Signalized Intersections Informational Guide 

Second Edition 

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http://sofety.fhwa.dot.gov 
Signalized Intersections 

Informational Guide 

Second Edition

Publication No. FHWA-SA-13-027 

July 2013

http://sofety.fhwa.dot.gov
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FOREWORD 

This report, now in its Second Edition, complements the American Association of State Highway 

and Transportation Officials (AASHTO) Strategic Highway Safety Plan (SHSP) efforts to develop 

guidance on enhancing the safety of unsignalized and signalized intersections. The overarching goal is 

to reduce the number of traffic related deaths that occur on highways and streets in the United States. 

This guide is an introductory 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 or signing and markings, to high-cost 

measures such as intersection widening or reconstruction. Topics covered include fundamental 

principles of user needs and human factors, multimodal accommodations (emphasizing pedestrians 

and bicyclists), elements of geometric design, and traffic safety design and operation; safety, 

maintenance and operations practices; and a wide variety of treatments, techniques and strategies to 

address existing or anticipated problems at multiple levels, including corridor, approach and individual 

movement treatments. Each recommended treatment includes a discussion of safety performance, 

operations, multimodal issues, and physical and economic factors that the practitioner should 

consider. While some treatments may be better suited to high-volume intersections, most of the 

treatments are applicable for lower volume intersections and would be worthy of systemic 

implementation. Every attempt has been made to reflect the latest research and documentation on 

available treatments and best practices in use by jurisdictions across the United States at the time of 

publication. Since the scope of this guide is necessarily limited, additional resources and references 

are highlighted for the student, practitioner, researcher, or decision maker who endeavors to learn 

more about a particular subject. 

An electronic version of this document can be downloaded from the Federal Highway Administration, 

Office of Safety website at http://safety.fhwa.dot.gov/. A hard copy may be requested by contacting 

the National Highway Institute, 1310 North Courthouse Road, Suite 300, Arlington, VA 22201; 

telephone (703) 235-0500; fax (703) 235-0593. 

Michael Griffith 

Director 

Office of Safety Technologies 

NOTICE 

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

interest of information exchange. The U.S. Government assumes no liability for the use of the information 

contained in this document. 

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

names appear in this report only because they are considered essential to the objective of the document. 

QUALITY ASSURANCE STATEMENT 

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

industry, and the public in a manner that promotes public understanding. Standards and policies are used 

to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically 

reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Technical Report Documentation Page 

1. Report No.

FHWA-SA-13-027

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

4. Title and Subtitle

Signalized Intersections Informational Guide, Second Edition

5. Report Date

July 2013

6. Performing Organization Code

7. Author(s)

Principal Investigator: Brian E. Chandler

Co-Authors: Matthew C. Myers, Jennifer E. Atkinson;,Thomas E. Bryer,

Richard Retting, Jeff Smithline, Jeff Trim, Peter Wojtkiewicz, Gary B.

Thomas, Steven P. Venglar, Srinivasa Sunkari, Brian J. Malone, and Pedram

Izadpanah.

8. Performing Organization Report No.

9. Performing Organization Name and Address

SAIC

11251 Roger Bacon Drive

Reston, VA 20190

Subconsultants: CIMA+, Sam Schwartz Engineering, Texas A&M

Transportation Institute

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

Contract No. DTFH61-10-D-00024, Task

Order No. T-11-006

12. Sponsoring Agency Name and Address

Federal Highway Administration

Office of Safety

1200 New Jersey Avenue SE

Washington, DC 20590

13. Type of Report and Period Covered

Informational Guide Book

August 2011 to July 2013

14. Sponsoring Agency Code

FHWA HSA

15. Supplementary Notes

Jeffrey Shaw (jeffrey.shaw@dot.gov), Office of Safety Technologies (http://safety.fhwa.dot.gov/), served as the Technical

Manager for the Federal Highway Administration (FHWA). The following FHWA staff members contributed as technical

working group members, reviewers and/or provided input or feedback to the project at various stages: Timothy Taylor, Bruce

Friedman, Tom Elliott, Jim Sturrock, Paul Olson, Mark Doctor, John Broemmelsiek, Joe Bared, James Coylar, Jim McCarthy,

Eddie Curtis, Joe Glinski, Ed Rice (retired), Scott Wainwright (retired), Carol Tan, Caroline Trueman and Don Petersen.

Additionally, many individual safety partners representing federal, state and local agencies, professional associations,

academia and industry, made significant contributions to this project; special thanks to Tom Hicks (retired – Maryland SHA),

Mark Hagan (Virginia DOT), Julie Stotlemeyer (Missouri DOT), Jake Kononov (retired – Colorado DOT), Dwight Kingsbury 

(Florida DOT), Julie Bradley (Pennsylvania DOT), Jim Ellison (retired – Pierce County, WA), Peter Koonce (City of

Portland, OR), Dr. Praveen Edara (University of Missouri), Doug Noble (Institute of Transportation Engineers), Melissa

Anderson (U.S. Access Board), and Fred Ranck (traffic safety consultant).

16. Abstract

This is the Second Edition of a document that was originally published in 2004. This document serves as an introduction to and 

guide for evaluating the safety, design, and operations of signalized intersections. It also provides tools to deliver better

balanced solutions for all users. It takes a holistic approach to signalized intersections and considers the safety and operational 

implications of a particular treatment on all system users (e.g., motorists, pedestrians, bicyclists, and transit users). Readers will 

find the tools and information necessary to make insightful intersection assessments and to understand the impacts of potential

improvement measures. The information in this guide 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 and other countries.

17. Key Words

Signalized Intersections, Intersection Safety, Intersection Design, Intersection

Performance, Intersection Treatments

18. Distribution Statement

No restrictions

19. Security Classif. (of this report) 

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

323

22. Price

N/A

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized. 
https://www.fhwa.dot.gov/publications/convtabl.cfm

SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL 

 

 

SYMBOL WHEN YOU KNOW MULTIPLY BY TO FIND SYMBOL 

 

 

 

 

SI* (MODERN METRIC) CONVERSION 

FACTORS APPROXIMATE CONVERSIONS TO SI UNITS 

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 or (F-32)/1.8 Celsius oC 

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 

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 lbf/in2 

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

Section 4 of ASTM E380.

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Table of Contents 

1.0 INTRODUCTION .........................................................................................................................................1-2 

1.1 Background ...........................................................................................................................................1-2

1.2 Performance Measurement and Asset Management .............................................................................1-6

1.3 Scope of the Guide ................................................................................................................................1-7

1.4 Audience for this Guide ........................................................................................................................1-7

1.5 Organization of the Guide .....................................................................................................................1-7

2.0 HUMAN FACTORS......................................................................................................................................2-2 

2.1 Overview of Human Factors.................................................................................................................2-2

2.2 Intersection Users..................................................................................................................................2-5

2.3 Applying Human Factors....................................................................................................................2-22

3.0 DATA COLLECTION AND WARRANTS ................................................................................................3-1 

3.1 Commitment..........................................................................................................................................3-2

3.2 Where Do You Start? Importance of an Engineering Analysis and Study...........................................3-2

3.3 Intersection Data Collection Needed.....................................................................................................3-2

3.4 Intersection Counts................................................................................................................................3-2

3.5 Traffic Signal Warrants.........................................................................................................................3-6

3.6 When is Not Signalizing an Intersection the Right Decision? ...................................................................3-9

4.0 GEOMETRIC DESIGN................................................................................................................................4-3 

4.1 Number of Intersection Legs.................................................................................................................4-4

4.2 Channelization ......................................................................................................................................4-5

4.3 Horizontal and Vertical Alignment .....................................................................................................4-10

4.4 Corner Radius .....................................................................................................................................4-12

4.5 Sight Distance .....................................................................................................................................4-14

4.6 Pedestrian Treatments.........................................................................................................................4-16

4.7 Bicycle Facilities.................................................................................................................................4-20

4.8 Transit Facilities..................................................................................................................................4-22

5.0 TRAFFIC DESIGN AND ILLUMINATION..............................................................................................5-3 

5.1 Traffic Signal Phasing...........................................................................................................................5-3

5.2 Vehicle and Pedestrian Displays.........................................................................................................5-13

5.3 Traffic Signal Pole Layout ..................................................................................................................5-20

5.4 Traffic Signal Controller and Cabinet.................................................................................................5-21

5.5 Detection Devices ...............................................................................................................................5-22

5.6 Traffic Signal Control Type ................................................................................................................5-25

5.7 Basic Signal Timing Parameters.........................................................................................................5-25

5.8 Signing and Pavement Marking Design..............................................................................................5-31

5.9 Illumination Design.............................................................................................................................5-34

6.0 SAFETY ANALYSIS METHODS ...............................................................................................................6-3 

6.1 Qualitative Approach ............................................................................................................................6-4

6.2 Quantitative Approach ..........................................................................................................................6-6

6.3 Network Screening or Selection of an Intersection...............................................................................6-6

6.4 Diagnosis.............................................................................................................................................6-14

6.5 Selecting Countermeasures.................................................................................................................6-27

6.6 Economic Appraisal............................................................................................................................6-32

6.7 Project Prioritization ...........................................................................................................................6-35

6.8 Safety Effectiveness Evaluation..........................................................................................................6-37

7.0 OPERATIONAL ANALYSIS METHODS .................................................................................................7-2 

7.1 Operational Performance Measures ......................................................................................................7-5

7.2 Traffic Operations Elements ...............................................................................................................7-11

7.3 General Considerations Sizing an Intersection....................................................................................7-13

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7.4 Critical Lane Analysis.........................................................................................................................7-14

7.5 HCM Operational Procedure for Signalized Intersections..................................................................7-17

7.6 Arterial and Network Signal Timing Models......................................................................................7-18

7.7 Microscopic Simulation Models .........................................................................................................7-19

7.8 Operational Performance Model Selection .........................................................................................7-20

8.0 SYSTEM-WIDE TREATMENTS................................................................................................................8-3 

8.1 Median Treatments................................................................................................................................8-3

8.2 Access Management............................................................................................................................8-13

8.3 Signal Coordination ............................................................................................................................8-22

8.4 Signal Preemption and/or Priority.......................................................................................................8-25

9.0 INTERSECTION-WIDE TREATMENTS..................................................................................................9-3 

9.1 Pedestrian Treatments...........................................................................................................................9-3

9.2 Bicycle Treatments..............................................................................................................................9-18

9.3 Transit Treatments ..............................................................................................................................9-21

9.4 Traffic Control Treatments..................................................................................................................9-23

9.5 Street Lighting and Illumination .........................................................................................................9-32

9.6 Remove Traffic Signal ........................................................................................................................9-35

10.0 APPROACH TREATMENTS....................................................................................................................10-2 

10.1 Signal Head Placement and Visibility.................................................................................................10-2

10.2 Signing and Speed Control Treatments.............................................................................................10-12

10.3 Roadway Surface Improvements.......................................................................................................10-14

10.4 Sight Distance Treatments ................................................................................................................10-20

10.5 Dilemma Zone Detection ..................................................................................................................10-23

10.6 Red Light Camera Enforcement........................................................................................................10-25

11.0 INDIVIDUAL MOVEMENT TREATMENTS.........................................................................................11-3 

11.1 Left-Turn Treatments..........................................................................................................................11-3

11.2 Right-Turn Treatments......................................................................................................................11-18

11.3 Variable Lane Use Treatments..........................................................................................................11-36

List of Acronyms......................................................................................................................................................A-1 

Glossary of Terms................................................................................................................................................... G-1 

References ................................................................................................................................................................R-1 

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Chapter 1. Introduction 

CHAPTER 1

INTRODUCTION

TABLE OF CONTENTS

1.0 INTRODUCTION ................................................................................................................ 1-2

1.1 Background ............................................................................................................... 1-2

1.2 Performance Measurement and Asset Management ............................................... 1-6

1.3 Scope of the Guide ................................................................................................... 1-7

1.4 Audience for this Guide............................................................................................. 1-7

1.5 Organization of the Guide ......................................................................................... 1-7

LIST OF EXHIBITS

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

during 2009...................................................................................................................... 1-4

1-2 Vehicle detection by inductive loop (left) and video (right)................................................. 1-5

1-3 Inside a signal controller cabinet ........................................................................................ 1-5

1-4 Signalized intersection with four approaches ..................................................................... 1-7

1-5 Organization of the guide.................................................................................................... 1-8

1-6 List of intersection treatments discussed in this guide. ...................................................... 1-9

Signalized Intersections: Informational Guide 1-1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 1. Introduction 

References to be used throughout 

the Guide include: 

o TRB Highway Capacity 

Manual (2010) 

o FHWA Manual on Uniform 

Traffic Control Devices (2009) 

o AASHTO A Policy on 

Geometric Design of 

Highways and Streets (2011) 

o AASHTO Highway Safety 

Manual (2010) 

o TRB NCHRP Report 500 series 

o FHWA Alternative 

Intersections and 

Interchanges Informational 

Report (2010) 

o U.S. Access Board Draft Public 

Rights-of-Way Accessibility 

Guidelines (2011) 

o U.S. Access Board ADAAG 

Requirements for Detectable 

Warnings (2008) 

o U.S. Access Board ADA 

Standards for Accessible 

Design (2010) 

o FHWA Traffic Signal Timing 

Manual (2008) 

o FHWA Traffic Detector 

Handbook (2006) 

o ITE Traffic Control Devices 

Handbook (2011) 

o IESNA American National 

Standard Practice for 

Roadway Lighting (2005) 

1.0 INTRODUCTION

This document serves as an introduction to and guide for

evaluating the safety, design, and operations of signalized

intersections. It also provides tools to deliver better balanced

solutions for all users. The treatments in this guide range from lowcost measures such as improvements to signal timing and signing,

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 (e.g., motorists, pedestrians,

bicyclists, and transit users). When applying operational or safety

treatments, it is often necessary to consider the impact one will

have on the other. This guide will introduce the user to these

trade-offs and their respective considerations.

Practitioners will find the tools and information necessary to

make insightful intersection assessments and to understand the

impacts of potential improvement measures. The information in

this guide 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 and other countries.

Additional resources and references are mentioned for the 

practitioner who wishes to learn more about a particular subject.

This guide does not replicate or replace traditional traffic

engineering documents such as the Manual on Uniform Traffic

Control Devices (MUTCD),

(1) the Highway Capacity Manual (HCM)

2010 (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 best

practices and treatments intended to help practitioners make 

informed, thoughtful decisions.

1.1 BACKGROUND

Traffic Signal Basics

Traffic signals are electrically operated traffic control devices

that provide indication for roadway users to advance their travels

by assigning right-of-way to each approach and movement. Traffic

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

agencies to address roadway operations and safety issues. They

allow the shared use of road space by separating conflicting 

movements in time and allocating delay, and can be used to

enhance the mobility and safety of some movements.

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Chapter 1. Introduction 

Consider the installation of traffic signals when attempting to obtain any of the following:

• Optimization of travel delay

• Reduction of crash frequency and/or severity

• Prioritization of specific roadway user type or movement (such as pedestrians or left turn

movements)

• Accommodation of a new intersection approach or increase in traffic volumes (such as

the addition of an approach at a new development)

Analysis of traffic volume data, crash history, roadway geometry, and other field conditions

are the determining factors when deciding upon the installation of traffic signals. Planners,

designers, and traffic engineers work together to determine if conditions are right for installation.

Several safety and mobility factors should be considered as new traffic signal installation is being

discussed. Chapter 4C of the MUTCD outlines basic warrants for when installation of a traffic

signal may be justified. In addition to the considerations presented in the MUTCD, practitioners

should give thought to roadway/intersection geometry and sight distance, driver expectancy, and 

the locations of other nearby traffic signals when considering the installation of new traffic signals.

When weighing the options for traffic control types at an intersection, consider the following

important factors:

• The design and operation of traffic signals will require choosing elements that may lead

to trade-offs in safety and mobility.

• It is possible to lower the overall crash severity at intersections with traffic signals, but

increase the crash frequency. Table 14-7 of the 2010 Highway Safety Manual illustrates

the effects of converting a stop controlled intersection to a signalized intersection.

• There will be ongoing operational costs attributed to the maintenance of signal equipment

and costs for electrical power.

Once installed, the traffic engineers and field traffic signal technicians who operate and

maintain the traffic signals should regularly perform site visits to:

• Ensure that safety and mobility targets for the intersection are being met, and make

adjustments to signal timings, if necessary, to meet the targets;

• Inspect corresponding intersection signing and pavement markings to ensure they

properly convey the intended instructions to roadway users;

• Log site visit findings for use when making adjustments or recommendations for change;

and

• Communicate traffic signal maintenance and repair needs to field technicians.

Ideally, field traffic signal technicians are qualified to perform maintenance inspections at

regular intervals. Repairs are made such that the signal operates safely and efficiently at all

times. Technicians are also responsible for the general upkeep and operation of signal

equipment located at the intersection.

An agency will identify that a traffic signal needs upgrades, replacement or decommission at

some point during its life. Degradation of equipment, new technology, or changing conditions at

the site, such as lane additions or the need for alternate phasing, may necessitate an upgrade or

full replacement. In some instances, the traffic signal may be completely removed if traffic

patterns cease to warrant its use.

Signalized Intersections: Informational Guide 1-3
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 1. Introduction 

Traffic Operations: Safety and Mobility

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

Research has shown that the proper installation and operation of traffic signals can reduce the

severity of crashes. However, unnecessary or inappropriately designed signals can adversely

affect traffic, safety, and mobility. Care in their placement, design, and operation is essential.

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

changing demands, one element may need to be sacrificed to achieve improvements in the other.

In all cases, it is important to understand the degree to which traffic signals are providing mobility

and safety for all roadway users.

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, while maintaining a high level of safety.

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.”(4)

Exhibit 1-1 shows that in 2009, 21 percent of all crashes and 24 percent of all fatalities and

injury collisions occurred at signalized intersections.

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

in the United States during 2009.

Total Crashes Fatalities/Injuries

Number Percent Number Percent

Non-Intersection Crashes 3.295,000 60 841,027 54

Signalized Intersection Crashes 1,158,000 21 372,299 24

Non-Signalized Intersection Crashes 1,052,000 19 332,471 22

Total 5,505,000 100 1,547,797 100

Source: Adapted from table 29 of Traffic Safety Facts 2009.(5)

How a Traffic Signal Works

Traffic signals are designed to allow for the safe and efficient passage of road users when

demand exists. Types of traffic signal operation include pre-timed, semi-actuated, fully-actuated,

hybrid, adaptive, or traffic responsive. Pre-timed signals give right-of-way to movements based

on a predetermined allocation of time. Semi-actuated signals use various detection methods to

identify roadway users on the minor approaches, while fully-actuated signals recognize users on 

all approaches. Chapter 5 discusses each of these methods in further detail.

