delineators are used 

to prohibit left turns). These should not present difficulties for pedestrians with mobility 

impairments, nor obstruct sight distance. 

8.2.8 Socioeconomic Impacts 

A review of the literature indicates inconsistency in the socioeconomic effects of access 

management. Surveys conducted in Florida reported a relatively low rate of acceptance of access 

management: most drivers felt that the inconvenience of indirect movements offset the benefits to 

traffic flow and safety. Businesses also were unsupportive: 26 percent reported a loss in profits, 

and 10 to 12 percent reported a large loss.(94) Conversely, experience in Iowa indicates rapid 

growth in retail sales after access management projects were completed. An opinion survey 

conducted among affected motorists indicated that a strong majority supported all projects but 

one.(92)

The reactions of drivers, property owners, pedestrians, and others concerned with access to 

properties adjacent to intersections would be expected to vary widely. Access management 

strategies should be considered only in the context of a roadway corridor with the approval and 

backing of those affected. 

Relocation or closing of driveways should be part of a comprehensive corridor accessmanagement plan. The optimal situation is to avoid driveway conflicts before they develop. This 

requires coordination with local land use planners and zoning boards in establishing safe 

development policies and procedures. Avoidance of high-volume driveways near congested or 

otherwise critical intersections is desirable. 

Highway agencies also need to have an understanding of the safety consequences of 

driveway requests. The power of a highway agency to modify access provisions is derived from 

legislation that varies in its provision from State to State. Highway agencies generally do not have 

the power to deny access to any particular parcel of land, but many do have the power to require, 

with adequate justification, relocation of access points. Where highway agency powers are not 

adequate to deal with driveways close to intersections, further legislation may be needed. 

8.2.9 Enforcement, Education, and Maintenance 

Periodic enforcement may be needed to ensure that drivers obey restrictions at driveways 

where such restrictions cannot be physically implemented with raised channelization, such as 

signed prohibitions. 

Education other than appropriate signing should not be needed when implementing changes 

to access. 

8.2.10 Summary 

Table 40 summarizes issues associated with providing access management. 
Signalized Intersections: Informational Guide 179

System-Wide Treatments

Table 40. Summary of issues for providing access management. 

Characteristic Potential Benefits Potential Liabilities 

Safety Fewer access points generally result in a 

lower crash rate along a corridor. 

None identified. 

Operations Fewer access points generally result in 

smoother operation of a corridor. 

An increased number of U-turns at a 

signalized intersection due to access 

management may reduce the overall 

capacity of the intersection. 

Multimodal Fewer access points reduce the number of 

potential conflicts for bicycles and 

pedestrians. 

Potential increases in operating speed along 

the arterial may negatively impact safety 

relative to bicycle and pedestrian modes. 

Physical None identified. Turn restrictions may require adding 

horizontal and vertical features to driveways. 

Socioeconomic Socioeconomic benefits are mixed, with 

some studies reporting economic 

improvement and others reporting economic 

losses. 

Both economic improvement and economic 

losses have been reported. 

Enforcement, 

Education, and 

Maintenance 

None identified when raised channelization is 

used. 

Periodic enforcement may be needed where 

signs are used instead of raised 

channelization. 

8.3 SIGNAL COORDINATION 

8.3.1 Description 

Drivers may have difficulty making permissive turning maneuvers at signalized intersections 

(e.g., permissive left turns, right turn on red after stop) because of lack of gaps in through traffic. 

This can contribute to both operational and safety problems. Left-turning vehicles waiting to turn 

can block through traffic, even if a left-turn lane is provided. This can lead to rear-end crashes 

between turning and through vehicles. Collisions may also occur when left-turning drivers 

become impatient and accept a gap that is smaller than needed to complete a safe maneuver. 

Such collisions could be minimized if longer gaps were made available. (This could also be 

accomplished through turn prohibitions and changes in signal phasing, although this particular 

treatment does not address these potential countermeasures.) 

One method of providing longer gaps is to coordinate adjacent traffic signals to promote 

platooning of vehicles. Signals within 0.8 km (0.5 mi) of each other on a major route, or in a 

network of major routes, should be coordinated; signals spaced farther than 0.8 km (0.5 mi) may 

be candidates for coordination if platooning can be maintained. Signal progression can help 

improve driver expectancy of changes in right-of-way assignment due to signal changes. 

Increased platooning of vehicles can create more defined gaps of increased length for permissive 

vehicle movements at intersections and can result in improved intersection operation. Increased 

platooning of vehicles may also result in a decrease in rear-end crashes. Effective coordination of 

signals should reduce the required number of stops for the higher priority movements 

(presumably the major street through movement). 

8.3.2 Applicability 

Signal coordination may be applicable for intersections where: 

• Rear-end conflicts/collisions are occurring due to the higher probability of having to 

stop at each light. 
180 Federal Highway Administration

• Lack of coordination is causing unexpected and/or unnecessary stopping of traffic 

approaching from adjacent intersections. 

• Congestion between closely spaced intersections is causing queues from one 

intersection to interfere with the operation of another. 

8.3.3 Safety Performance 

Apart from its operational benefits, signal coordination is known to reduce vehicle conflicts 

along corridors where traffic signals are coordinated. Largely, it reduces the number of rear-end 

conflicts, as vehicles tend to move more in unison from intersection to intersection. 

Studies have proven the effectiveness of signal coordination in improving safety. The ITE 

Traffic Safety Toolbox: A Primer on Traffic Safety cites two studies of coordinated signals with 

intersection crash frequencies that dropped by 25 and 38 percent.(95) One study showed a 

decrease in crash rates for midblock sections as well. A study on the effectiveness of traffic signal 

coordination in Arizona concluded that there is a small but significant decrease in crash rates on 

intersection approaches after signal coordination.(96) Crashes along the study corridor decreased 

6.7 percent. Another study of the safety benefits of signal coordination carried out in Phoenix 

compared coordinated signalized intersections to uncoordinated signalized intersections citywide. 

The coordinated intersections were found to have 3 to 18 percent fewer total collisions, and 14 to 

43 percent fewer rear-end collisions.(97)

Selected findings of safety benefits associated with signal coordination are shown in table 41. 

Table 41. Selected findings of safety benefits associated with signal coordination or progression. 

Treatment Finding 

Signal Coordination(97) 3 to 18% estimated reduction in all collisions along corridor 

14 to 43% estimated reduction in rear-end collisions along corridor 

Provide Signal Progression (98) 10 to 20% estimated reduction in all collisions along corridor 

8.3.4 Operational Performance 

The potential benefits of coordination are directly related to the traffic characteristics and 

spacing of intersections. Coordinated operation works best when traffic arrives in dense 

platoons. These platoons occur more frequently when the intensity of traffic volume between 

intersections increases and distance between intersections decreases, to a practical limit. 

Selection of the system cycle length defines the relationship that allows coordinated operations 

between the intersections, while the offset represents the difference in start times for the through 

green at adjacent intersections. 

A key to success in signal coordination is the appropriate spacing of the signals. Signals 

within a half-mile (or sometimes even more if platooning can be maintained) of each other should 

be coordinated. As with all signals, coordinated signals too close together can present problems 

when drivers focus on a downstream signal and do not notice the closer signal they are 

approaching, or the proceed through a green signal and are not able to stop for a queue at a 

signal immediately downstream. Dispersion of platoons can occur if signals are spaced too far 

apart, resulting in inefficient use of signal coordination and loss of any operational benefit. 

Operations on cross streets may be negatively impacted. The Colorado Access Demonstration 

Project concluded that 0.8-km (0.5-mi) spacing could reduce vehicle hours of delay by 60 percent 

and vehicle-hours of travel by over 50 percent compared with signals at one-quarter mile intervals 

with full median openings between signals (reference 87, adapted from reference 99). 

Grouping the signals to be coordinated is a very important aspect of design of a progressive 

system. Factors that should be considered include geographic barriers, volume-to-capacity ratios, 
Signalized Intersections: Informational Guide 181

System-Wide Treatments

and characteristics of traffic flow (random versus platoon arrivals). When systems operating on 

different cycle lengths are adjacent to or intersect each other, changes to provide a uniform cycle 

length appropriate for both systems should be considered, so that the systems can be unified, at 

least for certain portions of the day. Half-cycles or double cycles should also be considered for 

some locations if that facilitates coordination. 

8.3.5 Multimodal Impacts 

Signal coordination, by providing for a more orderly flow of traffic, may aid pedestrians in 

anticipating vehicle movements, lessening the likelihood of a pedestrian-vehicle conflict. In 

addition, in some cases it may be possible to provide progression for pedestrians in one or both 

directions along with vehicle progression. 

8.3.6 Physical Impacts 

No particular physical needs have been identified. 

8.3.7 Socioeconomic Impacts 

Signal coordination will also reduce fuel consumption, noise, and air pollution, by reducing 

the number of stops and delays. 

8.3.8 Enforcement, Education, and Maintenance 

Signals working in coordination should reduce excessive speed, as motorists realize that they 

cannot “beat” the next traffic signal. Incidents of aggressive driving should be reduced as well. 

Signal timing plans need to be updated as traffic volumes and patterns change. This should 

be factored into periodic maintenance of the traffic signal. 

8.3.9 Summary 

Table 42 summarizes the issues associated with providing signal coordination. 

Table 42. Summary of issues for providing signal coordination. 

Characteristic Potential Benefits Potential Liabilities 

Safety Fewer rear-end and left-turn collisions. May promote higher speeds. 

Operations Improves traffic flow. Usually longer cycle lengths. 

Multimodal May reduce pedestrian-vehicle conflicts. May result in longer pedestrian 

delays due to longer cycle lengths. 

Physical No physical needs. None identified. 

Socioeconomic Reduces fuel consumption, noise, and 

air pollution. 

None identified. 

Enforcement, 

Education, and 

Maintenance 

May result in less need for speed 

enforcement. 

Signal timing plans need periodic 

updating. 

8.4 SIGNAL PREEMPTION AND/OR PRIORITY 

8.4.1 Description 

One difficulty in understanding preemption and priority is the lack of standard terms in current 

practice and the multiple approaches that have been employed to date. The recent development 
182 Federal Highway Administration

in the Signal Control and Prioritization (SCP) standard has provided some guidance, but some 

detail will be provided here. 

Preemption is primarily related to the transfer of the normal control (operation) of traffic 

signals to a special signal control mode for the purpose of servicing railroad crossings, 

emergency vehicle passage, mass transit vehicle passage, and other special tasks, the control of 

which requires terminating normal traffic control to provide the serve the special task. 

Priority is defined by the preferential treatment of one vehicle class (such as a transit vehicle, 

emergency service vehicle, or a commercial fleet vehicle) over another vehicle class at a 

signalized intersection without causing the traffic signal controllers to drop from coordinated 

operations. Priority may be accomplished by a number of methods, including changing the 

beginning and end times of greens on identified phases, changing the phase sequence, or 

including special phases, all without interrupting the general timing relationship between specific 

green indications at adjacent intersections. 

8.4.2 Emergency Vehicle Preemption 

A specific vehicle often targeted for signal preemption is the emergency vehicle. Signal 

preemption allows emergency vehicles to disrupt a normal signal cycle to proceed through the 

intersection more quickly and under safer conditions. The preemption systems can extend the 

green on an emergency vehicle’s approach or replace the phases and timing for the whole cycle. 

The MUTCD discusses signal preemption, standards for the phases during preemption, and 

priorities for different vehicle types that might have preemption capabilities.(1) 

Several types of emergency vehicle detection technologies are available, and include the use 

of light, sound, pavement loops, radio transmission, and push buttons to detect vehicles 

approaching an intersection: 

• Light—an emitter mounted on emergency vehicles sends a strobe light toward a 

detector mounted at the traffic signal, which is wired into the signal controller. 

• Sound—a microphone mounted at the intersection detects sirens on approaching 

vehicles; the emergency vehicles do not need any additional equipment to implement 

signal priority systems. 

• Pavement loop—a standard pavement loop connected to an amplifier detects a signal 

from a low frequency transponder mounted on the emergency vehicle. 

• Push button—a hardwire system is activated in the firehouse and is connected to the 

adjacent signal controller. 

• Radio—a radio transmitter is mounted on the vehicle and a receiver is mounted at the 

intersection. 

Many of these systems have applications in transit-vehicle priority as well as signal 

preemption for emergency vehicles. Some jurisdictions use signs that alert drivers that a police 

pursuit is in progress. 

8.4.3 Applicability 

Preemption/priority is considered where: 

• Normal traffic operations impede a specific vehicle group (i.e. emergency vehicles). 

• Traffic conditions create a potential for conflicts between a specific vehicle group and 

general traffic. 
Signalized Intersections: Informational Guide 183

System-Wide Treatments

8.4.4 Safety Performance 

No research is known on the safety implications of emergency vehicle preemption, although it 

is expected that the number of conflicting movements associated with an emergency vehicle’s 

having to run a red light would be reduced. 

Installation of signal preemption systems for emergency vehicles has been shown to 

decrease response times. A review of signal preemption system deployments in the United 

States shows decreases in response times between 14 and 50 percent for systems in several 

cities. In addition, the study reports a 70 percent decrease in crashes with emergency vehicles in 

St. Paul, MN, after the system was deployed.(100)

Signal preemption has also been considered for intersections at the base of a steep and/or 

long grade. These grades can create a potentially dangerous situation for large trucks if they lose 

control and enter the intersection at a high speed. Preemption could be used to reduce the 

likelihood of conflicts between runaway trucks and other vehicles. 

8.4.5 Operational Performance 

Preemption of signals by emergency vehicles will temporarily disrupt traffic flow. Congestion 

may occur, or worsen, before traffic returns to normal operation. Data gathered on signal 

preemption systems in the Washington, DC, metropolitan area suggested that once a signal was 

preempted, the coordinated systems took anywhere between half a minute to 7 minutes to 

recover to base time coordination. During these peak periods in more congested areas, vehicles 

experienced significant delays. Agency traffic personnel indicated that signal preemption seems 

to have more impacts on peak period traffic in areas where the peak periods extend over longer 

time periods than it does where peak periods are relatively short.(100)

8.4.6 Multimodal Impacts 

Priority for transit vehicles can enhance transit operations, reducing delays and allowing for a 

tighter schedule. Impacts to pedestrians and bicycles are minimal. 

8.4.7 Physical Impacts 

The key to success is ensuring that the preemption system works when needed by providing 

clear sight lines between emergency vehicles and detectors. Also, it is important to ensure that 

vehicles from a variety of jurisdictions will be able to participate in the signal preemption program. 

Light-based detectors need a clear line of sight to the emitter on the vehicles; this line could 

become blocked by roadway geometry, vehicles, foliage, or precipitation. Also, systems from 

different vendors may not interact well together. Other alarms, such as from nearby buildings, 

may be detected by a sound-based system. 

8.4.8 Socioeconomic Impacts 

The reduction in response time by emergency services is a societal benefit, as is more 

predictable transit service. Costs, particularly when applied to an entire road network, can be 

significant. 

8.4.9 Enforcement, Education, and Maintenance 

Preemption directly benefits emergency vehicles, although most police agencies do not use 

signal preemption. Preempted signals that stop vehicles for too long may encourage disrespect 

for the red signal, although this has not been reported. 

8.4.10 Summary 

Table 43 summarizes the issues associated with providing signal preemption and/or priority. 
184 Federal Highway Administration

Table 43. Summary of issues for providing signal preemption and/or priority. 

Characteristic Potential Benefits Potential Liabilities 

Safety Quicker response time for emergency 

vehicles. 

On steep grades, preemption could be 

used to minimize conflicts between 

runaway trucks and other vehicles. 

None identified. 

Operations None identified. Can be disruptive to traffic flow, 

particularly during peak hours. 

Multimodal Delay to transit vehicles is reduced. None identified. 

Physical None identified. Requires a clear line of sight between 

the emergency vehicle and the 

transmitter; other nearby radio 

systems may be affected or interfere. 

Socioeconomic Lower emergency service response time. 

More reliable transit service. 

Can be costly. 

Enforcement, 

Education, and 

Maintenance 

Improves emergency vehicle response 

time. 

None identified. 
Signalized Intersections: Informational Guide 185

Intersection-Wide Treatments 

CHAPTER 9 

INTERSECTION-WIDE TREATMENTS 

TABLE OF CONTENTS 

9.0 INTERSECTION-WIDE TREATMENTS.............................................................................187 

 9.1 Pedestrian Treatments..............................................................................................187 

 9.1.1 Reduce Curb Radius....................................................................................187 

 9.1.2 Provide Curb Extensions .............................................................................190 

 9.1.3 Modify Stop Bar Location.............................................................................192 

 9.1.4 Improve Pedestrian Signal Displays ............................................................194 

 9.1.5 Modify Pedestrian Signal Phasing ...............................................................196 

 9.1.6 Grade-Separate Pedestrian Movements .....................................................199 

 9.2 Bicycle Treatments....................................................................................................201 

 9.2.1 Provide Bicycle Box .....................................................................................201 

 9.2.2 Provide Bike Lanes ......................................................................................202 

 9.3 Transit Treatments....................................................................................................203 

 9.3.1 Relocate Transit Stop ..................................................................................203 

 9.4 Traffic Control Treatments ........................................................................................205 

 9.4.1 Change Signal Control from Pre-Timed to Actuated ...................................205 

 9.4.2 Modify Yellow Change Interval and/or Red Clearance Interval...................208 

 9.4.3 Modify Cycle Length ....................................................................................211 

 9.4.4 Late Night/Early Morning Flash Removal ....................................................212 

 9.5 Street Lighting and Illumination.................................................................................214 

 9.5.1 Provide or Upgrade Illumination...................................................................214 

LIST OF FIGURES 

Figure Page

67 A curb radius from 4.6 m (15 ft) to 15.2 m (50 ft) increases the pedestrian crossing 

distance from 18.9 m (62 ft) to 30.5 m (100 ft), all else being equal...............................188 

68 Intersection with curb extension .........................................................................................191

69 Examples of countdown and animated eyes pedestrian signal displays............................195 

70 A pedestrian grade separation treatment ...........................................................................200 

71 Typical lighting layouts........................................................................................................215 
186 Federal Highway Administration

LIST OF TABLES 

Table Page

44 Summary of issues for curb radius reduction .....................................................................190 

45 Summary of issues for curb extensions..............................................................................192 

46 Summary of issues for stop bar alterations ........................................................................194 

47 Safety benefits associated with addition of pedestrian signals: Selected findings.............195 

48 Summary of issues for pedestrian signal display improvements........................................196 

49 Summary of issues for pedestrian signal phasing modifications........................................199 

50 Summary of issues for pedestrian grade separation..........................................................201 

51 Summary of issues for providing a bicycle box ..................................................................202 

52 Summary of issues for providing bicycle lanes...................................................................203 

53 Summary of issues for near-side/far-side transit stops ......................................................205 

54 Safety benefits associated with upgrading an intersection from pre-timed to actuated 

operation: Selected findings ............................................................................................207 

55 Summary of issues for providing signal actuation ..............................................................208 

56 Safety benefits associated with modifying clearance intervals: Selected findings .............210 

57 Summary of issues for modifying yellow/red clearance intervals .......................................211 

58 Summary of issues for cycle length modifications..............................................................212 

59 Safety benefits associated with removal of signal from late night/early morning flash 

mode: Selected findings ..................................................................................................213 

60 Summary of issues for flash mode removal .......................................................................214 

61 Safety benefits associated with providing illumination: Selected findings..........................216 

62 Summary of issues for providing illumination .....................................................................217
Signalized Intersections: Informational Guide 187

Intersection-Wide Treatments 

9. INTERSECTION-WIDE TREATMENTS 

This chapter discusses five groups of intersection-wide treatments: 

• Pedestrian treatments. 

• Bicycle treatments. 

• Transit treatments. 

• Traffic control treatments. 

• Illumination. 

9.1 PEDESTRIAN TREATMENTS 

Accommodation of pedestrians has a significant effect on both the design and operations of a 

signalized intersection and should therefore be an integral part of the design process. Key 

factors to consider are: 

• Crossing locations with a high number of pedestrians should be protected (where 

possible) from conflicting through traffic. 

• Crossing distances should be minimized as much as possible. 

• Adequate crossing time needs to be provided. 

• Pedestrian ramps need to be located within the crosswalk; diagonal ramps are 

discouraged. 

• Pedestrian ramp location and design must meet ADA requirements. 

One common way to better accommodate pedestrians and improve their safety is to reduce 

their crossing distance. Reducing crossing distance decreases a pedestrian’s exposure to traffic, 

which may be particularly helpful to pedestrians who are disabled or elderly. It also reduces the 

amount of time needed for the pedestrian phase, which reduces the delay for all other vehicular 

and pedestrian movements at the intersection. Three common methods of reducing pedestrian 

crossing distance are: 

• Curb radius reduction. 

• Curb extensions. 

• Provision of median crossing islands. 

Traffic engineers have also made modifications to the location of the stop bar and crosswalk 

to try to control where motorists stop on the intersection approach and where pedestrians cross. 

Traffic control improvements directly applicable to pedestrians include: 

• Improving the signal display to the pedestrian through the use of redundancy, 

including the use of pedestrian signals, accessible pedestrian signals, and 

enhancements to the pedestrian signal display. 

• Modifying the pedestrian signal phasing. 

Each of these treatments is discussed in the following sections; median crossing islands were 

addressed in chapter 8. 

9.1.1 Reduce Curb Radius 

Description 

Curb radius reduction has been suggested in research because one common pedestrian 

crash is when right-turning vehicles at intersections strike pedestrians. A wide curb radius 
188 Federal Highway Administration

typically results in high-speed turning movements by motorists. Existing guidelines recommend 

reconstructing the turning radius to a tighter turn to reduce turning speeds, shorten the crossing 

distance for pedestrians, and improve sight distance between pedestrians and motorists. Figure 

67 demonstrates that increasing the curb radius increases pedestrian crossing distance. Tighter 

turning radii are most important where street intersections are not at right angles.(101) 

Figure 67. A curb radius increase from 4.6 m (15 ft) to 15.2 m (50 ft) increases the pedestrian 

crossing distance from 18.9 m (62 ft) to 30.5 m (100 ft), all else being equal. 

Applicability 

Reducing the curb radii is an appropriate consideration wherever there are pedestrians. 

Small curb radii facilitate the use of two perpendicular curb ramps rather than a single diagonal 

ramp (see chapter 3 for further discussion). Note that the need to accommodate the design 

vehicle may limit how much the curb radius can be reduced. Depending on State vehicle code, it 

may be acceptable to allow large vehicles to turn right into the second lane (the lane next to the 

curb lane). 

Safety Performance 

Reducing the curb radius lowers the speed of right-turning vehicles. It is expected that the 

frequency of pedestrian-vehicle collisions will be reduced as a result, and any remaining collisions 

will be of a lesser severity due to the lower speeds involved. However, vehicles turning right will 
Signalized Intersections: Informational Guide 189

Intersection-Wide Treatments 

be forced to decelerate more rapidly in attempting the right turn. This may lead to rear-end 

conflicts with through vehicles, particularly if a separate right-turn lane is not provided and the 

through movements have high speeds. 

Operational Performance 

Reducing pedestrian crossing distance with smaller curb radii reduces the amount of time 

needed to serve the pedestrian clearance time. This may result in shorter cycle lengths and less 

delay for all users. However, a curb radius reduction may reduce the capacity of the affected 

right-turn movement. 

Multimodal Impacts 

Pedestrians benefit from a shorter crossing distance and the reduced speed of right-turning 

vehicles. 

Larger vehicles and transit may have difficulty negotiating the tighter corner, either swinging 

out too far into the intersection or having their rear wheels ride up over the curb onto the 

sidewalk. Caution should be exercised in reducing curb radius if right-turning large trucks or 

buses are frequent users. It may be necessary to move the stopbar locations on the roadway the 

trucks are turning into to allow them to briefly swing wide into the opposing lanes. 

Physical Impacts 

Reducing the curb radius reduces the size of the intersection and allows for additional space 

for landscaping or pedestrian treatments. Traffic signal equipment may need to be relocated. 

Socioeconomic Impacts 

Depending on the degree of improvement, low to moderate construction costs will be 

associated with the reconstruction of the curb radius. 

Enforcement, Education, and Maintenance 

The effectiveness of this treatment may be enhanced by police enforcement of drivers failing 

to come to a complete stop on a red signal when making a right turn and/or not yielding to 

pedestrians in the crosswalk. 

Summary 

Table 44 summarizes issues associated with curb radius reduction. 
190 Federal Highway Administration

Table 44. Summary of issues for curb radius reduction. 

Characteristic Potential Benefits Potential Liabilities 

Safety Reduction in right-turning 

vehicle/pedestrian collisions. 

Fewer right-turn-on-red violations. 

May increase right-turning/through vehicle 

rear-end collisions due to increased speed 

differential. 

Large vehicle off-tracking. 

Operations Less overall delay due to reduced 

time needed to serve pedestrian 

movement. 

Reduction in capacity for affected right-turn 

movement. 

Multimodal Shorter crossing distance. 

Facilitates the use of two 

perpendicular ramps rather than a 

single diagonal ramp. 

May be more difficult for large trucks and 

buses to turn right. 

Physical Reduces the size of the intersection. None identified. 

Socioeconomic Low to moderate costs. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement of yielding to pedestrians may 

be necessary. 

9.1.2 Provide Curb Extensions 

Description 

Curb extensions, also known as “bulbouts” or “neckdowns,” involve extending the sidewalk or 

curb line into the street, reducing the effective street width. These are often used for traffic 

calming on neighborhood streets, but the technique is applicable for higher volume signalized 

intersections. Curb extensions improve the visibility of the pedestrian crosswalk. They reduce the 

amount of roadway available for illegal or aggressive motorist activities such as failing to yield to 

pedestrians, making high-speed turns, and passing in the parking lane. It has also been observed 

that motorists are more inclined to stop behind the crosswalk at a curb extension, and that 

pedestrians are more inclined to wait on the curb extension than in the street. An example of a 

curb extension is shown in figure 68. 

Application 

This treatment would be applicable to urban intersections with heavy pedestrian traffic and a 

high number of pedestrian collisions. It would not be appropriate at high-speed rural intersections, 

and caution should be used at intersections with a high proportion of right-turning movements. 

Curb extensions can be used to terminate parking lanes; care should be exercised if they are 

used to terminate travel lanes. 

The earlier observations on reduced curb radius also apply here. 
Signalized Intersections: Informational Guide 191

Intersection-Wide Treatments 

Photograph Credit: Synectics Transportation Consultants, Inc. 

Figure 68. Intersection with curb extension. 

Safety Performance 

By reducing the pedestrian crossing distance and subsequent exposure of pedestrians to 

traffic, this treatment should reduce the frequency of pedestrian collisions. A New York City study 

suggested that curb extensions appear to be associated with lower frequencies and severities of 

pedestrian collisions.(102) Curb extensions should also reduce speeds on approaches where they 

are applied. 

Operational Performance 

The operational performance effects of curb extensions are similar to those for reduced curb 

radii. The reduction in pedestrian crossing distance reduces the amount of time needed to serve 

the pedestrian clearance time. This may result in shorter cycle lengths and less delay for all 

movements. However, the reduced curb radius resulting from the curb extension may reduce the 

capacity of the affected right-turn movement. If a right-turn lane is present, the curb radius 

reduction should not impede through movements. 

Because curb extensions are essentially a traffic-calming treatment, they will likely reduce 

speeds and may possibly divert traffic to other roads; right-turn movements would be particularly 

affected by this treatment. Emergency services (fire, ambulance, and police) should be consulted 

if this treatment is being considered. 

Multimodal Impacts 

Pedestrians benefit greatly from the provision of curb extensions. The curb extension can 

greatly improve the visibility between pedestrians and drivers. In addition, the reduction in 

pedestrian crossing distance reduces pedestrian exposure and crossing time. 

Bicycle movements and interactions with motor vehicles need to be considered in the design 

of any curb extensions. 

Caution should be used if this treatment is being considered along heavy truck routes. All 

types of trucks and transit, in particular those needing to turn right at the intersection, would be 

negatively affected by this treatment. 
192 Federal Highway Administration

Physical Impacts 

Drainage should be evaluated whenever curb extensions are being considered, as the curb 

extension may interrupt the existing flow line. 

Socioeconomic Impacts 

Costs associated with this improvement would be low to moderate. 

Enforcement, Education, and Maintenance 

No specific effects have been identified. 

Summary 

Table 45 provides a summary of the issues associated with curb extensions. 

Table 45. Summary of issues for curb extensions. 

Characteristic Potential Benefits Potential Liabilities 

Safety Reduction in right-turning 

vehicle/pedestrian collisions. 

Fewer right-turn-on-red violations. 

May increase right-turning/through vehicle 

rear- end collisions due to increased speed 

differential. 

Large vehicle offtracking. 

Operations Less overall delay due to reduction in time 

needed to serve pedestrian movement. 

May adversely affect operation if curb 

extension replaces a travel lane. 

Right-turn movements delayed. 

Emergency vehicles may be significantly 

delayed. 

Multimodal Shorter crossing distance. 

Facilitates the use of two perpendicular 

ramps rather than a single diagonal ramp. 

Better visibility between pedestrians and 

drivers. 

May be more difficult for large trucks and 

buses to turn right. 

Physical None identified. Drainage may be adversely affected. 

Socioeconomic Low to moderate costs. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

9.1.3 Modify Stop Bar Location 

Description 

Visibility is a key consideration for determining the location of stop bars. The FHWA 

Pedestrian Facilities Users Guide—Providing Safety and Mobility suggests the use of advance 

stop lines as a possible countermeasure.(35) At signalized pedestrian crossing locations, the 

vehicle stop line can be moved 5 to 10 m (15 to 30 ft) further back from the pedestrian crossing 

than the standard 1.2 m (4 ft) distance to improve visibility of through cyclists and crossing 

pedestrians for motorists (and particularly truck drivers) who are turning right. Advanced stop 

lines benefit pedestrians, as the pedestrians and drivers have a clearer view and more time to 

assess each other’s intentions when the signal phase changes. 

Applicability 

Relocating the stop bar may be applicable to intersections with a high number of right-turnon-red vehicle/pedestrian collisions. 
Signalized Intersections: Informational Guide 193

Intersection-Wide Treatments 

One reference has recommended that marked crosswalks alone are insufficient in situations: 

• Where the speed limits exceeds 64.4 km/h (40 mph). 

• On roadways with four or more lanes without a raised median or crossing island that 

has (or will soon have) an ADT of 12,000 or greater. 

• On roadways with four or more lanes with a raised median or crossing island that has 

(or will soon have) an ADT of 15,000 or greater.(35)

Safety Performance 

One evaluation study found that advance stop lines resulted in reducing right-turn-on-red 

conflicts with cross traffic; more right-turn-on-red vehicles also make a complete stop behind the 

stop line. Another study determined that stop line relocation resulted in better driver compliance 

with the new location and increased elapsed time for lead vehicles entering the intersection. This 

may decrease the risk of pedestrian collisions involving left-turning vehicles.(101,103,104) However, 

placing the crosswalk at least 3 m (10 ft) or more from the cross-street flow line or curb also 

provides more time to drivers to react for the presence of pedestrian crossing on the street they 

are about to enter.(105)

Operational Performance 

Advance stop lines increase the clearance time for vehicles passing through the intersection. 

As a result, there may be an increase in loss time. 

Multimodal Impacts 

Advance stop lines keep the opposing lanes at intersections free, allowing trucks to turn wide 

and thereby allowing smaller curb radii that are more pedestrian friendly. 

Physical Impacts 

No physical needs have been identified. 

Socioeconomic Impacts 

Minimal costs are associated with stop bar alterations. 

Enforcement, Education, and Maintenance 

Enforcement of the relocated stop bars may be necessary. 

Summary 

Table 46 summarizes the issues associated with stop bar alterations. 
194 Federal Highway Administration

Table 46. Summary of issues for stop bar alterations. 

Characteristic Potential Benefits Potential Liabilities 

Safety Decreased risk of pedestrian collisions 

involving left-turning vehicles. 

None identified. 

Operations None identified. Increase in vehicular clearance time and 

loss time. 

Multimodal Relocation of stop bars facilitates 

turning movements of heavy trucks. 

None identified. 

Physical No physical needs identified. None identified. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement of the stop bars may be 

necessary. 

9.1.4 Improve Pedestrian Signal Displays 

Traffic signals should allow adequate crossing time for pedestrians and an adequate 

clearance interval based on walking speed. Pedestrian signal enhancements include: 

• Separate pedestrian signals (WALK/DON’T WALK). 

• Accessible pedestrian signal. 

• Countdown displays. 

• Animated eyes display. 

Application 

Chapter 4 provided guidance on the use of pedestrian signals and accessible pedestrian 

signals. Current thinking suggests that redundancy in information to pedestrians benefits all 

pedestrians. For example, sighted pedestrians may react more quickly to the WALK indication 

when provided an audible cue in addition to the pedestrian signal display. Therefore, accessible 

pedestrian signals may enhance the usability of the intersection for all pedestrians, not just those 

with visual impairments. 

Countdown signals, shown in figure 69a, display the number of seconds remaining before the 

end of the DON’T WALK interval. The WALKING PERSON symbol and flashing and steady 

UPRAISED HAND symbol still appear at the appropriate intervals. The countdown signals do not 

change the way a signal operates; they only provide additional information to the pedestrian. 

Countdown pedestrian signals have been included in the 2003 MUTCD for optional use.(1)

Another innovative pedestrian signal treatment is an animated eyes display, shown in figure 

69b. The animated, light-emitting diode (LED) signal head, is used to prompt pedestrians to look 

for turning vehicles at the start of the WALK indication. The signal head includes two eyes that 

scan from left to right. Animated eyes have been included in the 2003 MUTCD for optional use 

with the pedestrian signal WALK indication.(1)
Signalized Intersections: Informational Guide 195

Intersection-Wide Treatments 

 (a) Countdown display. (b) Animated eyes display. 

Figure 69. Examples of countdown and animated eyes pedestrian signal displays. 

Safety Performance 

Collision modification factors listed in table 47 all suggest that pedestrian signals improve 

safety. However, a number of older studies found that pedestrian signalization does not improve 

safety.(106,107) Larger pedestrian signal heads were described in the literature as a treatment to 

enhance conspicuity; however, no research on the effect on pedestrian safety was found. 

Accessible pedestrian signals assist visually impaired pedestrians. Different devices 

generating audible messages (audible at pedestrian head or audible at push button), vibration at 

push button, and transmitted messages are in use.(108) A recent study found a 75-percent 

reduction in the percentage of pedestrians not looking for threats and a similar reduction in 

conflicts at an intersection equipped with speakers providing messages prompting pedestrians to 

look for turning vehicles during the walk interval.(109)

Countdown displays may reduce vehicle-pedestrian conflicts resulting from pedestrians’ 

attempting to cross the intersection at inappropriate times. Several studies of these pedestrian 

countdown signals found no statistically significant reductions in pedestrian crash rates. The 

countdowns did result in a higher percentage of successful crossings by pedestrians (completed 

their crossing before conflicting traffic received the right of way). (See references 105, 110, 111, 

and 112.) 

Preliminary results from studies of the use of animated-eye displays show increased 

pedestrian observation of traffic behavior, even after 6 months. Pedestrian/vehicle conflicts 

appear to decrease at a variety of intersection configurations. Overuse of the device may 

decrease its effectiveness.(105,113)

Table 47 presents the results of selected references involving the addition of pedestrian 

signals. 

Table 47. Safety benefits associated with addition of pedestrian signals: Selected findings. 

Treatment Implication 

Install WALK/DON’T WALK signals (68) 15 to 17% estimated reduction in pedestrian collisions 

Add pre-timed, protected pedestrian phase (98) 10% estimated reduction in pedestrian collisions 
196 Federal Highway Administration

Operational Performance 

These treatments should have a negligible effect on vehicle operations. Use of redundant 

visual and audible displays may reduce the delay pedestrians experience in initiating their 

crossing, which may reduce the delay for right-turning vehicles. 

Multimodal Impacts 

Some treatments described above are of specific benefit to people with visual disabilities, 

although all pedestrians are likely to benefit from redundancy. They should be considered when 

modifying intersections. 

Apart from pedestrians, there are no specific impacts to other transportation modes. 

Physical Impacts 

No particular specific physical needs have been identified. 