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Chapter 1. Introduction 

In addition to the signal heads seen by the road users, signalized intersections may include

additional components, such as loop detectors and video detection equipment. The following

paragraphs provide information related to each component.

Exhibit 1-2. Vehicle detection by inductive loop (left) and video (right)

(Source: Left: South Carolina DOT / Right: Jeff Shaw, FHWA)

Detection.

Semi- and fully actuated signals use various methods to detect road users. Detection 

methods for motorists include in-pavement loop detectors or sensors (Exhibit 1-2 (left)) and 

cameras mounted to signal poles (Exhibit 1-2 (right)). Detection methods for pedestrians and

bicyclists include push buttons and weight sensors.

Traffic signal controller.

Each detection method sends vehicle presence information to a traffic signal controller. The 

controller acts as the “brain” of the traffic signal, changing signal indications based on 

programmed instructions. The controller will determine when the indication for the approach will

change and how much time will be given to each 

movement. A controller is shown in Exhibit 1-3.

Traffic control algorithms determine the priority and

length of time of each approach movement. These

algorithms are tailored to the needs of each intersection, 

based on historical user demand, crash history, and other

roadway network considerations.

Signal heads.

Traffic signal heads inform roadway users of when

their movement can proceed through the intersection.

Signal heads for motorists and bicyclists are usually

mounted on mast arms or span wires above the travel

lane, and are sometimes repeated on the signal pole.

Pedestrian signal heads are often installed on the traffic

signal pole, or independently on separate poles

depending on the intersection design. Signal heads vary

in configuration, shape, and size depending on the 

movement for which they are used. Exhibit 1-3. Inside a signal controller

cabinet. 

Photo Credit: Missouri DOT

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Chapter 1. Introduction 

Types of Signalized Intersections

In their most common form, signalized intersections have indications for users on each

intersection approach. Exhibit 1-4, below, shows a basic signalized intersection with four vehicle

approaches and two pedestrian approaches.

In addition to signalizing intersections, it may be necessary to consider the use of pedestrian

signals at locations along a corridor with high concentrations of pedestrians. This type of traffic

control can be used at signalized intersections with the addition of pedestrian push-buttons and

signal heads, or at non-signalized locations that have high volumes of pedestrians crossing. This 

guide also provides direction on the use of treatments such as the Pedestrian Hybrid Beacon. 

Pedestrian signals are discussed in more detail in Chapter 5.

1.2 PERFORMANCE MEASUREMENT AND ASSET MANAGEMENT

Agencies face the challenge of providing outstanding customer service with limited

resources. Performance measures allow practitioners to assess the effectiveness of a signalized

intersection or corridor. These measures can help agencies more effectively allocate resources.

Travel performance criteria include: stopped delay, travel speed, arrivals on red, and excessive

queuing. Safety performance criteria include crash frequency, crash types, and severity. Traffic 

signal maintenance data could be categorized according to time of day or types of repair. Over

time, practitioners and agencies can refine or adjust these measures.

The practitioner should review this data to assess problem areas to correct. Other

information that may be needed includes comments from the practitioner’s annual signal timing

reviews and annual preventive maintenance program. Examples of questions that may arise

from such a review:

• What intersections require monthly visits to fix?

• What types of repetitive repairs are being conducted over a wide number of

intersections?

• Are phasing (or other) changes necessary to reduce the number of crashes?

Practitioners should create queries that identify problematic intersections. These queries can

also identify global intersection treatments that reduce systematic problems. For example, an

agency could choose to install uninterrupted power supply (UPS) units for frequent power

outages. The following information can be utilized to monitor performance:

• Detection failures by type of device.

• Outages due to power surges and outages.

• Customer complaints and complements.

• Emergency personnel comments.

• Frequent equipment hits by errant vehicles.

• Damage by weather events.

• Intermittent issues.

• Number of red failures.

Reviews of these measures should involve traffic engineers, technicians, and operations

personnel to create a culture of continuous improvement.

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Chapter 1. Introduction 

1.3 SCOPE OF THE GUIDE

This 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.

Roundabouts and other alternative intersection designs are not addressed directly in this

document; for more information, please refer to Roundabouts: An Informational Guide, Second

Edition (6) and the FHWA Alternative Intersections/Interchanges Informational Report.

(55)

1.4 AUDIENCE FOR THIS GUIDE

This guide is intended for planners, designers, traffic engineers, operations analysts, and 

signal technicians 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 system users.

• Evaluate operational performance experienced by system users.

• 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 signal technicians, design and traffic engineers,

planners, and decision-makers who:

• Wish to be introduced to basic and intermediate traffic signal concepts.

• 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.

1.5 ORGANIZATION OF THE GUIDE

This guide is arranged in three parts:

• Part I: Fundamentals.

• Part II: Project Process and Analysis

Methods.

• Part III: Treatments.

Part I (Chapters 2-5) provides key

background information on three topic areas:

user needs, data collection, signal warrants,

geometric design, and traffic design and illumination. These chapters provide a foundation of

knowledge of signalized intersections useful as a learning tool for entry-level engineers and as a

refresher for more experienced engineers. Parts II and III reference the information in these 

chapters.

Part II (Chapters 6-7) describes project process and analysis methods. These chapters

outline the steps that should be carried out and the tools to consider for evaluating the safety and

operational performance of an intersection and determining geometric and timing needs.

Exhibit 1-4. Signalized intersection with four

approaches.

Source: FHWA

Signalized Intersections: Informational Guide 1-7
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 1. Introduction 

Part III (Chapters 8-11) provides a description of treatments that can be applied to mitigate a

known safety or operational deficiency. The treatments are organized by chapter, based on the

intersection element. 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).

Exhibit 1-5 depicts the organization of the guide.

Exhibit 1-5. Organization of the guide.

Part Chapter

1

Title

Introduction

Part I: Fundamentals 2

3

4

5

User Needs

Data Collection and Warrants

Geometric Design

Traffic Design and Illumination

Part II: Project Process and

Analysis Methods

6

7

Safety Analysis Methods

Operational Analysis Methods

Part III: Treatments 8

9

10

11

System-Wide Treatments

Intersection-Wide Treatments

Approach Treatments

Individual Movement Treatments

Exhibit 1-6 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 the following:

• Key design elements;

• Operational and safety impacts;

• Impacts on other modes;

• Socioeconomic and physical impacts; and

• Education, enforcement, and maintenance issues.

The treatments in Exhibit 1-6 represent some, but not all, possible treatments.

Signalized Intersections: Informational Guide 1-8 
 

 

 

 

 

 

 

Chapter 1. Introduction 

Exhibit 1-6. List of intersection treatments discussed in this guide.

.

Treatment Type Treatments

System-Wide 

Treatments

(Chapter 8)

• Median treatments

• Access management

• Provide signal coordination

• Provide signal preemption/priority

• Reduce curb radius

• Provide curb extensions

• Provide bicycle box (experimental)

• Provide bike lanes

Intersection-Wide 

Treatments

(Chapter 9)

• Modify stop line location

• Improve pedestrian signal

display

• Modify pedestrian signal

phasing

• Grade separate pedestrian

movements

• High visibility crosswalks

• Relocate transit stop

• Change signal control from pre-timed to

actuated 

• Modify change and clearance intervals

• Modify cycle length

• Remove late night/early morning flash

• Provide or upgrade illumination

• Convert signalized intersection to a

roundabout or all-way stop control.

Approach Treatments

(Chapter 10)

• Convert to over-the-road

signal heads

• Add supplemental signal

heads

• Increase size of signal

heads

• Increase number of signal

heads

• Provide backplates

• Provide advance warning

• Improve lane use and street name signing

• Reduce operating speed

• Improve pavement surface

• Improve cross section

• Remove obstacles from clear zone

• Improve sight lines

• Provide dilemma zone protection

• Provide red light camera enforcement

Individual Movement

Treatments

(Chapter 11)

• Add single left-turn lane

• Add multiple left-turn lane

• Add channelizing islands

• Add single right-turn lane

• Provide double right-turn

lanes

• Restrict turns, U-turns

• Provide auxiliary through lane

• Delineate through path

• Provide reversible lane

• Provide variable lane use assignments

Signalized Intersections: Informational Guide 1-9 
 

 

 

 

 

 

Part I

Fundamentals

Part I discusses the fundamentals of signalized intersections as they relate to Human Factors

(Chapter 2), Data Collection and Warrants (Chapter 3), Geometric Design (Chapter 4), and Traffic

Signal Design and Illumination (Chapter 5). 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.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

CHAPTER 2

Human Factors

TABLE OF CONTENTS

2.0 HUMAN FACTORS............................................................................................................. 2-2

2.1 Overview of Human Factors ..................................................................................... 2-2

2.1.1 Positive Guidance ........................................................................................ 2-4

2.1.2 Roadway Safety Fundamentals ................................................................... 2-4

2.2 Intersection Users ..................................................................................................... 2-5

2.2.1 Human Factors Common to All Road Users................................................ 2-5

2.2.2 Motorists....................................................................................................... 2-9

2.2.3 Bicyclists .................................................................................................... 2-13

2.2.4 Pedestrians ................................................................................................ 2-17

2.3 Applying Human Factors......................................................................................... 2-22

LIST OF EXHIBITS

2-1 Signs confused with background information. .................................................................... 2-6

2-2 Example of sign clutter. ...................................................................................................... 2-6

2-3 Fatal two-vehicle intersection crashes by traffic control device and driver age ................. 2-8

2-4 Estimated number of registered vehicles by type, 2010................................................... 2-10

2-5 Fatalities by mode, 2009................................................................................................... 2-11

2-6 Injuries by mode, 2009 ..................................................................................................... 2-11

2-7 Proportion of crashes by collision type at signalized intersections................................... 2-11

2-8 Enforcement cameras, as shown in the photo above, are used at signalized intersections

to identify red light runners ............................................................................................ 2-12

2-9 Typical dimensions of a bicyclist....................................................................................... 2-15

2-10 Bicyclist conflicts at signalized intersections .................................................................... 2-17

2-11 Examples of pedestrians of various abilities preparing to cross an intersection .............. 2-18

2-12 Typical dimensions for a sample of types of pedestrians................................................. 2-19

2-13 Typical dimensions for a turning wheelchair..................................................................... 2-19

2-14 Crosswalks are used by a variety of users with different speed characteristics .............. 2-20

2-15 Pedestrian conflicts at signalized intersections ................................................................ 2-21

Signalized Intersections: Informational Guide 2-1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

2.0 HUMAN FACTORS

This chapter describes road user needs at and around signalized intersections. The 

description is based on three assumptions:

• Practitioners should 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 involving one or more road user types.

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

performance in the pursuit of informed and balanced decision-making.

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

intersection users. This chapter provides an introduction to human factors research, 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.

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 surroundings. The

goals of human factors analysis in road transportation are to:

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

characteristics of road users.

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

• Capitalize on this knowledge through improvements in engineering design and 

operations.

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

safety and mobility requires a systems-oriented and human-centered approach. A systems

approach helps capture the dynamic interaction between the road user and the roadway

environment. It 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 decision-makers—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 respective capabilities

under a broad range of circumstances.

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

• Anticipating how road users may react to specific situations to increase the likelihood of

predictable, timely, accurate, and correct responses, thus avoiding situations that violate

road users’ expectations.

• Designing and applying conspicuous, legible, comprehensible, and credible traffic control

devices that provide sufficient time to respond in an appropriate manner.

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

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

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Chapter 2. Human Factors 

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

pedestrians. Each road user group includes multiple user types. For example, motorists include

passenger car, commercial truck, bus, and motorcycle operators. Bicyclists include recreational

and commuting bicyclists with a wide range of ages and abilities. Pedestrians include all age 

groups (children, adults, elderly). Some pedestrians may also have cognitive, mobility, or vision 

impairments. Practitioners should account for road users’ abilities and characteristics when

designing an intersection.

At the most basic level, signalized intersections sequence the right-of-way between 

intersecting streams of road 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. Signalized 

intersections are often located on primary routes leading to commercial activities, which may

involve motor carriers and other heavy vehicles. Intersections also serve as public right-of-way

and include space for public utilities such as power and communication lines; water, sewage, and 

storm drainage pipes; and traffic signs and signal equipment.

Each category of road user has different needs when traversing an intersection. Motorists

and bicyclists must detect the intersection on the 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.

The Americans with Disabilities Act (ADA) of 1990 prohibits discrimination and ensures equal

opportunity and access for persons with disabilities.

(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, such as motorized and non-motorized wheelchairs, guide dogs,

walkers, and walking canes, and may have multiple impairments. ADA standards were updated 

in 2012 and serve as guidelines for the design and management of accessible facilities, not public

rights-of-way.

The Proposed Accessibility Guidelines for Pedestrian Facilities in the Public Right-of-Way (54)

was developed specifically for pedestrian facilities in the public right-of-way. It addresses

conditions and constraints in the public right-of-way. The requirements in the proposed guidelines

make allowances for typical roadway geometry and permit flexibility in alterations to existing 

facilities where existing physical constraints make it impractical to fully comply with new

construction requirements. The proposed guidelines also include requirements for elements and

facilities that exist only in the public right-of-way, such as pedestrian signals and roundabouts.

(8)

While these guidelines are proposed and not legal standards, they do represent best practice. In 

some cases, State and local agencies have adopted policies and standards equal to or more 

stringent than those presented in the proposed guidelines.

Road users can only process a limited amount of information. The pace at which vehicle

drivers and bicyclists encounter information increases with travel speed. The number of choices

facing drivers and bicyclists at any one time should be minimized. The information presented 

should be concise, complete, explicit, and located sufficiently in advance of the choice point to

allow for a comfortable response.

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Chapter 2. Human Factors 

2.1.1 Positive Guidance

In the 1980s, FHWA’s Office of Human Factors developed 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.(9)

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 positive guidance concepts are 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: providing drivers with all of the information

they need, in a format they can readily read, interpret and apply, and in sufficient time to react

appropriately, reduces the chances of driver error and improves relative safety. 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 correct driver expectations and restructure incorrect driver expectations. They must

provide the information necessary to support rapid decision-making 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 competition

for driver attention by information irrelevant to driving-related tasks can exceed drivers’

information-processing limitations. This may have a negative impact on traffic 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 suggests 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. However, 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 Fundamentals

In the past, roads were considered to be “safe” if they were designed, built, operated, and

maintained in accordance with nominal standards of the day. 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 do not just “happen,” they are “caused,”

and the roadway environment sometimes 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.(10) More recently, AASHTO published the Highway Safety

Manual (HSM). The HSM provides tools to practitioners to conduct quantitative safety, allowing 

Signalized Intersections: Informational Guide 2-4 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

for safety to be quantitatively evaluated alongside other transportation performance measures

such as traffic operations, environmental impacts, and construction costs in project planning and

development decision-making.

(11)

By addressing the environmental and situational elements that contribute to the occurrence of

driver error, the forgiving roadway seeks to break the chain of causation between the erroneous

decisions and/or actions and their undesirable outcomes (e.g., crashes). The forgiving 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 and in sufficient time to react. Implicit in the forgiving

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.

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

deal with 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

perception-reaction times. The following section discusses human factors 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. The 

following sections discuss each of these factors.

Human Vision

Road users who are not visually impaired 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.(12) This means that information searches and the

reading of long messages are carried out during a series of glances rather than with one long 

look. Complex or cluttered backgrounds, such as those shown in Exhibits 2-1 and 2-2, 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 2-5 
 

 

Chapter 2. Human Factors 

Exhibit 2-1. Signs confused with background information.

Exhibit 2-2. Example of sign clutter.

Signalized Intersections: Informational Guide 2-6 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

Information Processing and Memory

Road users perform best under moderate levels of demand. Information 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.(13) 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.

Humans have limited short-term memory. Only a small percentage of what they see is

actually remembered, including information presentations viewed while driving, bicycling, or

walking. Long-term memory is made up of experiences ingrained through repetition. These are 

the source of our expectations, which 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.

In addition to expectations, road users recognize and use patterns 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

and in time to perceive and react to it in an appropriate manner.

User Error

Information presentations must be conspicuous, legible, readable at a glance, and explicit as

to their meaning. A study cited in the NCHRP 600 Human Factors Guidelines (153) refers to an 

increase in both the number of glances and duration of each glance as the length of a message 

increases, while the retention of the information

significantly decreases for messages longer than 

The risk of user error tends eight characters. Uniformity and consistency are

paramount. For example, drivers must receive the to increase when needed

information: same clues and information in similar situations so 

that their expectations will be consistent with reality, • Is missing or

or their expectations will be restructured accordingly. incomplete. The presentations must be located in advance to • Is difficult to locate, provide time to react, and they must be spaced—both 

read, or interpret. from each other and from other competing sources of

information—so as not to confuse or overload the • Lacks credibility.

road user. • Leads to false 

Drivers in particular often have difficulties expectations.

following through the sequence of driving tasks, which • Provides insufficient 

leads to driving errors. The most common driving time for decision and

errors include improper lookout (faulty visual appropriate action.

surveillance), inattention, false assumption, excessive

speed, improper maneuvers, improper evasive action,

and internal distraction.(14)

Signalized Intersections: Informational Guide 2-7 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

Bicyclists 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 (e.g., violations by other road users, emergency vehicles traveling 

through red light).

• Inappropriate inputs (e.g., extraneous or conflicting signage).

• The shedding of important information when overloaded.

• Stress, frustration, inexperience, fatigue, intoxication.

• Imperfect decision-making.

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, bicyclists, 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.(15)

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.(15) 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 leftturn against oncoming

traffic. As shown in Exhibit

2-3, fatal crash 

involvement is much

higher at signalized

intersections for drivers

less than 20 years old and 

more than 70 years old.

Exhibit 2-3. Fatal two-vehicle intersection crashes by traffic

control device and driver age 

Source: NHTSA, Intersection Crashes among Drivers in Their

60s, 70s, and 80s, 2011.

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Chapter 2. Human Factors 

As one ages, specific functions related to the driving task may deteriorate, such as vision,

depth perception, hearing, sensation, and cognitive and motor abilities. Decreased 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 as drivers

and pedestrians).

• Following pavement markings.

• Responding to traffic signals.

Young drivers aged 16 to 24 have a higher risk (2.5 times) of being involved in a collision

compared to other drivers.

(16) Young pedestrians (i.e., pedestrians under the age of 12) also have 

a higher risk of being in a collision. These younger road users may:

• Have difficulty 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

• Fix their eyes on an object for longer periods.

• Have difficulty integrating information.

• Be easily distracted by unrelated events (e.g. cell phone use, texting, and using GPS).

• 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

254 million licensed vehicles in the United States.(17) Traffic engineers have traditionally sought to

design and operate intersections with a 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.

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., teenage drivers, older drivers, and aggressive drivers).

Most drivers traveling through signalized intersections will be operating passenger vehicles.

These may be cars, minivans, pickups, or sport utility vehicles (SUVs). A total of 6,763 people

died in intersection-related motor vehicle crashes in 2010. These deaths occurred in 2,415

crashes involving 4,471 motor vehicles.(18) However, commercial vehicles (tractor-trailers, singleunit trucks, and cargo vans) account for more than their share of fatal collisions, based on fatal

crash rates per mile.(19) These vehicles need to be properly accommodated at intersections.

Signalized Intersections: Informational Guide 2-9 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

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 to

consider.

Exhibit 2-4 identifies general characteristics of vehicle types, and Exhibits 2-5 and 2-6 show

the frequency of fatalities and injuries by mode, respectively. 

Exhibit 2-4. Estimated number of registered vehicles by type, 2010

Percent of 

Vehicle Type Number of Registered Vehicles Total

Light duty vehicle, short wheel base 190,202,782 76

Motorcycle * 8,212,267 3

Light duty vehicle, long wheel base 40,241,658 16

Truck, single-unit 2-axle 6-tire or

more ** 8,217,189 3

Truck, combination 2,552,865 1

Bus 846,051 < 1

Total 250,272,812

*The new category Light duty vehicle, short wheel base replaces the old category Passenger car

and includes passenger cars, light trucks, vans and sport utility vehicles with a wheelbase (WB)

equal to or less than 121 inches.

**The new category Light duty vehicle, long wheel base replaces Other 2-axle, 4-tire vehicle and 

includes large passenger cars, vans, pickup trucks, and sport/utility vehicles with wheelbases

(WB) larger than 121 inches.

Source: Bureau of Transportation Statistics, 2010.

(17)

Signalized Intersections: Informational Guide 2-10 
 

 

 

Exhibit 2-7. Proportion of crashes by collision type at four-leg signalized intersections.

(Excerpted from Highway Safety Manual (2010), Table 10-6)

 

 

 

 

 

 

Chapter 2. Human Factors 

Exhibit 2-5. Fatalities by mode,

2009. 

Source: Bureau of Transportation 

Statistics, 2009.

Exhibit 2-6. Injuries by mode, 2009.

Source: Bureau of Transportation 

Statistics, 2009.

Collision Type Percent

Head on 5

Sideswipe 12

Rear end 43

Angle 27

Ran Off Road 6

Bicycle/Pedestrian <1

Other 6

TOTAL 100

As shown in Exhibit 2-7, the most frequently occurring collision is a rear-end crash, which

represents 43 percent of all reported intersection crashes in the database.

States commonly include strategies targeting signalized intersections in their Strategic

Highway Safety Plans (SHSP) spanning engineering, enforcement, and educational

opportunities.

Signalized Intersections: Informational Guide 2-11 

55%

4%

34% 

1%

<1%

3%

2%

<1%

Injuries by Mode, 

2009 

Passenger

Cars

Motorcycles

Truck, Light

Truck, Large

Bus Occupants

Pedestrians

39% 

13% 

1%

<1%

12%

2% 2%

Fatalities by Mode, 

2009 

Passenger

Cars

Motorcycles

30%

Truck, Light

Truck, Large

Bus Occupants

Pedestrians
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

The engineering improvements may include:

• Reduce frequency and severity of intersection conflicts through traffic control and

operational improvements.

• Reduce frequency and severity of intersection conflicts through geometric improvements.

• Improve sight distance at signalized intersections.

• Improve driver awareness of intersections and signal control.

• Improve driver compliance with traffic control devices.

• Improve access management near signalized intersections.

• Improve drainage in intersection and on approaches.

(21)

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. 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.

According to the National Highway Traffic Safety Administration’s Traffic Safety Facts 2008

Report, there were 762 deaths and 165,000 persons injured by red-light running.(22) A study of

Highway Safety Information System (HSIS data) determined that red light runners cause 16 to 20 

percent of all collisions at signalized intersections.(23)

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 shown in Exhibit 2-8.

Exhibit 2-8. Enforcement cameras, as shown in the photo above, are used at signalized 

intersections to identify red light runners.

Source: Brian Chandler

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Chapter 2. Human Factors 

Driver Distraction

Despite the complexity of the driving task, drivers commonly engage 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. An estimated 16 percent of fatal crashes in 2009 involved reports

of distracted driving.

(24) Drivers involved in collisions at intersections were more likely to report

that they “looked but didn’t see.” According to a 2010 NHTSA report, 32 percent of drivers

involved in collisions between 2005 and 2007 were distracted by the following sources:

(25)

• Conversing with a passenger (15.9%).

• Cell phone use/texting (3.4%).

• Other objects within the vehicle (3.2%).

• The actions of other occupants (3.0%).

• Retrieving objects from the floor/seat (2.0%).

• Eating or drinking (1.7%).

• Adjusting the radio/CD player (1.2%).

• Retrieving objects from another location (0.7%).

• Smoking (0.5%).

• Reading map/directions/newspaper (0.4%).

• Adjusting other vehicle controls (0.3%).

• Talking on a CB radio (0.2%).

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 bicycling. Given the increases in traffic

congestion over the past few decades, particularly in urban areas, the number of people using

bicycles to commute to work is on the rise.(26)

Bicyclists have unique needs at signalized intersections. Bicyclists are particularly vulnerable

because they share the roadway with motorists and are required to follow the same rules of the

road, yet they do not possess comparable 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 motor 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.

To accomplish this, planning for bicycle use, whether existing or potential, should be integrated 

into the overall transportation planning process.(26)

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.

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Chapter 2. Human Factors 

Bicycle Users

Bicyclists range widely in terms of skills, experience, and preferences. An FHWA report 

defined the following general categories (A, B, and C) of bicycle user types (27):

• “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 well-defined

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

Although the physical width of a bicycle is approximately 30 inches, the forward movement of

bicyclists requires a minimum operating width of 4 ft and a preferred operating width of 5 ft to 

accommodate the natural side-to-side movement that varies with speed, wind, and bicyclist

proficiency.

(28) In addition, because most bicyclists ride a distance of 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. Where drain inlets are unavoidable, their drainage slots should not run parallel

to the direction of travel, as this 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.

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Chapter 2. Human Factors 

Exhibit 2-9. Typical dimensions of a bicyclist.

Source: AASHTO, Guide for the Development of Bicycle Facilities, 4th Edition, 2012.

• Width – The minimum operating width of 4 ft, sufficient to accommodate forward

movement by most bicyclists, is greater than the physical width momentarily occupied by

a rider because of natural side-to-side movement that varies with speed, wind, and

bicyclist proficiency. Additional operating width may be needed in some situations, such

as on steep grades, and the figure does not include shy distances from parallel objects

such as railings, tunnel walls, curbs, or parked cars. In some situations where speed

differentials between bicyclists and other road users are relatively small, bicyclists may

accept smaller shy distances.

• Height – The operating height of 8.3 ft can accommodate an adult bicyclist standing

upright on the pedals.(26)

The Danish Road Directorate identifies key elements to incorporate in the planning of cycling

facilities:

• Accessible and coherent. The bicycle 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 bicycle network is not direct, logical, and easy to use, some

bicyclists will choose roads not planned for bicycle traffic.

• Safe and secure. Adequate visibility and curve radii should make it possible for bicyclists

to travel safely at a minimum of 15 mph. Parked cars, vegetation, barriers, etc. can result

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Chapter 2. Human Factors 

in poor or reduced visibility. Awareness of the 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 bicyclists 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.(29)

Bicycle Safety

In 2009, 630 bicyclists were killed and 51,000 injured in motor vehicle traffic crashes.(30),(31)

Bicyclist deaths accounted for 2 percent of all motor vehicle traffic fatalities and made up 2 

percent of all the people injured in traffic crashes during the year. 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.(32) 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 three 

common crash types that occur at intersections:(33)

• Motorist left turn facing the bicyclist.

• Bicyclist left turn in front of a motorist.

• Bicyclist ride-out from a stop sign or flashing red signal.

Exhibit 2-10 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 additional

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 bicyclists 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

Exhibit 2-10. As the size of the intersection increases, the difficulty for bicyclists to weave to the 

left turn lane can be daunting for Category B and even some Category A bicyclists.

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Chapter 2. Human Factors 

Exhibit 2-10. Bicyclist conflicts at signalized intersections.

From 2005-2009, 1,357 bicycle fatalities occurred at intersections on American roads,

according to the Fatality Analysis Reporting System (FARS) database maintained by NHTSA, 

with 564 of the fatalities occurring at signalized intersections. Intersection-related fatalities are far

more common on urban rather than rural roads, and during daylight instead of after dark.

FARS data indicated that 15 percent of all bicycle collisions occur at signalized intersections.

In 2010, FARS cited that 30 percent of police-reported collisions between bicyclists and motorists

occurring at intersections take place within the pedestrian crosswalk.

2.2.4 Pedestrians

Walking is the oldest and most basic form of transportation. Nearly every trip includes a

walking element. According to the 2009 Nationwide Personal Transportation Survey, 10.4 percent

of all daily trips occurred via the walk mode.

(34) 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. There has also been an increase in nonmotorized travel due to successful ongoing public health campaigns that encourage people to

walk in lieu of motorized commuter 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 Exhibit 2-11. The design of intersection facilities should accommodate all types of

pedestrians, because the user cannot be anticipated.

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Chapter 2. Human Factors 

Exhibit 2-11. 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 18 by 24 

inches.(35) 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. Exhibit 2-12 shows dimensions for

various types of pedestrians.

The Americans with Disabilities Act Accessibility Guidelines (ADAAG) specifies a 60-inch

square area to allow a wheelchair user to make a 180-degree turn (Exhibit 2-13).(32) For parallel

approaches, ADAAG specifies a minimum low-side reach of 9 inches and a maximum high-side 

reach of 54 inches. For a forward approach, ADAAG specifies a minimum low-reach point of 15

inches and a maximum high-reach point of 48 inches.

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Minimum width

Operating width

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 2. Human Factors 

Exhibit 2-12. Typical dimensions for a sample of types of pedestrians.

User and Characteristic

Pedestrian (walking)

Width

Dimension

1.6 ft

Affected Intersection Features

Sidewalk width, crosswalk width

Wheelchair

2.5 ft

3.0 ft

Sidewalk width, crosswalk

width, ramp landing areas

Person pushing stroller

Length 5.6 ft Median island width at

crosswalk

Skaters

Typical operating width 6 ft Sidewalk width

Source: (6), as adapted from (28).

Exhibit 2-13. Typical dimensions for a turning wheelchair.

Source: U.S. Department of Justice, ADA Standards for Accessible Design (ADAAG). 2010.

Pedestrian Characteristics

Pedestrian walking speeds generally range between 2.5 to 6.0 ft/s.(3) The MUTCD (Page 497

Sect. 4E.06-07, Paragraph 7) uses a walking speed of 3.5 ft/s for determining crossing times.

(1)

However, FHWA pedestrian design guidance recommends a lower speed 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.(37),(38) The HCM

2010 indicates that if elderly persons constitute more than 20 percent of the total pedestrians, the 

average walking speed decreases to 3.0 ft/s.(39)

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Chapter 2. Human Factors 

Exhibit 2-14. Crosswalks are used by a variety of users with different speed characteristics.

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.

(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

Exhibit 2-15 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.

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Chapter 2. Human Factors 

Exhibit 2-15. Pedestrian conflicts at signalized intersections.

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

motorists’ view of each other, thus putting the pedestrian at greater risk. This type of conflict may

occur at signalized intersections in the following situations:

• Double right-turn movements. These take the form of either two exclusive right-turn 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

Pedestrian safety 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. In 2009 there were 4,092 pedestrian 

fatalities involved in motor vehicle crashes, which represents 12 percent of all the 33,808 motor

vehicle deaths.

(29)

An estimated 59,000 pedestrians were injured in motor vehicle collisions during

this period.

(29)

Of all crashes between single vehicles and pedestrians in 2009, 1,063 (26 percent) occurred

at intersections (both signalized and unsignalized).(18) Speed plays a major role in motoristpedestrian collisions, particularly fatalities; a pedestrian struck at 40 mph has an 85 percent

chance of being killed, at 30 mph the probability of fatality is 45 percent, and at 20 mph the

probability of fatality drops to 5 percent.(39) Compounding the problem, motorists rarely stop to

yield to a pedestrian when their speeds are greater than 45 mph; they are likely to stop when their

speeds are less than 20 mph.(40)

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

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Chapter 2. Human Factors 

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 (40) error.

The time required for a driver to detect a pedestrian, decelerate, and come to a complete 

stop is frequently underestimated or not even considered as part of the geometric design of an 

intersection. AASHTO’s A Policy on Geometric Design of Highways and Streets states that a

brake reaction time of 2.5 seconds is considered adequate for determining stopping sight

distance.(3) Additional research has suggested that the value of 2.5s has limitations and 

represents nearly ideal conditions with younger, alert drivers.(41) 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.(40) 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.”(40)

Accessibility for pedestrians is also a key element. The ADA of 1990 mandates, among other

things, that transportation facilities be accessible to meet the diverse functional needs of people

with disabilities.

(7) This requires that new or altered facilities be designed to allow pedestrians with

access and functional needs to identify the crossing location, access the pushbutton, know when

to cross, and know where to cross. The ADAAG published by the U.S. Access Board in 1991 

identifies minimum design standards that must be applied to all new construction or alteration 

projects to adequately accommodate people with disabilities.(36) Accommodation of all users’

needs should 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 reduce road user error 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 decision-making 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.

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Chapter 2. Human Factors 

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.

• All road users must have a clear presentation of the intersection on approach, or be

appropriately forewarned by traffic control devices.

• Adequate visibility 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 the MUTCD.(1)

• Phasing and change 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.

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Chapter 3. Data Collection and Warrants 

CHAPTER 3

Data Collection and Warrants

TABLE OF CONTENTS

3.0 DATA COLLECTION AND WARRANTS

3.1 Commitment.............................................................................................................. 3-2

3.2 Where Do You Start? Importance of an Engineering Analysis and Study............... 3-2

3.3 Intersection Data Collection Needed ........................................................................ 3-2

3.4 Intersection Counts ................................................................................................... 3-2

3.4.1 What is a Typical Day?.................................................................................... 3-3

3.4.2 Procedures for Future Intersections................................................................ 3-3

3.4.3 Vehicle Classification ...................................................................................... 3-4

3.4.4 Pedestrians ..................................................................................................... 3-4

3.4.5 Bicyclists.......................................................................................................... 3-5

3.4.6 Speed Study of Each Approach ...................................................................... 3-5

3.4.7 Knowledge of the Region ................................................................................ 3-5

3.5 Traffic Signal Warrants ............................................................................................. 3-6

3.5.1 What do the Warrants Constitute?.................................................................. 3-6

3.5.2 Volume Warrants............................................................................................. 3-6

Warrant 1: Eight-Hour Vehicular Volume..................................................... 3-6

Warrant 2: Four-Hour Volume...................................................................... 3-6

Warrant 3: Peak Hour Volume..................................................................... 3-6

3.5.3 Specialty Conditions........................................................................................ 3-7

Warrant 4: Pedestrian Volume..................................................................... 3-7

Warrant 5: School Crossing ......................................................................... 3-7

Warrant 6: Coordinated Signal System ....................................................... 3-7

Warrant 7: Crash Experience....................................................................... 3-7

Warrant 8: Roadway Network ...................................................................... 3-8

Warrant 9: Intersection near a Grade Crossing ........................................... 3-8

3.6 When is Not Signalizing an Intersection the Right Decision?................................... 3-9

LIST OF EXHIBITS

3-1 Automated intersection count station.................................................................................. 3-3

3-2 Pedestrians crossing at a signal......................................................................................... 3-4

3-3 Pennsylvania Avenue, Washington, DC............................................................................. 3-5

3-4 Pennsylvania Avenue, Washington, DC............................................................................. 3-5

3-5 Warrant 9: intersection near a Grade Crossing .................................................................. 3-8

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Chapter 3. Data Collection and Warrants 

3.0 DATA COLLECTION AND WARRANTS

3.1 COMMITMENT

When an agency decides to install a signal, they make a long-term investment of resources

at a specific point on the transportation network. Signals require consistent care throughout their

life. For example, agencies must respond to emergency repairs such as power outages; adjust

timing due to changing traffic patterns; replace outdated equipment as the state of technology

changes; and monitor safety performance for all users.

3.2 WHERE DO YOU START? IMPORTANCE OF AN ENGINEERING ANALYSIS 

AND STUDY

When evaluating changes to intersection traffic control, engineers can refer to a wide range

of research and best practices. Some examples are the ITE Traffic Engineer’s Handbook, State

DOT MUTCD manuals, and the Minnesota DOT Intersection Control Evaluation (ICE).

(43)

Engineers should keep in mind that signalizing an intersection has broad implications for the 

transportation network, both positive and potentially negative. For example:

• Signalizing an intersection can eliminate barriers to pedestrians created by arterials

bisecting adjacent neighborhoods.

• Signals can attract drivers away from unintended by-pass routes that were previously

used to avoid busy unsignalized intersections.

• Signals can reduce, but not eliminate, right angle crashes.

• Signals can significantly increase rear end crashes.

3.3 INTERSECTION DATA COLLECTION NEEDED

Studying an intersection requires a basic set of information. This list of information is not an

exclusive list (e.g., in some cases detecting a horse in an Amish community is needed).

However, the vast majority of intersections will require most of the items on this list:

• Number and turning movement of vehicles.

• Physical roadway attributes (e.g., number of lanes, approach grade).

• Vehicles’ classification, especially specialty vehicles (e.g., school buses).

• Number of pedestrians.

• Number of bicyclists.

• Speed study of each approach.

• Knowledge of the region, such as surrounding development (e.g., large specific traffic

generators).

• Location of transit stops and facilities.

• Most importantly, field observations of peak hours.

3.4 INTERSECTION COUNTS

Easily the most important piece of information that is needed to study an intersection is traffic

count data. Reviewing the count is a starting point to understanding how traffic ebbs and flows

throughout the day. An intersection count should cover 12 hours of a typical day and should be

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Chapter 3. Data Collection and Warrants 

conducted in 15-minute intervals. Counts typically occur manually or with automated count

stations (see Exhibit 3-1). From the count, the engineer can easily start to see what movements

are critical to the overall operation of the intersection.