Socioeconomic Impacts 

Pedestrian signals and the pedestrian signal enhancements described above have moderate 

costs. 

Enforcement, Education, and Maintenance 

As some of the treatments described above have not seen widespread use (e.g., the 

animated eyes display), some education of the meaning of the devices should be considered 

upon their introduction to the public. 

Summary 

Table 48 summarizes the issues associated with pedestrian signal display improvements. 

Table 48. Summary of issues for pedestrian signal display improvements. 

Characteristic Potential Benefits Potential Liabilities 

Safety Give pedestrians improved awareness 

of traffic. 

None identified. 

Operations None identified. None identified. 

Multimodal All pedestrians, but especially visually 

impaired pedestrians, are likely to 

benefit. 

None identified. 

Physical None identified. None identified. 

Socioeconomic None identified. Some enhancements are expensive. 

Enforcement, 

Education, and 

Maintenance 

None identified. Education may be necessary. 

9.1.5 Modify Pedestrian Signal Phasing 

Description 

In general, shorter cycle lengths and longer WALK intervals provide better service to 

pedestrians and encourage greater signal compliance. The MUTCD uses a walk speed of 1.2 m/s 

(4.0 ft/s) for determining crossing times.(1) However, the Pedestrian Facilities User Guide 

recommends a lower speed of 1.1 m/s (3.5 ft/s), as discussed in chapter 2.(35) Other researchers 

suggest that this speed is still inadequate to meet the needs of older pedestrians. A 15th-
Signalized Intersections: Informational Guide 197

Intersection-Wide Treatments 

percentile walking speed of older pedestrians has been recommended as the criterion to be used 

to assess adequacy of crossing time.(114)

Three options beyond standard pedestrian signal phasing are: 

• The leading pedestrian interval. 

• The lagging pedestrian interval. 

• The exclusive pedestrian phase. 

A leading pedestrian interval entails retiming the signal splits so that the pedestrian WALK 

signal begins a few seconds before the vehicular green. As the vehicle signal is still red, this 

allows pedestrians to establish their presence in the crosswalk before the turning vehicles, 

thereby enhancing the pedestrian right-of-way. 

A lagging pedestrian interval entails retiming the signal splits so that the pedestrian WALK 

signal begins a few seconds after the vehicular green for turning movement. The 2001 ITE guide, 

Alternative Treatments for At-Grade Pedestrian Crossings, indicates that this treatment is 

applicable at locations where there is a high one-way to one-way turning movement and works 

best where there is a dedicated right-turn lane.(105) This benefits right-turning vehicles over 

pedestrians by giving the right turners a head start before the parallel crosswalk becomes 

blocked by a heavy and continuous flow of pedestrians. 

An exclusive pedestrian signal phase allows pedestrians to cross in all directions at an 

intersection at the same time, including diagonally. It is sometimes called a “barn dance” or 

“pedestrian scramble.” Vehicle signals are red on all approaches of the intersection during the 

exclusive pedestrian signal phase. The objective of this treatment is to reduce vehicle turning 

conflicts, decrease walking distance, and make intersections more pedestrian-friendly. The 2001 

ITE guide refers to research that indicates that leading intervals were more effective treatments 

than this scramble pattern.(105)

Application 

Leading pedestrian phasing may be considered where: 

• There is moderate to heavy pedestrian traffic. 

• A high number of conflicts/collisions occur between turning vehicles and crossing 

pedestrians. 

Lagging pedestrian phasing may be considered where: 

• There is moderate to heavy pedestrian traffic. 

• There is right-turn channelization that is heavily used by vehicles. 

• A high number of conflicts/collisions occur between right-turning vehicles and crossing 

pedestrians. 

Exclusive pedestrian phasing (scramble) may be considered where: 

• There is heavy pedestrian traffic. 

• Delay for vehicular turning traffic is excessive due to the heavy pedestrian traffic. 

• There are a large number of vehicle-pedestrian conflicts involving all movements. 

Note that for any of the three treatments, the use of accessible pedestrian signals is 

recommended to give people with visual disabilities information of the walk phase in the absence 

of predictable surging traffic. 

Safety Performance 

Several studies have demonstrated that imposing of leading pedestrian intervals significantly 

reduces conflicts for pedestrians.(102,105,115) Crash analysis conducted at 26 locations with leading 
198 Federal Highway Administration

pedestrian intervals in New York City (based on up to 10 years of data) showed that leading 

pedestrian intervals have a positive effect on pedestrian safety, especially where there is a heavy 

concentration of turning vehicles. This evidently occurs regardless of pedestrian volume. 

None of the studies of lagging pedestrian intervals considered the safety effect of this 

treatment. 

Using exclusive pedestrian intervals that stop traffic in all directions has been shown to 

reduce pedestrian crashes by 50 percent in some locations (i.e., downtown locations with heavy 

pedestrian volumes and low vehicle speeds and volumes).(101,116)

Operational Performance 

The leading pedestrian phase will increase delay at the intersection due to a loss in green 

time. A solution for the issue of loss of green time for vehicles when using a leading pedestrian 

interval is based on trading the leading pedestrian interval seconds at the beginning of the cycle 

for seconds at the end of the cycle. The effect would be that all movements get less green time, 

but that time is optimized. However, this timing was not investigated empirically.(102)

A main operational disadvantage of lagging pedestrian intervals is that they cause additional 

delays to pedestrians. 

With concurrent signals, as described above, pedestrians usually have more crossing 

opportunities and shorter waits. Unless a system more heavily penalizes motorists, pedestrians 

will often have to wait a long time for an exclusive pedestrian phase. As a result, many 

pedestrians will simply choose to ignore the signal and cross if and when a gap in traffic 

occurs.(101,116) In addition, an exclusive pedestrian phase may increase the overall cycle length of 

the intersection, thus increasing delay for all users. On the other hand, an exclusive pedestrian 

phase removes pedestrians from the vehicular phases, thus increasing vehicular capacity during 

those phases. 

Multimodal Impacts 

Pedestrians may become impatient or ignore a lagging pedestrian interval or exclusive 

pedestrian phase and begin crossing the road during the DON’T WALK phase. 

Physical Impacts 

No specific physical needs were identified. 

Socioeconomic Impacts 

Minimal costs are associated with the retiming of the pedestrian signals. The exclusive 

pedestrian phase, if implemented, may require additional signing and pavement markings to 

indicate that diagonal crossings may be made (see 2003 MUTCD, section 3B.17(1)). 

Enforcement, Education, and Maintenance 

Where leading or lagging pedestrian phases are being considered, they should be 

accompanied by police enforcement to ensure that vehicles and pedestrians obey traffic signals. 

Summary 

Table 49 summarizes the issues associated with pedestrian signal phasing modifications. 
Signalized Intersections: Informational Guide 199

Intersection-Wide Treatments 

Table 49. Summary of issues for pedestrian signal phasing modifications. 

Characteristic Potential Benefits Potential Disbenefits 

Safety Reduce pedestrian/vehicle collisions. None identified. 

Operations Exclusive phase: Increased capacity 

for vehicular turning movements. 

Lead phase: Increased vehicular delay. 

Exclusive phase: Increased vehicular 

delay due to potentially longer cycle 

length. 

Multimodal Lead phase: Reduced pedestrian 

delay. 

Lag phase: Increased pedestrian delay. 

Exclusive phase: Increased pedestrian 

delay due to potentially longer cycle 

length. 

Physical None identified. None identified. 

Socioeconomic Lead or lag phases: Little or no cost. Exclusive phase: Moderate costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement may be necessary. 

9.1.6 Grade-Separate Pedestrian Movements 

Description 

In some situations, it may be feasible to consider separating pedestrian movements from an 

intersection. Pedestrian overpasses and underpasses allow for the uninterrupted flow of 

pedestrian movement separate from the vehicle traffic. However, it increases out-of-direction 

travel, both horizontally and vertically, for the pedestrian in the process. 

Applicability 

Pedestrian grade separation, an example of which is shown in figure 70, may be appropriate 

in situations where: 

• An extremely high number of pedestrian/vehicle conflicts or collisions are occurring at 

the existing crossing location. 

• School crossings exist or high volumes of children cross. 

• A crossing has been evaluated as a high-risk location for pedestrians. 

• Turning vehicles operate with high speeds. 

• Sight distance is inadequate. 

Usually, a warrant for a grade pedestrian separation is based on pedestrian and vehicle 

volume, vehicle speed, and area type. Warrants usually differ for new construction projects and 

existing highways. In the first case, greater opportunities for grade separation are available. In 

some cases, safety can be a major factor; e.g., New Jersey Department of Transportation 

guidelines consider pedestrian overpasses and/or underpasses warranted if a safety evaluation 

indicates that erection of a fence to prohibit pedestrian crossing.(117) 
200 Federal Highway Administration

Photograph Credit: Synectics Transportation Consultants, Inc. 

Figure 70. A pedestrian grade separation treatment. 

Safety Performance 

Pedestrian grade separations ideally should completely remove any pedestrian/ vehicle 

conflicts at the location in question. However, studies have shown that many pedestrians will not 

use overpasses or underpasses if they can cross at street level in about the same amount of 

time, or if the crossing takes them out of their way. Some pedestrians may avoid a pedestrian 

tunnel or overpass due to personal security concerns. 

Operational Performance 

Completely eliminating a pedestrian crossing area should improve traffic flow. However, a 

pedestrian overpass is not likely to be used if it is too inconvenient. Use of a median pedestrian 

barrier should be considered to reduce midblock crossings and encourage pedestrians to use the 

grade-separated crossing. 

Multimodal Impacts 

Pedestrian access and convenience may be negatively affected by grade separation. 

Pedestrians with disabilities or low stamina may have difficulty with the out-of-direction travel and 

elevation changes associated with grade separation. 

Physical Impacts 

Construction of a bridge overpass or tunnel is required. Note that any new or modified 

pedestrian grade separation treatment must comply with ADA requirements. This may involve 

adding long ramps with landings at regular intervals or installing elevators. 

Socioeconomic Impacts 

Grade separation can be very expensive and difficult to implement. As a result, grade 

separation is usually only feasible where pedestrians must cross high-speed, high-volume 

arterials.(101) In most cases, other treatments are likely to be more cost effective. 

Enforcement, Education, and Maintenance 

Maintenance issues associated with litter and graffiti are significant with pedestrian 

overpasses and underpasses. Additional police enforcement may be needed because of the fear 

of crime in these facilities. 
Signalized Intersections: Informational Guide 201

Intersection-Wide Treatments 

Summary 

Table 50 summarizes the issues associated with pedestrian grade separation. 

Table 50. Summary of issues for pedestrian grade separation. 

Characteristic Potential Benefits Potential Liabilities 

Safety Reduced pedestrian-vehicle 

collisions. 

Pedestrians may cross in unexpected locations 

due to inconvenience of grade separation. 

Operations Improved vehicular capacity. None identified. 

Multimodal Fewer conflicts between 

pedestrians and vehicles. 

Increased walking distance, delay, and difficulty 

for pedestrians. 

Physical None identified. Grade separation structure required, as well as 

ramps or elevators to meet ADA requirements. 

Socioeconomic None identified. Significant costs (grade separation). 

Enforcement, 

Education, and 

Maintenance 

None identified. Graffiti removal and enforcement for personal 

security may be necessary. 

9.2 BICYCLE TREATMENTS 

9.2.1 Provide Bicycle Box 

Description 

A bicycle box uses advance stop bars that are placed on the approach to a signalized 

intersection, typically in the rightmost lane, at a location upstream from the standard stop bar 

location. These create a dedicated space for bicyclists—a bicycle box—to occupy while waiting 

for a green indication. Advance stop bars are used in conjunction with bicycle lanes or other 

similar bicycle provisions. 

Applicability 

This treatment may be applicable in situations where vehicle/bicycle collisions have been 

observed in the past, or vehicle/bicycle conflicts are observed in field observations. The treatment 

may be considered if a bike lane exists on the approach. 

In locations with a high volume of right-turning traffic, use of this treatment may be 

problematic.

Safety Performance 

Such a treatment was found to be effective in Europe, resulting in a 35 percent reduction in 

through-bicycle/right-turning-vehicle collisions.(118) 

Operational Performance 

This treatment is not expected to have a significant effect on traffic operations unless a high 

volume of right-turning traffic is present. 

Multimodal Impacts 

Bicycle boxes permit bicyclists to pass other queued traffic on the intersection approach leg, 

giving them preferential treatment in proceeding through the intersection. 
202 Federal Highway Administration

Enforcement, Education, and Maintenance 

Concerns with providing a bicycle box include motorist violation of existing stop bar, a lack of 

uniformity with other intersections, and right-turn-on-red movements. 

Summary 

Table 51 summarizes the issues associated with providing a bicycle box. 

Table 51. Summary of issues for providing a bicycle box. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in collisions between 

through bicycles and right-turning 

vehicles. 

None identified. 

Operations None identified. This treatment may not be compatible with a 

high volume of right-turning traffic. 

Multimodal Bicyclists can bypass queued traffic, 

thus reducing delay. 

None identified. 

Physical None identified. None identified. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement of the box may be necessary. 

9.2.2 Provide Bike Lanes 

Description 

While bicycle lanes are frequently used on street segments, AASHTO cautions against the 

use of bicycle lane markings through intersections.(21) Special lanes for bicyclists can cause 

problems to the extent that they encourage bicyclists and motorists to violate the rules of the road 

for drivers of vehicles. Specifically, a bike lane continued to an intersection encourages rightturning motorists to stay in the left lane, not the right (bike) lane, in violation of the rule requiring 

that right turns be made from the lane closest to the curb. Similarly, straight-through, or even leftturning, cyclists are encouraged to stay right. 

Some advocate placing the bike lane between the through lane and the right-turn only lane. A 

right-turn-only lane encourages motorists to make right turns by moving close to the curb (as the 

traffic law requires). A cyclist going straight can easily avoid a conflict with a right-turning car by 

staying outside of the right-turn lane. A bike lane to the left of the turn lane encourages bicyclists 

to stay out of the right-turn lane when going straight. 

Applicability 

This treatment may be applicable in situations where there are a high number of bicyclists 

using the road or where bicycle use is being promoted or encouraged. 

Safety Performance 

Some European literature suggests that bicycle lane markings can increase motorist 

expectation of bicyclists; one Danish study found a 36-percent reduction in bicycle collisions 

when these were marked.(119) Other research concludes that bicycle paths along arterials typically 

increase cyclists’ vulnerability to a collision at signalized intersections; however, raised and 

brightly colored crossings reduce the number of bicycle/vehicle conflicts and should improve 

safety.(120) 
Signalized Intersections: Informational Guide 203

Intersection-Wide Treatments 

Multimodal Impacts 

Bicycle lanes delineate roadway space between motor vehicles and bicycles and provide for 

more predictable movements by each.(21)

Physical Impacts 

Bicycle lanes may require additional right-of-way unless width is taken from the existing travel 

and/or parking lanes, either by lane narrowing or the removal of a lane. 

Summary 

Table 52 summarizes of the issues associated with providing bicycle lanes. 

Table 52. Summary of issues for providing bicycle lanes. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in vehicle/bicycle 

collisions. 

None identified. 

Operations None identified. None identified. 

Multimodal Bicycle lanes delineate roadway space 

between motor vehicles and bicycles and 

provide for more predictable movements by 

each. 

None identified. 

Physical None identified. Bicycle lanes may require additional rightof-way unless width is taken from existing 

lanes. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

9.3 TRANSIT TREATMENTS 

9.3.1 Relocate Transit Stop 

Placement of bus stops in the vicinity of intersections can have a significant influence on the 

safety and operational performance. Approximately 2 percent of pedestrian accidents in urban 

areas and 3 percent in rural areas are related to bus stops.(121) Proper placement and provisions 

at bus stops can reduce several safety and mobility problems. Traffic engineers often have two 

choices with regard to bus stop placement in the vicinity of an intersection: on the near side 

(upstream) or far side (downstream). The 1996 Transit Cooperative Research Program (TCRP) 

Report 19: Guidelines for the Location and Design of Bus Stops provides a comprehensive 

comparative analysis of far-side, near-side, and midblock placement of bus stops.(121) 

Application 

Relocation of a transit stop to a location upstream of the intersection (near side) should be 

considered in situations where there is congestion on the far side of the intersection during peak 

periods. 

Relocation of a transit stop to a location downstream of the intersection (far side) should be 

considered in situations where: 

• There is a heavy right-turn movement. 
204 Federal Highway Administration

• There have been a number of conflicts between vehicles trying to turn right, through 

vehicles, and stationary near-side buses, resulting in rear-end and sideswipe 

collisions. 

• There have been a number of pedestrian collisions because pedestrians cross in front 

of a stationary bus and are struck by a vehicle. 

Safety Performance 

One advantage of near-side placements is that the bus driver has the entire width of the 

intersection available to pull away from the curb. Near-side bus placements increases conflicts 

between right-turning vehicles, through traffic, and the bus itself. When the bus is stopped at the 

bus stop, traffic control devices, signage, and crossing pedestrians are blocked from view. 

Vehicles on the adjacent approach to the right may have difficulty seeing past a stopped bus 

while attempting a right turn on red. 

Far-side bus stop placements minimize conflicts between right-turning vehicles and buses. 

Relocating the bus stop to the far side of the intersection can also improve safety because it 

eliminates the sight distance restriction caused by the bus and encourages pedestrians to cross 

the street from behind the bus instead in front of it.(122) The 1996 TCRP report recommends a 

minimum clearance distance of 1.5 m (5 ft) between a pedestrian crosswalk and the front or rear 

of a bus stop.(121) Finally, the bus driver can take advantage of gaps in the traffic flow that are 

created at signalized intersections. However, far-side bus stops may cause rear-end collisions, as 

drivers often do not expect buses to stop immediately after the traffic signal. 

In conclusion, as a whole, it would appear that far-side bus stops offer greater overall safety. 

Operational Performance 

Near-side bus stop placements minimize interference with through traffic in situations where 

the far side of the intersection is congested. This type of placement also allows the bus driver to 

look for oncoming traffic, including other buses with potential passengers for the stopped bus. 

However, if the bus stop is being used for more than one bus, the right and through lanes may be 

temporarily blocked. 

Far-side bus stop placements improve the right-turn capacity of the intersection. Yet they 

may block the intersection during peak periods by stopping buses or by a traffic queue extending 

back into the intersection. Also, if the light is red, it forces the bus to stop twice, decreasing the 

efficiency of bus operations. 

Multimodal Impacts 

Near-side bus stop placements allow pedestrians to access buses closest to the crosswalk, 

and allows pedestrians to board, pay the fare, and find a seat while the bus is at a red light. 

However, placing the bus stops on the near side of intersections or crosswalks may block 

pedestrians’ view of approaching traffic and the approaching drivers’ view of pedestrians.(101) 

Physical Impacts 

Near-side bus stops/bus shelter placements may interfere with the placement of a red-light 

camera. 

Socioeconomic Impacts 

Relocation of a bus stop is a relatively low-cost improvement, unless it involves the relocation 

of a bus bay and shelter. 

Enforcement, Education, and Maintenance 

Some jurisdictions have implemented or are considering a yield-to-bus law. If implemented, 

this would require all motorists to yield to buses pulling away from a bus stop and reduce 

transit/vehicle conflicts. 
Signalized Intersections: Informational Guide 205

Intersection-Wide Treatments 

Far-side bus bays provide a safe haven for police officers carrying out red light running or 

speed enforcement and can also facilitate U-turns. 

From a driver education point of view, the traffic engineer and transit agency may consider 

consistently placing the bus stop either on the near side or the far side, so that motorists have an 

expectation of where the bus is going to stop at all signalized intersections in their jurisdiction. 

Summary 

Table 53 summarizes of the issues associated with providing near-side or far-side transit 

stops. 

Table 53. Summary of issues for near-side/far-side transit stops. 

Characteristic Potential Benefits Potential Liabilities 

Safety Right-turning vehicle conflicts (far 

side). 

Sight distance issues for crossing 

pedestrians/vehicles on adjacent 

approach (far side). 

Rear-end conflicts (near side). 

Right-turning vehicle conflicts (near side). 

Sight distance issues for crossing 

pedestrians/vehicles on adjacent approach 

(near side). 

Rear-end conflicts (far side). 

Operations Eliminates double stopping (near 

side). 

Right-turn/through lanes may be blocked 

(near side). 

Intersection may be blocked (far side). 

Multimodal Passenger can board while light is 

red (near side). 

Less walking distance to crosswalk 

(near side). 

None identified. 

Physical None identified. May interfere with red-light camera 

placement (near side). 

Socioeconomic None identified. Relocation (far or near) may be costly if it 

involves relocation of bus bay/bus shelter. 

Enforcement, 

Education, and 

Maintenance 

Far-side bus bays provide space for 

enforcement vehicles. 

Enforcement of yielding to buses may be 

necessary. 

9.4 TRAFFIC CONTROL TREATMENTS 

Intersection-wide traffic control treatments have either operational or safety benefits on all 

approaches and all movements. Signal coordination improves traffic flow for through traffic and 

provides gaps for left-turn movements. Signal preemption and priority identifies and 

accommodates critical movements and users. Signal controller upgrades (from pre-timed to 

actuated) accommodate intersections where traffic flow is highly variable, reducing delays and 

driver frustration. Clearance interval adjustments can address a red light running problem. Cycle 

length can also be adjusted based on the nature of the traffic flow through the intersection. 

Finally, the advisability of removal of a signalized intersection from late night/early morning flash 

mode should be evaluated. 

9.4.1 Change Signal Control from Pre-Timed to Actuated 

Description 

Traffic signal control at an intersection may be pre-timed or actuated. This mode of control 

could be a function of the capabilities of the controller (older controllers may not have actuated 

capabilities), or it could be a byproduct of the lack of detection at the intersection (for example, a 

modern controller with full actuated capabilities may be required to run pre-timed if no detection is 
206 Federal Highway Administration

in place). The mode of control used can have a profound effect on the operational efficiency and 

safety of the signalized intersection. 

A pre-timed controller operates within a fixed cycle length using preset intervals and no 

detection. Pre-timed traffic control signals direct traffic to stop and permit it to proceed in 

accordance with a single predetermined time schedule or series of schedules. 

The traffic engineer may want to consider upgrading an intersection from pre-timed to 

actuated control. These signals service movement based on demand. Actuated signals use 

detection to respond to vehicle calls and are categorized as either semiactuated or fully actuated.

Semiactuated traffic signals have detectors located on the minor approaches and in the left-turn 

lanes of the major approaches. Fully actuated traffic signals have detection on all approaches. 

Selecting the best type of control for a location requires full knowledge of local conditions, 

but, in general, can be based on: 

• Variations in peak and average hourly traffic volumes on the major approaches. 

• Variations in morning and afternoon hourly volumes. 

• Percentage of volumes on the minor approaches. 

• Usage by large vehicles, pedestrians, and bicycles.

Applicability 

Converting a signal from pre-timed to actuated may be considered in situations: 

• Where fluctuations in traffic cannot be anticipated and thus cannot be programmed 

with pre-timed control. 

• At complex intersections where one or more movements are sporadic or subject to 

variations in volume. 

• At intersections that are poorly placed within a traffic corridor of intersections with 

pre-timed traffic signals. 

• To minimize delay in periods of light traffic. 

Safety Performance 

Actuated traffic signals provide better service to all movements at an intersection, reducing 

driver frustration and the likelihood of red light running. However, they also make it more difficult 

for pedestrians with visual impairments to predict what will happen in the intersection. 

There is little research on the effect of signal actuation on collisions, apart from some 

references from Michigan and New York State (table 54). These references suggest that actuated 

signalized intersections have fewer collisions than intersections with fixed timing. 
Signalized Intersections: Informational Guide 207

Intersection-Wide Treatments 

Table 54. Safety benefits associated with upgrading an intersection from pre-timed to actuated 

operation: Selected findings. 

Treatment Finding 

Upgrade signal controller (98) 20 to 22% estimated reduction in all collisions. 

Install signal actuation (98) 20% estimated reduction in all collisions. 

Change in signal operations (pre-timed 

to traffic actuated)(123)

28% estimated reduction in all collisions. 

32% estimated reduction in right-angle collisions. 

26% estimated reduction in rear-end/overtaking collisions. 

60% estimated reduction in head-on/sideswipe collisions. 

30% estimated reduction in left-turn collisions. 

Operational Performance 

Actuated intersections used in appropriate situations, can reduce delays to vehicles, 

particularly in light traffic situations and for movements from minor approaches. 

Actuated traffic control is not necessary in situations where traffic patterns and volumes are 

predictable and do not vary significantly. They may not be the best choice where there is a need 

for a consistent starting time and ending time for each phase to facilitate signal coordination with 

traffic signals along a traffic corridor. Actuated signals are dependent on the proper operation of 

detectors; therefore, they are affected by a stalled vehicle, vehicles involved in a collision, or 

construction work. This may disrupt operations at a signalized intersection. 

Multimodal Impacts 

Pre-timed traffic signals may be more acceptable than traffic-actuated signals in areas where 

there is large and fairly consistent pedestrian traffic crossing the road. Actuated traffic signals 

may cause confusion with the operation of pedestrian push buttons. Actuated pedestrian push 

buttons must be located in appropriate locations and be accessible to be ADA compliant. 

Physical Impacts 

Detectors are required on the approaches where actuation is needed. Depending on the type 

of detector, this may create physical impacts (see chapter 4 for further discussion of detector 

types). 

Socioeconomic Impacts 

Generally speaking, actuated traffic controllers cost more to purchase and install than pretimed traffic controllers, although almost all traffic controllers purchased today are capable of 

actuated operation. Detection can be a significant percentage of the cost of a signalized 

intersection. 

Enforcement, Education, and Maintenance 

Pre-timed traffic signals may lead to driver frustration in low-volume situations, as in the late 

evening/early morning hours, as the driver may be waiting for the signal to change green while no 

other vehicles are present on the other approaches. This may lead to red light running. 

Traffic-actuated signals are more complicated and less easily maintained than pre-timed 

traffic signals, especially because of detector maintenance needs. 

Summary 

Table 55 summarizes the issues associated with providing signal actuation. 
208 Federal Highway Administration

Table 55. Summary of issues for providing signal actuation. 

Characteristic Potential Benefits Potential Liabilities 

Safety Improves safety. 

Reduces driver frustration, red light 

running. 

None identified. 

Operations Provides better service to minor 

approaches. 

Accommodates widely fluctuating 

volumes. 

Can sometimes reduce smooth platooning 

in coordinated systems. 

Requires proper operation of detectors. 

Multimodal None identified. May be problematic in high pedestrian 

areas. 

Physical None identified. Detectors required. 

Socioeconomic None identified. Can be costly. 

Enforcement, 

Education, and 

Maintenance 

Enforcement needs may decrease. Maintenance costs will likely increase to 

maintain detection. 

9.4.2 Modify Yellow Change Interval and/or Red Clearance Interval 

Description 

The yellow change interval warns approaching traffic of the change in assignment of right-ofway. Yellow change intervals, a primary safety measure used at traffic signals, are the subject of 

much debate. The yellow change interval is normally between 3 and 6 s. Since long yellow 

change intervals may encourage drivers to use it as a part of the green interval, a maximum of 

5 s is commonly employed. Local practice dictates the length of the change interval. 

Current thought is that longer intervals will cause drivers to enter the intersection later and 

breed disrespect for the traffic signal. One before-and-after study showed that the time vehicles 

entered the intersection increased with a longer yellow change interval.(124) Additional research is 

needed to further understand the effect of lengthening the yellow change interval on driver 

behavior.

The red clearance interval is an optional interval that follows the yellow change interval and 

precedes the next conflicting green interval. The red clearance interval provides additional time 

following the yellow change interval before conflicting traffic is released. The decision to use a red 

clearance interval is determined based on engineering judgment and assessment of any of the 

following criteria: 

• Intersection geometrics. 

• Collision experience. 

• Pedestrian activity. 

• Approach speeds. 

• Local practices. 

The red clearance interval is either set by local policy or calculated using an equation that 

determines the time needed for a vehicle to pass through the intersection. The equation most 

commonly used is described in various documents(125) (and chapter 4). As intersections are 

widened to accommodate additional capacity, the length of the calculated clearance interval 

increases. This increase may contribute to additional lost time at the intersection, which negates 

some of the expected gain in capacity due to widening. 
Signalized Intersections: Informational Guide 209

Intersection-Wide Treatments 

Applicability 

Modifying the yellow or red clearance interval may be considered where: 

• A high number of angle/left-turn collisions occur due to through/left-turning drivers 

failing to clear the intersection or stop before entering the intersection at onset of the 

red. 

• A high number of rear-end collisions occur because drivers brake sharply to avoid 

entering the intersection at the onset of the red. 

• A high incidence of red-light violations is recorded. 

Safety Performance 

A 1985 study examined the relationship between the timing of clearance intervals and crash 

rates.(126) The study focused on 91 intersections across the United States that represent a variety 

of intersection characteristics including average approach speed, cross-street width, yellow 

phase, and all-red phase. Results from a cluster analysis showed that intersections with 

inadequate clearance intervals (meaning the implied deceleration rate exceeded 1982 

Transportation and Traffic Engineering Handbook recommendations of 3 m/s2 (10 ft/s2

) resulted in 

either: (1) drivers’ entering the intersection without adequate cross-street protection, thus 

increasing the risk of right-angle collisions; or (2) drivers’ braking suddenly to avoid entering the 

intersection, thus increasing the risk for rear-end collisions. The study concludes that accepted 

standards for timing clearance intervals are commonly ignored and that improved procedures 

need to be adopted throughout the United States. 

A 1997 paper studied the effects of clearance interval timing on red light running and late 

exits (vehicles that fail to exit the intersection before the onset of green for the cross-street 

movement, resulting in a right-of-way conflict).(127) The clearance interval timing for the 

intersections that were studied was compared to the recommended timing calculated when using 

the procedures identified in “Determining Vehicle Change Intervals: A Proposed Recommended 

Practice.”(128) Results from the study showed that the number of red light running and late exit 

instances were highest at intersections where clearance intervals were too short. Based on the 

results of the study, drivers did not appear to become habituated to longer yellow signals or 

increased all-red periods. The paper concludes by indicating that although the positive influence 

of a longer clearance interval may partially erode over time, the findings of the research suggest 

that longer change intervals can provide a sustainable safety benefit. 

A 2000 paper(129) evaluated the potential crash effects associated with modifying clearance 

intervals to conform with ITE’s “Determining Vehicle Change Intervals: A Proposed 

Recommended Practice.”(128) The study focused on 122 intersections that were randomly 

assigned to experimental and control groups. During the 3-year period following the 

implementation of the signal timing changes, the intersections with the modified time experienced 

an 8 percent reduction in reported crashes, a 12 percent reduction in injury crashes, and 37 

percent reduction in pedestrian and bicycle crashes. Given the positive results from the study, 

the authors conclude that modifying the clearance intervals to conform to the ITE proposed 

recommended practice should be strongly considered by agencies to reduce the number of 

crashes. 

A Texas study of 12 intersection approaches suggested that red light running frequency is 

minimized with yellow change intervals between 4.0 and 4.5 seconds.(130)

A Michigan study concerning the adjustment of yellow change intervals and all-red intervals 

at three intersections showed a significant reduction in red light running violations. All red 

intervals were lengthened from 0.1 second to 1.6 to 4.0 seconds, according to ITE guidelines. 

Reductions in red light running violations were significant and some preliminary data appears to 

suggest that collisions have been reduced as well.(131)

Table 56 presents selected findings associated with signal clearance modifications. 
210 Federal Highway Administration

Table 56. Safety benefits associated with modifying clearance intervals: Selected findings. 

Treatment Finding 

Add all-red clearance interval (98) 15 to 30% estimated reduction in all collisions. 

Increase yellow change interval (98) 15 to 30% estimated reduction in all collisions. 

Retime traffic signal (98) 10% estimated reduction in all collisions. 

Add all-red clearance interval and increase 

yellow change interval(132)

15% estimated reduction in all collisions. 

30% estimated reduction in right-angle collisions. 

Operational Performance 

Extending the yellow and red interval will increase the amount of lost time, decreasing the 

overall efficiency of the intersection. 

Multimodal Impacts 

Either extending the yellow and/or red clearance interval or providing a red clearance interval 

will benefit pedestrians, going them additional time to clear the intersection. The elderly or people 

with mobility disabilities may benefit substantially. 

Physical Impacts 

No physical impacts are associated with this treatment. 

Socioeconomic Impacts 

The treatment has been shown to reduce red light running at a wide variety of signalized 

intersections. It is a low-cost alternative to the use of police or automated enforcement. 

Enforcement, Education, and Maintenance 

Local practice varies as to legal movements during the yellow phase. Police, traffic 

engineering staff, and the public need to be clear and in agreement about what is permissible in 

their jurisdiction. 

Summary 

Table 57 summarizes the issues associated with modifying yellow and/or red clearance 

intervals at signalized intersections. 
Signalized Intersections: Informational Guide 211

Intersection-Wide Treatments 

Table 57. Summary of issues for modifying yellow/red clearance intervals. 

Characteristic Potential Benefits Potential Liabilities 

Safety Angle collisions are reduced. 

Left-turn collisions are reduced. 

Rear-end collisions are reduced. 

None identified. 

Operations None identified. Increased lost time. 

Multimodal The elderly and people with mobility disabilities have 

more time to cross. 

None identified. 

Physical No physical requirements. None identified. 

Socioeconomic Low-cost alternative to police and automated 

enforcement. 

None identified. 

Enforcement, 

Education, and 

Maintenance 

Red-light enforcement may become less necessary. None identified. 

9.4.3 Modify Cycle Length 

Description 

The calculation and selection of cycle length requires good judgment on the part of the traffic 

engineer/analyst. General practice is to have a cycle length between 50 and 120 s. For low-speed 

urban roads, a shorter cycle length is preferable (50 to 70 s). For wider roadways (over 15 m (50 

ft)) with longer pedestrian crossing times (greater than 20 s), or in situations where heavier traffic 

is present and left-turning vehicles are not being effectively accommodated, a cycle length of 60 

to 90 s may be preferable. At high-volume intersections where heavy turning movements are 

accommodated by multiple phases, a cycle length of 90 to 120 s may be most appropriate.(133)

However, cycle lengths longer than 120 s may be needed at large intersections to accommodate 

multiple long pedestrian crossings in combination with heavy turning movements, especially 

during peak periods. 

Safety Performance 

Longer cycle lengths may lead to driver frustration and red light running, as it may take 

several cycles for a motorist to get through the intersection, particularly when attempting a left 

turn against opposing traffic. 

No known research or specific collision modification factors exist for modifying cycle length. 

Operational Performance 

A cycle length of 90 s is often considered optimum, since lost time is approaching a 

maximum, capacity is approaching a minimum, and delay is not too great.(133) Longer cycle 

lengths may lead to excessive queuing on the approach and will interfere with turning movements 

(left- and right-turn channelization) if through traffic is severely backed up. 

Conversely, intersection capacity drops substantially when cycle lengths fall below 60 s, as a 

greater percentage of available time is used up in the yellow and red clearance intervals. 

Multimodal Impacts 

A shorter cycle length may not provide pedestrians with sufficient time to safely cross the 

intersection, particularly if it has turning lanes. Conversely, a longer cycle length may encourage 

impatient pedestrians to cross illegally during the red phase. 
212 Federal Highway Administration

Physical Impacts 

No physical impacts are associated with the modification of cycle length. 

Socioeconomic Impacts 

No significant costs are associated with this treatment, apart from labor. 

Summary 

Table 58 summarizes the issues associated with cycle length modification. 

Table 58. Summary of issues for cycle length modifications. 

Characteristics Potential Benefits Potential Liabilities 

Safety Less red light running (with shorter 

cycle lengths). 

More red light running (with longer cycle 

lengths). 

Operations Reduction in delay optimized at 

90 s. 

Excessive queuing (with longer cycle lengths). 

Inadequate capacity (with cycle lengths that are 

too short). 

Multimodal None identified. Inadequate crossing time for pedestrians (with 

cycle lengths that are too short). 

Physical None identified. None identified. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. More red light running (with longer cycle 

lengths). 

9.4.4 Late Night/Early Morning Flash Removal 

Description 

Some jurisdictions operate traffic signals in flashing mode during various periods of the night, 

the week, or for special events. Flashing operation may be of some advantage to traffic flow, 

particularly with pre-timed signals, when traffic is very light (late evening/early morning hours, or 

on a Sunday or holiday in an industrial area). 

Two modes of flashing operation are typically used: red-red and red-yellow. Red-red (all 

approaches receive a flashing red indication) is used where traffic on all approaches is roughly 

the same. In this instance, the intersection operates the same as an all-way stop. Red-yellow (the 

minor street receives a flashing red indication and the major street receives a flashing yellow 

indication) is used in situations where traffic is very light on the minor street. In this instance, the 

intersection operates similar to a two-way stop. 

Safety Performance 

A 1987 Michigan study involved the conversion of 59 signalized intersections previously 

operating in late-night/early morning flashing mode.(134) Late night and early morning collisions 

before and after the conversion were compared and tested using a paired t-test. Right-angle 

collisions during when signalized intersections were in flash mode dropped by 91 percent; rightangle injury collisions dropped by 95 percent. Rear-end collisions increased slightly, but the 

change was not significant. 

In a study in Winston-Salem, NC, signals from 20 intersections were taken out of late 

night/early morning flashing operation.(135) There was a 78-percent reduction in right-angle 
Signalized Intersections: Informational Guide 213

Intersection-Wide Treatments 

collisions and a 32-percent reduction in all collisions during times the traffic signal had been in 

flashing mode. 

Some studies have indicated a safety benefit of removing traffic signals from flashing mode 

under some circumstances, as positive control is provided rather than leaving the driver to decide 

when it is safe to proceed into the intersection. 

Selected study findings associated with the removal of a traffic signal from a flashing mode 

operation (such as during the late-night/early morning time period) are shown in table 59. 

Table 59. Safety benefits associated with removal of signal from late night/early morning flash 

mode: Selected findings. 

Treatment Finding 

Remove signal from late 

night/early morning flash 

mode (135)

78% estimated reduction in right-angle collisions during time of previous 

flashing operation. 

32% estimated reduction in all collisions during time of previous flashing 

operation. 

Operational Performance 

If the signalized intersection removed from flashing operation is not fully actuated and 

responsive to traffic demand, there will be a tendency for red-light violations and/or complaints 

about unnecessary long waits on red signals. 

Multimodal Impacts 

Removing a traffic signal from a flash mode will require vehicles to come to a complete stop 

during the red phase. This treatment should give vehicles more time to see, respond, and yield to 

any pedestrians. 

Physical Impacts 

No physical impacts are associated with this treatment. 

Socioeconomic Impacts 

No costs are associated with this treatment. 

Enforcement, Education, and Maintenance 

When a traffic signal is taken out of flash mode, police enforcement could be undertaken at 

the location to ensure that habituated drivers are not continuing to proceed through the 

intersection as if the signal were still operating in flashing mode. The traffic engineer may 

consider temporary signage/publicity to inform motorists of the change in operations and to 

explain the safety benefits. 

Summary 

Table 60 summarizes the issues associated with flash mode removal. 
214 Federal Highway Administration

Table 60. Summary of issues for flash mode removal. 

Characteristic Potential Benefits Potential Liabilities 

Safety Angle collisions are reduced. None identified. 

Operations None identified. Increased delay for through traffic. 

Multimodal Motorists forced to yield to pedestrians. None identified. 

Physical None identified. None identified. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement and temporary signage 

may be needed for a period after 

conversion. 

9.5 STREET LIGHTING AND ILLUMINATION 

9.5.1 Provide or Upgrade Illumination 

Description 

The purpose of roadway lighting is to enhance visibility for drivers, bicyclists, and 

pedestrians, thereby improving their ability to see each other and the physical infrastructure of the 

intersection. This allows them to react more quickly and accurately to each other when natural 

light goes below a certain level⎯either at night or during bad weather. 

Applicability 

Intersection lighting should be considered at all signalized intersections. Upgrades may be 

justified if more collisions than expected are occurring at night, and particularly if the nighttime 

collisions involve pedestrians, bicyclists, and/or fixed objects. 

Design Features 

The illumination design at an intersection should meet lighting criteria established by the 

Illuminating Engineering Society of North America (IESNA) in IESNA RP-8-00, American National 

Standard Practice for Roadway Lighting.(63) The basic principles and design values for 

intersections have been presented previously (chapter 4) and include overall light level and 

uniformity of lighting. 

Some of the factors that affect the light level and uniformity results include: 

• Luminaire wattage, type, and distribution. 

• Luminaire mounting height. 

• Pole placement and spacing. 

These factors are interrelated. For example, higher mounting heights improve uniformity by 

spreading the light over a larger area; however, the overall light level decreases unless larger 

wattages are used or poles are placed closer together. A good illumination design balances these 

various factors against an overall desire to minimize the number of poles and fixtures (both for 

cost savings and for minimizing the number of fixed objects in the right-of-way). 

Pole Placement and Spacing 

Besides the types of poles and fixtures, the placement is also an important aspect of a good 

roadway design. Several factors need to be considered in pole placement. First is safety. Most 

important is to place the pole at an offset distance that can assist in preventing crashes (vehicles 

and pedestrians). Second is to determine the pole spacing that is most efficacious for the initial 
Signalized Intersections: Informational Guide 215

Intersection-Wide Treatments 

and the long-term maintenance costs and yet still meets the lighting requirement. At intersections, 

shared use of poles for signal equipment and illumination is recommended. Figure 71 shows 

examples from RP-8-00 of illumination pole layouts typical at signalized intersections with and 

without channelized right-turn lanes. However, recent research to improve lighting at midblock 

pedestrian crosswalks suggests that it may be desirable to locate poles approximately one third 

to one half the luminaire mounting height back from the crosswalk to improve lighting for 

pedestrians, which may involve having separate poles for signal equipment and luminaires.(136)

For intersections where separate pedestrian pedestals are provided at the crosswalk, the mast 

arm poles for vehicle signal heads could be located to be optimal for illumination as well. 

(a) Typical lighting layout for intersection without right-turn bypass lane. 

(b) Typical lighting layout for intersection with right-turn bypass lane. 

Figure 71. Typical lighting layouts.(63, figure D3)
216 Federal Highway Administration

Safety Performance 

When illumination and visibility are optimal, the chance of nighttime accidents declines, and 

traffic flow is enhanced. Roadway lighting also increases sight distance, security, and the use of 

surrounding facilities. 

Selected findings from the literature suggest safety improvements associated with adding 

illumination to an intersection (see table 61). 

Table 61. Safety benefits associated with providing illumination: Selected findings. 

Treatment Finding 

Add lighting (132) 30% reduction in all collisions. 

50% reduction in nighttime collisions. 

Add lighting (137) 43% reduction in fatal crashes. 

17% reduction in injury crashes. 

Operational Performance 

There is no documented relationship between illumination and the operational performance of 

an intersection. The authors believe that illumination likely has little effect on traffic flow, delay, 

and queuing. 

Multimodal Impacts 

As noted above, illumination has been demonstrated to reduce pedestrian crashes and 

provide a more secure environment for all intersection users at night. 

Physical Impacts 

The provision of illumination typically has little effect on the overall footprint of an intersection. 

Commonly, combination poles are used to support both signal heads and luminaires, so 

additional poles are rarely needed in the immediate vicinity of the intersection. However, the 

recent research cited previously suggests the possibility of improved pedestrian visibility using 

additional poles upstream from the crosswalk. 

Socioeconomic Impacts 

Illumination has a positive benefit in reducing the fear of crime at night and in promoting 

business and the use of public streets at night.(63)

In addition to the initial capital cost and maintenance of illumination fixtures, illumination 

requires energy consumption. The Roadway Lighting Committee of IESNA believes that lighting 

of streets and highways is generally economically practical and that such preventive measures 

can cost a community less than the crashes caused by inadequate visibility.(63) Judicious design 

of luminaire types, wattages, mounting height, and pole spacing may increase visibility at the 

intersection without significantly increasing energy costs. 

Summary 

Table 62 summarizes the issues associated with providing illumination. 
Signalized Intersections: Informational Guide 217

Intersection-Wide Treatments 

Table 62. Summary of issues for providing illumination. 

Characteristic Potential Benefits Potential Disbenefits 

Safety Reported reductions in nighttime collisions. None identified. 

Operations None identified. None identified. 

Multimodal May reduce pedestrian crashes. None identified. 

Physical Little impact. None identified. 

Socioeconomic May reduce fear of nighttime crime. Additional energy consumption. 

Enforcement, 

Education, and 

Maintenance 

None identified. Maintenance of illumination will be 

necessary. 

Signalized Intersections: Informational Guide 219

Alternative Intersection Treatments

CHAPTER 10 

ALTERNATIVE INTERSECTION TREATMENTS 

TABLE OF CONTENTS 

10.0 ALTERNATIVE INTERSECTION TREATMENTS..............................................................221 

 10.1 Intersection Reconfiguration and Realignment Treatments .....................................222 

 10.1.1 Remove Intersection Skew Angle................................................................222 

 10.1.2 Remove Deflection in Travel Path for Through Vehicles.............................225 

 10.1.3 Convert Four-Leg Intersection to Two T-Intersections ................................227 

 10.1.4 Convert Two T-Intersections to Four-Leg Intersection ................................229 

 10.1.5 Close Intersection Leg .................................................................................230 

 10.2 Indirect Left-Turn Treatments ...................................................................................232 

 10.2.1 Jughandle.....................................................................................................232 

 10.2.2 Median U-Turn Crossover............................................................................242 

 10.2.3 Continuous Flow Intersection.......................................................................249 

 10.2.4 Quadrant Roadway Intersection ..................................................................256 

 10.2.5 Super-Street Median Crossover ..................................................................260 

 10.3 Grade Separation Treatments ..................................................................................264 

 10.3.1 Split Intersection...........................................................................................265 

 10.3.2 Diamond Interchange...................................................................................269 

LIST OF FIGURES 

Figure Page

72 Illustration of conflict points for a four-leg signalized intersection ......................................222 

73 Diagrams of different types of intersection realignment .....................................................223 

74 Example of deflection in travel paths for through vehicles .................................................226 

75 Conflict point diagram for two closely spaced T-intersections............................................228 

76 Diagram of a jughandle intersection ...................................................................................233 

77 Vehicular movements at a jughandle intersection..............................................................233 

78 Example of a jughandle intersection...................................................................................234 

79 Another example of a jughandle intersection .....................................................................234 

80 Design layout of near-side jughandle .................................................................................236 

81 Design layout of far-side jughandle ....................................................................................237 

82 Example of jughandle and associated signing ...................................................................238 

83 Signal phasing of a jughandle intersection.........................................................................239 

84 Conflict point diagram for a four-leg signalized intersection with two jughandles ..............240 

85 Diagram of a median U-turn crossover from the main line.................................................242 

86 Vehicular movements at a median U-turn intersection.......................................................243 

87 Example of median U-turn signing in Michigan ..................................................................244 

88 Diagram of general placement of a median U-turn crossover............................................245 

89 Diagram of a median U-turn crossover from the main line with a narrow median..............245 

90 Conflict diagram for a four-leg signalized intersection with median U-turns.......................247 

91 Diagram of a continuous flow intersection..........................................................................250 

92 Vehicular movements at a continuous flow intersection.....................................................250 

93 Continuous flow intersection...............................................................................................251 

94 Displaced left turn at a continuous flow intersection...........................................................251 

95 Signal phasing of a continuous flow intersection................................................................252 

96 Conflict diagram for a continuous flow intersection with displaced left turns on the major 

street only ........................................................................................................................253 

97 Diagram of a quadrant roadway intersection......................................................................257 

98 Vehicular movements at a quadrant roadway intersection.................................................257 

99 Signal phasing of a quadrant roadway intersection............................................................258 

100 Conflict point diagram for four-leg signalized intersection with quadrant roadway ............259 

101 Illustration of super-street median crossover......................................................................261 

102 Vehicular movements at a super-street median crossover ................................................261 

103 Signal phasing of a super-street median crossover ...........................................................262 
220 Federal Highway Administration

CHAPTER 10 FIGURES, CONTINUED 

Figure Page

104 Conflict diagram for a super-street median crossover....................................................... 263 

105 Illustration of a split intersection......................................................................................... 266 

106 Conflict point diagram for a split intersection..................................................................... 267 

107 Diagram of a single-point interchange............................................................................... 270 

108 Diagram of a compressed diamond interchange............................................................... 271 

109 Typical signal phasing of a single-point interchange ......................................................... 271 

110 Typical signal phasing of a compressed diamond interchange......................................... 272 

111 Single-point diamond interchange conflict point diagram .................................................. 273 

112 Compressed diamond interchange conflict point diagram................................................. 274 

LIST OF TABLES 

Table Page

63 Summary of issues for removing intersection skew........................................................... 225 

64 Summary of issues for removing deflection of vehicle path .............................................. 227 

65 Number of conflict points at a four-leg signalized intersection compared to two closely 

spaced T-intersections.................................................................................................... 227 

66 Safety benefits of converting a four-leg signalized intersection to two T-intersections: 

Expert opinion................................................................................................................. 228 

67 Summary of issues for converting a four-leg intersection to two T-intersections .............. 229 

68 Summary of issues for converting two T-intersections to one four-leg intersection .......... 230 

69 Safety benefits associated with street closures: Selected findings ................................... 231 

70 Summary of issues for closing an intersection approach leg ............................................ 232 

71 Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a jughandle ......................................................................... 240 

72 Safety benefits of converting a four-leg signalized intersection to a four-leg signalized 

intersection with two jughandles: Expert opinion............................................................ 240 

73 Summary of issues for jughandles..................................................................................... 242 

74 Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a median U-turn crossover configuration ........................... 246 

75 Safety benefits of converting a four-leg signalized intersection to median U-turn 

crossover configuration: Expert opinion ......................................................................... 247 

76 Summary of issues for median U-turn crossovers............................................................. 249 

77 Number of conflict points at a four-leg signalized intersection compared to a continuous 

flow intersection with displaced left turns on the major street only ................................ 253 

78 Safety benefits of converting a four-leg signalized intersection to a CFI: Expert opinion.. 254 

79 Summary of issues for continuous flow intersections........................................................ 256 

80 Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a quadrant roadway............................................................ 258 

81 Safety benefits of adding a quadrant roadway to a four-leg signalized intersection: 

Expert opinion................................................................................................................. 259 

82 Summary of issues for quadrant roadways ....................................................................... 260 

83 Number of conflict points at a four-leg signalized intersection compared to a super-street 

median crossover ........................................................................................................... 263 

84 Safety benefits of converting a four-leg signalized intersection compared to a super-street 

median crossover: Expert opinion .................................................................................. 263 

85 Summary of issues for super-street median crossovers ................................................... 264 

86 Number of conflict points at a four-leg signalized intersection compared to a split 

intersection ..................................................................................................................... 267 

87 Safety benefits of converting a four-leg signalized intersection to a split intersection: 

Expert opinion................................................................................................................. 268 

88 Summary of issues for split intersections .......................................................................... 269 

89 Number of conflict points at a four-leg signalized intersection compared to a 

compressed diamond and single-point diamond interchange........................................ 273 

90 Safety benefits of converting a four-leg signalized intersection to a 

compressed diamond and single-point diamond interchange: Expert opinion............... 275 

91 Summary of issues for single-point and compressed diamond interchanges ................... 276 
Signalized Intersections: Informational Guide 221

Alternative Intersection Treatments

10. ALTERNATIVE INTERSECTION TREATMENTS 

A recent study has shown that conventional methods of adding capacity to an intersection—

adding left-turn, through, and right-turn lanes—have diminishing returns.(138) For example, if the 

addition of a second through lane adds 15 years to the life of the intersection before it reaches 

capacity, the addition of a third through lane adds only 10 years, and a fourth through lane adds 

only 6 years. Large intersections increase loss time due to longer clearance intervals, protected leftturn phasing, longer pedestrian clearance times, greater imbalances in lane utilization, and potential 

queue blockages caused by the resulting longer cycle lengths. Each of these issues suggests the 

need to look for alternative methods to conventional lane additions to solving congestion-related 

problems. 

This chapter describes reconstruction treatments for signalized intersections in three 

categories: intersection reconfiguration, at-grade indirect movements, and grade separation. Many 

of these treatments are commonplace; others have seen limited or regional use. The common 

element in each treatment is the reduction in conflict points at the intersection, which provides 

safety and operational benefits by reducing the number of phases and conflicting volume at a single 

location. These reconstruction treatments are often necessary when relatively low-cost treatments 

(such as improving signal timing and signing or adding an auxiliary lane) do not suffice. 

Given that limited data are available regarding the safety of these treatments, a conflict point 

diagram is provided so that the treatments presented here can be compared to a conventional fourleg signalized intersection (figure 72). At a conventional four-leg signalized intersection, conflict 

points can be categorized as follows: 

• Eight merge and eight diverge conflict points. Collisions associated with 

merging/diverging movements are rear-end and sideswipe collisions, occurring on a 

particular leg and involving another vehicle on the same leg. 

• Sixteen crossing conflict points. Of these, 12 crossing movements are associated with 

left-turning vehicles. Collisions associated with this crossing movement occur when a 

vehicle attempting a left turn at a signal is struck by traffic passing through the 

intersection on another approach. The remaining four crossing movements involve 

through movements on two adjacent approaches. Angle collisions may occur as a result 

of this type of conflict. 

Conflict points provide a means to compare the relative safety for vehicles of a typical four-leg 

signalized intersection to the alternative intersection treatments presented in this chapter. With 

each of these treatments, an expert opinion is provided stating what the expected change in 

collisions might be if the alternative treatment were introduced. 
222 Federal Highway Administration

Figure 72. Illustration of conflict points for a four-leg signalized intersection. 

10.1 INTERSECTION RECONFIGURATION AND REALIGNMENT TREATMENTS 

This section discusses several conventional at-grade treatments that can solve specific 

intersection problems. 

10.1.1 Remove Intersection Skew Angle 

Description 

The AASHTO policy suggests maintaining an intersection angle of 75 to 90 degrees for new 

construction.(3) Angles as low as 60 degrees are acceptable if cost and other constraints dictate a 

need for this degree of skew. If reconstructed intersections have a skew angle below 60 degrees, 

examination of collision rates and patterns may be required. 

Signalized intersections may have sight-distance-related safety problems that cannot be 

addressed inexpensively (such as clearing sight triangles, adjusting signal phasing, or prohibiting 

turning movements). These may require horizontal or vertical realignment of approaches. 

Realigning both of the minor-road approaches so that they intersect the major road at a different 

location or a different angle can help address horizontal sight distance issues. Such strategies 

should generally be considered only at intersections with a persistent crash pattern that cannot be 

changed by less expensive methods, such as clearing sight triangles at intersections and in 

medians. 

Examples of different types of realignment are shown in figure 73.
Signalized Intersections: Informational Guide 223

Alternative Intersection Treatments

 

(a) Realignment to one side. (b) Realignment to both sides. 

 

(c) Offset T with interior left turns. (d) Offset T with exterior left turns. 

(e) Realignment to T intersection. 

Figure 73. Diagrams of different types of intersection realignment.(3, Exhibit 9-18)

Applicability 

Realignment of the approaches on an intersection may be applicable where severe collision 

problems occur. 

Safety Performance 

At skewed intersections, crossing distances are lengthened and the conflict area within the 

intersection is greater. This increases the potential for collisions. 

Roads that intersect with each other at angles less than 90 degrees can present sight-distance 

and operational problems for drivers. A high incidence of right-angle accidents, particularly involving 

vehicles approaching from the acute angle, may be the result of a problem associated with skew. 

Because vehicles have a longer distance to travel through the intersection (increasing their 

exposure to conflicts), drivers may find it difficult to look to the left at an approach on an acute 

angle, and vehicles turning right at an acute angle may encroach on vehicles approaching from the 

opposite direction. When right turns on red are permitted, drivers may have more difficulty judging 

gaps when turning. Also, crossing distances for pedestrians are increased. 

Skewed intersections, in addition to potentially having intersection sight-distance problems, 

could also present a different sight obstruction for drivers. It is possible that the vehicle body itself 

could block a driver’s view of the cross road, depending on the angle of the skew, the position of 

the vehicle on the roadway, and the position of the driver in the vehicle.(43)

Skewed intersections pose particular problems for older drivers, many of whom experience a 

decline in head and neck mobility. A restricted range of motion reduces older drivers’ ability to 
224 Federal Highway Administration

effectively scan to the rear and sides of the vehicle to observe blind spots. They may also have 

trouble identifying gaps in traffic when making a left turn, or safely merging with traffic when making 

a right turn.(12)

No specific references to safety benefits of removing intersection skew were found. 

If utility poles and/or illumination running alongside the road remain in the same location after 

alignment, they may create a visual illusion that the road is still in its old alignment. A low-cost 

solution is to provide delineation on the curves at the beginning of the realignment, but some 

collisions may still occur. 

Operational Performance 

Any improvement to intersection skew will improve operations involving turning vehicles. In 

addition, improvement to intersection skew often reduces vehicle and pedestrian clearance time, 

which may result in an overall reduction in delay to all users. Because such projects are significant 

undertakings, the number of through and turning lanes and signal phasing should be reevaluated; 

this may result in a significant improvement in intersection operations. 

Multimodal Impacts 

As highly skewed intersections mean longer crossing distances for pedestrians, any 

improvement in skew angle will reduce pedestrian exposure to traffic and likely improve pedestrian 

safety. 

Longer commercial vehicles will have considerable difficulty turning at an intersection where 

adjacent legs meet at an angle at less than 60 degrees. Considerable off-tracking will occur. Any 

improvement to skew angle will particularly improve the safety and operation when these vehicles 

attempt such turns. 

Physical Impacts 

Traffic signals, controllers, signage, and illumination may all have to be relocated if this 

treatment is undertaken. 

Socioeconomic Impacts 

Removing intersection skew may involve acquisition of adjacent land, removal of structures, 

and relocation of road furniture. If this is the case, this improvement may be costly. 

Summary 

Table 63 summarizes the issues associated with removing intersection skew. 
Signalized Intersections: Informational Guide 225

Alternative Intersection Treatments

Table 63. Summary of issues for removing intersection skew. 

Characteristic Potential Benefits Potential Liabilities 

Safety Reduce left-turn/oncoming collisions. 

Reduce right-turn-on-red collisions. 

Possible increase in run-off-road collisions 

Operations Improve turning operations. 

Reduce vehicle and pedestrian 

clearance time. 

None identified. 

Multimodal Reduce crossing distance for 

pedestrians. 

Improve alignment for pedestrian 

accessibility. 

None identified. 

Physical None identified. Relocation of all signal equipment, signage 

and other street furniture. 

Socioeconomic None identified. Will be expensive to implement. 

Adjacent property issues. 

Relocation of street furniture. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

10.1.2 Remove Deflection in Travel Path for Through Vehicles 

Intersections with substantial deflections between approach alignments can produce 

operational and safety problems for through vehicles as they navigate through an intersection. 

Forced path changes for through vehicles violate driver expectations and may pose problems for 

unfamiliar drivers. Violation of driver expectancy can result in reduced speeds through the 

intersection. Crashes influenced by a deflection in travel path are likely to include rear-end, 

sideswipe, head-on, and left-turning/through crashes. Acceptable deflection angles through 

intersections vary by individual agency, but are typically related to the design and/or posted speed 

on an intersection approach. Typical maximum deflection angles are 3 to 5 degrees. An example of 

deflection in through-vehicle travel paths is shown in figure 74. 

Applicability 

Removing deflection in the through vehicle travel path is applicable as a treatment where: 

• Deflection angles exceed 3 to 5 degrees. 

• Conflicts result from driver confusion in proceeding through the intersection or turning 

left. 

• A high number of rear-end, sideswipe, head-on, and left-turning/through collisions 

occur on the affected approaches. 

Safety Performance 

Redesign of an intersection approach (or approaches) to eliminate deflection in the through 

vehicle travel path should eliminate crashes related to the situation. Proper design of an 

intersection should provide traffic lanes that are clearly visible to drivers at all times, clearly 

understandable for any desired direction of travel, free from the potential for conflicts to appear 

suddenly, and consistent in design with the portions of the highway approaching the intersection. 

The sight distance should be equal to or greater than minimum values for specific interchange 

conditions.
226 Federal Highway Administration

Photograph Credit: Lee Rodegerdts, 2003 

Figure 74. Example of deflection in travel paths for through vehicles. 

Operations 

Eliminating deflection for through vehicles will improve traffic flow, although the amount of 

improvement may be difficult to quantify. No existing analytical or simulation models are sensitive to 

deflection of through vehicles. 

Multimodal Impacts 

Redesign of an intersection approach or approaches will particularly benefit heavy vehicles and 

buses by reducing the amount of off-tracking as they proceed through the intersection. 

Physical Impacts 

Additional right-of-way may be required to realign through lanes. 

Socioeconomic Impacts 

Eliminating deflection should be done for a low to moderate cost. Impacts may be largely 

confined to one side of the intersection. 

Summary 

Table 64 summarizes the issues associated with the removal of vehicle path deflection. 
Signalized Intersections: Informational Guide 227

Alternative Intersection Treatments

Table 64. Summary of issues for removing deflection of vehicle path. 

Characteristic Potential Benefits Potential Liabilities 

Safety Decrease in all collision types. None identified. 

Operations Improvement in traffic flow. None identified. 

Multimodal Heavy trucks/transit. None identified. 

Physical None identified. Additional right-of-way may be required. 

Socioeconomic None identified. Low to moderate costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

10.1.3 Convert Four-Leg Intersection to Two T-Intersections 

For some signalized four-leg intersections with very low through volumes on the cross street, 

the best method of improving safety may be to convert the intersection to two T-intersections. This 

conversion to two T-intersections can be accomplished by realigning the two cross-street 

approaches an appreciable distance along the major road, thus creating separate intersections that 

operate relatively independently of one another. 

Applicability 

This improvement may be applicable to signalized four-leg intersections with very low through 

volumes on the cross street, yet having a relatively high number of unusually severe collisions. 

Safety Performance 

In a study conducted by Hanna et al., offset intersections had collision rates that were 

approximately 43 percent of the accident rate at comparable four-leg intersections.(139) This study 

did not differentiate between signalized and nonsignalized intersections. 

Table 65 shows the number of merging, diverging and crossing (left-turn and angle) conflicts for 

two closely spaced T-intersections as compared to a four-leg signalized intersection. Compared to 

a four-leg signalized intersection, two closely spaced T-intersections have less merge/diverge and 

left-turn crossing conflict points and no angle crossing conflict points. Figure 75 shows the conflict 

point diagram for two closely spaced T-intersections. 

Table 65. Number of conflict points at a four-leg signalized intersection compared to two closely 

spaced T-intersections. 

Conflict Type Four-Leg Signalized 

Intersection 

Two Closely Spaced TIntersections 

Merging/diverging 16 12 

Crossing (left turn) 12 6 

Crossing (angle) 4 0 

Total 32 18 
228 Federal Highway Administration

Figure 75. Conflict point diagram for two closely spaced T-intersections 

Table 66 summarizes the expert opinion of the authors with regard to the safety benefits of a 

conversion of a four-leg signalized intersection to two T-intersections. 

Table 66. Safety benefits of converting a four-leg signalized intersection to two 

T-intersections: Expert opinion. 

Treatment Surrogate Implication 

Convert four-leg 

intersection to two 

T-intersections 

Conflict points Estimated minor decrease in merging/diverging collisions 

Estimated significant decrease in left turn collisions 

Estimated major decrease in angle collisions 

Operational Performance 

If through volumes on the minor street are high, the intersection may be safer if left as a 

conventional four-leg intersection. Converting it to two T-intersections would only create excessive 

turning movements at each of the T-intersections. 

Another potential difficulty with this strategy is the spacing between the two 

T-intersections. If they are not spaced far enough apart, two problems can occur. First, there may 

not be enough storage length for the left-turning vehicles between the two intersections if left-turn 

movements overlap (negative offset). Second, the operation of the two intersections may interfere 

with one another. In general, the offset T-intersection arrangement where major street left turns do 

not overlap (positive offset) is better because it eliminates the problem of queue overlap for the 

major street left turns. 

Another difficulty may occur in providing safe access to the properties adjacent to the former 

four-leg intersection. Driveway access should be considered during the design process. 

Multimodal Impacts 

No significant multimodal impacts are expected. The smaller T-intersections may have shorter 

pedestrian clearance times and shorter cycle lengths, resulting in shorter overall delay for 

pedestrians and cyclists. 

Physical Impacts 

The intersections should be separated enough to ensure the provision of adequate turn-lane 

channelization on the major road. 

Relocation of traffic signals, signage, and other street furniture would be required. 
Signalized Intersections: Informational Guide 229

Alternative Intersection Treatments

This treatment would involve purchasing an additional set of traffic signals. 

Socioeconomic Impacts 

Significant costs would be associated with this improvement. 

Enforcement, Education, and Maintenance 

Due to the change in traffic patterns necessitated by this treatment, public acceptance and 

understanding of the issues and reasons for converting the intersection will be an important 

consideration. 

Summary 

Table 67 summarizes the issues associated with the conversion of a four-leg intersection to two 

T-intersections. 

Table 67. Summary of issues for converting a four-leg intersection to two 

T-intersections. 

Characteristic Potential Benefits Potential Liabilities 

Safety Angle collisions. 

Left-turn collisions. 

None identified. 

Operations None identified. Operations of each intersection may interfere 

with each other if spacing is insufficient. 

Multimodal May have shorter delay at each 

intersection. 

None identified. 

Physical None identified. Relocation of traffic signal, signage, street 

furniture. 

Additional set of traffic signals required. 

Socioeconomic None identified. Significant costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. Education may be needed on the issues and 

reasons for conversion. 

10.1.4 Convert Two T-Intersections to Four-Leg Intersection 

For some signalized offset T-intersections with very high through volumes on the cross street, 

the best method for improving safety may be to convert the intersection to a single four-leg 

intersection. This can be accomplished by realigning the two cross-street approaches to meet at a 

single point along the major road. 

Applicability 

This improvement may be considered for signalized offset T-intersections with very high 

through volumes on the cross street and a high frequency of collisions associated with turning 

movements involving traffic on the cross street. 

Safety Performance 

In the previous section, it was suggested that converting a four-leg intersection to two Tintersections would lead to an improvement in safety using conflict points as a surrogate. However, 

in some circumstances, two T-intersections may be experiencing safety problems due to the 

conditions described above that could be addressed through a conversion to a four-leg intersection. 

It is expected that this strategy would reduce collisions involving left-turning traffic from the major 

road onto the cross street at each of the two T-intersections. It can reduce or eliminate safety 

problems associated with insufficient spacing between existing offset T-intersections. 
230 Federal Highway Administration

Operational Performance 

The success of this strategy depends on the through volume of the cross street. If through 

volumes are low, the intersection may be safer if left as two offset T-intersections. Two offset Tintersections with low through volumes on the cross street are generally safer than a four-leg 

intersection. 

Multimodal Impacts 

No significant multimodal impacts are expected. The larger single intersection may have longer 

pedestrian clearance times and longer cycle lengths, resulting in longer overall delay for 

pedestrians and cyclists. 

Physical Impacts 

Relocation of traffic signals, signage, and other street furniture would be required. 

This treatment would involve the removal of one set of traffic signals. 

Socioeconomic Impacts 

Significant costs would be associated with this improvement. 

Enforcement, Education, and Maintenance 

Due to the change in traffic patterns involved in carrying out this treatment, public acceptance 

and understanding of the issues and reasons for converting the intersection will be an important 

consideration. 

Summary 

Table 68 summarizes the issues associated with the conversion of two T-intersections to a fourleg intersection. 

Table 68. Summary of issues for converting two T-intersections to one four-leg intersection. 

Characteristic Potential Benefits Potential Liabilities 

Safety Left-turn/rear-end collisions. Angle collisions. 

Operations Improved operations for through 

traffic. 

None identified. 

Multimodal None identified. May have longer delay. 

Physical None identified. Relocation of traffic signal, signage, street 

furniture. 

Removal of a set of traffic signals required. 

Socioeconomic None identified. Significant costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. Education may be needed on the issues and 

reasons for conversion. 

10.1.5 Close Intersection Leg 

For some signalized intersections with severe crash histories, the best way to improve safety 

may be to close a leg or convert one leg to a one-way movement away from the intersection. 

Closing a leg should generally be considered only when less restrictive measures have been tried 

and have failed. Closing a leg can be accomplished by closing and abandoning a minor approach 

using channelizing devices or by reconstructing the minor approach so it ends before reaching the 

intersection with the major street. Though it is a significant modification to an intersection, it can be 
Signalized Intersections: Informational Guide 231

Alternative Intersection Treatments

a low-cost treatment. This treatment may be most applicable to intersections with more than four 

legs. 

Applicability 

This treatment may be considered in situations where other treatments with fewer impacts have 

failed. Possible applications are in situations where a high and unusually severe number of 

collisions are occurring that involve movements to and from the leg in question. 

Safety Performance 

Closing a leg should eliminate crashes related to that leg. Consideration must be given to the 

adjacent intersections and to alternative routes onto which traffic would be diverted, and the 

potential impact to safety on those routes. Estimates of safety benefits are shown in table 69. 

Table 69. Safety benefits associated with street closures: Selected findings. 

Treatment Implication 

Street closure—cross intersection(137) 50% estimated reduction in adjacent approach collisions. 

50% estimated reduction in opposing turn collisions. 

50% estimated reduction in pedestrian collisions. 

100% estimated reduction in loss-of-control collisions. 

Street closure—close stem of Tintersection(140)

100% estimated reduction in adjacent approach collisions . 

100% estimated reduction in opposing turn collisions. 

50% estimated reduction in pedestrian collisions. 

100% estimated reduction in loss-of-control collisions. 

Operational Performance 

Closing a leg will mean simplifying the signal phasing and may mean a shorter cycle. However, 

closing a leg will considerably alter traffic patterns in the area if volumes on the leg to be closed are 

significant. The capacity of surrounding roads and intersections to accommodate the diverted traffic 

will need to be considered. 

Transit operations may be significantly impacted if routes use the leg being closed. 

Physical Impacts 

In closing a leg, a barrier will need to be constructed. This barrier should be aesthetically 

pleasing, even if temporary. Landscaping should be considered after it is determined that this 

closure will be permanent. 

Multimodal Impacts 

It may be possible to maintain pedestrian and bicycle connections to the closed leg, thus 

maintaining existing circulation patterns. If such connections can be maintained, the closure may 

help to promote a more pedestrian-friendly environment. 

Socioeconomic Impacts 

Due to the significant change in traffic patterns involved, public acceptance and understanding 

of the issues and reasons for converting the intersection are critical (particularly for residents or 

businesses on the closed leg). 

Enforcement, Education, and Maintenance 

Such a treatment would need agreement from all emergency services, as emergency response 

could be significantly affected. 

Summary 

Table 70 summarizes the issues associated with closing an intersection approach leg. 
232 Federal Highway Administration

Table 70. Summary of issues for closing an intersection approach leg. 

Characteristic Potential Benefits Potential Liabilities 

Safety Eliminates all collisions involving 

movements on affected approach. 

Collision migration to another location. 

Operations Shorter cycle length. Alternation of traffic patterns; increased 

congestion elsewhere. 

Multimodal Bike lanes/sidewalks can remain for 

accessing closed street; may create 

pedestrian-friendly environment. 

None identified. 

Physical A landscaped barrier will improve 

aesthetics. 

Barrier required. 

Socioeconomic None identified. Buy-in from emergency services required. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

10.2 INDIRECT LEFT-TURN TREATMENTS 

Indirect left turns can improve the safety and operations of high-volume intersections. These 

designs remove the left-turning vehicles from the traffic stream without causing them to slow down 

or stop in a through-traffic lane, thereby reducing the potential for delay and rear-end crashes. 

Right-angle crashes are also likely to decrease after indirect left-turn treatments are implemented. 

Such treatments are effective on divided highways with medians too narrow to accommodate leftturn lanes with sufficient storage capacity. An overview of these types of intersection forms can be 

found in several sources.(141,142,143)

In some cases, it is possible to implement indirect left turns using appropriate signing. 

Implementation costs and time could be quite high, however, if right-of-way needs to be acquired to 

construct indirect left turns. Care should be taken to ensure that safety problems are not transferred 

to nearby intersections if drivers choose alternative routes. Clear signing is a necessity for indirect 

left-turn designs, especially if there are not similar treatments at other intersections in an area. 