3.4.1 What is a Typical Day?

Knowledge of the area may alter what is considered a “typical” day. A large recreational area

or shopping area may require a weekend count. Recent advances in counting technology, such

as automated intersection counting stations, make it easier to evaluate weekdays, weekends,

holidays, and special events, and to perform counts longer than a standard, manual 12-hour

count.

Exhibit 3-1. Automated intersection count station.

Source: Traffic Technology Today

http://www.traffictechnologytoday.com/news.php?NewsID=39788

3.4.2 Procedures for Future Intersections

Some agencies have enacted procedures to estimate traffic volumes for future intersections.

Traffic impact studies commonly require estimated traffic volumes, typically completed using the 

guidelines found in the ITE Trip Generation Manual.(42) The practitioner should be able to 

generate the number of trips resulting from the proposed development. These trips are 

distributed over the street network to determine future traffic patterns. An engineer must be

comfortable that actual traffic volume will be sufficient to require a traffic signal. Some planning

agencies use traffic planning software to estimate future traffic patterns on the network. The 

MUTCD recommends evaluating the intersection after a year to be sure the initial assumptions

were correct.

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Chapter 3. Data Collection and Warrants 

3.4.3 Vehicle Classification

Practitioners must also consider the expected types of vehicles when designing a signalized

intersection. Intersection counts should capture this information. Examples of various vehicle

combinations that should be counted or noted are:

• Tractor-trailer units in either single or combination trailers.

• City transit and tour buses.

• School buses.

• Large recreational vehicles in single or combination units.

• Emergency vehicles (e.g., ladder trucks).

Practitioners should note any vehicles larger than a WB-50 truck and their frequency of

occurrence. These vehicles’ large turning radius, long start up time, and safety impacts can

affect intersection design. In some cases, larger vehicles can be calculated into Passenger Car

Equivalents (PCEs) to account for their additional impacts on the system.

In addition, practitioners may adjust type and location of detection, timing parameter settings, 

and target lengths of turn lanes and auxiliary lanes to accommodate the queue needs of these 

larger vehicles.

3.4.4 Pedestrians

Pedestrians are the most vulnerable class of roadway users. Counting pedestrians is the first

step to ensuring their needs are incorporated into the signal design and operations. This

information is necessary to help practitioners develop signal timing and design pedestrian cross

walks and refuge islands. Practitioners should also consider the environment in which an 

intersection is located. An area lacking in sidewalks may still have pedestrians to be

accommodated at an intersection. This information can be collected during the intersection

counts and should include the size of pedestrian groups, their frequency, and their walking speed.

Exhibit 3-2. Pedestrians crossing at a signal

Source: PBIC Image Library Alpena, Michigan, Dan Burden, 2006.

http://www.pedbikeimages.org/pubdetail.cfm?picid=1019

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Chapter 3. Data Collection and Warrants 

3.4.5 Bicyclists

Practitioners can also capture bicyclists’

information during intersection counts.

Bicyclists using crosswalks should be

included in the pedestrian count.

3.4.6 Speed Study of Each 

Approach

ITE recommended practices for

calculating clearance intervals requires

assessing approach speeds. ITE

recommends using the 85th and 15th

percentile speeds for this purpose.

Practitioners should also perform a “spot

speed” survey for each approach. These 

surveys can be done manually using radar

or automatically using counting technology.

This information is also used to determine

dilemma zone concerns.

(44)

3.4.7 Knowledge of the Region

Warrant analysis covers the basic

reasons for installing a signal; however, a signal should also support the overall function of a

regional transportation network. Signalized intersections offer the most benefits when installed at

major street junctions. Signals should almost always enhance through movements of any major

street while balancing access to minor streets and pedestrians. Practitioners should be aware 

that many mid-size cities and counties have identified key intersections in their long range 

transportation plan. These planning documents are often a small part of a larger planning effort 

that combines both transportation engineering and a vision for the community’s future. Signals

can also support completing connections between large industrial sites, mixed use developments,

schools, and emergency services.

Exhibit 3-3. Pennsylvania Ave., Washington, DC

Source: Google

Exhibit 3-4. Pennsylvania Ave., Washington, DC

Source: Matthew Myers, 2011

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Chapter 3. Data Collection and Warrants 

3.5 TRAFFIC SIGNAL WARRANTS

Practitioners perform engineering studies of planned signalized intersections to predict their

immediate and future impacts. The basis of every engineering study concerning signals is the set

of warrants found in the MUTCD. The warrants are part of the basic principles in the MUTCD

that govern the design and use of traffic control devices. In addition, Code of Federal

Regulations (CFR) 655.603 adopts the MUTCD as the National standard for all traffic control

devices installed on any street, highway, bikeway, or private road open to public travel (see 

definition in Section 1A.13). When a State or Federal agency manual or supplement is required,

that manual or supplement shall be in substantial conformance with the National MUTCD.

3.5.1 What Do the Warrants Constitute?

The warrants represent the basic areas an engineer’s analysis should cover: intersections

where users have difficulty maneuvering through the intersection due to high mainline volumes;

drivers trying to cross streets with inadequate gaps; and pedestrians trying to cross large 

expanses of pavement.

3.5.2 Volume Warrants

Warrant 1: Eight-Hour Vehicular Volume

Warrant 1, the Eight-Hour Vehicular Volume Warrant, is one of the most widely used and

familiar warrants. It is a count of the number of entering vehicles at an intersection in an 8-hour

period. The practitioner will review the operations of a “typical” day at the intersection. Overall,

satisfying this warrant indicates that a signal can be a reasonable investment towards improving

the overall efficiency and safety of the intersection.

The engineer will find two conditions under this warrant. The warrant is satisfied when one of

the conditions is met. Condition A indicates that the total number of entering vehicles from every

approach causes undue delay, and condition B is satisfied when an imbalance occurs between

the major and minor route, causing undue delay to motorists entering from minor roads.

This warrant should cause the practitioner to ask “What is the typical day or week for this

intersection?” For example, high-use recreational areas, such as a lake or shopping mall, are

different than a city arterial serving large subdivisions.

Right-turning Vehicles. One question often asked by practitioners is, “How should we count

right turning vehicle traffic?” Many times this movement is unimpeded and does not contribute to 

the approach delay or other operational deficiencies of the intersection. The engineer, through

their judgment, may subtract the volume of right-turning vehicles from the warrant analysis,

especially those turning from the side street. Practitioners should consult the policies of the local

governing agency responsible for the intersection for possible details concerning right-turning 

vehicles.

Left-turning Vehicles – Major Approach. In some cases, major approach left turns may queue

past the available storage and reduce the capacity of the approach. In this situation the engineer

should consider using a heavy left turn off of the major approach to satisfy the minor approach 

volume. This is an example in which engineering judgment is necessary throughout a warrant

analysis to determine if signalizing an intersection will improve the overall operations and safety

of the intersection.

Warrant 2: Four-Hour Volume and Warrant 3: Peak Hour Volume

Both of these warrants address unusually high, short duration side street traffic volumes.

Practitioners should take care when using these warrants. Many types of businesses generate

these volumes at any given time. In most cases, this would not constitute justification for installing

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Chapter 3. Data Collection and Warrants 

a signal. In fact, some agencies place additional emphasis on making sure these warrants are

used sparingly compared to Warrant 1.

3.5.3 Specialty Conditions

Warrant 4: Pedestrian Volume

This warrant is similar in application to the previous warrants. The data necessary are major

street traffic volume and pedestrian volume, and the warrant is satisfied either for four hours or a

single peak hour. 

Many regions of the United States have recently placed a higher emphasis on non-motorized

travel. However, many arterials were built to standards that created barriers to non-motorized 

users. Many cities now create networks focused on non-motorized travel. Signalizing 

intersections for pedestrians supports these networks. Agencies and practitioners implement

treatments to improve the pedestrian safety, such as enhanced crosswalks using medians and 

signing. Agencies may also implement other available alternatives to traditional traffic signals,

such as Pedestrian Hybrid Beacons (also known as High Intensity Activated Crosswalks

(HAWKs). Additional information on the Pedestrian Hybrid Beacon is available on the FHWA

Office of Safety website at:

http://safety.fhwa.dot.gov/provencountermeasures/fhwa_sa_12_012.htm.

As more communities focus their efforts on non-motorized travel, facilities more widely

support bicyclists and pedestrians. Bicyclists should be counted as either vehicles or pedestrians

depending on how they enter the intersection. In a community with high bicycle use, practitioners

will likely encounter both at an intersection.

Warrant 5: School Crossing

This warrant is similar to Warrant 4, but deals specifically with school age pedestrians.

Installing a signal can eliminate the barrier created by a busy and wide intersection that

pedestrians find difficult to cross safely. Practitioners are asked to measure the frequency of

adequately sized gaps in traffic flow that permit the average group of school age children cross

the major street. The warrant is met if no gaps occur.

The engineer should be aware of any policies or procedures the agency has in place for 

school crossings, such as requiring an adult crossing guard to supervise the crosswalk. Also,

these signals may “rest” in green for the majority of the day, which can cause issues for drivers

who do not expect them to change. Adding advance signing helps increase drivers’ awareness

when the signal is active during selected hours of the day. Pedestrian hybrid signals, mentioned 

previously, are an alternative to traditional signals. The city of Tucson, Arizona has been

successful with these types of treatments.

Warrant 6: Coordinated Signal System

Practitioners may need to use a signal to platoon traffic flow down a major road, improving

the overall effectiveness of a signalized corridor. The MUTCD warns that this warrant should not

be used if the intersection spacing is less than 1,000 ft. Warrant 6 is not widely used

For signal coordination purposes, the spacing between signals should range from 1⁄4 to 1⁄2 

mile. Signal spacing less than 1,000 ft is difficult to coordinate.

Warrant 7: Crash Experience

Practitioners must analyze the intersection’s crash history as part of the engineering study. 

Many practitioners focus on the threshold listed in this warrant. Signals can provide some safety

benefits under the right situations, but other crash types at the intersection can increase 

dramatically, especially rear end crashes. Often right angle crashes will decrease, but these 

crash types will not be completely eliminated.

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Chapter 3. Data Collection and Warrants 

Information related to assessing the impact of a traffic signal can be found in the following 

resources:

• Highway Safety Manual

• States Strategic Highway Safety Plans

• Crash Modification Factors (CMF) Clearinghouse website

These resources can help practitioners develop a focused, data-driven approach to reducing

the severity of roadway crashes; screening the roadway network for intersections to review;

quantifying safety impacts associated with modifying existing signalized intersections; and/or

establishing the installation of a new signal.

Warrant 8: Roadway Network

An efficient and safe network of transportation options requires significant effort by

metropolitan planning organizations, regional planning commissions, cities, counties, and State

DOTs. Increased travel demand due to regional growth necessitates change. Traffic control at

arterial and other major roadway intersections requires maintaining adequate levels of user

service. These organizations may have conducted preliminary studies to determine which

intersections should be signalized intersections or roundabouts. Practitioners who are evaluating

future traffic impacts due to signals should seek out this information from these organizations. 

Warrant 9: Intersection near a Grade Crossing

Practitioners must ensure that drivers and other road users are able to clear railroad tracks to

prevent any conflicts from approaching trains. The figures used in this warrant offer the 

practitioner guidance and information on factors related to buses, tractor-trailers, and frequency

of trains per day. Figure 4C-9 from the MUTCD is one of the figures related to this warrant. This

warrant addresses any intersection within 140 feet of a railroad track.

Exhibit 3-5. Warrant 9: Intersection near a Grade Crossing.

Source: MUTCD, 2009

Preemption control shall be provided at any signal near railroad tracks installed under this

warrant, and any other signalized intersection that regularly queues traffic onto a set of tracks.

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Chapter 3. Data Collection and Warrants 

3.6 WHEN IS NOT SIGNALIZING AN INTERSECTION THE RIGHT DECISION?

This is one of the perplexing questions a practitioner and the general public may ask. The 

MUTCD acknowledges the importance of engineering judgment. The warrants represent best

practice, but a signal can dramatically change traffic patterns. Signalized intersections should

complement a transportation network, even if it is only an isolated signal. Corridors with closely 

or oddly spaced signals are difficult to time effectively and can cause a premature decline of the

network. 

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Chapter 4. Geometric Design 

CHAPTER 4

GEOMETRIC DESIGN

TABLE OF CONTENTS

4.0 GEOMETRIC DESIGN ....................................................................................................... 4-3

4.1 Number of Intersection Legs..................................................................................... 4-4

4.2 Channelization ......................................................................................................... 4-5

4.3 Horizontal and Vertical Alignment........................................................................... 4-10

4.4 Corner Radius ......................................................................................................... 4-12

4.5 Sight Distance ......................................................................................................... 4-14

4.5.1 Stopping Sight Distance............................................................................. 4-14

4.5.2 Decision Sight Distance ............................................................................. 4-14

4.5.3 Intersection Sight Distance ........................................................................ 4-15

4.6 Pedestrian Treatments............................................................................................ 4-16

4.6.1 Curb Ramp Design .................................................................................... 4-17

4.6.2 Detectable Warning Surfaces .................................................................... 4-20

4.7 Bicycle Facilities...................................................................................................... 4-20

4.8 Transit Facilities ...................................................................................................... 4-22

LIST OF EXHIBITS

4-1 Intersection functional boundaries ...................................................................................... 4-3

4-2 A large corner radius that impacts pedestrian safety ......................................................... 4-3

4-3 Potential conflicts at intersections with three and four legs................................................ 4-4

4-4 Photograph of a six-leg intersection ................................................................................... 4-5

4-5 This raised median restricts left-turn egress movements from a driveway located between

two intersections.............................................................................................................. 4-6

4-6 Single point urban intersection (SPUI) with pavement marking delineation for turning

movements ...................................................................................................................... 4-6

4-7 Various right-turn treatments may be used, depending on the speed environment........... 4-7

4-8 Providing a dedicated left-turn lane reduces potential rear end collisions between

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

and through traffic............................................................................................................ 4-8

4-9 The photo shows how double and triple left-turn lanes can be used to accommodate

high-priority movements .................................................................................................. 4-9

4-10 Pedestrian refuge and bicyclist wayfinding......................................................................... 4-9

4-11 Intersection angle increases both the intersection width and pedestrian crossing

distance ......................................................................................................................... 4-12

4-12 Intersection skew. ............................................................................................................. 4-12

4-13 Design values for stopping sight distance ........................................................................ 4-14

4-14 Design values for decision sight distance for selected avoidance maneuvers ................ 4-15

4-15 A pedestrian grade separation treatment restricts sight distance of the traffic signal as

motorists approach the intersection. ............................................................................. 4-15

4-16 Intersection sight distance ................................................................................................ 4-16

4-17 Curb ramp components. ................................................................................................... 4-18

4-18 Examples of preferred designs ......................................................................................... 4-19

4-19 Examples of acceptable curb ramp designs..................................................................... 4-19

4-20 Examples of designs prohibited by 2010 ADAAG ............................................................ 4-19

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Chapter 4. Geometric Design 

4-21 This crosswalk design incorporates the use of detectable warning surfaces into the curb

ramps to facilitate navigation by a visually impaired pedestrian ................................... 4-20

4-22 MUTCD diagram of right-turn lane bicycle accommodation............................................. 4-21

4-23 Transit facility in Santa Barbara, CA................................................................................. 4-22

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Chapter 4. Geometric Design 

4.0 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 horizontal and vertical dimensions.

Exhibit 4-1 illustrates the functional boundaries of a signalized intersection.

Exhibit 4-1. Intersection functional boundaries.

Source: “Intersection Design Guidelines,” Institute of Transportation Engineers,

http://www.ite.org/css/online/DWUT10.html

Geometric design profoundly influences 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 

impediments, reducing the need for lane changes and merge

maneuvers, and minimizing the required distance to traverse an

intersection all improve intersection safety and operational efficiency.

All possible road users’ (see Chapter 2) needs must be considered

to achieve optimal safety and operational levels at an intersection.

When road user groups’ design objectives conflict, 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. For instance, practitioners may

design corner radii to accommodate large vehicles. However, these

larger radii would be detrimental to pedestrian safety due to the

increase in walking distances and the increase in speed of turning

vehicles. Exhibit 4-2 shows a typical example of this situation.

This chapter addresses the following topics:

• Number of intersection approaches. Source: PBIC Image Library, Dan 

Burden • Principles of channelization.

• Horizontal and vertical alignment.

• Corner return radius access control.

Exhibit 4-2. A large corner radius that

impacts pedestrian safety.

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Chapter 4. Geometric Design 

• Sight distances.

• Pedestrian treatments.

• Curb ramp design.

• Detectable warnings.

• Bicycle facilities.

• Transit facilities.

4.1 NUMBER OF INTERSECTION LEGS

The complexity of an intersection increases as the number of approach legs to the

intersection increases. Exhibit 4-3, below, shows the number and type of conflicts that occur at

intersections with three and four legs, respectively. Exhibit 4-4 shows a complex intersection with

six approach legs. 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.

(a) Three-leg intersection.

(b) Four-leg intersection.

Exhibit 4-3. Potential conflicts at intersections with three and four legs.

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Chapter 4. Geometric Design 

Exhibit 4-4. Photograph of a six-leg intersection.

Source: Google 2012

4.2 CHANNELIZATION

A primary goal of intersection design is to limit and/or reduce the severity of potential road

user conflicts. Basic principles of intersection channelization that can reduce conflicts are 

described below.(45)

1. Discourage undesirable movements. Designers can utilize corner radii, raised

medians, or traffic islands to prevent undesirable or wrong-way movements. Examples

include:

• Restricting left turns from driveways or minor streets based on safety or operational

concerns.

• Designing channelization to discourage wrong way movements onto freeway ramps, oneway streets, or divided roadways.

• Designing approach alignment to facilitate intuitive movements.

Exhibit 4-5 shows how a raised median can be used to restrict undesirable turn movements

within the influence of signalized intersections.

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Chapter 4. Geometric Design 

Exhibit 4-5. This raised median restricts left-turn egress movements from a driveway located 

between two intersections.

Source: Google 2012

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 complex geometry or traffic

patterns such as highly skewed intersections, multi-leg 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 safety and traffic flow at an intersection. Exhibit 4-6 shows how

pavement markings can be applied to delineate travel paths.

Exhibit 4-6. Single point urban intersection (SPUI) with pavement marking delineation for turning 

movements.

Source: Google 2012

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Chapter 4. Geometric Design 

3. Encourage safe speeds through design. 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,

practitioners may want 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 corner radii. On low-speed roadways or

in areas with pedestrians, practitioners may want to promote lower turning speeds. This can

be accomplished with smaller turning radii, narrower lanes, and/or channelization features.

These are illustrated in Exhibit 4-7.

(a) Higher speed design

(b) Lower speed design

Exhibit 4-7. Various right-turn treatments may be used, depending on the speed environment.