10.2.1 Jughandle 

As defined in the New Jersey Department of Transportation (NJDOT) design manual, a 

jughandle is “an at-grade ramp provided at or between intersections to permit the motorists to make 

indirect left turns and/or U-turns.”(144) The NJDOT has used jughandles for years to minimize leftturn conflicts at intersections. Other States that have implemented jughandles to a lesser degree 

include Connecticut, Delaware, Oregon, and Pennsylvania. 

Jughandles are one-way roadways in two quadrants of the intersection that allow for removal of 

left-turning traffic from the through stream without providing left-turn lanes. All turns—right, left, and 

U-turns—are made from the right side of the roadway. Drivers wishing to turn left exit the major 

roadway at a ramp on the right and turn left onto the minor road at a terminus separated from the 

main intersection. Less right-of-way is needed along the roadway because left-turn lanes are 

unnecessary. However, more right-of-way is needed at the intersection to accommodate the 

jughandles. 

Figure 76 illustrates a jughandle intersection with the ramps located in advance of the 

intersection. The various possible movements are illustrated in figure 77. As can be seen, vehicles 

on the major street use the ramp to make turning movements at the intersection. Examples are 

shown in figures 78 and 79. 
Signalized Intersections: Informational Guide 233

Alternative Intersection Treatments

Figure 76. Diagram of a jughandle intersection.(adapted from 145)

 (a) Major street movements. (b) Minor street movements. 

Figure 77. Vehicular movements at a jughandle intersection. 
234 Federal Highway Administration

Figure 78. Example of a jughandle intersection. 

Figure 79. Another example of a jughandle intersection. 

Applicability 

Jughandles may be appropriate at intersections with high major street through movements, lowto-medium left turns from the major street, low-to-medium left turns from the minor street, and any 

amount of minor street through volumes.(141) Intersections too small to allow large vehicles to turn 

left, as well as intersections with medians too narrow to provide a left-turn lane, may also be 

appropriate locations for jughandles. 
Signalized Intersections: Informational Guide 235

Alternative Intersection Treatments

Jughandles address safety deficiencies involving left-turn collisions and operational deficiencies 

due to the lack of available green time for major-street through movements. 

Design Features 

The NJDOT design manual provides design guidelines for jughandles.(144) Jughandles 

commonly are constructed in advance of the intersection (see figure 80). If left-turn movements 

onto the cross street are problematic, a loop ramp may be constructed beyond the intersection to 

allow these vehicles to make a right turn onto the cross street, as shown in figure 81. The 

disadvantage is that additional right-of-way is needed to accommodate the loop ramp and the travel 

distance is greater. Note that although the cited guidelines do not show pedestrian or bicycle 

facilities, these should be included in as appropriate. 

Key features from the design manual are summarized below: 

• Deceleration lane = length should be determined based on speed of mainline and speed 

of exit curve. 

• Desirable exit curve = 75 to 90 m (250 to 300 ft) radius. 

• Ramp length = sufficient to accommodate vehicle storage. 

• Number of lanes = one or two lanes. 

• Lane width = the minimum width for a one-lane ramp should not be less than 6.6 m (22 

ft). 

• Ramp design speed = 25 to 40 km/h (15 to 25 mph). 

• Ramp location = should be located a sufficient distance from the adjacent signalized 

intersection to avoid queue spill back from the signal. 

• Access = No access should be permitted to the ramp. 

• Right-turn radius at cross street = A minimum radius of 10.5 m (35 ft) should be used 

from the right-turn movement from the ramp to the cross street. This movement should 

be channelized. 

Signing at jughandle intersections is critical, as drivers need to be given an indication that they 

must exit to the right to make a left turn. Figure 82 gives an example of signing used in New Jersey. 

Because jughandles are relatively common in New Jersey, the signing employed is perhaps more 

minimal than might be considered in other areas where jughandles are more novel. 
236 Federal Highway Administration

Figure 80. Design layout of near-side jughandle.(adapted from 144)
Signalized Intersections: Informational Guide 237

Alternative Intersection Treatments

Figure 81. Design layout of far-side jughandle.(adapted from 144)
238 Federal Highway Administration

Photograph Credit and Copyright: Arthur Eisdorfer, 2002. 

Figure 82. Example of jughandle and associated signing. 

Operational Features 

The jughandle should operate with stop control at the minor street approach. Right turns onto 

the cross street may operate with yield control. Signing is needed in advance of the jughandle ramp 

to indicate that motorists destined to the left need to exit the roadway from the right-hand lane. 

With the removal of left-turn lanes at the signalized intersection location, the signal can be 

operated with either two or three phases, as shown in figure 83. The third phase would be needed 

to accommodate minor street left-turn movements. The reduction in phases allows for either shorter 

cycle times or allocation of green times to the major street through movements. Shorter cycle 

lengths should be considered to minimize vehicle queues on the cross street. 
Signalized Intersections: Informational Guide 239

Alternative Intersection Treatments

Figure 83. Signal phasing of a jughandle intersection. 

Safety Performance 

Jughandles remove left-turning vehicles from the through lanes and thus are likely to reduce 

crashes as long as sufficient signing is provided to help eliminate driver confusion. The NJDOT has 

constructed many jughandle intersections; these are considered to be safe. No significant increase 

in crashes has been experienced since the implementation of the jughandles, though a decrease in 

crashes is not reported, either.(146)

Driver confusion may result when jughandles are first constructed in an area. Also, areas with 

significant numbers of unfamiliar drivers may experience problems related to driver confusion, even 

after the jughandles are no longer new. Signing should be used to inform drivers how to make 

turns. A public information campaign leading up to the opening of the new ramp(s) may be 

appropriate. 

Visual cues can reduce the amount of driver confusion. A raised concrete median barrier, 

installed to separate opposing directions of travel, may lead drivers to expect that turns from the left 

are not possible, and may explain why the collision experience at New Jersey jughandles has been 

good.(146)

Pedestrians on the cross street will have to cross the ramp terminal, thus increasing their 

exposure to potential conflict. The main intersection, however, will maintain a minimum width, and 

crossing distance will not increase (as it would with construction of a left-turn lane). 

Table 71 shows the number of conflict points at a four-leg signalized intersection as compared 

to a four-leg signalized intersection with two jughandles. A four-leg signalized intersection with two 

jughandles would have fewer crossing (left-turn) conflict points. Figure 84 shows the conflict point 

diagram for a four-leg signalized intersection with two jughandles. 
240 Federal Highway Administration

Table 71. Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a jughandle. 

Conflict Type 

Four-Leg Signalized 

Intersection 

Four-Leg Signalized Intersection with 

Two Jughandles 

Merging/diverging 16 16 

Crossing (left turn) 12 6 

Crossing (angle) 4 4 

Total 32 26 

Figure 84. Conflict point diagram for a four-leg signalized intersection with two jughandles. 

Table 72 summarizes the expert opinion of the authors with regard to the safety benefits of a 

conversion of a four-leg signalized intersection to four-leg signalized intersection with two 

jughandles. 

Table 72. Safety benefits of converting a four-leg signalized intersection to a four-leg signalized 

intersection with two jughandles: Expert opinion. 

Treatment Surrogate Implication 

Convert signalized fourleg intersection to 

signalized four-leg 

intersection with two 

jughandles 

Conflict 

points 

Offers the potential for significant decrease in left-turn 

collisions. 

Operational Performance 

The operations of a jughandle are best represented through the use of microsimulation models. 

A microsimulation model reflects the queue interaction between the signalized intersection and the 

minor street/ramp terminal intersection. An isolated intersection analysis can be used to determine 

the appropriate phases and signal timing parameters for the signalized intersection. 
Signalized Intersections: Informational Guide 241

Alternative Intersection Treatments

General findings regarding the operational performance of jughandles are summarized below: 

• Simulation studies using a range of intersection configurations (number of through lanes 

on the major and minor street) and volumes from intersections in Virginia and North 

Carolina suggest a reduction in overall travel time through the intersection when 

compared to a conventional intersection: –6 to +51 percent during off-peak conditions, 

and +4 to +45 percent during peak conditions. The studies also show a large increase in 

the overall percent of stops when compared to a conventional intersection: +15 to +193 

percent during off-peak conditions, and +19 to +108 percent during peak conditions.(145) 

• Because left-turning vehicles must travel a longer distance through the intersection, 

jughandle intersections do not allow for better travel times for left turns than 

conventional intersections with the same conditions. They may lead to longer delay and 

travel distances than other indirect left-turn alternatives. However, the overall delay for 

the intersection may be lower than that for a conventional intersection. 

• The ramp terminals are typically stop-controlled for left turns. This leads to more stops 

for left-turning vehicles. If cross-street volumes are high, it is possible that the queue of 

vehicles on the cross street will block the ramp terminal, increasing delay for vehicles at 

the terminal waiting to turn left onto the cross street. 

• The operations and green time requirements for minor-street through volumes should be 

evaluated with and without the jughandle to ensure that the benefits realized by the main 

line through movements are not offset by the impact of additional minor-street through 

traffic. 

Multimodal Impacts 

With jughandle ramps in place, left-turn lanes are not needed along the mainline; this may 

reduce the roadway cross section and reduce the amount of pedestrian crossing distance. The 

elimination of the major street left-turn phase may enable shorter cycle lengths that reduce the 

amount of delay for pedestrians. 

Bicycle lanes should remain at the outside lane and include dotted lines where right-turning 

vehicles are required to cross to enter the jughandle. Conflicts are reduced at the intersection 

given that right turns have already been separated from the through travel lane. 

Because of the close proximity of the jughandle ramps to the main intersection, transit stops 

should be located outside the influence area of the intersection, including the jughandle ramps. This 

will minimize potential queuing conflicts. 

Physical Impacts 

The amount of land required for construction of a jughandle ramp depends on the storage and 

super elevation requirements of the ramp. The NJDOT design manual recommends a minimum of 

30 m (100 ft) between the ramp terminal intersection at the cross street and the stop bar for the 

signalized intersection.(144) Hummer and Reid suggest that each jughandle typically requires a 

triangle 120 m (400 ft) by 90 m (300 ft).(141)

The infield area created by the ramp may be used as a drainage basin; however, the water 

surface should be located outside the clear zone.(144) Additional landscaping maintenance may be 

required for the infield area. 

An option that may have fewer impacts is to implement a virtual jughandle by using an existing 

grid network to divert traffic around the block rather than permitting left turns at the major street 

intersection. 

Summary 

Table 73 summarizes the issues associated with jughandles. 
242 Federal Highway Administration

Table 73. Summary of issues for jughandles. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in left-turn collisions. None identified. 

Operations Potential reduction in overall travel time 

and stops. 

Longer travel time and more stops for 

left-turning vehicles using the jughandle. 

Multimodal Pedestrian crossing distance may be 

less due to lack of left-turn lanes on the 

major street. 

Pedestrian delay may be reduced due 

to potentially shorter cycle lengths. 

Increased exposure for pedestrians 

crossing the ramp terminal. 

Ramp diverges may create higher speed 

conflicts between bicyclists and motor 

vehicles. 

Transit stops may need to be relocated 

outside the influence area of the 

intersection. 

Physical None identified. Additional right-of-way may be required. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Education may be needed unless good 

visual cues are provided. 

10.2.2 Median U-Turn Crossover 

Median U-turn crossovers eliminate left turns at intersections and move them to median 

crossovers beyond the intersection. For median U-turn crossovers located on the major road, 

drivers turn left off the major road by passing through the intersection, making a U-turn at the 

crossover, and turning right at the cross road. Drivers wishing to turn left onto the major road from 

the cross street turn right onto the major road and make a U-turn at the crossover. 

Figure 85 illustrates a median U-turn configuration, and figure 86 illustrates some of the vehicle 

movements at such an intersection. 

Figure 85. Diagram of a median U-turn crossover from the main line.(adapted from 145)
Signalized Intersections: Informational Guide 243

Alternative Intersection Treatments

 (a) Major street movements. (b) Minor street movements. 

Figure 86. Vehicular movements at a median U-turn intersection. 

The median crossover may also be located on the minor road. In this case, drivers wishing to 

turn left from the major road turn right on the minor road, and left through the median crossover. 

Minor road vehicles turn left onto the major road by proceeding through the intersection, making a 

U-turn, and turning right at the major road. Median U-turn crossovers also may be provided on both 

the major and minor roads at an intersection. 

Median U-turn crossovers are very common in Michigan, and drivers are very familiar with 

them. They have been in use for more than 30 years, and the signing has evolved to become more 

user friendly.(141) Figure 87 shows an example of median U-turn signing used in Michigan. 
244 Federal Highway Administration

Photograph Credit: Lee Rodegerdts, 2002 

Figure 87. Example of median U-turn signing in Michigan. 

Applicability 

Due to the design, median U-turn crossovers require a wide median to enable the U-turn 

movement. Median U-turns may be appropriate at intersections with high major-street through 

movements, low-to-medium left turns from the major street, low-to-medium left turns from the minor 

street, and any amount of minor street through volumes.(141) Locations with high left-turning 

volumes may not be good candidates because the out-of-direction travel incurred and the potential 

for queue spill back at the median U-turn location could outweigh the benefits associated with 

removing left-turns from the main intersection.(141) Median U-turns can be applied on a single 

approach. 

Design Features 

Key design features of median U-turns identified in the literature are summarized below: 

• Median U-turn lanes should be designed to accommodate the design vehicle. 

• Appropriate deceleration lengths and storage lengths should be provided based on the 

design volume and anticipated traffic control at the median 

U-turn. 

• The Michigan Department of Transportation advises that the optimum location for the 

crossover is 170 to 230 m (560 to 760 ft) from the main intersection as shown in figure 

88.(147)

• To accommodate a semi-trailer combination design vehicle, AASHTO policy 

recommends that the median on a four-lane arterial should be 18 m (60 ft) wide.(3) If 

design vehicles do not have enough space to turn, additional pavement should be 

added outside the travel lane to allow these vehicles to complete the maneuver, as 

shown in figure 89. 
Signalized Intersections: Informational Guide 245

Alternative Intersection Treatments

Figure 88. Diagram of general placement of a median U-turn crossover.(adapted from 147)

Figure 89. Diagram of a median U-turn crossover from the main line with a narrow 

median.(adapted from 148)

Operational Features 

Key items regarding the operational features of median U-turns are summarized below: 

• Median U-turn crossovers allow for two-phase signal operation. This can reduce signal 

cycle length and delays for through vehicles. Left-turning vehicles have to travel further 
246 Federal Highway Administration

to complete the turn, which may offset some operational benefits achieved for through 

vehicles. 

• Signing is needed to alert motorists of the presence of median U-turns and the 

restriction of left-turn movements at the signalized intersection. 

• Installing traffic signals at median U-turn locations requires additional storage for the Uturn movement and requires coordination with adjacent signalized intersections. 

• The reduction in phases at the signalized intersection improves the ability to coordinate 

traffic signals along a corridor. 

Safety Performance 

According to NCHRP 420, the collision rate along road sections having directional median 

openings (facilitating U-turn and left turns) versus road sections having full median openings 

(facilitating all movements) was 49 to 52 percent less for signalized corridors having more than one 

traffic signal per mile.(85)

Table 74 shows the number of conflict points at a four-leg signalized intersection as compared 

to a four-leg signalized intersection with a median U-turn crossover. A median U-turn crossover 

configuration eliminates all crossing (left turn) conflict points. It also reduces the number of 

merge/diverge conflict points as compared to a four-leg signalized intersection. Figure 90 shows the 

conflict point diagram for a four-leg signalized intersection with a median U-turn crossover 

configuration. 

Table 74. Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a median U-turn crossover configuration. 

Conflict Type Four-Leg Signalized 

Intersection 

Median U-Turn Crossover 

Configuration 

Merging/diverging 16 12 

Crossing (left turn) 12 0 

Crossing (angle) 4 4 

Total 32 16 
Signalized Intersections: Informational Guide 247

Alternative Intersection Treatments

Figure 90. Conflict diagram for a four-leg signalized intersection with median U-turns. 

Table 75 summarizes the expert opinion of the authors with regard to the safety benefits of a 

conversion of a four-leg signalized intersection to a median U-turn crossover configuration. 

Table 75. Safety benefits of converting a four-leg signalized intersection to median U-turn 

crossover configuration: Expert opinion. 

Treatment Surrogate Implication 

Convert signalized four-leg 

intersection to a median Uturn crossover 

configuration 

Conflict points Offers the potential for a minor decrease in merging/diverging 

collisions 

Offers the potential for a major decrease in left-turn collisions 

Operational Performance 

Key elements regarding the operational performance of median U-turns are summarized below: 

• Median U-turns reduce the number of stops for mainline through movements.(141) 

• The median crossovers can be signalized or unsignalized. Signalized crossovers can be 

synchronized with the other signals in a corridor to provide progression. If a traffic signal 

is installed at a median U-turn, the median should be designed to accommodate the 

maximum design queue to avoid spillover to the main line. 

• The operations of a median U-turn should be evaluated using a microsimulation model 

to determine the effect of progression and queue interaction from the signalized 

intersection. 

• A study on a Michigan corridor used simulation to compare median U-turn crossovers 

with two-way left-turn lanes (TWLTL). The study showed that during peak hours, the 

corridor with median U-turn crossovers had a lower travel time by 17 percent and a 25 

percent higher average speed than the same corridor with a TWLTL. However, vehicles 

made more stops on the arterial with median U-turn crossovers. In nonpeak hours, the 

median U-turn crossovers had the same efficiency as the TWLTL, even though a higher 
248 Federal Highway Administration

delay for left-turning vehicles had been expected due to the higher travel distance a 

vehicle must cover to turn left using a median crossover.(149) 

• Simulation studies using a range of intersection configurations (number of through lanes 

on the major and minor street) and volumes from intersections in Virginia and North 

Carolina suggest a reduction in overall travel time for all movements through the 

intersection when compared to a conventional intersection: -21 to -2 percent during offpeak conditions, and -21 to +6 percent during peak conditions. The studies also show a 

general increase in the overall percent of stops when compared to a conventional 

intersection: -20 to +76 percent during off-peak conditions, and -2 to +30 percent during 

peak conditions.(145)

• Results from a simulation analysis using TRANSYT-7F and CORSIM found that the 

percentage of stops was reduced for the median U-turn configuration compared with a 

conventional intersection.(148)

Multimodal Impacts 

Roadways with median U-turns generally have a greater cross section width resulting in an 

increased crossing distance for pedestrians. The number of movements that conflict with 

pedestrians at intersections with upstream/downstream median U-turns is reduced. 

Turning paths of the median U-turn should be evaluated to ensure that vehicle paths do not 

encroach on bike lanes. 

Socioeconomic Impacts 

Access should be restricted on facilities within the influence of median U-turn locations. Local 

property owners may oppose such restrictions, particularly if the access already exists. 

Education, Enforcement, and Maintenance 

Education and enforcement are needed to ensure that vehicles are not making illegal left turns 

at the main intersection. 

Summary 

Table 76 summarizes the issues associated with median U-turn crossovers. 
Signalized Intersections: Informational Guide 249

Alternative Intersection Treatments

Table 76. Summary of issues for median U-turn crossovers. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential major reduction in left-turn 

collisions. 

Potential minor reduction in 

merging/diverging collisions. 

None identified. 

Operations Potential reduction in overall travel time. 

Reduction in stops for mainline through 

movements. 

Mixed findings with respect to overall 

stops. 

Mixed findings with respect to overall 

stops. 

Multimodal Number of conflicting movements at 

intersections is reduced. 

Increased crossing distance for 

pedestrians. 

Turning paths of the median U-turn may 

encroach in bike lanes. 

Physical None identified. May be additional right-of-way needs 

depending on width of existing median. 

Socioeconomic None identified. Access may need to be restricted within 

the influence of the median U-turn 

locations. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement and education may be 

necessary to prevent illegal left turns at 

the main intersection. 

10.2.3 Continuous Flow Intersection 

Continuous flow intersections (CFI), both full and partial, have recently been constructed in a 

small number of locations in the United States. Although too new for a full evaluation of the effect 

on operations and safety, continuous flow intersections are gaining in popularity. CFI are also 

sometimes referred to as crossover-displaced left-turn (XDL) intersections. 

Description 

A CFI removes the conflict between left-turning vehicles and oncoming traffic by introducing a 

left-turn bay placed to the left of oncoming traffic. Vehicles access the left-turn bay at a midblock 

signalized intersection on the approach where continuous flow is desired. Figure 91 shows the 

design of a CFI with crossover displaced left turns, and figure 92 illustrates some of the vehicle 

movements at such an intersection. As can be seen, the left turns potentially stop three times: once 

at the midblock signal on approach, once at the main intersection, and once at the midblock signal 

on departure. However, careful signal coordination can minimize the number of stops. Examples of 

implemented sites are shown in figures 93 and 94. Note that this section describes an at-grade CFI; 

a grade-separated version of the CFI was patented (U.S. Patent No. 5,049,000), but the patent 

expired in 2003. 
250 Federal Highway Administration

Figure 91. Diagram of a continuous flow intersection.(150)

 (a) Turning movements from Street A. (b) Turning movements from Street B. 

Figure 92. Vehicular movements at a continuous flow intersection. 
Signalized Intersections: Informational Guide 251

Alternative Intersection Treatments

Figure 93. Continuous flow intersection. 

Photograph Credit and Copyright: Francisco Mier, 1999 

Figure 94. Displaced left turn at a continuous flow intersection.(151)

The complete CFI design operates as a set of two-phase signals. As part of the first phase, 

traffic is permitted to enter the left-turn bay by crossing the oncoming traffic lanes during the signal 

phase serving cross-street traffic. The second signal phase, which serves through traffic, also 

serves the protected left-turn movements. Figure 95 shows the signal phase sequence used at a 

CFI. 
252 Federal Highway Administration

a. Street A movements at the major intersection, left turns on the advance intersections on Street A, and 

through movements on the advance intersections on Street B. 

b. Street A movements at the major intersection and through movements at all advance intersections. 

c. Street A movements at the major intersection, through movements on the advance intersections on 

Street A, and left turns on the advance intersections on Street B. 

d. Street B movements at the major intersection, left turns on the advance intersections on Street B, and 

through movements on the advance intersections on Street A. 

e. Street B movements at the major intersection and through movements at all upstream intersections. 

f. Street B movements at the major intersection, through movements on the advance intersections on 

Street B, and left turns on the advance intersections on Street A. 

Figure 95. Signal phasing of a continuous flow intersection.(adapted from 150)
Signalized Intersections: Informational Guide 253

Alternative Intersection Treatments

Intersections with high through and left-turn volumes may be appropriate sites for continuous 

flow intersections. There should be a low U-turn demand because U-turns are restricted with this 

design. Right-of-way adjacent to the intersection is needed for the left-turn ramps. 

Left-turning vehicles make more stops than at conventional intersections, and may experience 

a slightly higher delay. Through traffic benefits greatly from this design. 

Safety Performance 

Safety improvements may be experienced by the left-turn movement due to the relocation of 

the turn lane; rear-end crashes with through vehicles may be reduced. Congestion-related 

collisions (mainly rear ends) may also decrease if stop-and-go conditions occur less often. 

Table 77 shows the number of conflict points at a four-leg signalized intersection as compared 

to a continuous flow intersection. The number of merging/diverging conflict points is the same at a 

continuous flow intersection as compared to a conventional four-leg signalized intersection. All leftturn (crossing) conflicts are removed. However, the number of angle (crossing) conflicts would 

triple. Figure 96 shows the conflict point diagram for a continuous flow intersection. 

Table 77. Number of conflict points at a four-leg signalized intersection compared to a continuous 

flow intersection with displaced left turns on the major street only. 

Conflict Type Four-Leg Signalized 

Intersection 

Continuous Flow 

Intersection 

Merging/diverging 16 14 

Crossing (left turn) 12 6 

Crossing (angle) 4 10 

Total 32 30 

Figure 96. Conflict diagram for a continuous flow intersection with 

displaced left turns on the major street only. 
254 Federal Highway Administration

Table 78 summarizes the expert opinion of the authors with regard to the safety benefits of 

changing a four-leg signalized intersection to a CFI. 

Table 78. Safety benefits of converting a four-leg signalized intersection to a CFI: Expert opinion. 

Treatment Surrogate Finding 

Convert signalized fourleg intersection to 

continuous flow 

intersection 

Conflict 

points 

Offers the potential for a major reduction in left-turn collisions 

Offers the potential for a major increase in angle collisions 

Operational Performance 

The key operational benefit of this intersection is that multiphase signal operation is not 

required to provide protected left-turn movements. This benefits through traffic. Continuous flow 

intersections provide an at-grade intersection solution that can improve traffic operations beyond 

the capabilities of other conventional at-grade solutions.(152)

Jagannathan and Bared evaluated three different CFI configurations (four-leg intersection with 

displaced left on all approaches; four-leg intersection with displaced left on two approaches; and T 

intersection with displaced left on one approach) against a conventional intersection for a range of 

high entering volumes using VISSIM.(150) Operational benefits of the CFI were realized for all three 

CFI intersection configurations. For the case of the four-leg intersection with displaced left turns on 

all approaches, the following findings were documented: 

• Average delay was reduced with the CFI by 48 to 85 percent compared to the 

conventional intersection, with the lower value applying to an undersaturated case and 

the upper value applying to an oversaturated case. 

• The average number of stops with the CFI was reduced by 15 to 30 percent for undersaturated traffic flows and 85 to 95 percent for saturated traffic flow conditions at the 

conventional intersection. 

• Queue lengths with the CFI were reduced by 62 to 88 percent compared to the 

conventional intersection, with the lower value applying to an undersaturated case and 

the upper value applying to an oversaturated case. 

Goldblatt, Mier, and Friedman evaluated the performance of traffic at CFI designs by comparing 

it with the performance of conventional intersections under multiphase signal control.(152) Traffic 

demand was assumed equal on each approach leg to the intersection and turn movements were 

also assumed equal on each approach (15 percent left turns, 11 percent right turns). Traffic 

demand volumes for each approach were examined at 1,500, 2,000, and 3,000 vehicles per hour 

(veh/h). Key findings are as follows: 

• At the 1,500 veh/h demand level, the demand was processed by both conventional and 

continuous flow intersections. 

• At the 2,000 veh/h demand level, the capacity of the conventional intersection was 

exceeded (approximately by 20 percent) and the CFI serviced the entire demand. 

• At the 3,000 veh/h demand level, the capacity of both the conventional intersection and 

the continuous flow intersection were exceeded. However, the capacity of the CFI nearly 

50-percent greater than the conventional intersection. 

• The advantages of the CFI are most pronounced when the demand approaches exceed 

the capacity of conventional designs and when heavy left-turn movements require 

protected phases. 

In 1994 (the date of publication of Goldblatt, Mier, and Friedman), no known CFIs had been 

constructed.(152) Conclusions were drawn solely from operational simulation modeling. Actual 
Signalized Intersections: Informational Guide 255

Alternative Intersection Treatments

operational experience with CFIs are not widely available, but should become more so as more 

CFIs are built and evaluated. 

Abramson, Bergen, and Goldbatt also note the potential for improved arterial performance with 

CFIs.(153) Because left-turn signal phasing is effectively removed with a CFI, expanded green 

bands along the arterial can be achieved. 

Simulation studies using a range of intersection configurations (number of through lanes on the 

major and minor street) and volumes from intersections in Virginia and North Carolina suggest 

mixed results in overall travel time through the intersection when compared to a conventional 

intersection: –1 to +25 percent during off-peak conditions, and –12 to +27 percent during peak 

conditions. The studies also show a general increase in the overall percent of stops when 

compared to a conventional intersection: +21 to +87 percent during off-peak conditions, and +12 to 

+49 percent during peak conditions.(145)

Multimodal impacts 

Pedestrian safety is improved with the CFI design, according to Goldblatt et al.(152) Pedestrians 

cross at times when there are no conflicts with turning vehicles. Pedestrians do require two 

sequential signal phases to complete a street crossing. However, the layout and operation of the 

intersection may not be immediately apparent to pedestrians, particularly those with visual 

disabilities. As a result, pedestrians with visual disabilities may have challenges in way-finding 

through the intersection. The unconventional flows of vehicles will disrupt the audible cues that 

visually impaired pedestrians use; therefore, accessible pedestrian signals should be considered for 

use with this intersection configuration. 

Physical Impacts 

The footprint of a continuous flow intersection is greater than that of a conventional intersection 

because it requires right-turn lanes and acceleration lanes in each quadrant. It takes less space 

than an interchange, however. 

Socioeconomic Impacts 

According to Goldblatt et al., the construction cost of a CFI may be two to three times the cost 

of a standard intersection design due to increased right-of-way costs, and the need for additional, 

coordinated signal controllers.(152)

Enforcement, Education, and Maintenance 

Additional potential roadblocks to continuous flow intersections include: 

• Pedestrian acceptance (cross only at main intersection—no midblock crossing). 

• Driver acceptance (vehicles may be opposed by traffic on both sides). 

• Snow removal issues. 

• Breakdown of vehicles. 

• Providing access to adjacent parcels. 

• With less intersection delay, improvements in air quality can be realized. 

A public information campaign may be needed to educate drivers on the operation of the 

intersection. Abramson, Bergen, and Goldblatt provide a summary of a human factors study of 

continuous flow intersection operations.(153) Survey questionnaires were used to assess the learning 

curve of drivers utilizing a CFI in New York. Results indicated a positive response rate of 80 percent 

for first-time users of the design. After about a week of use, 100 percent of daily drivers expressed 

positive comments about the design. The basic conclusion is that unfamiliar drivers easily negotiate 

the intersection form and, after a short break-in period, nearly all drivers can become familiar and 

comfortable with the design. Key negative comments received in the survey dealt with adequate 

advance signing that must be provided. The authors detail the experience with one intersection only 

(and only one leg of the intersection had been designed as a CFI). 
256 Federal Highway Administration

The use of extensive special directional signing is key to maximizing driver understanding and 

acceptance. 

Summary 

Table 79 summarizes the issues associated with CFI. 

Table 79. Summary of issues for continuous flow intersections. 

Characteristics Potential Benefits Potential Liabilities 

Safety Left turns removed from main 

intersection. 

None identified. 

Operations More green for through. More stops and delay for left turns. 

Multimodal No conflicts during pedestrian crossing. Two-stage pedestrian crossing. 

Layout may not be immediately apparent, 

especially for visually impaired pedestrians. 

Physical Smaller footprint than interchange 

alternative. 

Right-of-way needed. 

Larger footprint than conventional 

intersection. 

Access management. 

Socioeconomic Air quality. Construction cost. 

Access management. 

Enforcement, 

Education, and 

Maintenance 

None identified. Public information campaign may be needed. 

10.2.4 Quadrant Roadway Intersection 

A quadrant roadway intersection includes an extra roadway between two legs of the 

intersection (see figure 97). Drivers who wish to turn left from either the major or minor road will 

travel further to do so, but all left turns will be removed from the main intersection, as shown in 

figure 98. This design creates two additional intersections, which operate as three-phase signals, 

but the signal at the main intersection can operate as a two-phase signal, as shown in figure 99. 

The signals at the quadrant ramps should be located a sufficient distance upstream of the main 

intersection to eliminate the potential for queue spillback. Reid identified a length of 150 m (500 ft) 

for his CORSIM evaluation.(154)
Signalized Intersections: Informational Guide 257

Alternative Intersection Treatments

Figure 97. Diagram of a quadrant roadway intersection.(adapted from 145)

 (a) Movements from Street A. (b) Movements from Street B. 

Figure 98. Vehicular movements at a quadrant roadway intersection.(adapted from 145)
258 Federal Highway Administration

Figure 99. Signal phasing of a quadrant roadway intersection.(adapted from 141)

Applicability 

Intersections of roadways with high through and turn movements may benefit from a quadrant 

roadway intersection design. If protected left turns at the main intersection are not necessary, more 

green time can be allocated to the through movements. This application can be useful where rightof-way is limited and there is an existing bypass street on any of the quadrants. 

Safety Performance 

Table 80 shows the number of conflict points at a four-leg signalized intersection as compared 

to a four-leg signalized intersection with a quadrant roadway. The number of merging/diverging 

conflict points would increase when a quadrant roadway is added. However, the number of crossing 

(left-turn) conflicts would decrease, provided that midblock restrictions are implemented at the 

original signalized intersection. Figure 100 shows the conflict point diagram for a four-leg signalized 

intersection with a quadrant roadway. 

Table 80. Number of conflict points at a four-leg signalized intersection compared to a four-leg 

signalized intersection with a quadrant roadway 

Conflict Type Four-Leg Signalized 

Intersection 

Four-Leg Signalized Intersection with 

a Quadrant Roadway 

Merging/diverging 16 20 

Crossing (left turn) 12 4 

Crossing (angle) 4 4 

Total 32 28 
Signalized Intersections: Informational Guide 259

Alternative Intersection Treatments

Figure 100. Conflict point diagram for four-leg signalized intersection with quadrant roadway. 

Table 81 summarizes the expert opinion of the authors with regard to the safety benefits of 

adding a quadrant roadway to a four-leg signalized intersection. 

Table 81. Safety benefits of adding a quadrant roadway to a four-leg signalized intersection: Expert 

opinion. 

Treatment Surrogate Finding 

Convert signalized fourleg Intersection to a 

quadrant roadway 

configuration 

Conflict points Offers the potential for a minor increase in rear-end collisions 

Offers the potential for a major decrease in left-turn collisions 

Operational Performance 

Compared with conventional intersections, quadrant roadway intersections have less total 

intersection delay and less queuing. There are conflict points at the primary intersection, which may 

result in lower crash rates for left-turn- and head-on-related crashes. The potential for driver 

confusion at these intersections is greater than that for conventional intersections, as it is with any 

alternative design. This can be addressed with advance signing. 

A study that compared simulation of a quadrant roadway intersection with a conventional 

intersection showed a 22-percent reduction in system travel time. It is important that signals at 

these intersections be fully coordinated. The quadrant roadway intersection performed best under 

higher volumes.(141)

Simulation studies using a range of intersection configurations (number of through lanes on the 

major and minor street) and volumes from intersections in Virginia and North Carolina suggest a 

reduction in overall travel time through the intersection when compared to a conventional 

intersection: –21 to +1 percent during off-peak conditions, and –21 to –1 percent during peak 

conditions. The studies also show a general increase in the overall percent of stops when 
260 Federal Highway Administration

compared to a conventional intersection: –12 to +96 percent during off-peak conditions, and –3 to 

+33 percent during peak conditions.(145)

Summary 

Table 82 summarizes the issues associated with quadrant roadways. 

Table 82. Summary of issues for quadrant roadways. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential major decrease in left-turn 

collisions. 

Potential minor increase in rear-end 

collisions. 

Operations Potential reduction in delay and 

queuing. 

None identified. 

Multimodal Pedestrian crossing distance at each 

intersection may decrease. 

Number of intersections to cross 

increases. 

Physical None identified. If the quadrant roadway does not exist, 

may be high construction and right-ofway costs. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Greater potential for driver confusion. 

10.2.5 Super-Street Median Crossover 

The super-street median crossover improves operation of the main road through maneuver, 

and also reduces delay for left turns off the major road. 

Description 

The super-street median crossover design, shown in figure 101, is similar to the median U-turn 

crossover in that an indirect maneuver is accomplished with a U-turn in the median. With a superstreet median crossover, crossroad drivers cannot proceed straight through the intersection, as can 

be seen in figure 102. A through movement is accomplished by turning right onto the major road, 

turning left through the crossover, and turning right again back onto the minor road. Also, as with 

the median U-turn design, drivers are not able to turn left from the crossroad onto the major road, 

and a median U-turn is used to accomplish the left-turn maneuver. Left turns from the major road 

are direct. 
Signalized Intersections: Informational Guide 261

Alternative Intersection Treatments

Figure 101. Illustration of super-street median crossover.(adapted from 155)

 (a) Movements from major street. (b) Movements from minor street. 

Figure 102. Vehicular movements at a super-street median crossover. 

The design of a super-street median crossover is similar to that of a median U-turn crossover. 

Crossovers should be located approximately 180 m (600 ft) from the main intersection. A semitrailer combination design vehicle would need a median width of 18 m (60 ft) to accommodate a Uturn. Additional right-of-way would not be required to construct this treatment where the major 

streets already have a wide median. 