Chapter 11 contains information pertaining to individual movements such as right- and leftturn lanes, including details concerning storage, multiple turn lanes, and warrants.

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. Exhibit 4-8 illustrates how the

addition of a left-turn lane can reduce conflicts with through vehicles traveling in the same

direction.

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Chapter 4. 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.

Exhibit 4-8. Providing a dedicated left-turn lane reduces potential rear end collisions between leftturning 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 drivers’ expectations and intersection capacity.

The highest movement volumes at an intersection, define the highest priority movements,

although practitioners may also consider route designations and functional classification of

intersecting roadways. 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. Exhibit 4-9 shows an

intersection where double and triple left-turn lanes are used to facilitate high-volume turning

movements. Information concerning when these treatments are warranted can be found in

Chapter 11.

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Chapter 4. Geometric Design 

Exhibit 4-9. The photo shows how double and triple left-turn lanes can be used to accommodate 

high-priority movements.

Source: Google 2012

6. Facilitate the desired traffic control scheme. The signalized intersection design should

allow the agency to accommodate changing traffic patterns throughout the life of the

intersection. Practitioners should ensure that intersection signs and markings are clearly

understood and support correct driver decisions. Other equipment at the intersection should

not block sight distance and should facilitate preventive maintenance by field personnel.

Practitioners should design for simultaneous left-turning movements and potential u-turning

movements. Operational impacts and the

design of pedestrian facilities should be

taken into account during the intersection’s

design.

7. 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 turning. 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 may

experience lower delay and fewer queues.

Exhibit 4-10. Pedestrian refuge and bicyclist

way finding.

Source: Steven Vance, 2010.

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Chapter 4. Geometric Design 

8. Provide safe refuge and way finding for bicyclists and pedestrians. Intersection

design must consider non-motorist roadway users’ needs. Intersection channelization can

provide refuge and/or reduce the exposure distance for pedestrians and bicyclists within an

intersection without limiting vehicle movement. Practitioners should also consider using

raised medians, traffic islands, and other pedestrian-friendly treatments during the design

process. Way finding may also be an issue, particularly at intersections with complicated

configurations. Practitioners can address this through pavement marking and signing, as

shown in Exhibit 4-10.

In locations where the horizontal or vertical alignment obscures raised or flush channelization

or markings, practitioners may need to extend the limits of channelization or use other methods to 

call the attention of road users. For example, should the limits of raised channelization begin at

the crest of a vertical curve, it should be extended to give motorists ample time to perceive and

react to its presence. In an instance where a right-turn lane taper begins within the outside of a 

horizontal curve, the channelization or marking may be slightly exaggerated to indicate the

presence of the tapered area.

4.3 HORIZONTAL AND VERTICAL ALIGNMENT

The approach to a signalized intersection should promote awareness of the 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.

Drivers’ or bicyclists’ expectations on approaches to an intersection could be violated 

under the following conditions, and mitigation efforts should be considered:

• Approach grades to an intersection of greater than 3 percent.

• Intersections located along a horizontal curve of the intersecting road.

• Intersection tables (including sidewalks) with a cross slope exceeding 2 percent.

The angle of the intersection of two roadways can influence both the safety and operational

characteristics of an intersection. Heavily angled 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 accommodating large vehicle turns. Additional pavement, channelization, and

right-of-way may be required. The increased pavement area poses potential drainage

problems and gives smaller vehicles more opportunity to “wander” from the proper path.

Enhanced pavement marking or color-treated pavement can sometimes address this

issue.

• Vehicles crossing the intersection are more exposed to conflicts. This requires longer

change and clearance intervals and increased lost time, which reduces the capacity of

the intersection.

• Longer pedestrian and bicyclist exposure to vehicular traffic. 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 be more likely 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.(46) Conversely, drivers become more confused as they traverse

curved or angled streets.

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Chapter 4. Geometric Design 

(a) Intersection angle at 90 degrees (i.e., no skew)

Angled intersections tend to have more frequent right-angle type crashes associated with

poor sight distance. AASHTO policy and many State design standards permit angled

intersections between 60 to 90 degrees.(3) NCHRP Report 500, Volume 12 (Signalized

Intersections) recommends 75 degrees or greater to avoid the issues related older drivers,

turning right on red, and judging gaps for left-turn maneuvers.

Gattis and Low conducted research to identify constraints on the angle of a left-skewed 

intersection as it is affected by a vehicle body limiting a driver’s line-of-sight to the right.(47) 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.(15)

Practitioners should strive to design approaches to intersect at or near right angles. Exhibit 4-11

shows how an angled intersection approach can increase the distance to clear the intersection for

pedestrians and vehicles.

(b) Intersection angle at 75 degrees (i.e., 15-degree skew)

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Chapter 4. Geometric Design 

(c) Intersection angle at 60 degrees (i.e., 30-degree skew).

Exhibit 4-11. Intersection angle increases both the intersection width and pedestrian crossing 

distance.

It should be noted that the intersection angle and intersection skew, by definition, are 

complimentary angles. The HSM shows that intersection skew is measured from orthogonal, as

shown in Exhibit 4-12.

Exhibit 4-12. Intersection skew.

4.4 CORNER RADIUS

Appropriately designed intersection corners accommodate all users. Practitioners should

select corner radii and curb ramp design based upon pedestrian crossing and design vehicle

needs at the intersection. In general, pedestrian crossings should be 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 for more efficient operation of the signal. It

also aids visually impaired pedestrians in their way finding task by eliminating changes in

direction that may not be detectable.

Practitioners should design corner radii to accommodate the turning path of a design vehicle

to avoid encroaching on pedestrian facilities and opposing lanes of travel. Section 4.6.1

addresses curb ramp design in greater detail.

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Chapter 4. Geometric Design 

Larger intersection curb radii have disadvantages for pedestrians. Larger radii increase

pedestrian crossing distance and the speeds of turning vehicles, creating increased exposure 

risks. This can be particularly challenging for pedestrians with impaired vision. Large radii also

reduce the corner storage space for pedestrians, move pedestrians out of the driver’s line of

sight, and make it more difficult for pedestrians to see vehicles. On the other hand, smaller radii

limit the speeds of turning vehicles and may reduce the operational efficiency of an arterial

intersection. A curb that protrudes into the turning radius of the design vehicle can cause vehicles

to drive over and damage the curb, as well as increase the potential of hitting a pedestrian 

standing at the curb.(48)

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. This can be represented as a standard

passenger car, motor home, single-unit truck, bus or semi-trailer. The AASHTO Green

Book describes representative design vehicles parameters. Practitioners should select an

appropriate design vehicle based on the existing and anticipated type of use and the

tradeoffs involved with design and spatial impact, and with input from stakeholders and

the public. They should select the largest class of vehicle that uses the facility on a

regular as the design vehicle. It should represent a cost-effective choice for the project

and be appropriate for its context. Use of the facility by the design vehicle should be both

a measurable (i.e., over 0.5 percent) and reasonably predictable percentage of the

average daily traffic.(49) Often, agency policy will mandate a design vehicle, regardless of

vehicle mix. In certain instances, more than one design vehicle may be appropriate,

depending on traffic patterns. There may be instances where it is necessary to consider

flush radii instead of raised curbs. By incorporating flush radii, vehicles with large turning

radii can be accommodated without modifications to curbed sections. However, not all

situations are ideal for flush radii; practitioners should consider the volume and type of

non-motorized transportation and locations of intersection infrastructure.

• Angle of intersection. Large intersection skew angles necessitate non-matching corner

radii, as well as very large or very small radii to accommodate the skew.

• 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. Multi-centered curves or simple curves with tangent offsets may better

match the turn path of the design vehicle and reduce required right-of-way. Additional

pavement may be added to either curbed or flush radii to serve as a truck apron.

• Encroachment. A designer must consider whether a turning vehicle's wheel path or

swept path should encroach into adjacent lanes (same direction), flush islands that

separate traffic, or even into opposing lanes. This concept is important in both right- and

left-turn maneuvers. The curb return radii imposed on raised median islands may affect

the ability to maintain speed and safely make left turns for motorists leaving or arriving at

the approach. Traffic signal infrastructure located within the radius of a right turn

maneuver may be damaged due to encroaching vehicles.

• Intersection size. Corner radius influences the overall width of the intersection. While

larger radii allow for use by vehicles with larger turning radii, it may increase the crossing

distance for pedestrians and lengthen overall intersection delay.

4.5 SIGHT DISTANCE

Drivers’ 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

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Chapter 4. Geometric Design 

intersections. It is imperative that drivers be given sufficient distance to perceive, recognize, and

react to the presence of traffic control elements such as traffic signal indications, pavement

markings, and signing, in addition to the possibility of queued vehicles and the need to maneuver

into auxiliary lanes prior to the intersection.

4.5.1 Stopping Sight Distance

Stopping sight distance is the roadway distance 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. Designers

should provide sufficient stopping sight distance to road users throughout the intersection and on

each entering and exiting approach. Exhibit 4-13 gives recommended stopping sight distances for

design, as computed from the equations provided in the AASHTO policy.(3)

Exhibit 4-13. Design values for stopping sight distance.

Computed

Distance*

(m)

Design

Distance

(m)

Computed

Distance*

(ft)

Design

Distance

(ft)

Speed

(km/h)

Speed

(mph)

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, 11.2 ft/s2 (3.4 m/s2) driver deceleration

Source: American Association of State Highway and Transportation Officials (AASHTO). A

Policy on Geometric Design of Highways and Streets. Washington, DC: AASHTO, 2011.

Practitioners should calculate stopping sight distance using an assumed height of driver’s eye

of 3.5 ft and an assumed height of object of 2.0 ft.(3)

4.5.2 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 applies to 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. Exhibit 4-14 gives recommended 

values for decision sight distance, as computed from equations in the AASHTO policy.(3)

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Chapter 4. Geometric Design 

Exhibit 4-14. Design values for decision sight distance for selected avoidance maneuvers.

U.S. Customary (ft)

Speed

(mph) A B C D E

30 220 490 450 535 620

35 275 590 525 625 720

40 330 690 600 715 825

45 395 800 675 800 930

50 465 910 750 890 1030

55 535 1030 865 980 1135

60 610 1150 990 1125 1280

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: American Association of State Highway and Transportation Officials (AASHTO). A Policy on Geometric Design of

Highways and Streets. Washington, DC: AASHTO, 2011.

4.5.3 Intersection Sight Distance and Line of Sight

The distance drivers without right-of-way at signalized intersections require to perceive and 

react to the presence of traffic signal indications, conflicting vehicles, and pedestrians is the

intersection sight distance. Horizontal and vertical sight distance must also be maintained such

that roadway users have an adequate line-of-sight to traffic control elements as they approach

the intersection. Any overhead structure could cause a sight obstruction to nearby traffic signal

heads. Practitioners should take care to design the structure and/or modify traffic control devices

such that overhead structures do not obstruct approaching road users’ view of traffic signals (and

other elements like signing). Exhibit 4-15 shows an example where an overhead walkway

obstructs the line-of-sight approaching a signalized intersection.

Exhibit 4-15. A pedestrian grade separation treatment restricts sight distance of the traffic signal

as motorists approach the intersection.

Source: Synectics Transportation Consultants, Inc.

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Chapter 4. Geometric Design 

Practitioners should refer to the AASHTO Green Book for a complete discussion of

intersection sight distance requirements.(3) Intersection sight distance at signalized intersections

is generally simpler than at 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.

• Right turns on red should satisfy the case for a stop-controlled right turn from the minor

road.

However, the sight distance needed for stop-controlled intersections should always be

maintained for signalized intersections in the event that traffic signals are installed to flash for

emergency situations or during instances of power failure where the traffic signal indications are

dark.

Intersection sight distance is traditionally measured through the determination of a sight

triangle. This triangle is bound 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 3.5 ft and an

assumed object height of 3.5 ft.(3) The area within the triangle is referred to as the sight triangle,

and any object at a height above the elevation of the adjacent roadways that would obstruct the

driver’s view should be removed or lowered, if practical. Such objects may include buildings,

parked vehicles, highway structures, roadside hardware, hedges, trees, bushes, un-mowed

grass, tall crops, walls, fences, and terrain itself. Exhibit 4-16 illustrates intersection sight

distance triangles that should be designed and maintained for all signalized intersections.

Exhibit 4-16. Intersection sight distance.

Source: Modified from the American Association of State Highway and Transportation Officials

(AASHTO) publication Policy on Geometric Design of Highway and Streets, 5th Edition, 2004.

4.6 PEDESTRIAN TREATMENTS

It is the policy of the USDOT to “incorporate safe and convenient walking and bicycling 

facilities into transportation projects,” which is accomplished by working with State and local

agencies that receive Federal-aid funding to plan, design and implement these features.

(197)

Furthermore, in 2008, the FHWA Office of Safety included walkways on its list of Proven Safety

Countermeasures, recognizing their significant safety benefits.

(198) Therefore, practitioners should

provide for pedestrian facilities at all intersections in urban and suburban areas, and at any

intersection with known or expected pedestrian activity. This is especially important for signalized 

intersections, since additional equipment is needed to accommodate pedestrians.

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Chapter 4. Geometric Design 

In general, practitioners should design the pedestrian facilities of an intersection with the 

most challenged users in mind, those pedestrians with mobility or visual impairments. The 

resulting design will serve all pedestrians well. The Proposed Accessibility Guidelines for

Pedestrian Facilities in the Public Right-of-Way provides technical requirements and advisory

information pertaining to the design, construction, and alteration of facilities such that they are

made accessible to and usable by individuals with disabilities. The guidelines take into

consideration three laws that require newly constructed and altered facilities to be accessible to

individuals with disabilities: the Americans with Disabilities Act, Section 504 of the Rehabilitation

Act, and the Architectural Barriers Act.(54) Therefore, providing pedestrian facilities that are 

accessible is not merely a matter of best practice, it is also the law.

Pedestrians may face a number of disincentives to walking, including centers and services

located far apart, physical barriers and interruptions along pedestrian routes, perceptions that

routes are unsafe due to motor vehicle conflicts or crime, and esthetically unpleasing routes.

(50)

Certain key elements of pedestrian facilities that practitioners should incorporate into their

design are listed and described below:(Adapted from 51)

• Pedestrian route. Ensure the routes and crossings are free of barriers, obstacles, and

hazards. Ensure curb ramps, transit stops (where applicable), equipment such as

pushbuttons, etc., are well located and meet accessibility standards.

• Exposure to traffic. Clearly indicate where crossings should occur and the actions

pedestrians are expected to take at crossing locations. Limit exposure to conflicting traffic

by minimizing the crossing distance as much as practical, ensure the crosswalk is a

direct continuation of the pedestrian’s travel path and provide refuges where

advantageous.

• Roadside features. Provide a separation buffer between the nearest vehicular travel

lane and the pedestrian route. Keep corners free of obstructions to provide enough room

for pedestrians waiting to cross. Design corner radii to ensure that vehicles do not

encroach into pedestrian areas.

• Visibility and conspicuity. Strive to design facilities so that pedestrians and traffic are

mutually visible by maintaining adequate lines of sight between drivers and pedestrians,

especially at crosswalks. When intersection lighting is provided, arrange the lighting to

achieve positive contrast of pedestrians.

• Level of service. Provide appropriate and regular intervals for crossings and minimize

wait time for pedestrians.

4.6.1 Curb Ramp Design

Curb ramps provide access for people who use wheelchairs and scooters. Curb ramps also

help people with strollers, luggage, bicycles, and other wheeled objects negotiate the intersection.

The basic components of a curb ramp, including ramp, landing, detectable warning, flare, and 

approach, are diagrammed in Exhibit 4-17. The Proposed Accessibility Guidelines for Pedestrian

Facilities in the Public Right-of-Way reflects the technical requirements for curb ramps as stated 

in the ADA and ABA Accessibility Guidelines (ADAAG). The ADAAG requires that curb ramps be 

provided wherever an pedestrian route crosses a curb, which includes crosswalks at new and

retrofitted signalized intersections.(36) While curb ramps increase access for mobility-impaired

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 (DWS) placed at the bottom of the ramp, which provides information 

on the boundary between the sidewalk and roadway. More information about DWS can be found 

later in this chapter.

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Chapter 4. Geometric Design 

Exhibit 4-17. Curb ramp components

The AADAG provides designers with Survey Form 4: Curb Ramps to help in development of

accessible curb ramps that meet the requirements of the AADAG, available at http://www.accessboard.gov/adaag/checklist/CurbRamps.html. Designers may also use FHWA’s Designing

Sidewalks and Trails for Access, Part 2: Best Practices Design Guide, as a source of

recommended fundamental practices for curb ramp design, along with the rationale behind each 

practice.(37) A designer can apply these principles in designing intersections in a wide variety of

circumstances.

Exhibits 4-18, 4-19, and 4-20 provide 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.(37)

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Chapter 4. Geometric Design 

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.

Exhibit 4-18. Examples of preferred designs.

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 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 48 inch clear space.

e. Two built-up curb ramps.

f. Partially built-up curb ramps.

Exhibit 4-19. Examples of acceptable curb ramp designs.

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.

Exhibit 4-20. Examples of designs prohibited.

Source: Reproduced from Report No. FHWA-EP-01-127, table 7-2 

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Chapter 4. Geometric Design 

4.6.2 Detectable Warning Surfaces

ADAAG and PROWAG require that a detectable warning surface (DWS) be provided at the 

bottom of 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 so they

can determine where the pedestrian route crosses traffic.(33) Detectible warning surfaces consist

of a pattern 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. They also provide 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 Exhibit 4-21. The U.S. Access Board and FHWA

encourage the use of the design pattern and application found in the 2011 PROWAG.

24” 

Exhibit 4-21. This crosswalk design incorporates the use of detectable warning surfaces into 

the curb ramps to facilitate navigation by a visually impaired pedestrian.

Source: Lee Rodegerdts, 2003

4.7 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 bicyclists 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. Widths

are typically 4 ft when curb and gutter are not present and 5 feet when the lane is

adjacent to parking, from the face of the curb or guardrail.

(26)

• Left turn bike lanes.

• Median refuges with a width to accommodate a bicycle: 6 ft = poor; 8 ft = satisfactory; 10

ft = good.(26, p. 52)

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Chapter 4. Geometric Design 

The interaction between motor vehicles and bicyclists at interchanges with merge and 

diverge areas is especially complex. Some signalized intersections also have merge and diverge

areas due to free right turns or diverted movements. 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.”(26)

Exhibit 4-22. MUTCD diagram of right-turn lane bicycle accommodation

Source: 2009 MUTCD, Figure 9C-4.