Two two-phase traffic signals are required at the main intersection—one for each minor street 

approach. Because no minor street through or left-turn movements are allowed, these two signals 

can operate independently with different signal cycle lengths, if desired. A typical phasing diagram 

is shown in figure 103, which shows the phasing for each of the two-phase signals on each half of 

the intersection. In addition, a traffic signal may be needed at each of the upstream median 

crossover locations; these signals would also have only two phases. Because the two halves of the 

intersection operate independently, it is possible to achieve a maximum amount of traffic 

progression in both directions along the major street. 
262 Federal Highway Administration

There are fewer conflict points with this intersection design than with conventional intersections. 

Though this design may cause confusion for pedestrians, there is less opportunity for conflicts with 

vehicles. The crossing is a two-stage process. 

This design is appropriate in situations where there are high through volumes on the major road 

but only relatively low volumes of through traffic on the cross road, since this through movement is 

interrupted. For crossroads with higher through volumes, offset super-street crossover design can 

be used. With this design, the approaches on the crossroad are offset, and are at the same location 

as the median crossovers. This allows minor road through vehicles to proceed straight from the 

crossover to the crossroad without turning. 

Figure 103. Signal phasing of a super-street median crossover. 

Safety Performance 

Table 83 shows the number of conflict points at a four-leg signalized intersection as compared 

to a super-street median crossover. The number of left-turn crossing conflicts would be reduced to 

two at a super-street median crossover. No crossing (angle) conflict points exist at a super-street 

median crossover. Figure 104 shows the conflict point diagram for a super-street median crossover. 
Signalized Intersections: Informational Guide 263

Alternative Intersection Treatments

Table 83. Number of conflict points at a four-leg signalized intersection compared to a super-street 

median crossover. 

Conflict Type Four-Leg Signalized Intersection Super-Street Median Crossover 

Merging/diverging 16 18 

Crossing (left turn) 12 2 

Crossing (angle) 4 0 

Total 32 20 

Figure 104. Conflict diagram for a super-street median crossover. 

Table 84 summarizes the expert opinion of the authors with regard to the safety benefits of 

changing a four-leg signalized intersection to a super-street median crossover. 

Table 84. Safety benefits of converting a four-leg signalized intersection to a super-street median 

crossover: Expert opinion. 

Treatment Surrogate Finding 

Convert signalized 

Four-leg intersection to 

super-street median 

crossover 

Conflict points Offers the potential for a major reduction in midblock collisions 

Offers the potential for a major reduction in angle collisions 

Operational Performance 

This design can result in more stops for through vehicles than other designs. It also creates outof-direction travel for cross street through and left-turn movements, which limits their capacity and 

increases their travel times. Left turns from the major road experience less delay, however. 

Simulation studies using a range of intersection configurations (number of through lanes on the 

major and minor street) and volumes from intersections in Virginia and North Carolina suggest 

mixed results in overall travel time through the intersection when compared to a conventional 

intersection: –8 to +18 percent during off-peak conditions, and –10 to +71 percent during peak 

conditions. The studies also show a substantial increase in the overall percent of stops when 

compared to a conventional intersection: –8 to +187 percent during off-peak conditions, and +16 to 

+146 percent during peak conditions.(145)

A study of a Michigan corridor comparing TWLTL to median U-turn crossovers also looked at 

super-street median crossovers. The study showed that during peak hours, travel time on the 
264 Federal Highway Administration

corridor with super-street median crossovers decreased by 10 percent; average speed was 15 

percent higher than in the same corridor with a TWLTL. In nonpeak hours, the super-street median 

crossovers had the same efficiency as the TWLTL, even though a higher delay for left-turning 

vehicles had been expected due to the higher travel distance for a vehicle to turn left using a 

median crossover.(149)

While travel time and delay will increase for cross street through and left-turn traffic, the major 

road through and left-turn movements will experience an improvement in intersection operations. 

Driver opinions and acceptance of the intersection design may vary according to which maneuver a 

driver typically makes at the intersection. 

Enforcement, Education, and Maintenance 

Super-street median crossovers have not been constructed in nearly as many locations as 

median U-turn crossovers. This treatment has not been implemented for an entire corridor. 

Therefore, opportunities for public response to the crossovers are low. 

Little enforcement will be needed for this design. It may be necessary to occasionally provide 

enforcement of traffic control devices at the median crossovers. 

There is a potential for driver and pedestrian confusion with this design. A public information 

campaign may be desirable in order to prepare drivers for the opening of the new intersection. 

Signs guiding drivers through the intersection will be appropriate, especially in areas where superstreet median crossovers are not common. 

Summary 

Table 85 summarizes the issues associated with the super-street median crossover. 

Table 85. Summary of issues for super-street median crossovers. 

Characteristic Potential Benefits Potential Liabilities 

Safety Fewer conflict points. None identified. 

Operations Improved delay for major street 

movements. 

Longer travel distance and time for minor 

street movements. 

Multimodal None identified. Two-stage pedestrian crossing. 

Potential way-finding challenges. 

Physical None identified. Wide median needed. 

Socioeconomic None identified. May result in restrictions to access. 

Enforcement, 

Education, and 

Maintenance 

None identified. Potential for driver and pedestrian 

confusion. 

10.3 GRADE SEPARATION TREATMENTS 

Grade separation treatments should be considered when at-grade intersection treatments are 

no longer feasible. Grade separation is costly, has substantial impacts on traffic during construction, 

and substantially affects pedestrians, bicyclists, and adjacent land uses. Grade separation does 

provide a significant benefit to the operations of through movements given that conflicts with 

opposing and adjacent traffic are eliminated. The reduction of conflicts also improves safety 

performance. 

The following sections discuss the split intersection and diamond interchange forms. Although 

the split intersection is an at-grade form, it is a logical intermediate stage to complete grade 

separation and thus is discussed in this section. 
Signalized Intersections: Informational Guide 265

Alternative Intersection Treatments

10.3.1 Split Intersection 

Description 

A split intersection, shown in figure 105, requires that the major road approaches to an 

intersection be converted into two one-way streets. Essentially, the split intersection becomes an 

at-grade diamond configuration. Rather than one intersection that would operate as a four-phase 

signal (assuming protected left-turn phasing), two intersections are created that can operate as 

three-phase signals. The split intersection can be a potential “stage” to constructing a diamond (or 

other) interchange. According to Bared and Kaisar, the split intersection facilitates smoother traffic 

flows with less delay and also may improve safety by reducing the number of intersection conflict 

points. (156)

Applicability 

A split intersection may be considered where: 

• Significant delays occur. 

• A high number of left-turn collisions occur. 

Safety Performance 

According to two studies split intersections can have the following safety benefits:(156,157)

• Separation of intersection conflict points. 

• Possible safety improvement because of separation of conflicts and reduction in signal 

phases (reduction in phases is related to likelihood that drivers will violate the traffic 

signal). 

However, with the split intersection design, there is the possibility of wrong-way movements. 
266 Federal Highway Administration

Figure 105. Illustration of a split intersection.(adapted from 145)

Table 86 shows the number of conflict points at a four-leg signalized intersection as compared 

to a split intersection. A split intersection would have the same number of merging/diverging and 

crossing (angle) conflict points as a four-leg signalized intersection. However, there are only 6 

crossing (left-turn) conflict points at a split intersection, compared to 12 at a four-leg signalized 

intersection. Figure 106 shows the conflict point diagram for a split intersection. 
Signalized Intersections: Informational Guide 267

Alternative Intersection Treatments

Table 86. Number of conflict points at a four-leg signalized intersection compared to a split 

intersection. 

Conflict Type Four-Leg Signalized Intersection Split Intersection 

Merging/diverging 16 12 

Crossing (left turn) 12 6 

Crossing (angle) 4 4 

Total 32 22 

Figure 106. Conflict point diagram for a split intersection. 

Table 87 summarizes the expert opinion of the authors with regard to the safety benefits of a 

conversion of a four-leg signalized intersection to a split intersection. 
268 Federal Highway Administration

Table 87. Safety benefits of converting a four-leg signalized intersection to a split intersection: 

Expert opinion. 

Treatment Surrogate Implication 

Convert signalized fourleg intersection to a split 

intersection 

Conflict 

points 

Offers the potential for a significant decrease in left-turn 

collisions 

Operational Performance 

Conversion to a split intersection (versus a standard intersection) can result in substantial 

increases in effective green time available to traffic.(157) This increase becomes even larger when 

the percentage of left-turning traffic rises. The minimum recommended spacing is 50 m (165 ft) and 

increases as a function of signal cycle length and left-turning volume. 

Bared and Kaisar performed a traffic simulation (using CORSIM) to compare a standard fourleg intersection and a split intersection.(156) Optimum traffic signal timing plans for both intersection 

configurations were developed using PASSER©. Results of the CORSIM analysis reveal that the 

split intersection is able to handle higher traffic volumes with less delay per vehicle than is a single 

intersection. As the entering volume and proportion of left-turning vehicles increases, the advantage 

of the split intersection relative to the standard intersection increases (in terms of reducing delay). 

Average delays for both intersections are similar for intersections with a total entering flow of 4,000 

veh/h and less. At higher entering volumes (5,000 to 6,000 veh/h), the reduction in delay with a split 

intersection was on the order of 40 to 50 percent. This increases as the percent of left-turning 

traffic increases from 15 to 30 percent of the total traffic. 

A limited number of split intersections have been constructed (none known in the United 

States). As such, operational experience with split intersections is limited. Operational experience 

and public response to one constructed in Israel has been positive.(156) Other split intersections in 

Israel have been converted to grade-separated interchanges. The majority of conclusions regarding 

split intersections have been gained from computer simulation runs of anticipated traffic operations. 

Simulation studies using a range of intersection configurations (number of through lanes on the 

major and minor street) and volumes from intersections in Virginia and North Carolina suggest a 

general reduction in overall travel time through the intersection when compared to a conventional 

intersection: –20 to –8 percent during off-peak conditions, and –15 to +9 percent during peak 

conditions. The studies also show an increase in the overall percent of stops when compared to a 

conventional intersection: +21 to +87 percent during off-peak conditions, and +12 to +49 percent 

during peak conditions.(145)

Split intersections can have the following operational benefits:(156,157)

• Increase capacity and reduce delay relative to a standard intersection. 

• Provide a stage to construction of a grade-separated interchange. 

Operational liabilities are the likelihood that the design will require two stops (versus one) in a 

poorly coordinated system. 

Multimodal Impacts 

At split intersections, pedestrian crossing distances (for the cross street) are significantly 

reduced. Because these types of intersections have the look and feel of a grade-separated 

interchange, pedestrians may find them intimidating, and motorists may be less aware of 

pedestrians’ presence. 

Physical Impacts 

These types of intersections would have a high initial construction cost yet provide a preliminary 

stage to eventual grade separation. 
Signalized Intersections: Informational Guide 269

Alternative Intersection Treatments

Socioeconomic Impacts 

A split intersection would have additional right-of-way requirements. 

Summary 

Table 88 summarizes the issues associated with constructing a split intersection. 

Table 88. Summary of issues for split intersections. 

Characteristic Potential Benefits Potential Liabilities 

Safety Reduced left-turn collisions. Wrong-way movements. 

Operations Frees up green time for through 

movements. 

None identified. 

Multimodal Shorter crossing distance. May not be perceived as being 

pedestrian friendly. 

Physical Preliminary stage to grade separation. High initial construction costs. 

Socioeconomic None identified. Right-of-way requirements. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

 

10.3.2 Diamond Interchange 

Description 

A diamond interchange is a treatment where the through movements on the major street are 

physically separated from the other turning movements, which are typically served by one or two 

intersections (ramp terminals) on the minor street. On- and off-ramps connect the major street to 

these ramp terminals, forming the shape of a diamond. Diamond interchanges have a variety of 

forms, and their function depends on the separation between the two ramp terminals and the 

associated traffic control strategy. Two of the more common types of diamond interchanges used 

in constrained urban environments are the single-point diamond and compressed diamond. 

Additional information on other interchange forms can be found in the AASHTO policy.(3)

A single-point diamond interchange (also referred to as a single-point urban interchange, or 

SPUI, although these interchanges are not inherently restricted to urban environments) operates as 

a single signalized intersection. Left turns from the ramps and on the cross street are aligned such 

that they oppose each other, eliminating a potential source of conflict. Because of the layout of the 

interchange, at-grade movements are served by a three-phase signal, although relatively long cycle 

lengths are typical. This is in part due to the fact that longer clearance intervals are required for a 

single-point interchange to allow vehicles to depart the intersection. Figure 107 shows a typical 

single-point interchange. 
270 Federal Highway Administration

Figure 107. Diagram of a single-point interchange.(adapted from 158)

A compressed diamond interchange (also referred to as a tight diamond interchange) operates 

as two closely spaced intersections, typically controlled by four-phase overlap signal phasing 

system for the two intersections. Layout of the left turns on the cross street are back to back, 

resulting in an increased cross section across/under the bridge relative to a single-point 

interchange. Even with this increased cross section, there is less open pavement area at a 

compressed diamond interchange relative to a single-point interchange, which allows for shorter 

clearance intervals. Figure 108 shows a typical compressed diamond interchange. 
Signalized Intersections: Informational Guide 271

Alternative Intersection Treatments

Figure 108. Diagram of a compressed diamond interchange.(adapted from 158)

A single-point interchange can operate with three or four phases; a three-phase signal phasing 

scheme is illustrated in figure 109. As can be noted from the phasing diagram, pedestrian 

movements across the arterial street or through movements on the ramp (as with frontage roads) 

cannot be accommodated without adding a fourth phase. 

Figure 109. Typical signal phasing of a single-point interchange. 

The compressed diamond interchange can operate with three or four phases; a four-phase 

signal phasing scheme is illustrated in figure 110. The figure shows the coordinated operation of the 

signals on each side of the interchange. This phasing scheme can accommodate pedestrians in all 

directions. 
272 Federal Highway Administration

Figure 110. Typical signal phasing of a compressed diamond interchange. 

Applicability 

Inconsistent findings relating to the single-point and compressed diamond interchange forms 

relate primarily to the operational and safety performance of each form. As analysis procedures and 

site conditions differ for each interchange application, it is difficult to draw firm conclusions 

regarding the merits of a particular interchange form without appropriately studying the specific 

conditions of a site. 

Safety Performance 

Safety information on the single-point interchange is limited. Smith and Garber report some 

safety findings, but indicate the findings may be more representative of changing design details 

than of true safety differences.(159) Leisch, Urbanik, and Oxley suggest that the potential for higher 

crash experience is present at single-point interchanges because of the large, uncontrolled 

pavement area and the opposing left turns.(160) No crash data are provided, however. 

Smith and Garber report that driver unfamiliarity with the new single-point interchange design 

was not a major factor in crash occurrence at the interchange, although there were complaints of 

confusion at single-point interchanges shortly after it was opened.(159) Rear-end crashes on the offramp were the predominant crash type. A study by Messer et al. indicated that the single-point 
Signalized Intersections: Informational Guide 273

Alternative Intersection Treatments

interchange design does not lead to a higher number of crashes than found in a typical at-grade 

intersection.(161)

Table 89 shows the number of conflict points at a four-leg signalized intersection as compared 

to a compressed diamond and single-point diamond interchange. The compressed diamond 

interchange would have a greater number of merging/diverging conflict points as compared to a 

four-leg signalized intersection. Both the compressed diamond and single-point diamond 

interchange would have fewer crossing (left-turn) conflict points. The single-point diamond 

interchange would have no crossing (angle) conflict points. Figures 111 and 112 show the conflict 

point diagrams for a single-point diamond and compressed diamond interchange, respectively. 

Table 90 summarizes the expert opinion of the authors with regard to the safety benefits of a 

conversion of a four-leg signalized intersection to a compressed diamond and single-point diamond 

interchange. 

Table 89. Number of conflict points at a four-leg signalized intersection compared to a compressed 

diamond and single-point diamond interchange. 

Conflict Type 

Four-Leg Signalized 

Intersection Compressed Diamond Single-Point Diamond 

Merging/diverging 16 20 16 

Crossing (left turn) 12 6 8 

Crossing (angle) 4 4 0 

Total 32 30 24 

Figure 111. Single-point diamond interchange conflict point diagram. 
274 Federal Highway Administration

Figure 112. Compressed diamond interchange conflict point diagram. 
Signalized Intersections: Informational Guide 275

Alternative Intersection Treatments

Table 90. Safety benefits of converting a four-leg signalized intersection to a compressed diamond 

and single-point diamond interchange: Expert opinion. 

Treatment Surrogate Implication 

Convert signalized fourleg intersection to a 

compressed diamond 

interchange 

Conflict points Offers the potential for a significant decrease in collisions 

involving major street through traffic 

Offers the potential for a minor increase in merge/diverge 

collisions 

Offers the potential for a significant decrease in midblock 

collisions 

Convert signalized fourleg intersection to a 

single-point diamond 

interchange 

Conflict points Offers the potential for a significant decrease in collisions 

involving major street through traffic 

Offers the potential for a significant decrease in midblock 

collisions 

Offers the potential for a major decrease in angle collisions 

Operational Performance 

With regard to the single-point interchange, left turns off the cross street are typically 

accommodated at 135-degree angles, while left turns at the ramps are typically 45 to 60 degrees. 

Because the left turns from the ramps are at a relatively shallow angle, these movements can take 

place at higher speeds and at higher saturation flow rates relative to a compressed diamond 

interchange. Saturation flow rates for the left turns from the ramp at a single-point interchange 

approach those for a through movement.(162)

Similar to the single-point interchange, a compressed diamond interchange can be constructed 

in a relatively confined right-of-way while serving high traffic demand volumes. A more conventional 

structure can be used to allow future modifications, if needed. In addition, the compressed diamond 

design can serve pedestrians effectively and work in combination with frontage roads without a 

substantial decrease in the efficiency of the interchange.

A single-point interchange combined with a frontage road would also decrease the overall 

efficiency of the interchange, as additional phases are required at the signal to serve traffic 

movements. 

Operational analyses of the two types of interchanges are mixed, with some studies reporting 

the single-point interchange as superior to the compressed diamond interchange in most 

circumstances, some reporting the opposite, and others reporting no significant difference. Several 

simulation-based studies have been performed that indicate that the single-point interchange 

performs better than a compressed diamond interchange for many volume scenarios.(158,163) Fowler 

reports that in most traffic scenarios, the single-point interchange provides more capacity than a 

compressed diamond interchange and that the capacity of the compressed diamond interchange is 

more sensitive to traffic volumes than is the single-point interchange.(162) The performance of the 

compressed diamond interchange improves relative to the single-point interchange when the: 

• Directional split of the cross-street through volume increases. 

• Volume of the cross-street left turns increases. 

• Off-ramp left turns become more unbalanced. 

On the other hand, Leisch, Urbanik, and Oxley found that the compressed diamond is more 

efficient than the single-point interchange for most traffic volume/pattern situations.(160) Bonneson 

and Lee found similar results when frontage roads are present.(164) Both studies show that the 

compressed diamond interchange can accommodate a greater variability of traffic patterns than the 

single-point interchange, and the cycle length requirements are shorter for the compressed 

diamond than the single-point interchange. Because of these wide variations in recommendations, 
276 Federal Highway Administration

no simple conclusion regarding operational performance can be made, and case-by-case analysis 

is therefore recommended. 

Multimodal Impacts 

Pedestrian issues are sensitive at a single-point interchange. At a single-point interchange, 

there is no phase to provide for pedestrian movements. Pedestrians will need two phases to cross 

the roadway (and require an adequate refuge area). Addition of an exclusive pedestrian phase 

would decrease the overall efficiency of the interchange. 

Physical Impacts 

An advantage of the single-point interchange is that the interchange can be constructed in a 

relatively confined right-of-way while serving high traffic demand volumes. However, deep span 

lengths are required with both overpass and underpass designs. The structure for a single-point 

interchange can be more difficult to modify to meet future needs than that for a compressed 

diamond interchange. 

Socioeconomic Impacts 

The primary disadvantage of a single-point interchange is the high construction cost of the 

bridge structure. 

Summary 

Table 91 summarizes the issues associated with constructing a single-point or compressed 

diamond interchange. 

Table 91. Summary of issues for single-point and compressed diamond interchanges. 

Characteristic Potential Benefits Potential Liabilities 

Safety Single-point: Potential for decrease in 

all types of collisions. 

Compressed diamond: Potential for 

decrease in major-street through 

movement and left-turn collisions. 

Compressed diamond: Potential for 

minor increase in merge/diverge 

collisions. 

Operations Mixed results. Mixed results. 

Multimodal Compressed diamond: All pedestrian 

movements can be served. 

Single-point: Pedestrians cannot be 

served on all movements without adding 

a pedestrian phase. 

Physical Single-point: May be constructable in 

confined right-of-way. 

Compressed diamond: May require 

more right-of-way. 

Socioeconomic Compressed diamond: Likely has a 

lower cost due to the structure. 

Single-point: Likely has a higher cost 

due to the structure. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 
Signalized Intersections: Informational Guide 277

Approach Treatments 

CHAPTER 11 

APPROACH TREATMENTS 

TABLE OF CONTENTS 

11.0 APPROACH TREATMENTS ..............................................................................................279 

 11.1 Signal Head Placement and Visibility .......................................................................279 

 11.1.1 Convert to Mast Arm or Span Wire Mounted Signal Heads ........................280 

 11.1.2 Add Near-Side Signal Heads.......................................................................281 

 11.1.3 Increase Size of Signal Heads.....................................................................282 

 11.1.4 Use Two Red Signal Sections .....................................................................284 

 11.1.5 Increase Number of Signal Heads...............................................................286 

 11.1.6 Provide Backplates ......................................................................................288 

 11.1.7 Provide Advance Warning ...........................................................................290 

 11.2 Signing and Speed Control Treatments....................................................................292 

 11.2.1 Improve Signing ...........................................................................................292 

 11.2.2 Reduce Operating Speed ............................................................................294 

 11.3 Roadway Surface Improvements..............................................................................294 

 11.3.1 Improve Pavement Surface .........................................................................294 

 11.3.2 Provide Rumble Strips .................................................................................297 

 11.3.3 Improve Cross Section.................................................................................298 

 11.3.4 Remove Obstacles from Clear Zone............................................................300 

 11.4 Sight Distance Treatments........................................................................................301 

 11.4.1 Improve Sight Lines .....................................................................................301 

LIST OF FIGURES 

Figure Page

113 Signal head with a double red signal indication..................................................................285 

114 Lane-aligned signal heads..................................................................................................287 

115 Illustration of sight distance triangles..................................................................................302 

LIST OF TABLES 

Table Page

92 Summary of approach treatments ......................................................................................279 

93 Safety benefits associated with using mast arms: Selected findings .................................280 

94 Summary of issues for using mast arm/span wire mounted signal heads .........................281 

95 Summary of issues for supplemental near-side traffic signal heads ..................................282 

96 Safety benefits associated with using 300-mm (12-inch) signal lenses: Selected 

findings ............................................................................................................................283 

97 Summary of issues for increasing the size of signal heads................................................284 

98 Safety benefits associated with using a double red indication (red “T”) display: Selected 

findings ............................................................................................................................285 

99 Summary of issues for using two red signal sections.........................................................286 

100 Safety benefits associated with addition of a signal head: Selected findings ....................288 

101 Summary of issues for adding a signal head......................................................................288 

102 Safety benefits associated with the use of signal backplates: Selected findings ...............289 

103 Summary of issues for using signal head backplates.........................................................290 

104 Safety benefits associated with advance warning signs and flashers: Selected findings ..291 

105 Summary of issues related to advance warning treatments...............................................292 

106 Safety benefits associated with sign treatments: Selected findings...................................293 

107 Summary of issues for improving signing...........................................................................294 
278 Federal Highway Administration

CHAPTER 11 TABLES, CONTINUED 

Table Page

108 Safety benefits associated with nonskid treatments, drainage improvements, or 

resurfacing: Selected findings .........................................................................................296 

109 Summary of issues for pavement treatments .....................................................................297 

110 Safety benefits associated with rumble strips: Selected findings .......................................297 

111 Summary of issues for rumble strips. .................................................................................298 

112 Summary of issues for cross section improvements ..........................................................300 

113 Summary of issues for removing obstacles from the clear zone........................................301 

114 Expected reduction in number of crashes per intersection per year by increased sight 

distance ...........................................................................................................................303 

115 Safety benefits associated with sight distance improvements: Selected findings..............303 

116 Summary of issues for visibility improvements...................................................................304 
Signalized Intersections: Informational Guide 279

Approach Treatments 

11. APPROACH TREATMENTS 

Approaches are critical components of a signalized intersection. It should be obvious to 

someone approaching by motor vehicle, bicycle, or on foot that an intersection is ahead, and the 

traffic control device is a traffic signal. Adequate signing and pavement marking is required to 

provide the driver with sufficient information to determine the appropriate lane to choose and 

direction to travel. The pavement on the approaches should provide the driver with a smooth, 

skid-resistant surface, with adequate drainage. The approaches ideally should meet at right 

angles and should be at grade and free of unnecessary clutter and obstacles. Sight distance for 

all approaches should be adequate for drivers proceeding through the intersection, particularly 

those making a left turn. 

This chapter will discuss various treatments related to signalized intersection approaches, as 

summarized in table 92. 

Table 92. Summary of approach treatments. 

Approach Treatment Type Treatment 

Traffic control Mast arm and span wire mounts 

Near-side traffic signal heads 

Larger traffic signal heads 

Two red signal sections 

Increase number of signal heads 

Backplates 

Advanced warning flashers 

Dilemma zone protection 

Operating speed 

Prohibit U-turns 

Pavement/cross section improvements Skid resistance 

Rumble strips 

Improved cross section 

Removal of obstacles 

Visibility Improved sight distance 

11.1 SIGNAL HEAD PLACEMENT AND VISIBILITY 

Traffic signals should be placed so the signal heads are visible at a distance upstream of the 

intersection and from all lanes on the approach. Approaches with poorly placed traffic signals are 

likely to experience an increase of rear-end conflicts and collisions. At intersections with a higher 

proportion of heavy trucks, drivers in adjacent lanes or following a heavy vehicle may not be able 

to see the signal indication, which may lead to inadvertent red light running. Many red light 

runners claim they did not see the traffic signal, and often the reason is the poor placement of 

traffic signal heads or a failure to make the traffic signal head visually prominent. 

Approach treatments that improve signal visibility will aid drivers in making decisions at the 

intersection and forewarn them of a signalized intersection. Subsequently, the probability of driver 

error, such as inadvertently running a red light and being involved in a collision, is lower. 

The following sections identify traffic control treatments that can be applied to improve the 

visibility of signal heads. 
280 Federal Highway Administration

11.1.1 Convert to Mast Arm or Span Wire Mounted Signal Heads 

Description 

Three major types of signal head placement are in popular use today: pedestal, span wire, or 

mast arm mounted. Merits and drawbacks of each were discussed in chapter 4. For a signalized 

intersection experiencing safety problems related to the placement or visibility of a pedestalmounted signal head, the traffic engineer may wish to consider either replacing signal heads or 

supplementing signal heads on existing mast arms or span wire. Replacing or supplementing 

signal heads may be considered when: 

• An approach where a pedestal-mounted traffic signal head is located against a 

backdrop with a considerable amount of visual clutter. 

• An approach where heavy truck traffic habitually prevents adjacent and following 

drivers from viewing a pedestal-mounted traffic signal head. 

Both mast arms and span wire mounted traffic signals improve the signal head’s prominence 

upstream of the intersection. 

Application 

This treatment should be considered: 

• At intersections where a high number of rear-end collisions occur. 

• At intersections where a high number of angle collisions occur that may be attributable 

to inadvertent red light runners. 

Safety Performance 

The impact of mast arm mounted signal heads and all-red intervals on safety at six 

intersections was evaluated in Kansas City, MO. Results showed that upgrading to mast-mounted 

signals on wide streets and implementing an all-red interval are cost-effective improvements that 

reduce the number of collisions at intersections. The upgrade was found to be particularly 

effective for intersections with pedestal-mounted signals that experienced a larger number of 

right-angle collisions, resulting in an overall 25 percent reduction in collisions and a 63 percent 

reduction in right-angle collisions.(165)

Safety benefits of signal upgrades from pedestal to mast arm are shown in table 93. 

Table 93. Safety benefits associated with using mast arms: Selected findings. 

Treatment Finding 

Replace pedestals with mast arms (166) 49% estimated reduction in all collisions. 

44% estimated reduction in fatal/injury collisions. 

51% estimated reduction in property-damage-only (PDO) collisions. 

74% estimated reduction in right angle collisions. 

41% estimated reduction in rear-end collisions. 

12% estimated reduction in left-turn collisions. 

Operational Performance 

Signal head placement has a negligible effect on intersection capacity. 

Multimodal Impacts 

The placement of traffic signal heads on span wires or mast arms will be particularly 

advantageous for heavy vehicles, giving them additional time to decelerate and come to a full 

stop. 
Signalized Intersections: Informational Guide 281

Approach Treatments 

Physical Impacts 

Span wire mounted signal heads have an advantage over mast arm mounted signal heads. 

At larger intersections, the length of the mast arm may limit its use. 

Socioeconomic Impacts 

Span wire installations are generally considered less aesthetically pleasing than mast arms 

because of overhead wires. 

Enforcement, Education, and Maintenance 

Span wire installations generally have higher maintenance costs than mast arms. Both types 

may need additional reinforcements if installed in a location known for strong winds. 

Summary 

Table 94 summarizes the issues associated with using mast arm or span wire mounts for 

signal heads. 

Table 94. Summary of issues for using mast arm/span wire mounted signal heads. 

Characteristic Potential Benefits Potential Liabilities 

Safety Increases signal visibility. 

Decreases angle collisions. 

None identified. 

Operations Negligible effect. None identified. 

Multimodal Heavy vehicles have more time to stop. None identified. 

Physical Greater flexibility in placement of span 

wire poles. 

Less flexibility in placement of mast arm 

poles. 

Socioeconomic None identified. Span wires not aesthetically pleasing. 

Enforcement, 

Education, and 

Maintenance 

None identified. Span wires typically require more 

maintenance than mast arms. 

11.1.2 Add Near-Side Signal Heads 

Description 

Supplemental pole mounted traffic signals may also be placed on the near side of the 

intersection. This may be particularly useful if: 

• Sight distance is an issue, such as on approaches to intersections on curves. 

• The intersection is particularly wide, so that a far-side signal cannot be placed within 

MUTCD sight distance requirements for approaching drivers.(1)

Applicability 

Near-side pole placements may be considered where there may be limited sight distance or 

at a particularly wide intersection with a high number of rear-end or angle collisions. Refer to 

section 4D.15 of the MUTCD for guidance on the location of signal heads.(1)

Safety Performance 

Supplemental pole-mounted traffic signals appear to reduce the number of fatal and injury 

collisions at an intersection, according to the limited research that has been done on their 

effectiveness at preventing collisions. 
282 Federal Highway Administration

Operational Performance 

Additional signal poles, when placed on the near side of an intersection have a negligible 

effect on intersection capacity. 

Multimodal Impacts 

A near-side placement of a traffic signal on a median benefits heavy trucks by giving them 

additional warning. 

The placement of the traffic signal should not interfere with the movement of pedestrians 

across the intersection or along the sidewalk. 

Physical Impacts 

As a pedestal traffic signal is mounted on the near side of an intersection, a median must be 

present in that location. Additional costs are likely required to provide electricity and conduit to 

connect to the traffic controller. 

Summary 

Table 95 summarizes the issues associated with supplemental near-side traffic signal poles. 

Table 95. Summary of issues for supplemental near-side traffic signal heads. 

Characteristic Potential Benefits Potential Liabilities 

Safety Increases signal visibility. 

Decreases angle collisions. 

None identified. 

Operations Negligible. None identified. 

Multimodal Heavy trucks have more time to stop. May interfere with movement of crossing 

pedestrians. 

Physical None identified. None identified. 

Socioeconomic None identified. Moderate costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.1.3 Increase Size of Signal Heads 

Description 

Two diameter sizes are currently in use for signal lenses: 200 mm (8 inches) and 300 mm (12 

inches). Of these, 300-mm (12-inch) signal faces for red, amber, and green indications are 

commonly used at medium- and high-volume intersections. A goal many jurisdictions are working 

toward is to limit use of 200-mm (8-inch) signal heads to only low-speed locations without 

confusing/complex backgrounds. The MUTCD indicates 300-mm (12-inch) signal faces shall be 

used (section 4D.15):(1)

• Where road users view both traffic control and lane-use control signal heads 

simultaneously. 

• If the nearest signal face is between 35 m (120 ft) and 45 m (150 ft) beyond the stop 

line, unless a supplemental near-side signal face is provided. 

• For signal faces located more than 45 m (150 ft) from the stop line. 
Signalized Intersections: Informational Guide 283

Approach Treatments 

• For approaches to all signalized locations for which the minimum sight distance 

cannot be obtained. 

• For arrow signal indications. 

Due to the large size and high speeds of many high-volume signalized intersections, the use 

of 300-mm (12-inch) signal faces is recommended as a general practice for these intersections. 

Application 

Using a 300-mm (12-inch) lens, in particular for the red indication, should improve visibility for 

the driver, and as such should reduce red light running and associated angle collisions. 

Safety Performance 

As part of a safety improvement program conducted in Winston-Salem, NC, 300-mm (12-

inch) signal lenses were installed on at least one approach at 58 intersections. The result was a 

47-percent drop in right angle collisions and a 10-percent drop in total collisions.(135) A beforeand-after study was undertaken to assess the effectiveness of larger (300 mm (12 inches)) and 

brighter signal head displays in British Columbia. Results from an EB analysis showed the 

frequency of total crashes was reduced by approximately 24 percent with the proposed signal 

displays. The results were found to be consistent with previous studies and laboratory tests that 

showed increased signal visibility results in shorter reaction times by drivers and leads to 

improved safety.(167) 

References regarding the safety benefits of installing 300-mm (12-inch) signal lenses are 

shown in table 96. 

Table 96. Safety benefits associated with using 300-mm (12-inch) signal lenses: Selected 

findings. 

Treatment Finding 

Install 300-mm (12-inch) signal lenses, use 

higher wattage bulbs(167)

24% estimated reduction in all collisions. 

Install 300-mm (12-inch) signal lenses(135) 47% estimated reduction in right angle collisions. 

10% estimated reduction in all collisions. 

Operational Performance 

This treatment has a negligible effect on intersection capacity. 

Socioeconomic Impacts 

Using 300-mm (12-inch) lenses costs nominally more than 200-mm (8-inch) lenses. 

Summary 

Table 97 summarizes the issues associated with increasing the size of signal heads. 
284 Federal Highway Administration

Table 97. Summary of issues for increasing the size of signal heads. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in collisions. None identified. 

Operations None identified. None identified. 

Multimodal None identified. None identified. 

Physical None identified. None identified. 

Socioeconomic None identified. Larger signal heads cost nominally more 

than smaller signal heads. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.1.4 Use Two Red Signal Sections 

Description 

This treatment involves doubling the red signal indication on a signal head, which is 

permissible by the MUTCD (section 4D.16).(1) A possible arrangement is shown in figure 113. 

Note that the use a double red lens in any face does not eliminate the need for a second 

signal head with at least 2.4 m (8 ft) of horizontal separation between the two heads (section 

4D.15).(1)
Signalized Intersections: Informational Guide 285

Approach Treatments 

Figure 113. Signal head with a double red signal indication. 

Application 

This treatment should be considered in situations where an unusually high number of angle 

collisions occur involving a red light running vehicle. 

Safety Performance 

Two red signal sections in a single signal head will also increase the conspicuity of the red 

display and further increase the likelihood that the driver will see the signal. This improvement 

has had success in Winston-Salem, NC, where red “T” displays were associated with a drop in 

right-angle collisions (33 percent) and total collisions (12 percent).(135)

Table 98. Safety benefits associated with using a double red indication (red “T”) display: 

Selected findings. 

Treatment Finding 

Red “T” display(135) 12% estimated reduction in all collisions. 

33% estimated reduction in right-angle collisions. 

Operational Performance 

This treatment has a negligible effect on intersection capacity. 
286 Federal Highway Administration

Socioeconomic Impacts 

The additional cost of using two red signal sections is minimal. 

Summary 

Table 99 summarizes the issues associated with using two red signal sections. 

Table 99. Summary of issues for using two red signal sections. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential for reduction in collisions, 

especially rear-end collisions. 

None identified. 

Operations Negligible impact. None identified. 

Multimodal None identified. None identified. 

Physical No physical impacts. None identified. 

Socioeconomic None identified. Minor cost. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.1.5 Increase Number of Signal Heads 

Description 

The number of signal heads may be increased so one signal head is over each lane of traffic 

on an approach. Current MUTCD requirements for signal head placement state “a minimum of 

two signal faces shall be provided for the major movement on the approach, even if the major 

movement is a turning movement” (section 4D.15).(1) In addition, at least one signal head must be 

not less than 12 m (40 ft) beyond the stop line and not more than 55 m (180 ft) beyond the stop 

line unless a supplemental near-side signal face is provided. Finally, at least one and preferably 

both of the signal faces must be within the 20-degree cone of vision. 

Placement of traffic signal heads on a mast arm above each lane is commonly used. Figure 

114 shows an example of an approach with dual left-turn lanes, two through lanes, and a rightturn lane with lane-aligned signal heads. 
Signalized Intersections: Informational Guide 287

Approach Treatments 

Figure 114. Lane-aligned signal heads. 

Application 

This treatment should be considered in situations where an unusually high number of angle 

collisions occur because a vehicle runs a red light. 

Safety Performance 

Increasing the number of signal heads is expected to decrease the occurrence of red light 

running at an intersection in situations where driver fail to see a red signal. In one study in 

Winston-Salem, NC where such an improvement was undertaken, the addition of signal heads 

was associated with a decrease in right-angle collisions by 47 percent.(135) A Canadian study 

also found that adding a primary signal head decreased collisions of all severities; right-angle 

collisions dropped 15 to 45 percent.(168) 

However, the same Winston-Salem, NC study found that collisions increased overall by 15 

percent.(135) This may be due to drivers’ unfamiliarity with such a treatment; more rear-end 

collisions may have occurred due to sudden braking on the approach as the indication turns red. 

Table 100 summarizes selected findings relating to the safety benefits of adding a signal 

head. 
288 Federal Highway Administration

Table 100. Safety benefits associated with addition of a signal head: Selected findings. 

Treatment Finding 

Add a signal head(135) 15% estimated increase in all collisions. 

47% estimated reduction in right-angle collisions. 

Add a primary signal 

head (168)

10 to 25% estimated reduction in fatal/injury collisions. 

30 to 35% estimated reduction in PDO collisions. 

15 to 45% estimated reduction in right-angle collisions. 

0 to 45% estimated reduction in rear-end collisions. 

Operational Performance 

This treatment has a negligible effect on intersection capacity. 

Socioeconomic Impacts 

The capital cost of adding an extra signal head is minimal if the existing mounting and pole 

can be used. If a new mast arm and/or pole is required, for instance, the costs could be 

significant. Additional maintenance and electricity costs are incurred over time. 

Summary 

Table 101 summarizes the issues associated with adding a signal head. 

Table 101. Summary of issues for adding a signal head. 

Characteristic Potential Benefits Potential Liabilities 

Safety General reduction in collisions. One study reported minor increase in 

collisions. 

Operations Negligible impact. None identified. 

Multimodal None identified. None identified. 

Physical None identified. May require new signal pole and 

foundation. 

Socioeconomic None identified. Costs may be high if a new mast arm and 

pole is required. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.1.6 Provide Backplates 

Description 

Backplates are a common treatment for enhancing the visibility of a signal head. There are 

two main types of backplates: 

• Those having a dull black finish, to enhance the contrast between the signal head and 

surrounding. 

• Those with a strip of yellow retroreflective tape around the outside edge of the 

backplate (currently considered “experimental” by the MUTCD).(1) 
Signalized Intersections: Informational Guide 289

Approach Treatments 

Applicability 

Both types of backplates serve to increase the contrast between the signal head and its 

surroundings, drawing the attention of approaching drivers, therefore increasing the likelihood 

that they will stop on a red indication. Both should be used in situations where a high number of 

angle collisions occur. 

The two different types of backplates are used in very different applications. Black backplates 

may be useful on east-west approaches where the sun often is low in the sky, or against bright or 

confusing backgrounds. Conversely, yellow retroreflective tape on a backplate may be helpful to 

improve conspicuity, particularly at night. 

Operational Features 

Backplates with a yellow retroreflective strip around the outside edge highlight the presence 

of the traffic signal. This is an advantage particularly during power outages. 

Safety Performance 

A study of black backplates in Winston-Salem, NC, found a 32-percent drop in right-angle 

collisions at intersections where backplates were installed.(135) A British Columbia study involving 

a comparison of collision frequency using the EB analysis before and after installation of 

backplates with a yellow retroreflective strip around the outside edge at a number of intersections 

concluded that they were effective at reducing the number of automobile insurance claims by 15 

percent.(169)

However, the Winston-Salem, NC study indicated that collisions appear to increase overall at 

intersections where black backplates were used.(135) The overall increase in collisions may be due 

to drivers’ unfamiliarity with such a treatment, causing more rear-end collisions due to sudden 

braking on the approach as the indication turns red. 

A summary of selected findings into the safety benefits of the use of backplates is shown in 

table 102. 

Table 102. Safety benefits associated with the use of signal backplates: Selected findings. 

Treatment Finding 

Backplates(135) 12% estimated increase in all collisions. 

32% estimated reduction in right-angle collisions. 

Operational Performance 

This treatment has a negligible effect on intersection capacity. 

Socioeconomic Impacts 

The cost of installing signal backplates on a signal head is minimal. In addition, extra wind 

loading caused by backplates may necessitate larger (more costly) support poles for both span 

wires and mast arms. 

Education/Enforcement/Maintenance 

Due to their larger size, signal heads with backplates may be more prone to movement 

during high winds. This may pose a particular problem if they are mounted on a span wire, 

leading to maintenance issues. 

Summary 

Table 103 summarizes the issues associated with using signal head backplates. 
290 Federal Highway Administration

Table 103. Summary of issues for using signal head backplates. 

Characteristic Potential Benefits Potential Liabilities 

Safety General reduction in collisions. One study reported minor increase in 

collisions. 

Operations Negligible impact. None identified. 

Multimodal None identified. None identified. 

Physical None identified. None identified. 

Socioeconomic None identified. Minor cost for backplates. Possible 

increased pole cost for increased wind 

loads. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.1.7 Provide Advance Warning 

Description 

Two treatments used to provide advance warning to motorists are those that: 

1. Provide a general warning of a signalized intersection ahead. 

2. Provide a specific warning of an impending traffic signal change (from green to red) 

ahead. 

Treatments that provide a general warning include static signs (SIGNAL AHEAD) and 

continuous advance-warning flashers. These flashers consist of a sign mounted on a pole with an 

amber flashing light. The sign may read BE PREPARED TO STOP or show a schematic of a 

traffic signal. This type of flasher flashes regardless of what is occurring at the signal. Both 

treatments are placed upstream of the traffic signal at a distance sufficient to allow drivers time to 

react to the signal. 

The second type of treatment provides a specific warning of an impending traffic signal 

change ahead. These advance-warning flashers inform drivers of the status of a downstream 

signal. This type is activated showing yellow flashing lights or illuminating an otherwise blank 

changeable message such as “Red Signal Ahead” for several seconds. 

The sign and the flashers are placed a certain distance from the stop line as determined by 

the speed limit on the approach. 

Applicability 

The SIGNAL AHEAD sign and advance warning flasher are recommended by the MUTCD in 

cases were the primary traffic control is not visible from a sufficient distance to permit the driver to 

respond to the signal. Advance warning flashers may be an effective countermeasure for: 

• Rear-end collisions where a driver appears to have stopped suddenly to avoid running 

a red light and was struck from behind. 

• Angle collisions caused by inadvertent red light running. 

• Queues from a red signal occurring at a location where approaching traffic cannot see 

it due to a vertical or horizontal curve. 

Advance-warning flashers are appropriate for high-speed, rural, isolated intersections where 

the signalized intersection may be unexpected or where there may be sight distance issues. They 
Signalized Intersections: Informational Guide 291

Approach Treatments 

appear to be most beneficial in situations where the minor approach volumes exceed 13,000 

AADT or greater. (170)

Operational Features 

A key factor in operating an advance-warning flasher is determining an appropriate time for 

coordinating the onset of flash with the onset of the yellow interval at the traffic signal. The 

recommended practice is to time the onset of flash as a function of posted speed for the distance 

from the flasher to the stop bar. Timing the onset of flash for speeds greater than the posted 

speed encourages speeding to clear the intersection before the onset of the red interval. 

Safety Performance 

The introduction of advance-warning flashers on the approaches to a signalized intersection 

appears to be associated with a reduction in right-angle collisions. 

Right-angle collisions were reduced by 44 percent at 11 signalized intersections in where a 

SIGNAL AHEAD sign was installed on one or more approaches.(135)

A study conducted in Minnesota involving the installation of an advance-warning flasher on 

one approach found a 29 percent reduction in the number of red light running events, in particular 

those involving trucks (63 percent). The study did not use a control or comparison group of 

intersection approaches.(171) 

Results from a study of 106 signalized intersections in British Columbia show that 

intersections with advance-warning flashers have a lower frequency of crashes than similar 

locations without flashers. The results were not statistically significant at the 95th-percent 

confidence level. Benefits were found primarily for moderate-to-high traffic volumes on the minor 

approach.(170)

Table 104 shows selected references to safety benefits of advance-warning devices. 

Table 104. Safety benefits associated with advance warning signs and flashers: Selected 

findings. 

Treatment Finding 

Post SIGNAL AHEAD warning signs—

urban(98)

16 to 35% estimated decrease in all collisions. 

Post SIGNAL AHEAD warning signs—

rural(98)

16 to 40% estimated decrease in all collisions. 

Post SIGNAL AHEAD signs(135) 44% estimated decrease in right-angle collisions. 

Advance-warning flasher (172) 44% estimated decrease in all fatal/injury collisions. 

53% estimated decrease in PDO collisions. 

73% estimated decrease in all fatal/injury-angle collisions. 

67% estimated decrease in all fatal/injury left-turn collisions. 

82% estimated increase in all rear-end fatal/injury collisions. 

Operational Performance 

Advance warning flashers have no documented effect on intersection capacity. 

Multimodal Impacts 

Flashers may be particularly useful for larger commercial vehicles, which need a greater 

distance to stop on intersection approaches. 
292 Federal Highway Administration

Socioeconomic Impacts 

Advance-warning flashers that activate before the onset of the yellow phase may be costly to 

install. 

Enforcement, Education, and Maintenance 

Another study investigated the effect of advance flashing amber signs at two intersection 

approaches. Results showed that only a few drivers responded to the start of flashing by slowing 

down. The majority of vehicles increased their speed; many significantly exceeded the speed 

limit. Fifty percent of drivers who saw the flashing amber within the first 3 seconds it was 

displayed continued through the stop line. Driver education and police enforcement should be 

applied to ensure that drivers respond appropriately to signal-activated advance warning 

flashers.(173)

 Summary 

Table 105 summarizes the issues associated with advance warning treatments. 

Table 105. Summary of issues related to advance warning treatments. 

Characteristics Potential Benefits Potential Liabilities 

Safety Decreases angle collisions. May induce some drivers to try to beat the 

light. 

Operations Negligible effect. None identified. 

Multimodal Heavy vehicles given more time to 

stop. 

None identified. 

Physical None identified. Activated advance-warning flashers require 

link to traffic controller at intersection. 

Socioeconomic Signage and continuous advancewarning flashers have low cost. Activated advance-warning flashers have 

significant costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement may be needed to ensure 

compliance with the signal indications. 

11.2 SIGNING AND SPEED CONTROL TREATMENTS 

11.2.1 Improve Signing 

Description 

For some intersections, the use of signs beyond the minimum required by the MUTCD may 

be beneficial in improving either safety or operations.(1)

Application 

Signing treatments to consider at signalized intersections include: 

• Increase the size of signs. Signs located on wide streets are more difficult to read from 

the far lane. Likewise, signs located overhead on mast arms appear smaller to drivers 

and therefore need to be substantially larger than ground-mounted signs to have the 

same target visibility.(62)

• Use overhead lane-use signs. These provide improved visibility and may help correct 

a problem with sideswipe crashes on approach due to last-minute lane changes. 

These are especially important for treatments involving indirect turning movements 
Signalized Intersections: Informational Guide 293

Approach Treatments 

that may violate driver expectation. In addition, ground-mounted signs may be less 

visible in a typical urban environment due to visual clutter. 

• Use large street name signs on mast arms. These signs, either retroreflective or 

internally illuminated, are visible from a greater distance. 

• Use advance street name signs that include the legend NEXT SIGNAL. 

Safety Performance 

No studies are available to document specific benefits of the use of advance signing. 

Advance lane-use signs may improve safety by reducing last-minute lane changes. 

Selected findings of safety benefits of other types of improved signage at signalized 

intersections are shown in table 106. 

Table 106. Safety benefits associated with sign treatments: Selected findings. 

Treatment Finding 

Install larger signs(98) 15% decrease in all collisions. 

Overhead lane-use signs(174) 10% decrease in rear-end collisions. 

20% decrease in sideswipe collisions. 

Operational Performance 

Advance lane use signing may improve lane utilization at the intersection and therefore 

improve capacity, if the affected movement is critical. 

Physical Impacts 

Sign supports are obstacles that could injure bicyclists, motorcyclists, pedestrians, and 

drivers.(62) Therefore, each sign should be carefully located to minimize the potential hazard. In 

addition, large advance signs can be difficult to locate in areas with tight right-of-way or where a 

sidewalk would be adversely affected by the sign or its support. 

Socioeconomic Impacts 

Advance signs, particularly if they are mounted overhead on a mast arm or sign bridge, can 

significantly add to the cost of the intersection. 

Summary 

Table 107 summarizes the issues associated with improving signing. 
294 Federal Highway Administration

Table 107. Summary of issues for improving signing. 

Characteristic Potential Benefits Potential Liabilities 

Safety Larger signs or overhead lane-use 

signs may reduce collisions. 

None identified. 

Operations Advance signing may improve lane 

utilization and capacity of the 

intersection. 

None identified. 

Multimodal None identified. None identified. 

Physical None identified. Sign supports must be designed to 

minimize potential hazard. 

Socioeconomic None identified. Advance signs mounted overhead may add 

significantly to the cost of the intersection. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.2.2 Reduce Operating Speed 

Excessive speed on an approach may lead to drivers’ running a red light, braking suddenly to 

avoid a signal change, or losing control of the vehicle while attempting a left or right turn. 

Reducing the operating speed on an intersection approach cannot be accomplished through 

simply lowering the posted speed limit. Research suggests that drivers use the road and the 

surrounding road environment in choosing the operating speed of their vehicle, as opposed to a 

posted speed limit. 

Possible countermeasures that may reduce the operating speed of vehicles are landscaping, 

rumble strips, medians, narrow travel lanes, bike lanes, on-street parking, and curb radii 

reductions. Several of these treatments are discussed elsewhere in the guide; the reader is 

encouraged to refer to those sections for more information. 

11.3 ROADWAY SURFACE IMPROVEMENTS 

11.3.1 Improve Pavement Surface 

Description 

An important objective of highway design is ensuring that pavement is skid resistant and 

provides for adequate drainage. A polished pavement surface, a surface with drainage problems, 

or a poorly maintained road surface can contribute to crashes at or within intersections. Within an 

intersection, the potential for vehicles on adjacent approaches to be involved in crashes 

contributes to the likelihood of severe (angle) crashes, particularly in crashes where the driver is 

unable to stop in time. 

Water can accumulate on pavement surfaces due to rutted wheel paths, inadequate crown, 

and poor shoulder maintenance. These problems can also cause skidding crashes and should be 

treated when present. While there is only limited research on such site-specific programs, the 

results provide confidence that pavement improvements are effective in decreasing crashes 

related to wet pavement. The effectiveness will vary with respect to location, traffic volume, 

rainfall intensity, road geometry, temperature, pavement structure, and other factors 

Vehicles often experience difficulties in coming to a safe stop at intersections because of 

reduced friction on wet or slippery pavement. A vehicle will skid during braking and maneuvering 

when frictional demand exceeds the friction force that can be developed between the tire and the 
Signalized Intersections: Informational Guide 295

Approach Treatments 

road surface; friction is greatly reduced on a wet and slippery surface, which has 20 to 30 percent 

less friction than a dry road surface.(175) 

Water pooling on or flowing across the roadway can prevent smooth operation of an 

intersection if vehicles are forced to decelerate or swerve in order to proceed safely through the 

intersection. It is necessary to intercept concentrated storm water at all intersection locations 

before it reaches the highway and to remove over-the-curb flow and surface water without 

interrupting traffic flow or causing a problem for vehicle occupants, pedestrians, or bicyclists. 

Improvements to storm drainage may be needed to improve intersection operations and safety. 

Potholes, if present on an approach, increase the likelihood of drivers’ swerving or braking to 

avoid damage to their vehicles. A rough surface may also allow water to pool, and in colder 

environments, can cause black ice to form on an intersection approach. 

Proper drainage and a high-quality surface will prevent problems related to pooled water and 

lack of skid resistance. Skid resistance is an important consideration in pavement design, and 

polished pavement surfaces should be addressed to reduce the potential for skidding. Both 

vehicle speeds and pavement condition affect the surface’s skid resistance. Improving the 

pavement condition, especially for wet weather conditions, can be accomplished by providing 

adequate drainage, grooving existing pavement, or overlaying existing pavement. 

Improvements to pavement condition should have high initial skid resistance, ability to retain 

skid resistance with time and traffic, and minimum decrease in skid resistance with increasing 

speed. 

Applicability 

Improvements related to skid resistance, drainage problems, and pavement surface should 

be considered when: 

• A high number of wet road surface collisions occur. 

• Angle collisions occur and many involve one or more vehicles’ skidding into the 

intersection and striking another vehicle. 

• Single-vehicle collisions occur where the driver lost control due to skidding. 

• Rear-end or sideswipe collisions occur when drivers swerve or brake to avoid potholes 

or puddles. 

 Safety Performance 

Several pavement treatments appear to reduce the number of skidding collisions. An early 

1974 before-and-after study showed an 85 percent drop in wet pavement collisions after 

longitudinal grooving was applied to pavement.(176) Grooves carry off water from the road surface 

and increase the coefficient of friction between tires and pavement. Another more contemporary 

paper describes a noncarbonate surface treatment used at a wide range of sites as part of a 

comprehensive Skid Accident Reduction Program. Wet pavement collisions dropped by 61 to 82 

percent; fatal and injury wet pavement collisions dropped by 73 to 84 percent.(177) It should be 

noted the collision reduction described in both studies includes both road segments and 

intersections. 

Apart from addressing wet road surface collisions, resurfacing the approaches to an 

intersection will likely reduce the number of rear-end or sideswipe collisions caused when 

vehicles swerve or slow to avoid potholes. It may, however, lead to a higher operating speed and 

an overall shift in the collision profile toward collisions of greater severity. 

References to safety benefits associated with nonskid treatments, drainage improvements or 

resurfacing are shown in table 108. 
296 Federal Highway Administration

Table 108. Safety benefits associated with nonskid treatments, drainage improvements, or 

resurfacing: Selected findings. 

Treatment Finding 

Groove pavement(132) 25% estimated reduction in all collisions. 

60% estimated reduction in wet pavement collisions. 

Overlay pavement(178) 27% estimated reduction in all collisions. 

29% estimated reduction in fatal collisions. 

16% estimated reduction in injury collisions. 

32% estimated reduction in PDO collisions. 

Resurfacing(132) 25% estimated reduction in all collisions. 

45% estimated reduction in wet pavement collisions. 

Improve pavement texture(179) 5% estimated reduction in all collisions. 

Noncarbonate surface treatment(177) 61 to 82% estimated reduction in wet pavement collisions. 

73 to 82% estimated reduction in fatal/injury collisions on wet 

pavement. 

Drainage improvement(98) 20% estimated reduction in all collisions. 

Operational Performance 

A pavement in poor condition can result in lower saturation flow rates and, consequently, 

reduce the capacity of the intersection. If vehicles need to proceed at slow speeds through an 

intersection or deviate from the travel path to avoid potholes, pooled water, or ice, operations 

likely will degrade. 

Pavement resurfacing and drainage improvements usually improve intersection operations, 

although no known research conclusively indicates the expected capacity benefit of these 

treatments. 

Multimodal Impacts 

If road improvements are being carried out, sidewalks and bike paths adjacent to the 

intersection should be considered for skid-resistant treatments, checked for adequate drainage, 

and repaired if uneven surfaces exist due to cracking, frost heaves, etc. This will reduce 

pedestrian tripping hazards and the likelihood of bicyclists’ swerving into traffic to avoid potential 

roadside hazards. 

Enforcement, Education, and Maintenance 

Pavement improvements (particularly resurfacing) may convey the message to drivers that 

they can now travel at higher speeds. Speeds on the approaches to the intersection should be 

monitored to ensure that the speed profile has not increased significantly in the postimplementation period. If speed has increased significantly and this is leading to degradation in 

safety, police speed enforcement should be considered. 

Summary 

Table 109 summarizes the issues associated with pavement treatments. 
Signalized Intersections: Informational Guide 297

Approach Treatments 

Table 109. Summary of issues for pavement treatments. 

Characteristic Potential Benefits Potential Liabilities 

Safety Wet-weather collisions reduced. 

Angle collisions due to skidding 

reduced. 

Rear-end/sideswipe collisions due to 

swerving/braking reduced. 

Higher speed profile a possible 

byproduct. 

Operations Improved traffic flow, less swerving. None identified. 

Multimodal None identified. Adjacent sidewalks should be 

considered as well. 

Physical No additional requirements. None identified. 

Socioeconomic Relatively low costs associated with 

improvements. 

None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement may be needed to control 

speeds. 

11.3.2 Provide Rumble Strips 

Description 

Rumble strips are warning devices that can be used to alert drivers to the presence of a 

traffic signal, thereby reducing the likelihood that the motorist will run a red light. They can also 

help reduce speeds on approaches. Rumble strips are a series of intermittent, narrow, transverse 

areas of rough-textured, slightly raised or depressed road surfaces. Rumble strips provide an 

audible and vibro-tactile warning to the driver. They are often used in conjunction with pavement 

markings. 

Application 

Rumble strips may be considered in rural areas, on approaches to signalized intersections 

where the traffic signal is not visible from a distance, and in situations where a high number of 

angle collisions occur. They generally result in too much noise in urban areas. 

Safety Performance 

Rumble strips may reduce the likelihood of a right angle collision by alerting the driver to the 

traffic signal. References to safety benefits associated with rumble strips are shown in table 110. 

Table 110. Safety benefits associated with rumble strips: Selected findings. 

Treatment Finding 

Rumble strips(132) 25% estimated reduction in all collisions. 

Operational Performance 

This treatment will increase the time headway between vehicles at an intersection, thus 

decreasing the capacity of the intersection and increasing delays and queuing. This will not be an 

issue if the application is for a high-speed rural intersection with lower volumes. However, the 

treatment may not be applicable to an urban intersection already experiencing congestion. 

Multimodal Impacts 

Rumble strips should not extend all of the way to the paved shoulder, because they would 

affect the safety of bicyclists traveling there. 
298 Federal Highway Administration

Socioeconomic Impacts 

Rumble strips may not be appropriate in residential areas due to the noise generated by 

vehicles traveling over them. 

Summary 

Table 111 summarizes the issues associated with rumble strips. 

Table 111. Summary of issues for rumble strips. 

Characteristics Potential Benefits Potential Liabilities 

Safety Angle collisions associated with 

inadvertent red light running should 

be reduced. 

None identified. 

Operations None identified. May not be desirable at intersections with a 

lower level of service 

Multimodal None identified. May negatively impact bicyclists. 

Physical No physical requirements. None identified. 

Socioeconomic None identified. May not appropriate for residential areas. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

11.3.3 Improve Cross Section 

Description 

Roadways should intersect on as flat a grade as possible to prevent difficulty in vehicle 

handling, especially when vehicles will likely need to wait for their turn to enter the intersection (as 

with left-turn lanes). However, it is not always feasible to design a level intersection, so 

consideration should be given to the profiles of the roadways as they intersect. The profiles and 

crowns of the roadways should be examined to determine whether the intersection of these 

slopes contributes to vehicle handling difficulties. Generally, the pavement of the minor road is 

warped so that the crown is tilted to the same plane as the major road profile. Another option is to 

flatten the cross sections of both roadways so that they are each inclined to intersect with the 

profile of the other road. This method can create a large pavement area, which in turn can lead 

to drainage problems; therefore, this design should only be used on smaller intersections or 

where the drainage problem can be solved. A third option involves maintaining constant cross 

sections on both roadways, and altering the centerline profiles to provide smooth pavement. This 

is a less desirable option than the previous two discussed, given that drivers from both directions 

must pass over three grade breaks at the intersection.(3) 

In addition to the benefits to vehicles, pedestrians and bicyclists benefit from improvements to 

the cross section of an intersection. Severe grades and cross slopes can be difficult for bicyclists 

and pedestrians to negotiate. For example, flatter uphill grades allow bicyclists to more easily 

accelerate from a complete stop. Low cross slopes of no more than 2 percent are essential for 

pedestrians with mobility impairments per ADAAG, as severe cross slopes can make a roadway 

inaccessible.(33)

Application 

This treatment may be applicable at intersections where the grades of intersecting roads are 

greater than 3 percent and one or both of the following is true: 
Signalized Intersections: Informational Guide 299

Approach Treatments 

• A high number of rear-end collisions are occurring due to driver hesitation on the 

approaches and while making left or right turns. 

• A high number of left-turn collisions are occurring due to poor sight distance. 

Safety Performance 

Cross section improvements discussed above will improve sight distance, and therefore 

should decrease left-turn conflicts with through vehicles. It will also allow a more uniform 

operating speed through the intersection on the major road approaches, reducing rear-end 

conflicts. 

Operational Performance 

Cross section improvements discussed above may reduce the time headway between 

vehicles and increase the capacity of the intersection. 

Multimodal Impacts 

Larger commercial vehicles and transit buses will particularly benefit from cross section 

improvements to the intersection. If the intersection is being reconstructed, the engineer must 

include improvements to the adjacent sidewalks if pedestrian facilities exist and are being used. 

Social-economic impacts 

Cross section improvements may have moderate costs. They may be difficult to implement in 

areas where there is little or no right-of-way. Coordination with adjacent landowners may be 

needed. 

Education/Enforcement/Maintenance 

Cross section improvements may convey the message that drivers can now travel at higher 

speeds. Speeds on the approaches to the intersection should be monitored to ensure that the 

speed profile has not increased significantly in the post-implementation period. If speed has 

increased significantly and this is leading to degradation in safety, police speed enforcement may 

be considered. Note that cross section improvements on hilly roadways may actually result in a 

reduction in speeds. 

The effectiveness of this treatment will likely be enhanced if performed in conjunction with a 

comprehensive and timely winter road maintenance program in colder climates. 

Summary 

Table 112 summarizes the issues associated with cross section improvements. 
300 Federal Highway Administration

Table 112. Summary of issues for cross section improvements. 

Characteristic Potential Benefits Potential Liabilities 

Safety Decrease in rear-end collisions due 

to driver braking. 

Decrease in left-and right-turning 

collisions involving inadequate sight 

distance. 

Higher speed profile. 

Operations Better traffic flow. None identified. 

Multimodal Improved driver handling of large 

trucks and transit. 

Sidewalks and curb ramps will be 

made more accessible by retrofitting 

to new cross section. 

None identified. 

Physical None identified. Significant right-of-way requirements. 

Socioeconomic None identified. Moderate costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. Speed enforcement may be necessary. 

Winter maintenance may be needed. 

11.3.4 Remove Obstacles from Clear Zone 

Description 

Roadside objects can be a particular hazard to motorists on high-speed approaches. Utility 

poles, luminaires, traffic signal poles, bus shelters, signs, and other street furniture should be 

moved back from the edge of the road if possible and feasible. In general, a signalized 

intersection and the entire area within the right-of-way should be kept free of visual clutter, 

particularly illegally placed commercial signs. 

Application 

Obstacles should be routinely removed from the clear zone on intersection approaches. 

Removing objects should be considered an immediate priority when: 

• There is an unusually high number of run-off-the-road injury and fatal collisions 

involving roadside obstacles. 

• There is evidence in the collision police report that drivers claim distraction by 

unnecessary or illegally placed signage or other visual clutter. 

Safety Performance 

This treatment should decrease the frequency of run-off-the-road injury and fatal collisions 

involving roadside obstacles. The number of collisions involving distracted drivers (such as rearend collisions) should also decrease. 

Physical Impacts 

Moving objects further away from the roadside may be difficult to implement in built-up areas 

where right-of-way is limited. 

Enforcement, Education, and Maintenance 

Traffic engineers should coordinate with their equivalents in the planning department and 

maintenance staff to ensure that the entire right-of-way surrounding the intersection and its 

approaches stays free of obstacles and extraneous signage. 
Signalized Intersections: Informational Guide 301

Approach Treatments 

Summary 

Table 113 summarizes the issues associated with removing obstacles from the clear zone. 

Table 113. Summary of issues for removing obstacles from the clear zone. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in single-vehicle 

collisions. 

None identified. 

Operations None identified. None identified. 

Multimodal None identified. None identified. 

Physical Obstacle removal may be difficult in built-up 

areas with limited right-of-way. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

 Ongoing maintenance will be needed to 

ensure that the clear zone remains free of 

obstacles. 

11.4 SIGHT DISTANCE TREATMENTS 

11.4.1 Improve Sight Lines 

Description 

Adequate sight distance for drivers contributes to the safety of the intersection. In general, 

sight distance is needed for left-turning vehicles to see opposing through vehicles approaching 

the intersection in situations where a permissive left-turn signal is being used. Also, where right 

turns on red are permitted, right-turning vehicles need adequate sight distance to view vehicles 

approaching from the left on the cross street, as well as opposing vehicles turning left onto the 

cross street. AASHTO’s A Policy on Geometric Design of Highways and Streets recommends 

providing adequate sight distance for all movements at signalized intersections where the signal 

operates on flash at times.(3) 

Figure 115 shows sight distance triangles in each direction for drivers on the minor approach 

to an intersection. 
302 Federal Highway Administration

(a) Sight distance triangle looking to the left. 

(b) Sight distance triangle looking to the right. 

Figure 115. Illustration of sight distance triangles.(3) 

Landscaping also must be carefully considered at signalized intersections, otherwise it will 

prevent motorists from making left and right turns safely due to inadequate sight distances. Care 

should be taken to ensure that traffic signs, pedestrian crossings, and nearby railroad crossing 

and school zones are not obstructed. Median planting of trees or shrubs greater than 0.6 m (2 ft) 

in height should be well away from the intersection (more than 15 m (50 ft)). No plantings having 

foliage between 0.6 m (2 ft) and 2.4 m (8 ft) in height should be present within sight triangles. Low 

shrubs or plants not exceeding a height of 0.6 m (2 ft) are appropriate on the approaches to a 

signalized intersection, either on the median, or along the edge of the roadway. The 1990 FHWA 

Guide, Vegetation Control for Safety: A Guide for Street and Highway Maintenance Personnel,

provides additional guidelines and insight on vegetation control with regard to sight distance 

issues.(84) 

Application 

Visibility improvements at a signalized intersections should be considered when: 

• Inadequate sight distance exists between vehicles and/or pedestrians due to 

vegetation and other obstacles within sight triangles. 
Signalized Intersections: Informational Guide 303

Approach Treatments 

• A high number of left- and right-turn collisions are occurring. 

Safety Performance 

It is expected that crashes related to inadequate sight distance (specifically, angle- and 

turning-related) would be reduced if sight distance problems were improved. Intersections with 

sight distance problems will experience higher collision rates.(167) Older drivers are likely to have 

problems at intersections with limited sight distances, as they may need more time to perceive 

and react to hazards. Table 114 shows the expected reduction in number of collisions per 

intersection per year, based on an FHWA report.(180) 

Table 114. Expected reduction in number of crashes per intersection per year by increased sight 

distance.(180)

Increased Sight Distance AADT* 

(1000s) 6 m–15 m 

(20 ft–49 ft) 

15 m–30 m 

(50 ft–99 ft) 

> 30 m 

(> 100 ft) 

< 5 0.18 0.20 0.30 

5-10 1.00 1.30 1.40 

10-15 0.87 2.26 3.46 

> 15 5.25 7.41 11.26 

* Annual average daily traffic entering the intersection 

A more recent FHWA report cites sight distance improvements as being one of the most costeffective treatments (see table 115). Fatal collisions were reduced by 56 percent and nonfatal 

injury collisions were reduced by 37 percent at intersections having sight distance 

improvements.(181)

Table 115. Safety benefits associated with sight distance improvements: Selected findings. 

Treatment Implication 

Sight distance improvements(181) 56% estimated reduction in fatal collisions. 

37% estimated reduction in injury collisions. 

Socioeconomic Impacts 

Sight distance improvements can often be achieved at relatively low cost by clearing sight 

triangles of vegetation or roadside appurtenances. 

The most difficult aspect of this strategy is the removal of sight restrictions located on private 

property. The legal authority of highway agencies to deal with such sight obstructions varies 

widely, and the time (and possibly the cost) to implement sight distance improvements by clearing 

obstructions may be longer if those obstructions are located on private property than if they are 

on public property. If the object is mature trees or plantings, then environmental issues may arise. 

Larger constructed objects (i.e., bus shelters, buildings) may not be feasibly removed. In these 

situations, other alternatives should be considered. 

Multimodal Impacts 

The appropriate use of landscaping can visually enhance a road and its surroundings. 

Landscaping may act as a buffer between pedestrians and motorists, and reduce the visual width 

of a roadway, serving to reduce traffic speeds while providing a more pleasant environment. 

However, landscaping should not interfere with the movement of pedestrians along sidewalks, 

nor should it block the motorist’s view of the pedestrian, or the pedestrian’s view of the motorist. 
304 Federal Highway Administration

Enforcement, Education, and Maintenance 

All plantings should have an adequate watering and drainage system, or should be drought 

resistant. This will minimize the amount of maintenance required and reduce the exposure of 

maintenance staff to traffic. Plantings should not be allowed to obstruct pedestrians at eye height 

or overhang the curb onto the pavement. 

Summary 

Table 116 summarizes the issues associated with visibility treatments. 

Table 116. Summary of issues for visibility improvements. 

Characteristics Potential Benefits Potential Liabilities 

Safety Left- and right-turning collisions involving 

inadequate sight distance. 

None identified. 

Operations Negligible. None identified. 

Multimodal Provides additional warning for heavy 

vehicles making left and right turns. 

Appropriate landscaping will provide a 

more pleasant environment for 

pedestrians. 

None identified. 

Physical None identified. May be significant right-of-way 

requirements. 

Socioeconomic Appropriate landscaping will visually 

enhance intersection and surroundings. 