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Chapter 4. Geometric Design 

4.8 TRANSIT FACILITIES

Transit facilities near intersections are

commonplace in urbanized areas and

occur in some rural areas. The placement

of the bus stop can impact the safety and

operational performance of the intersection.

A discussion of transit facilities is included

in Section 9.3 of Chapter 9, IntersectionWide Treatments.

Exhibit 4-23. Transit facility in Santa Barbara, CA

Source: PBIC Image Library, Dan Burden, 2006

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Chapter 5. Traffic Signal Design and Illumination 

CHAPTER 5

TRAFFIC SIGNAL DESIGN AND ILLUMINATION

TABLE OF CONTENTS

5.0 TRAFFIC DESIGN AND ILLUMINATION........................................................................... 5-3

5.1 Traffic Signal Phasing ............................................................................................... 5-3

5.1.1 “Permissive-Only” Left-Turn Phasing........................................................... 5-4

5.1.2 “Protected-Only” Left-Turn Phasing............................................................. 5-6

5.1.3 Protected-Permissive Left-Turn Phasing ..................................................... 5-7

5.1.4 Split Phasing .............................................................................................. 5-11

5.1.5 Prohibited Left-Turn Movements................................................................ 5-12

5.1.6 Right-Turn Phasing .................................................................................... 5-12

5.2 Vehicle and Pedestrian Displays ............................................................................ 5-13

5.2.1 Vehicle Displays......................................................................................... 5-13

5.2.2 Pedestrian Displays ................................................................................... 5-17

5.2.3 Pedestrian Hybrid Beacons ....................................................................... 5-18

5.3 Traffic Signal Pole Layout ....................................................................................... 5-20

5.4 Traffic Signal Controller and Cabinet...................................................................... 5-21

5.4.1 Physical Location of Equipment................................................................. 5-21

5.5 Detection Devices ................................................................................................... 5-22

5.5.1 Vehicle Detection ....................................................................................... 5-22

5.5.2 Pedestrian Detection.................................................................................. 5-24

5.6 Traffic Signal Control Type ..................................................................................... 5-25

5.7 Basic Signal Timing Parameters............................................................................. 5-25

5.7.1 Vehicle Timing—Green Interval................................................................. 5-26

5.7.2 Vehicle Timing—Detector Inputs ............................................................... 5-27

5.7.3 Vehicle Timing—Vehicle Clearance........................................................... 5-29

5.7.4 Pedestrian Timing ...................................................................................... 5-29

5.7.5 Vehicle Timing—Cycle Length................................................................... 5-31

5.8 Signing and Pavement Marking Design.................................................................. 5-31

5.9 Illumination Design.................................................................................................. 5-34

5.9.1 Illuminance................................................................................................. 5-35

5.9.2 Veiling Illuminance ..................................................................................... 5-35

LIST OF EXHIBITS

5-1 Standard NEMA ring-and-barrier structure......................................................................... 5-4

5-7 Possible signal head and signing arrangement for protected-permissive left-turn phasing5-8

5-15 Advantages and disadvantages of various configurations for displaying vehicle signal

5-2 Typical phasing diagram for “permissive-only” left-turn phasing ........................................ 5-5

5-3 Possible signal head arrangements for “permissive-only” left-turn phasing....................... 5-6

5-4 Typical phasing diagram for “protected-only” left-turn phasing .......................................... 5-7

5-5 Possible signal head arrangements for “protected-only” left-turn phasing......................... 5-7

5-6 Typical phasing diagram for protected-permissive left-turn phasing.................................. 5-8

5-8 Illustration of the yellow trap ............................................................................................. 5-10

5-9 Common signal head arrangement for split phasing........................................................ 5-12

5-10 Typical phasing diagram illustrating a right-turn overlap .................................................. 5-13

5-11 Examples showing five optional signal head locations..................................................... 5-15

5-12 Pedestrian signal indications ............................................................................................ 5-18

5-13 Pedestrian hybrid beacon ................................................................................................. 5-19

5-14 Sequence for a PHB ......................................................................................................... 5-19

indications...................................................................................................................... 5-20

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Chapter 5. Traffic Signal Design and Illumination 

5-16 Location of advanced vehicle detectors ........................................................................... 5-23

5-17 Illustration of maximum green functionality ...................................................................... 5-27

5-18 Illustration of variable initial feature .................................................................................. 5-28

5-19 Pedestrian intervals .......................................................................................................... 5-30

5-20 Example of advance street name sign for two closely spaced intersections.................... 5-32

5-21 Example of signing for a left-hand lane drop .................................................................... 5-32

5-22 Example of advance overhead signs and pavement markings indicating lane use for

various destinations....................................................................................................... 5-33

5-23 Example of pavement legends indicating destination route numbers

(“horizontal signing”)...................................................................................................... 5-34

5-24 Recommended illuminance for the intersection of continuously lighted urban streets..... 5-36

5-25 RP-8-00 guidance for roadway and pedestrian/area classification for purposes of

determining intersection illumination levels ................................................................... 5-37

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Chapter 5. Traffic Signal Design and Illumination 

5.0 TRAFFIC SIGNAL DESIGN AND ILLUMINATION

This chapter addresses traffic signal hardware and software—the infrastructure that controls

the assignment of right-of-way for all intersection users, including vehicles, pedestrians,

emergency vehicles, transit operators, trucks, and light-rail transit vehicles 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 signal 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.

5.1 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 many intersections in the United States makes use of a standard National

Electrical Manufacturers Association (NEMA) ring-and-barrier structure, shown in Exhibit 5-1. 

This structure organizes phases to prohibit conflicting movements (e.g., eastbound and 

southbound through movements) from timing concurrently, while allowing non-conflicting

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.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-1. Standard NEMA ring-and-barrier structure.

Depending on the complexity of the intersection, two to eight phases are typically used,

although most controllers provide far more 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 and pedestrians

and provides no special protected interval for left turns. As a general rule, practitioners should

keep the number of phases to a minimum because each additional phase in the signal cycle

reduces the time available to other phases, and each phase has its own startup delay time.

Provision of a separate left-turn lane, while not required, is recommended when providing a 

separate left-turn phase. Left-turn lanes increase operational efficiency by providing storage

space where vehicles can await an adequate gap without blocking other traffic movements at the

intersection. Left-turn lanes also increase the safety of an intersection by reducing rear-end and 

left-turn crashes. In most cases, the development of a signal phasing plan should involve an

engineering 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.

Practitioners must consider all intersection users during the development of a phasing plan,

including pedestrians, bicyclists, transit vehicles, older drivers, and children. 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. The presence of older pedestrians or

children may require a longer pedestrian clearance interval based on their slower walking speeds.

5.1.1 “Permissive-Only” Left-Turn Phasing

“Permissive-only” (also called “permitted-only”) phasing allows two opposing approaches to

time concurrently, with left turns allowed after motorists yield to conflicting traffic and pedestrians.

Exhibit 5-2 illustrates one possible implementation of this phasing pattern. Note that the two

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Chapter 5. Traffic Signal Design and Illumination 

opposing movements could be run in concurrent phases using two rings; for example, the

eastbound and westbound through movements shown in Exhibit 5-2 could be assigned as phase

2 and phase 6, respectively.

Exhibit 5-2. 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 because safety will be compromised in such situations, 

including left-turn safety. Minor side street movements, however, may function acceptably using 

“permissive-only” left-turn phasing, provided that traffic volumes are low enough to operate

efficiently and safely without additional left-turn protection.

“Permissive-only” displays are signified most commonly in one of two ways. In the first case,

if there is not an exclusive signal head assigned to a left-turn movement; instead, a three-section

head with a circular green, circular yellow, and circular red is used. In this case, no regulatory

sign is required.

In the second case, if there is a traffic signal head aligned with an exclusive left-turn lane, a

three-section head with a flashing yellow arrow, steady yellow arrow, and steady red arrow is

used.

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. Exhibit 5-3 shows common signal head arrangements that implement

“permissive-only” phasing; refer to the MUTCD for other configurations.

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Chapter 5. Traffic Signal Design and Illumination 

(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 over the left turn lane.

Exhibit 5-3. Possible signal head arrangements for “permissive-only” left-turn phasing

(Source: 2009 MUTCD)

5.1.1 “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. However, under lower volume conditions, this phasing scheme can cause an

increase in delay for left-turning drivers. Exhibit 5-4 illustrates this phasing pattern. Typical signal

head and associated signing arrangements that implement “protected-only” phasing are shown in

Exhibit 5-5; refer to the MUTCD for other configurations. Chapter 11 of this document provides

guidance on determining the need for protected left turns.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-4. Typical phasing diagram for “protected-only” left-turn phasing.

Exhibit 5-5. Possible signal head arrangement for “protected-only” left-turn phasing

(Source: 2009 MUTCD)

5.1.2 Protected-Permissive Left-Turn Phasing

A combination of protected and permissive left-turn phasing is referred to as protectedpermissive left-turn (PPLT) operation. Exhibit 5-6 illustrates this phasing pattern. The 2009

MUTCD allows two different signal phasing techniques for this type of operation. The first is

when the left-turn lane and the adjacent through lane share the same signal head. Exhibit 5-7(a)

shows a typical signal head and associated signing arrangement that implements this type of

protected-permissive phasing (refer to the MUTCD for other configurations).

The second phasing technique involves a separate signal head provided exclusively for a leftturn movement. In this case, the flashing yellow arrow is used for the permissive portion of the

left-turn movement. Exhibit 5-7(b) shows a typical signal head and associated signing 

arrangement that implements this type of protected-permissive phasing (refer to the MUTCD for

other configurations).

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-6. 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 optional sign.

(b) Protected-permissive left-turn phasing using a five-section signal head located directly above the

exclusive left-turn lane.

Exhibit 5-7. Possible signal head and signing arrangement for protected-permissive 

left-turn phasing.

Source: 2009 MUTCD

Observed improvements in signal progression and efficiency combined with driver

acceptance have led to expanded usage of PPLT over the years. PPLT signals offer operational

advantages when compared to “protected-only” operation. In protected-permissive phasing,

consideration can be given to when in the cycle the protected left-turn movement is given. Where

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Chapter 5. Traffic Signal Design and Illumination 

both protected left-turn movements on opposing approaches operate before the permissive 

phase, it is known as lead-lead operation. Conversely, where the permissive phases operate 

before the protected left-turn movements on opposing approaches, it is known as lag-lag

operation. Lead-lag operation involves a protected left-turn movement on one approach, while 

the opposite left-turn movement experiences a permissive left-turn. They include the following

(adapted with additions by the authors):(56)

• 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.

The primary disadvantage of the permissive phase is an increased potential for vehiclevehicle and vehicle-pedestrian conflicts. Younger and older drivers especially have difficulties

interpreting the sufficient gap distance need to safety make permissive left turns. The use of

permissive phasing also leaves pedestrians without a protected walk phase.

The controller phasing for protected-permissive mode is the most complicated phasing 

because of the safety implications created by the potential of a “yellow trap” occurring.

For ordinary lead-lead operations where both protected left-turn phases precede the 

permissive phases, the yellow trap does not occur, 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 leftturning driver is not indicative of the display seen by the opposing through driver. The opposing 

through display might remain green when the yellow signal indication is displayed to the

permissive left-turn movement. 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. Exhibit 5-8 illustrates this yellow trap.

Drivers who encounter this trap 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 yellow change or red

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 terminated at the same time that the

adjacent through movement is being terminated. Therefore, they may complete their turn 

believing that the opposing vehicles are slowing to a stop when in fact the opposing vehicles are

proceeding into the intersection with a circular green signal indication.

There are options to eliminate the yellow trap situation. The first, and arguably best, option is

the flashing yellow arrow operation for the permissive left-turn movement that became allowable

with the 2009 MUTCD.

However, there may be circumstances in which that option is not feasible. If that is the case,

the phase sequence at the intersection can be restricted to simultaneous leading (lead-lead) or

lagging (lag-lag) left-turn phasing. However, it should be noted that under very light side street

volumes, the leading left-turn phase can be activated such that it operates like a lagging left turn.

This can be prevented using detector switching or a diode in the controller cabinet. 

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-8. Illustration of the yellow trap.

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Chapter 5. Traffic Signal Design and Illumination 

5.1.3 Split Phasing

Split phasing consists of having two opposing approaches timed consecutively rather than

concurrently (i.e., all movements originating from the west followed by all movements from the

east). Split phasing can be implemented in a variety of ways, depending on signal controller

capabilities and how pedestrian movements are treated.

Because of the inefficiency of a split phasing operation, it should only be considered after

other operational methods or geometric solutions have been considered. In general, a new

intersection should not be designed such that split phasing will be required. However, the

following conditions could indicate that split phasing might be an appropriate design choice:

• Multiple Turn Lanes. 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. Practitioners should perform an operational analysis

to ensure this option is superior to a single turn lane option under various phasing

scenarios.

• Varied Traffic Volumes. 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 more efficient than conventional phasing.

• Offset Approach Issues. 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.

• Geometry. The geometry of the intersection is such that the paths of opposing left turns

would not be forgiving of errant behavior by turning motorists.

• Crash History. 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.

• Lane Usage. 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.

• Discrepant Demand. 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.

The MUTCD does not provide a standard method for indicating split phasing at an

intersection. The methods vary considerably depending on what type of phasing sequence has

been used. Exhibit 5-9 shows one way to implement split phasing that does not require the use of

additional signs. It involves using a four-section head displaying both a circular green and a green 

left-turn arrow simultaneously.

However, additional measures are needed when the left-turn arrow would conflict with a

concurrent pedestrian phase:

(57)

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Chapter 5. Traffic Signal Design and Illumination 

• A special logic package can suppress the green arrow display when serving the pedestrian

phase.

• A static sign indicating “LEFT TURN YIELD TO PEDS ON GREEN (symbolic circular green)”

located next to the leftmost signal head for emphasis.

• A blankout sign indicating “LEFT TURN YIELD TO PEDS” activated when the conflicting

vehicular and pedestrian phases run concurrently.

Exhibit 5-9. Common signal head arrangement for split phasing.

5.1.4 Prohibited Left-Turn Movements

Prohibiting left-turn movements at the intersection is an alternative to providing a left-turn

phase. Under this scenario, left-turning drivers must divert to another facility or turn in advance of

or beyond the intersection via a geometric treatment such as a jug handle or a downstream

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. FHWA’s

Alternative Intersections and Interchanges Informational Report discusses a variety of treatments

for redirecting left turns.

(58)

5.1.5 Right-Turn Phasing

Practitioners may control right-turn phasing in a permissive or protected manner with different

configurations depending on the presence of pedestrians and the lane configurations at the

intersections. 

Right turns can operate 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,

practitioners can assign various movements 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 

Exhibit 5-10. The overlap forms a separate movement deriving 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 non-conflicting left-turn phase from the cross

street). 

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-10. Typical phasing diagram illustrating a right-turn overlap.

A five-section head with a combination of circular and arrow indications is more commonly

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 non-conflicting left-turn phase on the cross street

and the circular indications to the same phase as the adjacent through movement. With the

introduction of the flashing yellow arrow, there are numerous possibilities for signalizing a rightturn overlap phase. Refer to MUTCD Sections 4D.22 through 4D.24.(1)

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 circular green 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.

Practitioners should note that a right-turn overlap may conflict with drivers making a legal Uturn on the concurrent (and protected) left-turn phase (in other words, both drivers are facing a 

green arrow for their movement). This conflict can be resolved by either prohibiting drivers from

making a U-turn (R3-4, Sec. 2B.18) on that approach or by installing a U-TURN YIELD TO

RIGHT TURN sign (R10-16, Sec. 2B.53) near the left-turn signal face.

5.2 VEHICLE AND PEDESTRIAN DISPLAYS

Signal displays can be generally categorized into those for vehicles and those for

pedestrians. The following sections discuss each type.

5.2.1 Vehicle Displays

Practitioners should evaluate the location of signal heads based on visibility requirements

and type of signal display. While MUTCD requirements govern signal head placement for signal

displays (discussed in the previous section), local policies typically determine the specific signal 

head placement.

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Chapter 5. Traffic Signal Design and Illumination 

When designing signal head placement, practitioners should consider the following the in 

addition to the minimum requirements described in the MUTCD:

• Consistency with other intersections in the area.

• Geometric design issues that could confuse a driver.

• A high 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.

The 2009 MUTCD recommends that on high-speed approaches (85th percentile greater than

45 mph) or on approaches with three or more through lanes that the primary number of signal

displays equal the number of through lanes. These signal displays should be installed over the

center of each lane. With the advent of light emitting diode (LED) signal displays, the power

requirements for additional signal displays is not significant.

At large signalized intersections, the use of additional signal heads may enhance the safety

and operation of the intersection. Exhibit 5-11 shows a typical intersection design with five types

of optional heads:

Optional Head #1: A near-right-side head that provides an advanced head at wide

intersections as well as a supplemental head for road users unable to see the signal heads over

the lanes due to their position behind large vehicles (trucks, etc.).

Optional Head #2: An extra through head that supplements 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: An extra left-turn head that guides left-turning vehicles across a wide 

intersection as they turn. It also improves visibility for vehicles behind large vehicles and for times

of day when the sun nears the horizon.

Optional Head #4: A near-left-side head that provides an advance indication a curve in the 

road upstream of the intersection hampers visibility. 

Optional Head #5: This head provides a display in direct view of a right-turn lane and 

provides a right-turn overlap phase in conjunction with the non-conflicting left-turn phase on the 

cross street. The head should contain either three circular indications or be a five-section head

with three circular indications and two right-turn arrows due to the concurrent pedestrian crossing.

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Chapter 5. Traffic Signal Design and Illumination 

(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.

Exhibit 5-11. Examples showing five optional signal head locations.

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Chapter 5. Traffic Signal Design and Illumination 

(d) Optional Head #4: Near-side head on curving approach.

(e) Optional Head #5: Far-side head for right-turning vehicles.

Exhibit 5-11 (cont’d). Examples showing five optional signal head locations.

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Chapter 5. Traffic Signal Design and Illumination 

5.2.2 Pedestrian Displays

According to section 4E.03 of the 2009 MUTCD, pedestrian signal heads shall 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 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 splitphase 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 shall use the UPRAISED

HAND (symbolizing DON’T WALK) and WALKING PERSON (symbolizing WALK) indications,

shown in Exhibit 5-12. The pedestrian displays shall be mounted so that the bottom of the 

pedestrian signal display housing (including mounting brackets) is no less than 7 ft and no more 

than 10 ft above sidewalk level.(1)

The 2009 MUTCD approves the use of pedestrian countdown displays. The countdown

displays the number of seconds remaining in the pedestrian change interval. Section 4E.07 of

the MUTCD requires them to be used on all crosswalks where the pedestrian change interval is

more than 7 seconds.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-12. Pedestrian signal indications.