None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Landscaping may require extensive 

maintenance. 
Signalized Intersections: Informational Guide 305

Individual Movement Treatments 

CHAPTER 12 

INDIVIDUAL MOVEMENT TREATMENTS 

TABLE OF CONTENTS 

12.0 INDIVIDUAL MOVEMENT TREATMENTS ........................................................................307 

 12.1 Left-Turn Treatments ................................................................................................307 

 12.1.1 Add Single Left-Turn Lane...........................................................................307 

 12.1.2 Multiple Left-Turn Lanes ..............................................................................318 

 12.1.3 Turn Prohibition............................................................................................322 

 12.2 Through Lane Treatments ........................................................................................324 

 12.2.1 Provide Auxiliary Through Lanes.................................................................324 

 12.2.2 Delineate Through Path...............................................................................326 

 12.3 Right-Turn Treatments..............................................................................................328 

 12.1.1 Add Single Right-Turn Lane.........................................................................328 

 12.1.2 Provide Double Right-Turn Lanes................................................................333 

 12.1.3 Provide Channelized Right-Turn Lane.........................................................334 

 12.4 Variable Lane Use Treatments .................................................................................336 

 12.4.1 Provide Reversible Lanes ............................................................................336 

 12.4.2 Provide Variable Lane Use Assignments ....................................................338 

LIST OF FIGURES 

Figure Page

116 Diagram of a single left-turn lane........................................................................................308 

117 Narrow (2.4-m (8-ft) left-turn lanes may be used effectively in retrofit situations ...............311 

118 Example of positive offset...................................................................................................312 

119 Intersection with turn paths delineated for dual left-turn lanes in Tucson, AZ (Kolb Road/ 

22nd Street), June 1998..................................................................................................321 

120 Diagram of an auxiliary through lane..................................................................................324 

121 Example of delineated paths ..............................................................................................327 

122 Diagram of a typical right-turn lane.....................................................................................328 

123 Narrow (2.4-m (8-ft) right-turn lanes may be used effectively in retrofit situations.............330 

124 Example illustration of a channelized right-turn lane..........................................................334 

125 Example use of variable lane use sign to add a third left-turn lane during certain 

times of day .....................................................................................................................339 

126 Example use of variable lane use sign to add a second right-turn lane along a corridor 

during certain times of day ..............................................................................................339 

LIST OF TABLES 

Table Page

117 Rule-of-thumb intersection capacities assuming various exclusive left-turn treatments....309 

118 Guidelines for use of left-turn phasing................................................................................313 

119 Guidelines for selection of type of left-turn phasing............................................................314 

120 Minimum recommended sight distance for allowing permissive left turns..........................315 

121 Safety benefits associated with left-turn lane design improvements: Selected findings ....316 

122 Summary of issues for left-turn lanes .................................................................................317 

123 Safety benefits associated with multiple left-turn lanes: Selected findings ........................319 

124 Summary of issues for multiple left-turn lanes....................................................................322 

125 Safety benefits associated with left-turn operational treatments: Selected findings ..........323 

126 Summary of issues for turn prohibitions .............................................................................324 

127 Summary of issues for auxiliary through lanes...................................................................326 
306 Federal Highway Administration

CHAPTER 12 TABLES, CONTINUED 

Table Page

128 Summary of issues for path delineation .............................................................................327 

129 Right-turn lane volume warrants.........................................................................................329

130 Safety benefits associated with right-turn improvements: Selected findings .....................331 

131 Summary of issues for right-turn lanes...............................................................................332 

132 Summary of issues for double right-turn lanes...................................................................334 

133 Safety benefits associated with right-turn channelization: Selected findings .....................335 

134 Summary of issues for channelized right-turn lanes...........................................................336 

135 Summary of issues for reversible lanes..............................................................................338 

136 Summary of issues for variable lane use............................................................................340 
Signalized Intersections: Informational Guide 307

Individual Movement Treatments 

12. INDIVIDUAL MOVEMENT TREATMENTS 

This section identifies treatments for vehicle movements at signalized intersections: left- and 

U-turn movements, through movements, and right-turn movements. In addition, this section 

addresses the use of variable lane use. The treatments in this section primarily address the 

following safety and operational deficiencies: 

• An overrepresentation of rear-end collisions under congested conditions. 

• An overrepresentation of collisions involving left-turning vehicles. 

• An overrepresentation of bicycle and/or pedestrian crashes. 

• Excessive queuing and/or delay for one (or more) approach movements. 

12.1 LEFT-TURN TREATMENTS 

This section discusses the key safety, operational, and design characteristics associated with 

left-turn treatments, including the addition of a single left-turn lane, multiple left-turn lanes, and 

left-turn prohibition. 

Left-turning vehicles encounter safety problems from several sources of conflict: pedestrians; 

bicyclists; opposing through traffic; through traffic in the same direction; and crossing traffic. 

These conflict types often lead to angle, sideswipe same direction, and rear-end crashes. Leftturn-related crashes typically account for a high percentage of total crashes at an intersection. 

The demand for a left-turn movement also affects the amount of green time that can be 

allocated to additional movements. Operational treatments may be justified to minimize the 

amount of green time that is allocated to left-turn movements to serve additional critical 

movements at an intersection. 

12.1.1 Add Single Left-Turn Lane 

Adding a single left-turn lane at an approach that currently has shared through and left-turn 

movements is applicable when the delay caused to through vehicles adversely affects the 

operations and/or safety of an approach. An example is shown in figure 116. A disproportionately 

high amount of rear-end crashes involving left-turning vehicles followed by through vehicles is an 

indication that a left-turn lane may be appropriate. Physically separating turning vehicles from the 

through stream removes slow or decelerating vehicles from through traffic, thus reducing the 

potential for rear-end collisions. Left-turn lanes also increase the capacity of the approach by 

adding an additional approach lane; they allow for a wider variety of phasing options. On the 

other hand, depending on how the left-turn lane is added, the left-turn lane may add distance, 

time, and exposure for pedestrians and may increase the overall intersection cycle length, adding 

delay to all users. 
308 Federal Highway Administration

L = Storage length 

R = Radius of reversing curve 

S = Stopping sight distance for a speed of (0.7)(design speed of highway) 

T = Tangent distance required to accommodate reversing curve 

W = Minimum distance of 12 m (40 ft) 

Figure 116. Diagram of a single left-turn lane.(182)

Applicability 

The adopted guidelines and practices of local agencies should be reviewed to determine 

whether left-turn lane warrants are in place for a particular roadway. Key elements that should be 

considered when determining whether a left-turn lane is warranted include: 

• Functional classification. A left-turn lane should be considered for higher class 

facilities (i.e., arterials and principal arterials) for consistency (if other similar class 

facilities have left-turn lanes) and to accommodate an expected growth in traffic 

volumes.

• Prevailing approach speeds. An increase in speed differentials between through 

and slower-speed left-turning vehicles may lead to an increase in rear-end collisions. 

• Capacity of an intersection. The addition of a left-turn lane increases the number of 

vehicles the intersection can serve. 

• Proportion of approach vehicles turning left. Higher volumes of left-turn traffic 

result in increased conflicts and delay to through vehicles. 

• Volumes of opposing through vehicles. High volumes of opposing vehicles reduce 

the number of gaps available for a left-turn movement (assuming permissive phasing), 

thus increasing conflicts and delay with approaching through movements. 

• Design conditions. A left-turn lane may be needed to improve sight distance. 

• Crash history associated with turning vehicles. A left-turn lane should be 

considered if there is a disproportionate amount of collisions involving left-turning 

vehicles on the approach. 

In the absence of site-specific data, the HCM 2000 indicates the probable need for a left-turn 

lane if the left-turn volume is greater than 100 vehicles in a peak hour, and the probable need for 

dual left-turn lanes if the volume exceeds 300 vehicles per hour.(2) The HCM also indicates a leftturn lane should be provided if a left-turn phase is warranted. 

Table 117 highlights several rule-of-thumb intersection capacities for various scenarios where 

exclusive left-turn treatments may be required on one or both approaches to an intersection. In 

general, exclusive left-turn lanes are needed when a left-turn volume is greater than 20 percent of 
Signalized Intersections: Informational Guide 309

Individual Movement Treatments 

total approach volume or when a left-turn volume is greater than 100 vehicles per hour in peak 

periods.(41)

Table 117. Rule-of-thumb intersection capacities assuming various exclusive left-turn treatments. 

Case I: No Exclusive Left-Turn Lanes 

Assumed critical signal phases* 2 

Left-turn volumes Critical major approach:** ≤ 125 veh/hr 

Critical minor approach: ≤ 100 veh/hr 

Planning-level capacity (veh/hr), Number of basic lanes,  major approach 

sum of critical approach volumes** * 2 3 4 

Number of basic lanes, 

minor approach 

1 

2 

3 

1,700 

2,400 

— 

2,300 

3,000 

— 

— 

— 

— 

Case II: Exclusive Left-Turn Lane on Major Approaches Only 

Assumed critical signal phases 3 

Left-turn volumes Critical major approach: 150-350 veh/hr 

Critical minor approach: ≤ 125 veh/hr 

Planning-level capacity (veh/hr), Number of basic lanes, major approach 

sum of critical approach volumes 2 3 4 

Number of basic lanes, 

minor approach 

1 

2 

3 

1,600 

2,100 

2,700 

2,100 

2,600 

3,000 

2,300 

2,800 

3,200 

Case III: Exclusive Left-Turn Lane on Both Major and Minor Approaches 

Assumed critical signal phases 4 

Left-turn volumes Critical major approach: 150-350 veh/hr 

Critical minor approach: 150-250 veh/hr 

Planning-level capacity (veh/hr), Number of basic lanes, major approach 

sum of critical approach volumes 2 3 4 

Number of basic lanes, 

minor approach 

1 

2 

3 

1,500 

1,900 

2,200 

1,800 

2,100 

2,300 

2,000 

2,400 

2,800 

Notes: *Critical signal phases are nonconcurrent phases 

 **A critical approach is the higher of two opposing approaches (assumes same number 

of lanes) 

 ***Use fraction of capacity for design purposes (e.g., 85 or 90 percent) 

 ****Basic lanes are through lanes, exclusive of turning lanes 

 Adapted from NCHRP 279, figure 4-11(41)

Key Design Features 

Key design elements of an exclusive left-turn lane include: entering taper, storage length, 

lane width, and offset. Design criteria for left-turn lanes are presented in the AASHTO A Policy 

on Geometric Design for Highways and Streets as well as in the policies of individual highway 

agencies.(3) 
310 Federal Highway Administration

Entering taper. Entering tapers should be designed to: (1) allow vehicles to depart the 

through travel lane with minimum braking; and (2) provide adequate length to decelerate and join 

the back of queue. An appropriate combination of deceleration and taper length will vary 

according to the situation at individual intersections. A relatively short taper and a longer 

deceleration length may be applicable at busier intersections where speeds are slower during 

peak hours. This allows more storage space during peak hours and reduces the potential for 

spillover into the adjacent through lane. However, off-peak conditions should be considered when 

vehicle speeds may be higher, thus requiring a longer deceleration length. 

AASHTO indicates a taper rate of 8:1 to 15:1 is common for high-speed roadways. Using a 

taper that is too short may require a vehicle to stop suddenly, thus increasing the potential for 

rear-end collisions. Using a taper that is too long may result in drivers’ inadvertently drifting into 

the left-turn lane, especially if located within a horizontal curve. AASHTO indicates that 

municipalities and urban counties are increasingly adopting the use of taper lengths such as 30 m 

(100 ft) for a single-turn lane.(3)

Storage length. The length of the left-turn bay should be sufficiently long to store the number 

of vehicles likely to accumulate during a critical period so the lane may operate independent of 

the through lanes. The storage length should be sufficient to prevent vehicles spilling back from 

the auxiliary lane into the adjacent through lane. Storage length is a function of the cycle length, 

signal phasing, rate of arrivals and departures, and vehicle mix. As a rule-of-thumb, the left-turn 

lane should be designed to accommodate one and one-half to two times the average number of 

vehicle queues per cycle, although methods vary by jurisdiction. The Highway Capacity Manual

can also be used to estimate queues, as noted in chapter 7.(2)

Lane width. Lane width requirements for left-turn lanes are largely based on operational 

considerations. Generally, lane widths of 3.6 m (12 ft) are desirable to maximize traffic flow; 

however, right-of-way or pedestrian needs may dictate use of a narrower lane width. For 

situations where it is not possible to achieve the standard width for a left-turn lane, providing a 

less-than-ideal lane is likely an improvement over providing no left-turn lane. Lane widths less 

than 2.7 m (9 ft) are not recommended for new design, but in some very constrained retrofit 

situations on lower speed roadways, lane widths as low as 2.4 m (8 ft) for some left-turning 

movements may be a better choice than not providing any left-turn lane or having too few left-turn 

lanes. Achieving more lanes through restriping from 3.6-m (12-ft) lanes to narrower lanes should 

be considered where appropriate.(50,183) Figure 117 shows an example from Montgomery County, 

MD, where a narrow left-turn lane has been used effectively. 
Signalized Intersections: Informational Guide 311

Individual Movement Treatments 

Figure 117. Narrow (2.4-m (8-ft)) left-turn lanes may be used effectively in retrofit situations. 

Offset. A left-turning driver’s view of opposing through traffic may be blocked by left-turning 

vehicles on the opposite approach. When left-turning traffic has a permissive green signal phase, 

this can lead to collisions between vehicles turning left from the major road and through vehicles 

on the opposing major-road approach. Offset left-turn lanes position vehicles on approaches 

further to the left, which removes the vehicles from the sight lines of the opposing left-turners. 

This helps improve safety and operations of the left-turn movement by improving driver 

acceptance of gaps in opposing through traffic and eliminating the potential for vehicle path 

overlap. This is especially true for older drivers who have difficulty judging gaps in front of 

oncoming vehicles. AASHTO policy recommends that medians wider than 5.4 m (18 ft) should 

have offset left-turn lanes. One method for laterally shifting left-turning vehicles is to narrow the 

turn-lane width using pavement markings. This is accomplished by painting a wider stripe or 

buffer area at the right side of the left-turn lane, which causes left-turning vehicles to position 

closer to the median. Wider lane lines were implemented at six intersections in Nebraska with 

positive results.(184) The width of these lines ranged from 150 mm to 900 mm (0.5 ft to 3 ft). The 

wider the left-turn lane line used to offset vehicles, the greater the effect on improving sight 

distance. 

Offset left-turn lanes should remain parallel to the through travel route. A tapered left-turn 

design positions a turning vehicle at an angle. If struck from behind, the left-turn vehicle could be 

pushed into the oncoming through lane. Figure 118 illustrates a positive offset of left-turn lanes at 

an intersection.(12)

Miscellaneous. In constrained areas, through lanes are sometimes converted to left-turn 

lanes. In this situation, it is important that through lanes converted to turn lanes do not appear to 

be through lanes. Making the driver aware of this situation using lane markings and/or signs is 

important. One study indicates that the incidence of rear-end crashes increases in these 

situations.(185) The design of the left-turn lane is critical to its effectiveness as a safety or 

operational improvement strategy. 
312 Federal Highway Administration

Figure 118. Example of positive offset.(adapted from 12)

Channelization 

Physical channelization of left turns emphasizes separation of left-turning vehicles from the 

through traffic stream. It guides drivers through an intersection approach, increasing capacity and 

driver comfort. 

A left-turn channelization design should incorporate consideration of the design vehicle, 

roadway cross section, traffic volumes, vehicle speeds, type and location of traffic control, 

pedestrians, and bus stops. In addition to these design criteria, consideration should be given to 

the travel path; drivers should not have to sharply change direction in order to follow the 

channelization. Channelizing devices should not cause drivers to make turns with angles that 

vary greatly from 90 degrees. If median treatments are used to channelized the left turn, 

pedestrian needs identified in chapter 8 should be considered. Additional guidance is provided in 

the AASHTO policy.(3)

Channelization can be provided using curbed concrete or painted islands, or delineators. The 

appropriateness of raised or flush medians depends on conditions at a given intersection. Painted 

channelization provides guidance to drivers without presenting an obstruction in the roadway, and 

would be more appropriate where vehicles may be proceeding through the intersection at high 

speeds. However, paint is more difficult to see at night, especially at intersections that are not 

lighted. 

Raised curbed islands should provide guidance in the intersection area but should not 

present a significant obstruction to vehicles. Safety advantages of left-turn lanes with raised 

channelization include: 

• Turning paths are clearly defined within an expansive median opening. 

• Improved visibility for left-turning drivers. 

• Simultaneous opposing left-turn lanes are offset from one another. 

• Sideswipe collisions due to motorists’ changing from left to through lanes or vice versa 

are prevented. 
Signalized Intersections: Informational Guide 313

Individual Movement Treatments 

Raised pavement markings and “flex-post” delineators should be considered when use of 

raised channelization is not possible. 

Operational Features 

The type of signal phasing used for a left-turn movement directly affects safety and 

operational performance of the turn. In general, less-restrictive phasing schemes are preferable 

where appropriate because they result in lower delay to all users of the intersection. 

Table 118 presents suggested guidelines for determining whether left-turn phasing is 

appropriate, and table 119 presents suggested guidelines for determining the type of left-turn 

phasing. In addition, table 120 presents the minimum recommended sight distance for permissive 

left turns. Note that many agencies have adopted guidelines such as these with localized 

variations to reflect State policy. Examples of deviations include the following: 

• Some States have a policy to always use protected-only left-turn phasing where the 

left-turn movement crosses three lanes, while other States allow the use of permissive 

phasing or protected-permissive phasing in those situations. 

• Some States use values in the criteria that are more conservative than provided here, 

such as lower crash frequency thresholds for protected-only left-turn phasing. 

• At least one municipality (Tucson, AZ) allows the use of protected-permissive phasing 

at double left turns, while most States use protected-only phasing for those locations. 

Table 118. Guidelines for use of left-turn phasing.(186,187)

Left-turn phasing (protected-permissive, permissive-protected, or protectedonly) should be considered if any one of the following criteria is satisfied: 

1. A minimum of 2 left-turning vehicles per cycle and the product of opposing and 

left-turn hourly volumes exceeds the appropriate following value: 

a. Random arrivals (no other traffic signals within 0.8 km (0.5 mi)) 

One opposing lane: 45,000 Two opposing lanes: 90,000 

b. Platoon arrivals (other traffic signals within 0.8 km (0.5 mi)) 

One opposing lane: 50,000 Two opposing lanes: 100,000 

2. The left-turning movement crosses 3 or more lanes of opposing through traffic. 

3. The posted speed of opposing traffic exceeds 70 km/h (45 mph). 

4. Recent crash history for a 12-month period indicates 5 or more left-turn collisions 

that could be prevented by the installation of left-turn signals. 

5. Sight distances to oncoming traffic are less than the minimum distances in table 

119. 

6. The intersection has unusual geometric configurations, such as five legs, when 

an analysis indicates that left-turn or other special traffic signal phases would be 

appropriate to provide positive direction to the motorist. 

7. An opposing left-turn approach has a left-turn signal or meets one or more of the 

criteria in this table. 

8. An engineering study indicates a need for left-turn signals. Items that may be 

considered include, but are not necessarily limited to, pedestrian volumes, traffic 

signal progression, freeway interchange design, maneuverability of particular 

classes of vehicles, and operational requirements unique to preemption systems. 
314 Federal Highway Administration

Table 119. Guidelines for selection of type of left-turn phasing.(186,187)

The type of phasing to use can be based on the following criteria: 

1. Permissive left-turn phasing may be considered at sites that do not satisfy any 

of the left-turn phasing criteria listed in table 118. 

2. Protected-permissive left-turn phasing may be considered at sites that satisfy 

one or more of the left-turn phasing criteria listed in table 118 but do not satisfy 

the phasing criteria for protected-only phasing (see criterion 4 below). 

Protected-permissive phasing is not appropriate when left-turn phasing is 

installed as a result of an accident problem. 

3. Permissive-protected left-turn phasing may be considered at sites that satisfy 

the criteria for protected-permissive phasing and one of the following criteria: 

a. The movement has no opposing left turn (such as at a “T” intersection) or 

the movement is prohibited (such as at a freeway ramp terminal). 

b. A protected-permissive signal display is used that provides the left-turning 

vehicle with an indication of when the driver must yield to opposing traffic, 

such as the “Dallas” display, flashing yellow arrow, or other such devices. 

4. Protected-only left-turn phasing should be considered if any one of the 

following criteria is satisfied: 

a. A minimum of 2 left-turning vehicles per cycle and the product of opposing 

and left-turn hourly volumes exceeds 150,000 for one opposing lane or 

300,000 for two opposing lanes. 

b. The posted speed of opposing traffic exceeds 70 km/h (45 mph). 

c. Left-turning crashes per approach (including crashes involving 

pedestrians) equal 4 or more per year, or 6 or more in 2 years, or 8 or 

more in 3 years. 

d. The left-turning movement crosses three or more lanes of opposing 

through traffic. 

e. Multiple left-turn lanes are provided. 

f. Sight distances to oncoming traffic are less than the minimum distances in 

table 120. 

g. The signal is located in a traffic signal system that may require the use of 

lead-lag left-turn phasing. This criterion does not apply if: 

i. An analysis indicates lead-lag phasing is not needed. 

ii. An analysis indicates that protected-permissive phasing reduces total 

delay more than lead-lag phasing. 

iii. A protected-permissive signal display is used that allows a permissive 

left turn to operate safely opposite a lagging protected left-turn phase 

(see chapter 2 for discussion of left-turn trap). 

h. An engineering study indicates a need for left-turn signals. Items that may 

be considered include, but are not necessarily limited to, pedestrian 

volumes, traffic signal progression, freeway interchange design, 

maneuverability of particular classes of vehicles, and operational 

requirements unique to preemption systems. 
Signalized Intersections: Informational Guide 315

Individual Movement Treatments 

Table 120. Minimum recommended sight distance for allowing permissive left turns. 

Metric U.S. Customary 

Design 

Speed 

(km/h) 

Design Intersection Sight 

Distance for Passenger 

Cars* (m) 

Design 

Speed 

(mph) 

Design Intersection Sight 

Distance for Passenger 

Cars* (ft) 

30 

40 

50 

60 

70 

80 

90 

100 

110 

120 

50 

65 

80 

95 

110 

125 

140 

155 

170 

185 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

165 

205 

245 

285 

325 

365 

405 

445 

490 

530 

*

 For a passenger car making a left turn from an undivided highway. For other conditions 

and design vehicles, the time gap should be adjusted and the sight distance recalculated. 

Source: Adapted from (3), exhibit 9-67 

Safety Performance 

Installation of a left-turn lane can be expected to decrease rear-end crashes and red light 

running crashes. NCHRP 279 reports a California study that found a 15 percent reduction in all 

crashes when left-turn lanes were constructed at signalized intersections without a protected leftturn signal phase, and a 35 percent reduction of crashes when a left-turn phase is provided.(41) A 

separate study found that the installation of a left-turn lane on one major-road approach at 

signalized intersections reduces total crashes by 18 percent, and by 33 percent when left-turn 

lanes are installed on both major-road approaches.(188)

The presence of a left-turn lane could create situations where vehicles are more likely to offtrack. Large trucks and buses are more likely to off-track than passenger cars. Off-tracking 

increases the likelihood of sideswipe and head on crashes between left-turning and adjacent 

through vehicles and between opposing left-turning vehicles. 

In providing left-turn lanes, vehicles in opposing left-turn lanes may block their respective 

drivers’ view of approaching vehicles in the through lanes. This potential problem can be resolved 

by offsetting the left-turn lanes. 

Table 121 shows safety benefits of left-turn geometric improvements. All collision 

modification factors suggest safety improvements associated with providing a left-turn lane at a 

signalized intersection. Collision types that would particularly benefit from a left-turn lane are rearend and left-turn collisions. Provision of a left-turn lane in conjunction with protected left-turn 

phasing would appear to provide the most benefit. 
316 Federal Highway Administration

Table 121. Safety benefits associated with left-turn lane design improvements: Selected findings. 

Treatment Finding 

Left-turn lane–physical channelization(123) 26% estimated reduction in all collisions. 

79% estimated reduction in head-on/sideswipe collisions. 

Left-turn lane–painted channelization(123) 45% estimated reduction in all collisions. 

63% estimated reduction in right-angle collisions. 

39% estimated reduction in rear-end/overtaking collisions. 

35% estimated reduction in left-turn collisions. 

. 

Left-turn lane with signal upgrade(166) 62% estimated reduction in all collisions. 

67% estimated reduction in injury/fatal collisions. 

58% estimated reduction in PDO collisions. 

51% estimated reduction in right-angle collisions. 

63% estimated reduction in rear-end collisions. 

78% estimated reduction in left-turn collisions. 

Left-turn lane, urban(189) 26% estimated reduction in all collisions. 

66% estimated reduction in left-turn collisions. 

Left-turn lane, no phase(132) 25% estimated reduction in all collisions. 

45% estimated reduction in left-turn collisions. 

Left-turn lane and phasing(190) 58% estimated reduction in all collisions. 

Left-turn lane, left-turn phase(179) 35% estimated reduction in all collisions. 

Operational Performance 

The addition of a left-turn lane increases capacity for the approach by removing left-turn 

movements from the through traffic stream. The addition of a left-turn lane may allow for the use 

of a shorter cycle length or allocation of green time to other critical movements. 

The additional pavement width associated with the left-turn lane increases the crossing width 

for pedestrians and may increase the minimum time required for pedestrians to cross. In addition, 

the wider roadway section likely will increase the amount of clearance time required for the minor 

street approach. Restriping the roadway with narrower lanes can minimize this problem. 

If a left-turn lane is excessively long, through drivers may enter the lane by mistake without 

realizing it is a left-turn lane. Effective signing and marking of the upstream end of the left-turn 

lane should remedy this problem. 

Multimodal Impacts 

For cases where widening is required to add a left-turn lane, the crossing distance and 

conflict area for pedestrians will increase. For wide roadway sections, pedestrian refuges (along 

with push buttons) should be considered. 

The design of a left-turn lane should consider the volumes of truck and bus traffic that would 

be using the lane. 
Signalized Intersections: Informational Guide 317

Individual Movement Treatments 

Physical Impacts 

Addition of a left-turn lane will increase the footprint of the intersection if no median is 

currently present, except when the approach is restriped with narrower lanes. The approach to 

the intersection will be wider to accommodate the auxiliary lane. 

Designers should also use caution when considering restriping a shoulder to provide or 

lengthen a left-turn lane. Part of the safety benefits of installing the turn lane may be lost due to a 

loss of shoulder, less proximity to roadside objects, and a reduction in intersection sight distance. 

In addition, the shoulder may not have been designed and constructed to a depth that will support 

considerable traffic volumes and may require costly reconstruction. 

Socioeconomic Impacts 

The potential reduction in travel time and in vehicle emissions is a benefit of left-turn lanes. A 

certain degree of comfort is provided to drivers when they are able to wait to turn outside of the 

through traffic stream, since they are not delaying other vehicles and can wait for a comfortable 

gap. 

The cost of construction and the accompanying signing and striping are one of the main 

economic disadvantages to installing a left-turn lane. Also, access to properties adjacent to the 

intersection approach may need to be restricted when a left-turn lane is installed. 

Enforcement, Education, and Maintenance 

Periodic enforcement may be needed to prevent red light running. 

Given that left-turn lanes are common at signalized intersections, no education should be 

needed to prepare drivers for installation of a lane at an intersection. 

Maintenance issues for left-turn lanes will be the same as for other areas of the intersection. 

Pavement markings and signs should be kept visible and legible. Pavement skid resistance 

should be maintained. 

Summary 

Table 122 provides a summary of the issues associated with left-turn lanes. 

Table 122. Summary of issues for left-turn lanes. 

Characteristic Potential Benefits Potential Liabilities 

Safety Separation of left-turn vehicles from 

though movements. 

Increased pedestrian exposure. 

Operations Additional capacity. Potential for 

shorter cycle lengths and/or allocation 

of green to other movements. 

None identified. 

Multimodal Left-turn lane may result in shorter 

pedestrian delays due to shorter cycle 

length. 

Depending on design, may result in longer 

crossing time and exposure for pedestrians. 

Physical None identified. Increased intersection size. 

Socioeconomic Travel time reduced. 

Vehicle emissions reduced. 

Right-of-way and construction costs. 

Access restrictions to property. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

* Applies to situations where the left-turn lane is added by physical widening rather than restriping. 
318 Federal Highway Administration

12.1.2 Multiple Left-Turn Lanes 

Multiple left-turn lanes are becoming more widely used at signalized intersections where 

traffic volumes have increased beyond the design volume of the original single left-turn lane. 

Multiple left-turn lanes can be used to address left-turn volumes that exceed or are expected 

to exceed a single turn lane. Multiple left-turn lanes allow for the allocation of green time to other 

critical movements or use of a shorter cycle length. 

Applicability 

Double and triple left-turn lanes are appropriate at intersections with significantly high left-turn 

volumes that cannot be adequately served in a single lane. As a rule of thumb, dual left-turn lanes 

are generally considered when left-turn volumes exceed 300 vehicles per hour (assuming 

moderate levels of opposing through traffic and adjacent street traffic). A left-turn demand 

exceeding 600 vehicles per hour indicates a triple left-turn may be appropriate. 

While effective in improving intersection capacity, double or triple lefts are not appropriate 

where: 

• A high number of vehicle-pedestrian conflicts occur. 

• Left-turning vehicles are not expected to evenly distribute themselves among the 

lanes. 

• Channelization may be obscured. 

• Sufficient right-of-way is not available to provide for the design vehicle. 

Design Features 

The design of multiple left-turn lanes is similar to that of single turn lanes. In addition, the 

interaction between vehicles in adjacent lanes and also width of the receiving lanes should be 

considered. The following are design considerations for triple left-turn lanes provided by 

Ackeret.(191) These same considerations apply for double left-turn lanes: 

• Widths of receiving lanes. 

• Width of intersection (to accommodate three vehicles abreast). 

• Clearance between opposing left-turn movements during concurrent maneuvers. 

• Pavement marking visibility. 

• Placement of stop bars for left-turning and through vehicles. 

• Weaving movements downstream of turn. 

• Potential for pedestrian conflict. 

The previous section provided criteria for selecting the type of signal phasing to be used. In 

general, protected-only left-turn phasing is used for most double-lane and triple-lane left-turn 

movements, although some agencies have used protected-permissive phasing for double left 

turns. 

Operational Features 

Drivers may be confused when attempting to determine their proper turn path on an approach 

with multiple left-turn lanes. Providing positive guidance for the driver in the form of pavement 

markings can help eliminate driver confusion and eliminate vehicle conflict by channeling vehicles 

in their proper turn path. 

Delineation of turn paths is especially useful to drivers making simultaneous opposing left 

turns, as well as in some cases where drivers turn right when a clear path is not readily apparent. 

This strategy is also appropriate when the roadway alignment may be confusing or unexpected. 
Signalized Intersections: Informational Guide 319

Individual Movement Treatments 

Delineation of turn paths is expected to improve intersection safety, though the effectiveness 

has not been well evaluated. The additional guidance in the intersection will help separate 

vehicles making opposing left turns, as well as vehicles turning in adjacent turn lanes. 

Additional operational features of dual and triple left-turn lanes are identified below. 

• Prominent and well-placed signing should be used with triple left-turn movements, 

especially in advance of the intersection. 

• The excess green time for left-turn movements resulting from the additional lane 

should be allocated to other critical movements or removed from the entire cycle to 

reduce the cycle length. 

• See tables 118 and 119 for left-turn phasing guidelines. 

Safety Performance 

A literature review shows that dual left-turn lanes with protected-only phasing generally 

operate with minimal negative safety impacts. Common crash types in multiple turn lanes are 

sideswipes between vehicles in the turn lanes. Turn path delineation guides drivers through their 

lane and can help reduce sideswipes at left-turn maneuvers. 

A study of double and triple left-turn lanes in Las Vegas, NV, showed that about 8 percent of 

intersection-related sideswipes occur at double lefts, and 50 percent at triple lefts.(192) These 

sideswipes are 1.4 and 9.2 percent of all crashes at the intersections with double and triple lefts, 

respectively. Turn path geometry and elimination of downstream bottlenecks are important 

considerations for reducing sideswipes. 

One study indicates that triple left-turn lanes have been shown to operate well, and drivers do 

not have trouble understanding the triple left turns.(193) In addition, construction of triple left-turn 

lanes has not resulted in unexpected or unacceptable crash experiences. Another study showed 

that 10 percent of the crashes at intersections with triple lefts occurred in the approach for the 

triple left. These are angle crashes that occur when left-turning vehicles collide with through traffic 

on the cross street. These crashes are attributed to short clearance intervals and limited sight 

distance, not operation of the triple left. Public education of the proper use of triple left turns will 

be necessary where these are being considered at an intersection. 

Table 123 presents selected findings of the safety benefits of multiple left-turn lanes. 

Table 123. Safety benefits associated with multiple left-turn lanes: Selected findings. 

Treatment Finding 

Double left-turn lane(172) 29% estimated reduction in all fatal/injury collisions. 

26% estimated reduction in all PDO collisions. 

29% estimated reduction in fatal/injury rear-end collisions. 

47% estimated reduction in fatal/injury left-turn collisions. 

20% estimated reduction in angle fatal/injury collisions. 

Operational Performance 

Multiple left-turn lanes can improve intersection operations by reducing the time allocated to 

the signal phase for the left-turn movement. Triple left-turn lanes have been constructed to meet 

the left-turn capacity demand without having to construct an interchange. This configuration can 

accommodate left-turn volumes of more than 600 vehicles per hour. Vehicle delays, intersection 

queues, and green time for the left-turn movement are all reduced, improving operation of the 

entire intersection. 

While dual left-turn lanes are largely operated with protected-only phasing, some agencies 

use protected-permissive signal phasing. This signal phasing improves capacity for the left-turn 

movements, particularly during nonpeak times when opposing traffic volumes are lower. Many 

agencies have safety concerns regarding permissive left-turns in a double turn lane. In fact, many 
320 Federal Highway Administration

agencies only allow dual left-turn lanes to be run as protected-only phasing. However, some 

agencies overcome this concern by offsetting the dual left turn lanes. 

Tucson, AZ, uses protected-permissive offset dual left-turns at approximately 30 

intersections. The city has been using this treatment for about 30 years with limited reported 

problems, and continues to install them where needed. The protected-permissive “offset” dual 

lefts are used on very high volume city streets (with ADTs exceeding 80,000). The capacity of the 

left-turn movement increases 75 to 80 percent and left-turn crashes increase only insignificantly 

with the protected-permissive phasing is implemented. One potential issue is sight distance for 

the left-turning vehicles. The City of Tucson addresses this concern by offsetting the far lane by 

1.2 to 1.5 m (4 to 5 ft) so that it has the same sight distance as a single left-turn lane, enabling 

drivers to see beyond the opposing left-turn vehicles, as shown in figure 119.(194)

For protected-permissive dual lefts, Tucson, AZ, also uses a lagging left-turn phase 

operation. The Arizona Insurance Information Association studied this operation in 2002.(195) The 

study found that Tucson, AZ, had lower crash rates than the leading left-turn operations in the 

Phoenix, AZ, area, and this benefit was attributed in part to the use of lagging left phases. 

On the other hand, in a study of four non-offset intersections with dual left-turn lanes in 

Atlanta, GA, operating with protected-permissive signal phasing, it was shown that this signal 

phasing needs to be carefully considered.(196) The advantage of increased capacity compared to 

the disadvantage of increased vehicle conflicts illustrated that this type of phasing may not be 

appropriate. This study was based on a limited data set, and more sites should be studied to 

verify these results. 
Signalized Intersections: Informational Guide 321

Individual Movement Treatments 

Photograph Credit and Copyright: City of Tuscon, Arizona, 1998 

Figure 119. Intersection with turn paths delineated for dual left-turn lanes and offsets in Tucson, 

AZ (Kolb Road/22nd Street), June 1998. 

Multimodal Impacts 

Adding turn lanes increases the crossing distance for pedestrians, as well as their exposure 

to potential conflicts if roadway widening is required. 
322 Federal Highway Administration

Physical Impacts 

Installation of a second or third turn lane will increase the footprint of the intersection, except 

when additional lanes can be accommodated through restriping. As with single left-turn lanes, 

right-of-way costs and access to adjacent properties are significant issues to consider. 

Socioeconomic Impacts 

A shorter green time for left-turning vehicles, made possible by multiple turn lanes, can 

provide more green time to other movements. As this reduces delay, it will also reduce vehicle 

emissions. 

Enforcement, Education, and Maintenance 

Little or no education should be needed for multiple left-turn lanes that operate with 

protected-only or split phasing other than lane assignment signing and markings. Some public 

information may be needed to educate drivers regarding a permissive movement at a double leftturn lane. 

Summary 

Table 124 summarizes the issues associated with multiple left-turn lanes. 

Table 124. Summary of issues for multiple left-turn lanes. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in collisions. None identified. 

Operations Potential improvement in capacity. None identified. 

Multimodal None identified. Longer crossing distance and more 

exposure. 

Physical None identified. Multiple turn lanes may increase 

the footprint of the intersection. 

Socioeconomic Potential reduction in vehicle 

emissions due to lower delay. 

None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Some education may be needed 

for double left-turn lanes with 

permissive phasing. 

12.1.3 Turn Prohibition 

Safety and operations at some signalized intersections can be enhanced by restricting 

turning maneuvers, particularly left turns, during certain periods of the day (such as peak traffic 

periods) or by prohibiting particular turning movements altogether. Signing or channelization can 

be implemented to restrict or prohibit turns at intersections. 

Prohibiting or restricting left turns should practically eliminate crashes related to the affected 

turning maneuver. Alternative routes should be analyzed to ensure that crash rates and 

operational problems do not increase due to diversion of traffic to these alternatives. Also, the 

benefit of restricting turns may be reduced by an increase in accidents related to formation of 

queues (rear-end collisions). 

U-turning vehicles proceed through an intersection at a slower speed than left-turning 

vehicles and can have an adverse effect on both operations and safety at the intersection. 

Prohibition of U-turns may be appropriate at intersections with high volumes for movement with 

which U-turns interfere. Slower moving U-turning traffic will reduce the capacity of a left-turn 

movement. Drivers attempting to make a U-turn during a permitted left-turn phase may interfere 
Signalized Intersections: Informational Guide 323

Individual Movement Treatments 

with opposing through traffic. Rear-end crashes involving U-turning vehicles followed by leftturning or through vehicles may be a sign of operational problems with the U-turn maneuver. 

Sight distance limitations should be considered. If opposing left-turning vehicles waiting in a 

turn lane block a U-turning driver’s view of oncoming through traffic, prohibition of 

U-turn (as well as left-turn) maneuvers on a permissive left-turn phase may be appropriate. 

The turning radius of the design vehicle should be accommodated by the combination of the 

median and receiving lane width. A shorter turn radius will cause slower speeds for U-turning 

vehicles, and will result in more delay to following vehicles. 

Due to the adverse effect U-turns have on intersection capacity and safety, it is sometimes 

preferable to prohibit U-turns, especially at busy intersections. U-turning vehicles have a greater 

operational effect on succeeding vehicles than do left-turning vehicles. One study suggests 

adjusting for U-turns differently from left-turns when determining saturation flow rates of left-turn 

lanes, to account for their larger effect on operations.(197)

Prohibition of a U-turn is typically implemented with signing. Enforcement may be necessary 

to ensure the prohibition is obeyed. 

Selected findings of the safety benefits for various left-turn operational treatments are 

presented in table 125. 

Table 125. Safety benefits associated with left-turn operational treatments: Selected findings. 

Treatment Finding 

Add protected left-turn(123) 56% estimated reduction in right-angle collisions. 

35% estimated reduction in rear-end/overtaking collisions. 

46% estimated reduction in left-turn collisions. 

Add protected left-turn(198) 64% estimated reduction in all collisions. 

Left-turn phasing(189) 12% estimated reduction in all collisions. 

38% estimated reduction in left-turn collisions. 

Add protected-permissive left-turn phase(132) 10% estimated reduction in all collisions. 

40% estimated reduction in left-turn collisions. 

Prohibit left turns(140) 50% estimated reduction in rear-end collisions. 

50% estimated reduction in turning collisions. 

50% estimated reduction in loss-of-control collisions. 

Summary 

Table 126 summarizes the issues associated with turn prohibitions. 
324 Federal Highway Administration

Table 126. Summary of issues for turn prohibitions. 

Characteristic Potential Benefits Potential Liabilities 

Safety Potential reduction in collisions. None identified. 

Operations Potential increase in capacity and 

reduction in delay due to reduction 

of the number of phases. 

None identified. 

Multimodal Fewer conflicts with turning vehicles. 

Lower delay to all users. 

None identified. 

Physical None identified. None identified. 

Socioeconomic None identified. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. Enforcement of turn restrictions may be 

needed. 

12.2 THROUGH LANE TREATMENTS 

12.2.1 Provide Auxiliary Through Lanes 

Auxiliary through lanes (i.e. additional through lanes with limited length) can be added at 

signalized intersections to provide added capacity for through movements. The amount of added 

capacity achieved depends on the extent to which through vehicles use the auxiliary lane. 

Various factors (such as the length of the auxiliary lane, turn volumes, and overall operation of 

the intersection) contribute to how many vehicles will use an auxiliary lane. 

Description 

Auxiliary lanes are generally provided on the approaches of a signalized intersection in 

advance of the intersection and dropped downstream of the intersection. Right-turn traffic may 

share the outside lane with a portion of the through vehicles, or there may be a separate 

exclusive right-turn lane. The auxiliary lane also provides an acceleration lane for vehicles 

turning right from the adjacent approach. Figure 120 illustrates an auxiliary through lane. 

Figure 120. Diagram of an auxiliary through lane.(adapted from 199)
Signalized Intersections: Informational Guide 325

Individual Movement Treatments 

Applicability 

Auxiliary lanes are applicable for arterials that have adequate capacity along midblock 

segments but require additional capacity at signalized intersection locations. The full benefit of 

an auxiliary lane will not be realized if a bottleneck or constraint exists on the arterial upstream or 

downstream of the intersection. 

Design Features 

The length of the auxiliary lane on both sides of an intersection is a determining factor in 

whether the lane will be used; longer lanes get more use by through vehicles than do shorter 

ones.(200) Ideally, the lane should be long enough to allow vehicles turning right off the road to 

decelerate, and vehicles turning right onto the road to accelerate and merge. 

Operational Features 

Unless a separate right-turn lane is provided, both through and right-turning vehicles may use 

the additional lane. More vehicles are likely to use the auxiliary lane if there is not adequate 

green time to clear the signal from the inside through lane. Using relatively short green times for 

the approach will clear vehicle queues and likely result in a higher utilization of the outside 

auxiliary lane. 

Safety Performance 

Based on the subjective assessment of the authors, the safety experience of an intersection 

with auxiliary through lanes should not be significantly different from conventional intersections 

without the additional lane. The downstream merge maneuver that this design requires may lead 

to an increase in merge-related collisions (sideswipes), but studies have not evaluated this. 

Operational Performance 

Tarawneh summarized research performed on auxiliary through lanes and concludes:(200)

• Auxiliary lane use by through vehicles increases with the increase in lane length 

downstream of the intersection and with the increase in delay experienced by the 

through/right-turning vehicles. 

• Auxiliary lane use by through vehicles decreases with an increase in right-turning 

vehicles (right-turn volume greater than 15 percent of the approach volume renders 

the auxiliary lane useless to through vehicles) unless there is a separate right-turn 

lane. 

• Auxiliary lane length, intersection delay, and the proportion of right-turning vehicles 

work together in determining the utility of an auxiliary through lane. 

• Lane utilization factors observed in this study (0.73 to 0.82) are less than HCM default 

values (0.91 for a three lane group).(2)

Hurley introduces the concept of captive and choice users of an auxiliary through lane.(199)

These concepts are described above. Sites were studied in Tennessee to identify the factors that 

affect the choice of using an auxiliary lane. These factors were: 

• Through flow rate. 

• Right turns off the facility in the last 150 m (500 ft) of an auxiliary lane. 

• Downstream auxiliary lane length. 

• Size of urban area. 

Multimodal Impacts 

Wider intersections result in longer crossing times for pedestrians and bicyclists, as well as 

increased exposure to vehicle conflicts. 
326 Federal Highway Administration

Physical Impacts 

Adding an auxiliary through lane will increase the footprint of the intersection if no median is 

currently present. The approach to the intersection will be wider to accommodate the auxiliary 

lane. 

Socioeconomic Impacts 

Driver perception of the benefits of the auxiliary through lane will determine how often the 

lane is used by through vehicles. If right-turn volumes are high enough that drivers do not benefit 

from using the lane, capacity of the through movement will not improve significantly. 

The cost of construction and the accompanying signing and striping are among the main 

economic disadvantages to installation of an auxiliary lane. Also, access to properties adjacent to 

the intersection approach may need to be restricted when another lane is constructed. Property 

owners affected by the restrictions, especially business owners, may be opposed to the auxiliary 

lanes. 

Enforcement, Education, and Maintenance 

Auxiliary through lanes do not present any special enforcement issues. 

No public education should be needed to inform drivers how to proceed through the 

intersection. Signs and pavement markings describing the lane arrangements should be 

sufficient. 

Maintenance issues for through auxiliary lanes will be the same as for other areas of the 

intersection. Pavement markings and signs should be kept visible and legible. 

Summary 

Table 127 summarizes the issues associated with auxiliary through lanes. 

Table 127. Summary of issues for auxiliary through lanes. 

Characteristic Potential Benefits Potential Liabilities 

Safety None identified. Potential for sideswipes downstream of 

merge. 

Operations Decreased delay for through 

vehicles. 

None identified. 

Multimodal None identified. Longer pedestrian crossing time and 

exposure. 

Physical None identified. Larger intersection footprint. 

Socioeconomic None identified. Construction costs. 

Driver perception of delay. 

Access to properties. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

12.2.2 Delineate Through Path 

At complex intersections where the correct path through the intersection may not be 

immediately evident to drivers, pavement markings may be needed to provide additional 

guidance. The same markings are used to delineate turning paths through intersections for 

multiple turn lanes. These markings are a continuation of the longitudinal lane stripes, but have a 

different stripe and skip pattern. An example of these markings is given in figure 121. 
Signalized Intersections: Informational Guide 327

Individual Movement Treatments 

Figure 121. Example of delineated paths. 

Intersections where through vehicles cannot proceed through the intersection in a straight 

line may benefit from pavement markings that guide drivers along the appropriate path. Skewed 

intersections, intersections where opposing approaches are offset, and multileg intersections may 

all present situations where additional guidance can improve safety and operations. 

Delineation of the through path should help reduce driver confusion in the intersection, which 

will reduce erratic movements as drivers steer into or out of the appropriate path. This would 

reduce the potential for sideswipe, rear-end, and head-on crashes. 

Pavement markings through the intersection should account for off-tracking of large (design) 

vehicles. The markings should be spaced far enough apart to allow off-tracking without crossing 

over the markings. 

The cost of installing and maintaining the pavement markings should be the only costs of this 

treatment, and should be similar to that of other pavement markings on the approaches. 

 Summary 

Table 128 summarizes the issues associated with path delineation. 

Table 128. Summary of issues for path delineation. 

Characteristic Potential Benefits Potential Liabilities 

Safety Fewer erratic maneuvers. None identified. 

Operations Fewer erratic maneuvers. None identified. 

Multimodal None identified. Potential off-tracking of large vehicles. 

Physical None identified. Installation costs. 

Socioeconomic None identified. Maintenance costs. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 
328 Federal Highway Administration

12.3 RIGHT-TURN TREATMENTS 

The treatments in this section are: addition of a right-turn lane, double right-turn lanes, and a 

channelized right-turn lane. 

12.3.1 Add Single Right-Turn Lane 

Significant volumes of right-turning traffic can have an adverse effect on both intersection 

operations and safety. The deceleration of the turning vehicles creates a speed differential 

between them and the through vehicles. This can lead to delay for the through vehicles, as well 

as rear-end crashes involving both movements. 

In addition to providing safety benefits for approaching vehicles, right-turn lanes at signalized 

intersections can be used to reduce vehicular delay and increase intersection capacity. 

Figure 122 illustrates the design features of a right-turn lane. 

Figure 122. Diagram of a typical right-turn lane.(adapted from 201)

Right-Turn Lane Warrants 

Similar to left-turn lane warrants, adopted guidelines and practices from local agencies 

should be reviewed when determining if a right-turn lane is warranted. Factors that should be 

considered include vehicle speeds, turning and through volumes, percentage of trucks, approach 

capacity, desire to provide right-turn-on-red operation, type of highway, arrangement/frequency of 

intersections, crash history involving right turns, pedestrian conflicts, and available right-of-way. 

NCHRP 279 identifies warrants for right-turn lanes on four-lane, high-speed roadways, shown 

in table 129.(41) These warrants are based on the percentage of vehicles turning right (as a 

percentage of through vehicles) during the peak period. 
Signalized Intersections: Informational Guide 329

Individual Movement Treatments 

Table 129. Right-turn lane volume warrants.(41)

State Conditions Warranting Right-Turn Lane off Major (Through Highway) 

Through Volume Right-Turn Volume Highway Conditions 

Alaska N/A DHV = 25 vph 

Idaho DHV = 200 vph DHV = 5 vph 2 lanes 

Michigan N/A ADT = 600 vpd 2 lanes 

Minnesota ADT = 1,500 vpd All Design speed > 70 km/h (45 mph) 

Utah DHV = 300 vph Crossroad ADT = 100 vpd 2 lanes 

Virginia DHV = 500 

All 

DHV = 1,200 vph 

All 

DHV = 40 vph 

DHV = 120 vph 

DHV = 40 vph 

DHV = 90 vph 

2 lanes 

Design speed > 70 km/h (45 mph) 

4 lanes 

West Virginia DHV = 500 vph DHV = 250 vph Divided highways 

Wisconsin ADT = 2,500 vpd Crossroad ADT = 1,000 vpd 2 lanes 

Notes: DHV = design hourly volume; ADT = average daily traffic; vph = vehicles per hour; vpd = vehicles per day 

Design features 

The key design criteria for right-turn lanes are: entering taper; deceleration length; storage 

length; lane width; corner radius; and sight distance. Design criteria for selecting an appropriate 

right-turn lane length are presented in A Policy on Geometric Design for Highways and Streets as 

well as in the policies of individual highway agencies.(3) 

Entering taper and deceleration length. The entering taper and deceleration length should 

be determined based on vehicle speed. The length of storage should be designed to 

accommodate the maximum vehicle queue expected for the movement under design year 

conditions. From a functional perspective, the entering taper should allow for a right-turning 

vehicle to decelerate and brake outside of the through traffic lanes. This is particularly important 

at higher vehicle speeds. In urban areas, this is often difficult to achieve and some deceleration 

of a turning vehicle is expected to occur in the through travel lane. 

Storage length. A right-turn lane should be sufficiently long to store the number of vehicles 

likely to accumulate during a critical period. The storage length should be sufficient to prevent 

vehicles from spilling back from the auxiliary lane into the adjacent through lane. At signalized 

intersections, the storage length required is a function of the cycle length, signal phasing 

arrangement, and rate of arrivals and departures. As a rule of thumb, the auxiliary lane should be 

designed to accommodate one and one-half to two times the average number of vehicle queues 

per cycle, although methods vary by jurisdiction. See chapter 7 for additional discussion 

regarding methodologies for estimating queue lengths/storage requirements. 

In some cases, a right-turn lane may already be provided, but an increase in traffic volumes 

may necessitate lengthening it, which can help improve operations and safety by providing 

additional storage for right-turning vehicles. If the length of a right-turn lane is inadequate, rightturning vehicles will spill back into the through traffic stream, thus increasing the potential for rearend collisions. Longer entering tapers and deceleration lengths can reduce this potential. 

Lane width. Lane width requirements for right-turn lanes are largely based on operational 

considerations. Generally, lane widths of 3.6 m (12 ft) are desirable to maximize traffic flow; 

however, right-of-way or pedestrian needs may dictate use of a narrower lane width. Achieving 

more lanes through restriping from 3.6 m (12 ft) lanes to narrower lanes should be considered 
330 Federal Highway Administration

where appropriate.(50) Figure 123 shows an example from Montgomery County, MD, where a 

narrow right-turn lane has been used effectively. 

Figure 123. Narrow (2.4-m (8-ft)) right-turn lanes may be used effectively in retrofit situations. 

Corner Radius. The corner radius influences the turning speed of vehicles. Large corner 

radii allow vehicles to turn at higher speeds. If low-speed, right-turn movements are desired, 

particularly in locations where pedestrian crossings occur, the curb radius should be minimized, 

yet still accommodate the turning path of the design vehicle. Pedestrian crossing distances will 

be minimized if curb radius is minimized. In addition, lower vehicle speeds can reduce the 

probability of a crash. 

A larger curb radius is appropriate for situations where it is desirable for right-turning vehicles 

to exit the through traffic stream quickly. The right turn may operate as a free-flow movement if an 

acceleration lane is provided on the cross street, or the movement may be controlled by a yield 

sign where the turning roadway enters the cross street. 

Increasing the turning radius can reduce the potential for sideswipe or rear-end collisions by 

reducing lane encroachments as a vehicle approaches a turn and as it enters the cross street. 

Also, some older drivers and drivers of large vehicles may have difficulty maneuvering; the rear 

wheels of their vehicles may ride up over the curb or swing out into other lanes where traffic may 

be present. For situations where a large turning radius is desired, the use of a channelization 

island may be appropriate to reduce unused pavement area. Unused pavement area contributes 

to driver confusion regarding the appropriate path through the intersection. 

Sight distance. Adequate sight distance should be provided for vehicles in the right-turn 

lane or channelized right-turn movement. If right turns on red are permitted, drivers turning right 

should be able to view oncoming traffic from the left on the crossroad. 

Safety Performance 

Right-turn lanes are often used to preclude the undesirable effects resulting from the 

deceleration of turning vehicles. ITE’s Transportation and Land Development indicates that a 

vehicle traveling on an at-grade arterial at a speed 16 km/h (10 mph) slower than the speed of the 

normal traffic stream is 180 times more likely to be involved in a crash than a vehicle traveling at 

the normal traffic speed.(86) Right-turn channelization has been shown to reduce right-turn angle 

crashes. However, the addition of a right-turn lane may result in an increase in sideswipe 

crashes. From a vehicular operations standpoint, larger curb radii generally result in vehicle 

turning paths that are in line with the pavement edge. In addition, larger curb radii produce higher 

vehicle speeds that can negatively impact the safety of pedestrians and bicyclists. 
Signalized Intersections: Informational Guide 331

Individual Movement Treatments 

The provision of right-turn lanes minimizes collisions between vehicles turning right and 

following vehicles, particularly on high-volume and high-speed major roads. A right-turn lane may 

be appropriate in situations where there is an unusually high number of rear-end collisions on a 

particular approach. Installation of a right-turn lane on one major road approach at a signalized 

intersection is expected to reduce total crashes by 2.5 percent, and crashes are expected to 

decrease by 5 percent when right-turn lanes are constructed on both major-road approach.(188)

Selected findings of safety benefits associated with various right-turn lane improvements are 

given in table 130. 

Table 130. Safety benefits associated with right-turn improvements: Selected findings. 

Treatment Implication 

Increase turn lane length(132) 15% estimated reduction in all collisions. 

Add right-turn lane on multilane 

approach(68)

40% estimated reduction in fatal/injury collisions. 

10% estimated reduction in PDO collisions. 

Acceleration/deceleration lanes(132) 10% estimated reduction in all collisions. 

Increase turning radii(132) 15% estimated reduction in all collisions. 

Operational Performance 

Right-turn lanes will remove decelerating and slower-moving vehicles from the through traffic 

stream, which will reduce delay for following through vehicles. Lin concluded that a right-turn lane 

may reduce vehicle delays substantially, even with the percentage of right-turns as low as 10 

percent.(202) 

It is possible that installation of a right-turn lane could create other safety or operational 

problems at the intersection. For example, vehicles in the right-turn lane may block the cross 

street drivers’ view of through traffic; this would be a significant issue where right turns on red are 

permitted on the cross street. If a right shoulder is restriped to provide a turn lane, there may be 

adverse impacts on safety due to the decrease in distance to roadside objects. Delineation of the 

turn lane should be carefully considered to provide adequate guidance through the intersection. 

If a right-turn lane is excessively long, through drivers may enter the lane by mistake without 

realizing it is a right-turn lane. Effective signing and marking the upstream end of the right-turn 

lane may remedy this. 

Also, if access to a right-turn lane is blocked by a queue of through vehicles at a signal, 

drivers turning right may block the movement of through traffic if the two movements operate on 

separate phases. This could lead to unsafe lane changes and added delay. 

Multimodal Impacts 

The speed of turning vehicles is a risk to pedestrian safety. 

The addition of a turn lane increases the crossing distance for pedestrians and may require 

additional time for the flashing DON’T WALK phase. Other issues to consider when designing a 

right-turn lane include potential conflicts between turning vehicles and cyclists proceeding through 

the intersection. 

Transit stops may have to be relocated from the near side of an intersection, due to possible 

conflicts between through buses and right-turning vehicles. 
332 Federal Highway Administration

Physical Impacts 

Addition of a right-turn lane will increase the footprint of the intersection, unless the shoulder 

is restriped to create a turn lane. The approach to the intersection will be wider to accommodate 

the auxiliary lane. 

Designers should use caution when considering restriping a shoulder to provide or lengthen a 

right-turn lane. Part of the safety benefits of installing the turn lane may be lost due to loss of 

shoulder, the greater proximity of traffic to roadside objects, and a possible reduction in 

intersection sight distance. 

Socioeconomic Impacts 

Installing or lengthening a right-turn lane on an intersection approach may involve restricting 

right turns in and out of driveways on that approach. Techniques include signing or construction 

of a raised median. 

The cost of construction (including relocation of signal equipment) and right-of-way 

acquisition is the main disadvantage to installation of a turn lane. Also, access to properties 

adjacent to the intersection approach may need to be restricted when a turn lane is installed. 

Enforcement, Education, and Maintenance 

Periodic enforcement may be needed to prevent red-light violations, especially if right turns 

on red are prohibited. 

 Right-turn lanes are common, and minimal education should be needed to prepare drivers 

for their installation. Drivers may need a reminder that they should be watching for pedestrians 

crossing the departure lanes. 

Maintenance issues for right-turn lanes will be the same as for other areas of the intersection. 

Pavement markings and signs should be kept visible and legible. Pavement skid resistance 

should be maintained. 

Summary 

Table 131 summarizes the issues associated with right-turn lanes. 

Table 131. Summary of issues for right-turn lanes. 

Characteristic Potential Benefits Potential Liabilities 

Safety Separation of right-turn vehicles. None identified. 

Operations Higher right-turn capacity. 

Shorter green time. 

Less delay for following through vehicles. 

Additional storage for approach queues. 

Potential for off-tracking of large vehicles. 

Multimodal None identified. Longer pedestrian crossing distance, time, 

and exposure. 

Higher speed of right-turning vehicles 

increases risk to pedestrians. 

May require transit stop relocation. 

Physical None identified. Larger intersection footprint. 

Socioeconomic None identified. Right-of-way/construction costs. 

Access restrictions to property. 

Enforcement, 

Education, and 

Maintenance 

None identified. Periodic enforcement may be needed to 

prevent red light violations, especially if 

right turns on red are prohibited. 
Signalized Intersections: Informational Guide 333

Individual Movement Treatments 

12.3.2 Provide Double Right-Turn Lanes 

High volumes of right-turning vehicles may support double right-turn lanes to increase 

capacity for the turns and reduce delay for other movements at the intersection. Double right-turn 

lanes can reduce both the length needed for turn lanes and the green time needed for that 

movement. 

Approaches with right-turn volumes that cannot be accommodated in a single turn lane 

without excessively long green times (and delays for other approaches) may be appropriate 

locations for double turn lanes. Also, locations where right-of-way is not available to provide a 

long turn lane but there is space for two shorter turn lanes may be ideal for double turn lanes. 

Clearly, multiple turn lanes are not appropriate where only one receiving lane is available; 

however, consideration may be given to providing a departing auxiliary lane to allow for double 

right turns with a downstream merge. 

As with single right-turn lanes, the design vehicle should be considered when determining 

length, width, and taper of the turn lane. The receiving lane should accommodate the turning 

radius of a large vehicle. Delineation of the turn path will guide drivers through the maneuver and 

help reduce crossing over into adjacent lanes while turning. 

Typically, right turns on red are only permitted on the outside right-turn lane, if at all. NO 

TURN ON RED signing with appropriate lane-specific legends should be placed in a location 

visible to drivers (such as overhead), especially those in the inside turn lane. 

Based on the subjective assessment of the authors, the safety experience of double right-turn 

lanes should be similar to that of single right-turn lanes. Rear-end collisions of decelerating rightturn vehicles and following through vehicles may be reduced after construction of the additional 

turn lane, because the turn lanes have a higher capacity for the slower vehicles. Even though the 

double turn lanes increase capacity, some deceleration may occur in the through lanes, 

depending on the length of the turn lanes. This could lead to rear-end crashes. 

Sideswipes between turning vehicles are a possibility at double turn lanes. This is especially 

an issue if the turn radius is tight and large vehicles are likely to be using the turn lanes. 

Delineation of turn paths should help address this. 

Construction of an additional right-turn lane can be reasonably expected to improve the 

operation of the intersection, provided that the affected right-turn movement is a critical 

movement. The additional deceleration and storage space should help prevent spillover into 

adjacent through lanes. Less green time should be needed for right-turn traffic, and this time thus 

can be allocated to other movements. However, a double turn lane will result in a wider footprint 

for the intersection and increase the distance pedestrians must cross, which increases their 

exposure to potential conflicts with vehicular traffic. 

Acquisition of right-of-way to provide an additional turn lane may be expensive. If a departure 

auxiliary lane is to be constructed to allow for a downstream merge, this may also increase rightof-way costs. Access to adjacent properties may need to be restricted to provide a merge area. 

Owners of adjacent property should be involved in early discussions regarding the plans. 

Lane use signing and signs prohibiting right turns on red from the inside turn lane should 

convey all the information that drivers would need. Periodic enforcement may be needed to 

ensure drivers obey any right turn on red prohibitions. 

Summary 

Table 132 summarizes the issues associated with double right-turn lanes. 
334 Federal Highway Administration

Table 132. Summary of issues for double right-turn lanes. 

Characteristics Potential Benefits Potential Liabilities 

Safety Separation of right-turn vehicles. Potential for sideswipes. 

Operations Higher right-turn capacity. 

Shorter green time. 

Less delay for following through vehicles. 

Off-tracking of large vehicles. 

Multimodal None identified. Longer pedestrian crossing distance, 

time, and exposure. 

Physical Potentially shorter intersection footprint 

than needed for single turn lane. 

Wider intersection footprint. 

Socioeconomic None identified. Right-of-way costs. 

Access restrictions to property. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

12.3.3 Provide Channelized Right-Turn Lane 

Channelization of the right turn with a raised or painted island can provide larger turning radii 

and allow for higher turning speeds, and also can provide an area for pedestrian refuge. Figure 

124 illustrates a channelized right-turn lane. 

Figure 124. Example illustration of a channelized right-turn lane. 

Applicability 

Channelized right-turn lanes are applicable for intersections with a high volume of rightturning vehicles that experience excessive delay due to the traffic signal. The larger the turn 

radius, the higher vehicle speeds can be. An important consideration is the desired speed of the 

turning vehicles as they enter the crossroad. The turn radius can be used to control speed, 
Signalized Intersections: Informational Guide 335

Individual Movement Treatments 

especially if the speed varies greatly from the road the vehicle is turning from. Larger turn radii 

and higher speeds are a safety issue for pedestrians. 

A channelized right-turn lane will have a larger footprint than an intersection with a 

conventional right-turn lane. Additional right-of-way may be needed to accommodate the larger 

corner radius. Constructing a departure auxiliary lane to allow for a downstream merge may also 

increase right-of-way costs. 

Key Design Features 

Channelizing islands can be raised or flush with the pavement. A Georgia study evaluated 

the effects of right-turn channelization in the form of painted islands, small raised islands, and 

large raised islands.(203) Results show that traffic islands appear to reduce the number of rightturn angle crashes, and the addition of an exclusive turn lane appears to correspond to an 

increased number of sideswipe crashes given the introduction of a lane change. 

Operational Features 

The right turn may operate as a free flow movement if an acceleration lane is provided on the 

cross street, or the movement may be controlled by a YIELD sign where the turning roadway 

enters the cross street. Periodic enforcement may be needed to ensure drivers obey any traffic 

control devices used for the right-turn roadway (such as a YIELD sign). 

Visibility of channelizing islands is very important. Islands can be difficult for drivers to see, 

especially at night and in inclement weather. This is particularly true for older drivers. Raised 

islands have been found to be more effective than flush painted islands at reducing nighttime 

collisions, because they are easier to see. 

Older drivers, in particular, benefit from channelization as it provides a better indication of the 

proper use of travel lanes at intersections. However, older drivers often find making a right turn 

without the benefit of an acceleration lane on the crossing street to be particularly difficult. 

Safety Performance 

A reduction in rear-end collisions involving right-turning vehicles and following through 

vehicles could be expected after construction of a right-turn roadway. Turning vehicles will not 

need to decelerate as much as they would for a standard right-turn lane, and therefore the speed 

differentials between turning and through vehicles would not be as great. 

The potential for rear-end and sideswipe crashes on the departure lanes may increase as the 

vehicles turning onto the crossroad merge with the vehicles already on the road. 

Higher speeds and a possibly longer crossing distance and exposure could lead to an 

increase in crashes involving pedestrians, and the resulting crashes will likely have more serious 

consequences. 

Safety benefits of right-turn channelization are shown in table 133. 

Table 133. Safety benefits associated with right-turn channelization: Selected findings. 

Treatment Finding 

Channelization(132) 25% decrease in all collisions. 

50% decrease in right-turn collisions. 

Operational Performance 

Through vehicles will experience less delay if right-turning vehicles do not have to decelerate 

in a through lane. If the volume of right turns is significant enough that the right turn is the critical 

movement on an approach, provision of a right-turn roadway may increase capacity enough that 

more green time can be provided for other movements. 
336 Federal Highway Administration

Multimodal Impacts 

Curbed islands offer a refuge for pedestrians. Crossing paths should be clearly delineated, 

and the island itself should be made as visible as possible to passing motorists. 

Right-turn roadways can reduce the safety of pedestrian crossings if an area is not provided 

for pedestrian refuge. Crossing distances are increased, as is pedestrian exposure to traffic. 

Elderly and mobility-impaired pedestrians may have difficulty crossing intersections with large 

corner radii. Right-turn channelization also makes it more difficult for pedestrians to cross the 

intersection safely, adequately see oncoming traffic that is turning right, and know where to cross. 

Proper delineation of the turning roadway may help, particularly at night. 

Larger turn radii result in higher vehicle speeds. In areas with significant pedestrian traffic, 

consideration should be given to minimizing the curb radii while still accommodating the turning 

path of the design vehicle. Minimizing the curb radii will reduce vehicular turning speeds, 

minimize pedestrian crossing distances, and reduce the potential severity of vehicle-pedestrian 

collisions. 

Socioeconomic Impacts 

Access to adjacent properties may need to be restricted to provide a merge area. Owners of 

adjacent property should be involved in early discussions regarding the plans. 

Summary 

Table 134 summarizes the issues associated with channelized right-turn lanes. 

Table 134. Summary of issues for channelized right-turn lanes. 

Characteristics Potential Benefits Potential Liabilities 

Safety Separation of decelerating right-turn 

vehicles. 

Potential for sideswipes and rear-end 

collisions on departure leg. 

Operations Higher right-turn capacity. 

Shorter green time. 

Less delay for following through 

vehicles. 

None identified. 

Multimodal Pedestrian refuge area. Longer pedestrian crossing distance and 

exposure. 

Higher vehicle speeds. 

Physical None identified. Larger intersection footprint. 

Socioeconomic None identified. Right-of-way costs. 

Access restrictions to property. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

12.4 VARIABLE LANE USE TREATMENTS 

12.4.1 Provide Reversible Lanes 

Reversible lanes are used along a section of roadway to increase capacity without additional 

widening when flows during peak periods are highly directional. These peak periods could be 

regular occurrences, as with normal weekday morning and evening peak traffic, or with special 

events, as with roadways near major sporting venues. Reversible lanes often extend for a 

considerable length of an arterial through multiple signalized intersections. 
Signalized Intersections: Informational Guide 337

Individual Movement Treatments 

According to the MUTCD, reversible lanes are governed by signs (section 2B.25) and/or the 

following lane use control signals (section 4J.02):(1)

• DOWNWARD GREEN ARROW. 

• YELLOW X. 

• WHITE TWO-WAY LEFT-TURN ARROW. 

• WHITE ONE-WAY LEFT-TURN ARROW. 

• RED X. 

At least three sources provide good information on the implementation of reversible lanes. 

First, the MUTCD provides guidance on the allowable applications of these lane use control signs 

and signals, as well as when lane use signals should be used instead of signs. Second, the 

Traffic Control Devices Handbook provides additional information on signal control transition logic 

that can be used when reversing the directional flow of a lane or changing a lane to or from twoway left-turn operation.(61) Third, the Traffic Safety Toolbox provides further discussion on 

planning and implementation considerations, in addition to a discussion of the effects on capacity 

and safety.(95)

Safety Performance 

Reversible lanes help reduce congestion and thus are likely to reduce rear-end collisions. As 

reported in the Traffic Safety Toolbox, “Studies of a variety of locations where reversible lanes 

have been implemented have found no unusual problem with head-on collisions compared to 

other urban facilities. Typically, the reversible lanes will have either no effect on safety conditions 

or will achieve small but statistically significant reductions in accident rates on the facility.” (95, p. 130)

Reversible lanes may preclude the use of median treatments as an access- management 

technique along an arterial street. 

Operational Performance 

Reversible lanes directly benefit operational performance by allowing better matching of the 

available right-of-way to peak direction demands. 

Multimodal Impacts 

The operation of a reversible lane precludes the use of a fixed median to physically separate 

opposing travel directions. Therefore, reversible lane operation precludes the use of medians as 

a refuge area for pedestrians, thus requiring pedestrians to cross the arterial in one stage. 

Physical Impacts 

Reversible lanes may postpone or eliminate the need to widen a facility. 

Socioeconomic Impacts 

Reversible lanes are a relatively low-cost treatment compared to the cost of physically 

widening a facility. 

Summary 

Table 135 summarizes of the issues associated with reversible lanes. 
338 Federal Highway Administration

Table 135. Summary of issues for reversible lanes. 

Characteristics Potential Benefits Potential Liabilities 

Safety Typically achieves small but 

statistically significant accident 

reductions due to reduced 

congestion. 

May preclude access management 

techniques. 

Operations Provides additional capacity to 

accommodate peak direction flows. 

None identified. 

Multimodal None identified. Reversible lanes may prevent the use of 

median pedestrian refuges. 

Physical May postpone or eliminate the need 

to widen a facility. 

None identified. 

Socioeconomic Relatively low cost. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 

12.4.2 Provide Variable Lane Use Assignments 

The concept of variable lane use treatments at signalized intersections is similar to that of the 

reversible lane but is typically applied locally to a single intersection. Variable treatments change 

individual lane assignments at a signalized intersection by time of day and thus can be used to 

accommodate turning movements with highly directional peaking characteristics. 

Issues to consider when implementing variable lane use signs include:(50)

• Adequate turning radius for the number of turning lanes intended during each mode of 

operation. 

• Adequate receiving lanes for each mode of operation. 

• Compatible signal phasing to accommodate each lane configuration. 

• The use of similar variable advance lane use signs to provide adequate notice to 

drivers of the lane use in effect. 

Signal phasing requires special attention when using variable lane use signs. While not 

necessary for all variable lane use operations, split phasing allows any legal combination of lanes 

to be implemented, provided that the other factors cited above are accommodated. Other 

techniques that could be used include variable left-turn phasing treatments (e.g., protected-only 

operation during some times of day, and protected-permissive operation during others). 

Figures 125 and 126 provide examples from Montgomery County, MD, where variable lane 

use signs have been provided for additional left and right turns, respectively. These signs have 

been employed in conjunction with advance variable lane use signs provided several hundred 

feet before the intersection. The signs are compliant with the MUTCD, which allows changeable 

message signs to use the reverse color pattern when displaying regulatory messages (sections 

2A.07 and 6F.52).(1) They are reported as being well received by the public and effective in 

reducing peak-period queuing.(50) 
Signalized Intersections: Informational Guide 339

Individual Movement Treatments 

(a) Double left turn during morning peak and off-peak periods. 

(b) Triple left turn during evening peak period. 

Figure 125. Example use of variable lane use sign to add a third left-turn lane during certain times 

of day. 

Figure 126. Example use of variable lane use sign to add a second right-turn lane along a 

corridor during certain times of day. 

Summary 

Table 136 summarizes the issues associated with variable lane use. 
340 Federal Highway Administration

Table 136. Summary of issues for variable lane use. 

Characteristics Potential Benefits Potential Liabilities 

Safety None identified. None identified. 

Operations Improved peak-period utilization of 

existing right-of-way. 

Reduced queuing during peak periods. 

None identified. 

Multimodal None identified. None identified. 

Physical Reduces or eliminates need for additional 

right-of-way. 

None identified. 

Socioeconomic Lower cost than adding lanes. None identified. 

Enforcement, 

Education, and 

Maintenance 

None identified. None identified. 
Signalized Intersections: Informational Guide 341

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