Source: 2009 MUTCD

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.09),

these factors include:

(1)

• Increasingly quiet cars.

• Right-turn overlaps (which mask 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.

• Unusual intersection geometrics.

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. Details 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).(59), (60), (61)

5.2.3 Pedestrian Hybrid Beacons

The 2009 edition of the MUTCD approved the optional use of pedestrian hybrid beacons

(PHB) as a traffic control device. A pedestrian hybrid beacon is a special type of traffic control

device used to warn and control traffic at an unsignalized location to assist pedestrians in

crossing a street or highway at a marked crosswalk. Chapter 4F of the MUTCD describes the 

design and operation of these devices in more detail. The PHB in the MUTCD is based on a 

design previously known as a HAWK signal, developed in Tucson, Arizona.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-13. Pedestrian hybrid beacon.

Source: FHWA Office of Safety

Although the PHB has been technically defined as a beacon and not a traffic signal, it may

still require enabling legislation, which depends directly on a given State's laws concerning

signals and what motorists are expected to do when approaching a "dark" signal. Many States

require drivers to come to a full and complete stop at a dark signal. The presumption is that in 

this case, there has been a power outage at the intersection. However, in most States, a dark

beacon does not require a motorist to stop, nor would a dark PHB. 

The sequence of the PHB is illustrated in Exhibit 5-15.

Exhibit 5-14. Sequence for a PHB.

Source: 2009 MUTCD

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Chapter 5. Traffic Signal Design and Illumination 

5.3 TRAFFIC SIGNAL POLE LAYOUT

Three primary types of signal configurations display vehicle signal indications:

• Mast arms.

• Span-wire configurations. Box span-wire design is preferred to diagonal design for new

installation.

• Pedestal or post-mounted signal displays.

Exhibit 5-15 identifies the advantages and disadvantages of each configuration.

Advantages Disadvantages

Mast arm vehicle signal

• Provides more precise signal head • More costly than span wire

placement • Mast arm lengths can limit use and be extremely

• Lower maintenance costs costly for some large intersections

• Many pole esthetic design options

Span wire vehicle signal

• Can accommodate large intersections • Higher maintenance costs

• Flexibility in signal head placement • Wind and ice can cause problems

• Lower initial cost than mast arms • May be considered aesthetically unpleasing

• Visibility not as good as a mast arm

Pedestal (post-mounted) vehicle signal

• Low cost • Difficult to meet MUTCD visibility requirements,

• Less impact on view corridors particularly at large signalized intersections

• Lower maintenance costs

• Esthetics

• Good for supplemental signals

Exhibit 5-15. Advantages and disadvantages of various configurations for displaying vehicle 

signal indications.

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.

• Overhead utility conflicts, as most power utilities require at least 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,(36) and the AASHTO Roadside Design Guide(62) 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 practically possible, not conflict with the pedestrian 

walking paths, and be located for easy access to the pushbuttons by all 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.

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Chapter 5. Traffic Signal Design and Illumination 

5.4 TRAFFIC SIGNAL CONTROLLER AND CABINET

The traffic controller is the brain of the intersection. Most of the early electro-mechanical

controllers have been replaced by solid state controllers across the country. Solid state

controllers consist of the NEMA type controllers, Type 170 controllers, ATC Type 2070

controllers, and Advanced ATC controllers. Modern controllers can perform the basic functions

needed at typical signalized intersections and have additional capabilities. These include the

ability to communicate with other vendor software using standardized communication protocol 

called National Transportation Communication for ITS Protocol (NTCIP), ability to provide transit

priority, control diamond interchanges, etc. 

NEMA TS-1 is the first generation of NEMA controllers using discrete solid state electronics

interface to the controller field-wiring back panel. TS-1 defines what the controller must do and

defines the interface between the controller and the cabinet. Software is built into the controller

and is not accessible by others. The newer version, TS-2, is similar to the TS-1 in the way the 

functionality is defined. However TS-2 specifies a cabinet bus interface unit (BIU) using RS-485 

with Synchronous Data Link Control protocol (SDLC) to connect the controller, malfunction 

management unit (MMU), the detection system, and the back panel. The use of BIU interface 

reduces the complexity of signal controller cabinet. There are two types of TS-2 controllers. TS-2 

Type 1 controller is a pure TS-2 controller whereas TS-2 Type 2 controller can be retrofitted into a 

TS-1 cabinet.

About the same time the TS-1 specifications were developed, the California Department of

Transportation, City of Los Angeles, New York State Department of Transportation, and FHWA

developed an open-architecture microcomputer for traffic control. This architecture facilitated the

use of software developed by a third party, and the user has access to the software.

The California Department of Transportation led the development of the ATC Type 2070 

architecture due to advancements in communications and processors. Model 2070 employs the

open-architecture to facilitate the installation of aftermarket processors and other devices in the

controllers. The 2070 controller can be placed either in a cabinet for a Type 170 controller or a 

NEMA controller with the right modules. Like Type 170 controller, software is provided by a third

party.

Finally, the Advanced ATC type controller is the second generation of ATC controller with a

single-board computer that provides a standard physical and electrical interface to all the other

components in the controller.

5.4.1 Physical Location of Equipment

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 less likely to be struck by an errant vehicle and not impeding

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.

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Chapter 5. Traffic Signal Design and Illumination 

5.5 DETECTION DEVICES

The detectors (or sensors) inform the signal controller of the presence, movement and/or

occupancy of motor vehicles, pedestrians, or bicycles at a defined location: the upstream

approach to, or downstream side of, an intersection. The signal controller can then use this

information to perform its functions, such as allocate the amount of green time, select timing

plans, and order signal phases.

5.5.1 Vehicle Detection

Vehicle detectors typically function as presence, pulse (advanced), or system (data). A

detector may have more than one function. The detector location, relative to the intersection,

often indicates its primary function: presence detectors are located in close proximity to the stop 

line; pulse detectors are located upstream, well in advance of the intersection; and system

detectors are typically located midblock or just downstream of the intersection.

• Presence detectors alert the controller to waiting vehicles during the red interval and calls

for additional green time (passage or extension) for moving vehicles during the green

interval.

• Pulse detectors extend the green signal indication for approaching vehicles. Pulse

detectors are often placed on high speed approaches to reduce the risk of motorists

encountering a yellow signal indication within the dilemma zone. During the red interval,

pulse detection of each vehicle can incrementally adjust green time above the ‘minimum

green’ controller setting to ensure servicing of the developed queue.

• System detectors collect data such as speed, volume, occupancy, and/or queue

information for the purpose of timing plan selection (when in traffic responsive operation),

real-time adaptive control, and timing plan overrides. An example of override activation

would be to order a special timing plan to prevent off-ramp, vehicle spillback onto an

expressway when the off-ramp, queue detector is occupied.

Detectors are placed either in-roadway or over the roadway surface. The performance of inroadway detectors such as inductive loops, magnetic, and magnetometer detectors depends

upon the quality of the installation, proximity to the vehicle, and the condition of the pavement

structure. These detectors are designed to be insensitive to inclement weather but are subject to

disruption of service due to pavement milling, utility cuts, and pavement movement. The main 

disadvantage of in-roadway detection is the disturbance to the roadway surface and exposure of

personnel to traffic during installation and maintenance. Over roadway detectors, such as video

detection and digital matrix radar, are generally auto-programmable, multi-lane, and multifunctional. Digital matrix radar detectors are insensitive to weather, continuously track vehicles in

the zone, and require little maintenance. Factors affecting the performance of video detection are

often related to the camera lens and mounting: wind, fog, shadows, occlusion, etc. Newer types

of detection feature remote monitoring and troubleshooting. Out of service or unreliable vehicle 

detection results in unused green time, diminished dilemma zone protection, omitted phases,

poor optimization, and driver frustration. The FHWA Traffic Detector Handbook includes further

discussion on detector technology.

The dilemma zone is that portion of the approach where a driver seeing a yellow indication

must make a decision whether to stop safely or to proceed through the intersection. Hence, the

minimum stopping distance usually dictates dilemma zone. The actual distances vary by

jurisdictional policies. Practitioners should review these policies before designing the traffic signal

and detector system. The typical location for advance detectors is based on stopping sight

distance, as shown in Exhibit 5-16. The stopping distance can be computed for both the average

stopping condition as well as the probability ranges for stopping. For higher speed approaches

(45 mph or greater) and to account for the desired probability of stopping, pulse or advanced 

detection should be used. More detailed information on detector placement, including the results

of several calculation methods, can be found in FHWA’s Manual of Traffic Detector Design.

(58)

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-16. Location of advanced vehicle detectors.

Multiple Detector Setback

Speed

Calculated Stopping

Distance

Single

Detector

Setback

10% 90%

Probability of Probability of

Stopping Stopping

20 mph 72.2 ft 70 ft — —

25 mph

30 mph

35 mph

104.4 ft

140.8 ft

182.9 ft

105 ft

140 ft

185 ft

— — 

— —

102 ft 254 ft

40 mph

45 mph

50 mph

231.0 ft

283.8 ft

341.9 ft

230 ft

*

*

122 ft 284 ft

152 ft 327 ft

172 ft 353 ft

55 mph 406.3 ft * 234 ft 386 ft

* Use multiple detectors or volume-density modules.

Source: Reference 63 (table 4-3); Reference 64 (table 7-1);

Proper settings of the detector equipment can help fine tune operations and safety

improvements at a signalized intersection. Both the detection equipment and the traffic signal

controller are typically capable of adjusting the outputs from the detector and/or inputs to the

controller. A few of the more common programmable features are lock, delay, extend, and switch.

• A Lock (Y or N) retains the call placed on the controller during the red signal indication

for the phase even though a vehicle moves outside the detection zone. The lock feature

is useful on left-turn lanes where a vehicle may creep forward while waiting on the

protected left-turn green signal indication.

• A Delay (in seconds) can be set on turning lane detection where permissive turns are

allowed in order to give vehicles time to select a safe gap to complete their turn, without

placing the call to the controller for the protected left turn phase.

• An Extend (in seconds) holds the call upon the controller for a defined period of time

after the vehicle leaves the zone of detection.

• A Switch dynamically changes the assignment of a vehicle detector to a different vehicle

phase during a specific portion of the cycle length. For example, a heavy side street

volume of left turners might benefit from unused green time from a lighter volume

adjacent through movement. Switching moves the detector call from the left-turn phase

(phase 7, protected lefts) to the adjacent through movement phase (phase 4, throughs &

permissive lefts) during the through movement green time to accommodate more left

turners. If switching were not used (as in this example), absent of a vehicle detection for

phase 4 or 8 (side street throughs), then the side street protected left-turn phase would

max out, cross the barrier, and return to the next phase to be served on the main street

(see Exhibit 5-6).

When selecting the type of detection for new signalized intersections or as a replacement for

detection at existing signalized intersections, the following considerations may be made:

• Is detection of multiple user groups required (i.e., motorists, pedestrians, motorcycles,

etc.)?

• Is the detection proprietary or is it compatible with various/existing interfaces?

• Is the detection reliable and does it have a good reputation?

• What is the expected life of the detection?

• Will the detection require changes in existing infrastructure?

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• Does the detection have the capability to be located where its repair will not require

interrupting traffic? Are alternatives available that won’t require the interruption of traffic

flow?

• Will repairs need to be accomplished by contract or in-house?

• How do environmental conditions affect the detection (e.g., wind, ice, glare, occlusion,

shadowing, and fog may limit the capabilities of some video and above-roadway

detection)? Is there potential for accelerated wear and tear of equipment due to weather

(freeze, thaw, heat) or pavement movement or failure?

• Does the detection have other capabilities aside from traffic detection (i.e., volume and

classification counts, occupancy, etc.)? Compared with other methods of data collection,

is this method reliable?

• What is the fail-safe condition for detected fault? Does the system have a diagnostic or

alert system due to fault?

• If in-roadway detection is used, in what type of surface will the detection be installed (i.e.,

concrete, old asphalt, gravel, etc.)? Will future pavement surface maintenance affect its

operation, temporarily (work zone during construction) or permanently?

• Will the detection require boring or trenching?

• What are the initial and lifecycle costs? Does the detection have ongoing regular

maintenance costs?

• Do the detector equipment specifications match the stated operational and safety needs?

5.5.2 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 (Sections 4E.08, 4E.09).

(1)

• Unobstructed and adjacent to a level all-weather surface to provide access by a

wheelchair with a wheelchair-accessible route to the ramp.

• Within 5 ft of the crosswalk extended.

• If possible, between 1.5 and 6 ft from edge of curb. If physical constraints make this

impractical, locate no more than 10 ft off 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 10 ft.

• Mounted at a height of at least 3.5 ft and no more than 4.0 ft above the sidewalk.

Types of passive detection devices include, but are not limited to, video and infrared camera

systems. Pedestrian detection can be helpful for assigning right-of-way when installed at

locations with high demands of both pedestrian and vehicle volumes. As one form of

transportation demand increases over another, the detection can instruct the signal controller to 

give precedence to the higher demand. Pedestrian detection may also allow for detection of users

that will require extended walk times. 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.(38)

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Chapter 5. Traffic Signal Design and Illumination 

5.6 TRAFFIC SIGNAL CONTROL TYPE

Traffic signals operate in pre-timed, semi-actuated, or actuated mode based on the presence 

and operations of detectors. Pre-timed signals operate with fixed cycle lengths and green splits,

and in turn can operate either in isolation or coordination with adjacent traffic signals. Pre-timed

coordinated signals can feature multiple timing plans with different cycle, split, and offset values

for different periods of the day. Pre-timed control is ideally suited to closely spaced intersections

where traffic volumes and patterns are relatively consistent on a daily or day-of-week basis.

(66)

Actuated signals vary the amount of green time allocated to each phase based on traffic

demand; these signals can operate either in a fully actuated or semi-actuated mode. 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.

An intersection that is fully actuated does not have a fixed cycle length; the durations of all

phases are dependent on either vehicle actuations on their approaches or on maximum green 

times. An intersection that is under semi-actuated control typically has detectors on the minor

street and on the major street left turns, but not on the major street through movements. The

signal controller dwells or rests in the major street through phases and services the minor

movements (i.e., minor streets and major street left-turns) upon demand. The intersection does

not have a fixed cycle length.

An actuated signal can also work in coordination with other nearby traffic signals. A

coordinated signal with actuated phases (actuated-coordinated) operates similarly to an

intersection under semi-actuated control. The major street through phases are usually not

actuated, the minor movements (including major street left turns) are actuated, and the

intersection operates with a fixed cycle length. By fixing the major street movements, the

coordination creates a “green band” for traffic to move smoothly through multiple adjacent

intersections. This green band can be increased if unused green time is available from the other

movements; it can be given to the major street through movement to further improve 

coordination. This unused time can also be shared with other movements as desired by the 

practitioner.

Some agencies have implemented more advanced traffic control plans using additional

detection or adaptive control plans. Traffic responsive systems typically include additional

“system detectors” between signals to provide more information to the system. Volume

thresholds for a set of sensors are pre-determined by the traffic engineer to invoke specific

cycles, splits, and offset combinations. This information can be used to help the controller choose 

the most appropriate plans for the current situations. Adaptive control has been use to improve 

traffic congestion and reduce delay using conventional signal control systems. Adaptive signal

control technology continuously adjusts the signal timing (including modifying cycle lengths)

beyond what is done by fully actuated or actuated-coordinated control by responding to changing

traffic patterns. Adaptive control can distribute green times equitably to all traffic movements,

improve travel time reliability and prolong the effectiveness of a traffic signal timing plan.

5.7 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 determining 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.

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Chapter 5. Traffic Signal Design and Illumination 

5.7.1 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.

In pre-timed operations, minimum green and maximum green are equal. The green interval

should meet the driver expectancy requirements, pedestrian requirements, and the requirements

to clear the expected queue at the stop line. When the detector is at the stop line, the minimum 

green time should meet driver expectancy requirements and pedestrian requirements.(1) The 

minimum green is generally set to approximately 5 to 15 seconds based on the type of street and

the type of movement to meet driver expectancy.

When the detector is located upstream of the stop line, the minimum green must meet the 

additional requirement to clear the vehicles queued between the stop line and the detector

nearest the stop line. Consider an intersection with the following properties: average vehicle

spacing is 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 100 ft from the stop line, the minimum green time is 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. Exhibit 5-17 illustrates the functionality of

maximum green timer. The maximum green timer begins when a call is placed on a conflicting

phase. The phase is said to "max-out" if the maximum green time is reached even if actuations

have been received that would typically extend the phase.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-17. Illustration of maximum green functionality.

5.7.2 Vehicle Timing—Detector Inputs

One advantage of actuated control is its capacity to 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 inputs. More information about

detector features and settings for various detector configurations can be found in the FHWA

Traffic Detector Handbook.(63)

Volume-density timing is used to improve the efficiency of intersection operation. A gapreduction feature called variable initial is used to improve intersection efficiency on approaches

where the detectors are not at the stop line (presence detection) but a distance upstream of the

stop line (advance or pulse detection). Variable initial, as illustrated in Exhibit 5-18, alleviates the

need to provide a large minimum green to clear all vehicles stored between the stop line and the

detector and thus improves intersection efficiency during low volume conditions. Another volume 

density feature called gap reduction 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

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Chapter 5. Traffic Signal Design and Illumination 

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.

Exhibit 5-18. Illustration of variable initial feature.

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. When coordination timings are used, the unused green time can be assigned

to the coordinated phase or divided amongst the other phases, but should not exceed the split

time.

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Chapter 5. Traffic Signal Design and Illumination 

5.7.3 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 CP = t + + (U.S. Customary) 2a + 64.4g V 

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 seconds, 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 to 6 seconds and that in most cases the red clearance interval should not exceed 

6 seconds (Section 4D.26).(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

considerably.

Longer clearance intervals may cause drivers to enter the intersection later, breeding

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.(67) NCHRP 705

showed mixed results for the extension of the yellow change interval and the yellow/red change

interval. It showed positive results on all crash types when the red change interval was extended.

5.7.4 Pedestrian Timing

Pedestrian timing requirements include a WALK interval and a pedestrian change (flashing 

upraised hand) interval. The WALK interval varies based upon local agency policy. The MUTCD

recommends a minimum WALK time of 7 seconds, although WALK times as low as 4 seconds

may be used if pedestrian volumes and characteristics do not require a 7-second interval (section

4E.06).(1) The WALK interval gives pedestrians adequate time to perceive the WALK indication

and depart the curb before the pedestrian change (flashing upraised hand) interval 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 times 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. The MUTCD uses a walk speed of 3.5 ft/s for

determining crossing times.(Error! Bookmark not defined.) However, FHWA pedestrian design guidance

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Chapter 5. Traffic Signal Design and Illumination 

recommends a lower speed if needed 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. Pedestrian clearance time is calculated using equation 1:

CrossingDistance Pedestrian Clearance Time = Walking Speed

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 3.5 ft/s as indicated above.

Pedestrian clearance time is accommodated during either a combination of pedestrian

change (upraised hand) interval time and yellow change and red clearance time or by pedestrian 

change (upraised hand) interval time alone. 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. According to the 2009 MUTCD,(1) a buffer interval illustrating a steady 

UPRAISED HAND symbolizing DON’T WALK shall be displayed following the pedestrian change 

interval for at least 3 seconds prior to the release of any conflicting vehicular movement. The 

pedestrian intervals are illustrated in Exhibit 5-19. 

Exhibit 5-19. Pedestrian intervals.

Source: 2009 MUTCD

Practitioners should also consider the impact of longer pedestrian intervals on vehicular

green time and overall cycle lengths. Consideration should be given to the volume of

pedestrians, the pedestrian walk speed used to calculate the pedestrian interval, and the volume

and turn movements of vehicular traffic.

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Chapter 5. Traffic Signal Design and Illumination 

5.7.5 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, cycle lengths for conventional, four-legged intersections should not exceed 120

seconds, although larger intersections may require longer cycle lengths of 140 to 150 seconds. 

Some busy intersections even operate at 180-second cycle lengths. Longer cycle lengths

generally result in increased delay and queues to all users, particularly minor movements.

5.8 SIGNING AND PAVEMENT MARKING DESIGN

Signs and pavement markings are important elements of signalized intersection design.

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 MUTCD is the primary reference for use in the design and placement of signs and

pavement markings.(1) Additional resources include State supplements to the MUTCD and

reference materials such as ITE’s Traffic Control Devices Handbook (TCDH)(68) and Traffic

Signing Handbook.(69)

Designing effective signing and pavement markings, particularly at high-volume signalized

intersections, 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 also are frequently located in urban areas where other intersections, driveways, and

urban land use create visibility conflicts. The following questions, adapted from the ITE Traffic

Signing Handbook,

(69) represent a basic thought process 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 provided at the intersection? Is advance street name information

(“XX Street, Next Signal,” etc.) and (if appropriate) route number directional signing provided

in advance of the intersection? Exhibit 5-20 gives an example of an advance sign that

provides street names for the next two signalized intersections.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-20. 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 and right-hand exits for left turns are both examples where driver expectancy is

violated and should be addressed with signing. Exhibit 5-21 shows an example of signing

used to advise motorists of a dropped lane at an upcoming intersection.

Exhibit 5-21. Example of signing for a left-hand lane drop.

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, signing and

corresponding pavement markings should convey this message to the user. Exhibit 5-22

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Chapter 5. Traffic Signal Design and Illumination 

provides an example of overhead signs and pavement markings used to assist drivers in 

selecting the proper lane on the approach to a signalized intersection.

Exhibit 5-22. Example of advance overhead signs and pavement markings 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 easily comprehend and attend 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. Additional signing enhancements,

consistent with the principles of sign and message spreading (separating overlapping or

numerous route signs onto two installations to improve comprehension and readability), may

include the use of overhead signs in advance of large intersections and/or large retroreflectorized or internally illuminated overhead signs (including street name signs) at the

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, warnings, 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 (dotted white lines) into the

intersection can be a helpful tool where the intersection is so large that the alignment of through

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Chapter 5. Traffic Signal Design and Illumination 

or turning lanes between 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 Exhibit 5-23.

Exhibit 5-23. Example of pavement legends indicating destination route numbers (“horizontal

signing”).

5.9 ILLUMINATION DESIGN

As noted in the 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.(70) 

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).

(70) 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:

• Illuminance is the amount of light incident on the pavement surface from the lighting

source.

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Chapter 5. Traffic Signal Design and Illumination 

• 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.

5.9.1 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 intersection lighting 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. RP8-00 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.(70)

Exhibit 5-24 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).

Exhibit 5-25 presents the roadway and pedestrian area classifications used for determining

the appropriate illuminance levels in exhibit 5-26. RP-8-00 clarifies that although the definitions

given in exhibit 5-25 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 exhibit 5-25 (section 2.0, p. 3).(70)

5.9.2 Veiling Luminance

Stray light from light sources within the field of view produces veiled luminance. 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.

(70) Exhibit 5-24 shows the maximum veiling 

luminance required for good intersection lighting design.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-24. Recommended illuminance for the intersection of continuously lighted urban streets.

Average Maintained Illuminance at

Pavement

Pedestrian/Area Classification

Pavement

Classification1

Roadway

Classification

High

(lux (fc)2

)

Medium

(lux (fc)2)

Low

(lux (fc)2)

Uniformity Ratio

(Eavg/Emin)3

ce 

4

an

)

ni

m

o

avg

i

L

u

t

L

Ra

ax/

gni

vm

l

L

ei

(

V

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

R1

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

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

R2/R3

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

Local/Local 18.0 (1.8) 14.0 (1.4) 8.0 (0.8) 6.0 0.4

1 R1 is typical for portland cement concrete surface; R2/R3 is typical for asphalt surface. 2 fc = footcandles 3 Eavg/Emin = Average illuminance divided by minimum illuminance 4 Lvmax/Lavg = Maximum veiling luminance divided by average luminance.

Source: Reference 70, table 9 (for R2/R3 values); R1 values adapted from table 2.

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Chapter 5. Traffic Signal Design and Illumination 

Exhibit 5-25. 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 Possible Guidance 

Conflict Area 

Classification Description

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 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 70, sections 2.1, 2.2, and 3.6

Signalized Intersections: Informational Guide 5-37 
 

 

 

 

Part II

Analysis Methods

Part II 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.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 6. Safety Analysis Methods 

CHAPTER 6

SAFETY ANALYSIS METHODS

TABLE OF CONTENTS

6.0 SAFETY ANALYSIS METHODS ........................................................................................ 6-3

6.1 Qualitative Approach................................................................................................. 6-4

6.2 Quantitative Approach .............................................................................................. 6-6

6.3 Network Screening or Selection of an Intersection................................................... 6-6

6.3.1 Average Crash Frequency ........................................................................... 6-7

6.3.2 Crash Rate................................................................................................... 6-8

6.3.3 Critical Rate.................................................................................................. 6-8

6.3.4 Equivalent Property Damage Only (EPDO) Average Crash Frequency...... 6-9

6.3.5 Relative Severity Index ................................................................................ 6-9

6.3.6 Excess Predicted Average Crash Frequency Using Safety Performance 

Functions ............................................................................................. 6-10

6.3.7 Excess Expected Average Crash Frequency with Empirical Bayes

Adjustment........................................................................................... 6-10

6.3.8 Summary.................................................................................................... 6-11

6.3.9 Case Study................................................................................................. 6-12

6.4 Diagnosis ................................................................................................................ 6-14

6.4.1 Step 1 – Conduct Safety Data Review ...................................................... 6-14

6.4.2 Step 2 – Assess Supporting Documentation ............................................. 6-16

6.4.3 Step 3 – Assess Field Conditions .............................................................. 6-17

6.4.4 Define Problem Statement(s)..................................................................... 6-28

6.4.5 Case Study................................................................................................. 6-20

6.5 Selecting Countermeasures.................................................................................... 6-27

6.5.1 Case Study................................................................................................. 6-30

6.6 Economic Appraisal ................................................................................................ 6-32

6.6.1 Step 1 – Estimate Benefits of Countermeasures....................................... 6-32

6.6.2 Step 2 – Estimate Costs of Countermeasures........................................... 6-34

6.6.3 Step 3 – Evaluate Cost Effectiveness of Countermeasures...................... 6-34

6.6.4 Case Study................................................................................................. 6-34

6.7 Project Prioritization ................................................................................................ 6-35

6.7.1 Case Study................................................................................................. 6-36

6.8 Safety Effectiveness Evaluation.............................................................................. 6-37

6.8.1 Before-After Study with Comparison Group .............................................. 6-37

6.8.2 Before-After Study with Empirical Bayes ................................................... 6-37

LIST OF EXHIBITS

6-1 Road safety management process ..................................................................................... 6-4

6-2 Societal crash costs and EPDO weights ............................................................................ 6-9

6-3 Common methods of assessing safety at a location ........................................................ 6-11

6-4 Top 10 ranked signalized intersections in a county.......................................................... 6-13

6-5 Example Problem Statements .......................................................................................... 6-19

6-6 Possible taxonomy for crash type classification ............................................................... 6-20

6-7 Study intersection ............................................................................................................. 6-21

6-8 Lane configuration of the study intersection ..................................................................... 6-22

6-9 Crashes in the study intersection from 2006 to 2010, by severity.................................... 6-22

6-10 Crashes at the study intersection from 2006 to 2010, by impact type............................. 6-23

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Chapter 6. Safety Analysis Methods 

6-11 Crash frequencies in terms of crash impact types and road surface conditions .............. 6-23

6-12 Crash frequencies in terms of crash impact types and light conditions............................ 6-24

6-13 Crash diagram for the intersection of Street A and Road B ............................................. 6-25

6-14 Field investigation findings................................................................................................ 6-26

6-15 Problem statements.......................................................................................................... 6-27

6-16 Crash types commonly identified, possible causes, and associated treatments ............ 6-29

6-17 Proposed long list of countermeasures ............................................................................ 6-30

6-18 Societal crash cost estimates by crash severity ............................................................... 6-33

6-19 Example calculation of safety benefit of adding a right-turn lane ..................................... 6-34

6-20 Summary of benefit-cost analysis..................................................................................... 6-35

6-21 Priority ranking of selected countermeasures .................................................................. 6-36

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Chapter 6. Safety Analysis Methods 

6.0 SAFETY ANALYSIS METHODS

In addition to operational needs, it is important for signalized intersections to operate safely.

Intersections constitute of a small portion of the National Highway System. However, intersection 

related crashes constitute more than 20 percent of fatal crashes.(71) In some cases a signal is

even installed for safety reasons (e.g., severe angle crashes at a stop-controlled intersection). As

a result, the safety performance of signalized intersections is as important as the operational

performance of these intersections. Signalized intersections must be systematically and

continuously monitored throughout their life.

Historically, safety practitioners have identified intersections with the highest number of

crashes in a specified time period and focused their efforts and resources at those intersections.

This reactive approach can be effective in addressing a small number of high-crash locations.

During the past two decades, road agencies have started to recognize the challenges

associated with a highly reactive approach to road safety.(71) 

The paradigm shift from a reactive approach to road safety (i.e., only investigate locations

with high crash frequency) to also incorporating a proactive approach (i.e., incorporate road

safety in all stages of a roadway cycle) occurred in conjunction with the development of analytical

tools by researchers and practitioners. These tools can be categorized into qualitative and

quantitative tools.

Qualitative approaches are often used when enough historical data is not available or when

an intersection is in the planning or design stage. A Road Safety Audit (RSA) is one of the

qualitative approaches. The RSA is a formal safety performance examination of an existing or

future road or intersection by an independent audit team.

Quantitative approaches have been mostly collected in the Highway Safety Manual (HSM),

published by AASHTO in 2010.(11) The HSM presents a systematic approach for a road safety

management process. The road safety management process shown in Exhibit 6-1 can be applied

to one road entity (e.g., an intersection) or a network (e.g., all signalized intersections in a

jurisdiction). This road safety management process starts with network screening in which the

main goal is identification of road locations likely to benefit the most from safety improvements.

The underlying assumption is that road design attributes often play a significant contributory role

in crash occurrence. In network screening, the safety performance of each individual location is

compared with the safety performance of similar locations in a jurisdiction to identify whether the

safety performance of the subject location is acceptable.

The next step in the road safety management process is diagnosis. This step examines the

contributing factors of crashes for locations identified in the network screening process to

determine the cause and prepare for the identification of treatments in the next steps.

Countermeasure selection and economic appraisal constitute the next steps in the road

safety management process. This involves the selection of treatments potentially able to address

the safety issues identified in the diagnosis step. In the course of this selection process, more 

than one countermeasure with the potential to mitigate the problem is often identified. A

subsequent economic appraisal will evaluate all options for all problem locations in order to 

ensure that the countermeasures are economically viable. In the prioritization of countermeasure

projects, the objective is to maximize benefits in terms of crash reductions subject to budget

restrictions. Safety effectiveness evaluation involves monitoring implemented improvements to 

assess their safety effectiveness. The information obtained in this step is extremely valuable for

prospective studies so that practitioners can make informed decisions about the effectiveness of

each countermeasure.

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Chapter 6. Safety Analysis Methods 

Exhibit 6-1. Road safety management process.(72)

The road safety management process is a continuous process demanding significant

resources from road authorities, particularly jurisdictions which constitute large geographic areas

(e.g., State agencies). The process requires an extensive amount of data, which should be

collected annually. Consequently, road authorities automated the road safety management

process as much as possible to increase the efficiency of their road safety programs. In response

to this increasing need of road authorities, AASHTO released SafetyAnalyst in 2009.

SafetyAnalyst is a software package that consists of four modules containing six analytical tools,

and these analytical tools correspond to the six steps of the road safety management process

outlined above.

6.1 QUALITATIVE APPROACH

Qualitative approaches to road safety are important tools that can help a traffic engineer to

have a better understanding of the safety issues at signalized intersections. These techniques are 

especially helpful in circumstances in which the intersection is in the planning or design stage and 

sufficient operational data (to quantitatively identify the safety problems) or historical data (e.g.,

collision, volume, etc.) data about the subject intersection is not available. Different qualitative

techniques are used by traffic engineers including:

• Positive guidance review.

• Driver behavior observation.

• Human factors review.

• Conflict analysis.

• Surrogate measures such as time to collision using traffic simulation models (e.g.,

Surrogate Safety Analysis Model (SSAM)).

The above techniques can be used independently or as part of a formal RSA process.

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Chapter 6. Safety Analysis Methods 

An RSA can be used in any phase of project development, from planning and preliminary

engineering to design and construction, regardless of the size of the project. RSAs applied early

in the planning and preliminary (functional) design of roads offer the greatest opportunity for

benefit. As design progresses into detailed design and construction, changes that may improve 

safety performance typically become more difficult, costly, and time consuming to implement.

An RSA audit team consists of a multidisciplinary group of experts who review the

intersection from different perspectives, such as safety, design, traffic operations, law

enforcement, maintenance, etc. The level of success that can be achieved in using the RSA

process is highly dependent on the knowledge, skills, experience, and attitudes of the auditors.

The team should be able to review project data critically, get the most from the field visits, and

engage in the kind of dialogue that leads to the identification of road safety issues. It is important

to ensure that a local contact person is included in the audit team.

RSA process includes the following steps:

• Step 1: Identify intersection to be audited.

• Step 2: Select RSA team.

• Step 3: Conduct a pre-audit meeting to review project information.

• Step 4: Perform field observations under various conditions.

• Step 5: Conduct audit analysis and prepare report of findings.

• Step 6: Present audit findings to project owner/design team.

• Step 7: Project owner/design team prepares formal response.

• Step 8: Incorporate findings into the project when appropriate.

When conducting the field investigation component of an RSA of an existing signalized

intersection, the following elements are reviewed:

Conformance, Consistency, and Condition 

• Relating to intersection and approach geometrics and geometric characteristics, traffic

control devices (traffic signals, signing, pavement markings etc.), illumination and

delineation devices, safety devices (guide rail systems, end treatments, crash cushions

etc.), and all other roadway features present within the roadway environment on the day

of the field investigation, including physical evidence of road user collisions.

Intersection and Approach Geometrics and Geometric Characteristics

• Layout and “readability” (perception) by drivers.

• Horizontal and vertical alignment (visibility all for road users - sight distance review as

required).

• Cross-section, lane configuration, and lane continuity.

• Driveway/side street accessibility.

• Access management and corner clearance.

• Active transportation/vulnerable road user facilities (walkability, bicycling, and mobility

restricted).

• Alternate mode facilities (e.g. transit).

Traffic Signals

• Visibility and conspicuity of signal displays on approach to and at the intersection

(including a sufficient number of indications, recommended one per lane over each lane).

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Chapter 6. Safety Analysis Methods 

• Placement of signal heads (horizontal and vertical; within the drivers cone of vision).

• Operations (vehicular volumes, level of service, queue lengths, volume/capacity etc.).

Signing

• Advance intersection signing (warning, lane use).

• Advance and turn-off roadway identification signing (lane use, route guidance).

• Signing at the intersection (regulatory and guide).

Pavement Markings

• Proper lane line and edge line markings based on intended lane uses.

• Transverse markings as appropriate (stop lines, horizontal signing, and supplemental

legends/symbols).

Illumination and Delineation Devices

• Roadway illumination and luminaire poles.

• Reflective guidance devices (guide posts, post mounted delineators, etc.).

Roadside Features

• Guide rail systems, end treatments, and crash cushions (within the roadway clear zone).

• Potential unprotected roadway and/or roadside hazards.

Site Operations and Road User Interactions

• Road user operations and interactions from the perspective of all users (pedestrians,

bicyclists, motorcycles, trucks, buses, automobiles etc.).

• Human factors (positive guidance principles).

• Traffic speed and classification.

• Traffic patterns and behavior from the perspective of all road users.

FHWA published RSA Guidelines in 2006 to help safety professionals conduct a valid and

successful RSA. The Guidelines include an intersection-specific prompt list that could prove 

valuable in reviewing a signalized intersection.(72)

6.2 QUANTITATIVE APPROACH 

The road safety management process systematically identifies deficient locations from safety

perspectives and addresses safety problems at these locations. The following sections detail the

road safety management process.

6.3 NETWORK SCREENING OR 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?

Selection of an intersection may be the result of a systemic network screening of all

signalized intersections in a jurisdiction or a complaint received by the traffic engineer in a

jurisdiction. This section briefly describes most commonly used techniques for selecting one or

more intersections that may have potential for safety improvements. This section also highlights

the advantages and disadvantages of these techniques. It should be noted that the poor safety

performance of an intersection (i.e., a sudden spike in frequency of crashes) during a few months

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Chapter 6. Safety Analysis Methods 

or a year should not warrant selection of the intersection for detailed review, because it is likely

that crash frequency will decrease in the next few months. This term is referred to as “regression 

to the mean.”

The crash history of a signalized intersection is the key indicator of its safety performance

and is the focus of the remainder of this section. The network screening techniques for evaluating

crash performance vary from 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.

Many jurisdictions carrying out a review of safety at a signalized intersection will usually have

a crash database that provides information on the location, time, severity, and other

circumstances surrounding each crash reported by police or the parties involved. Crash data in

this form can provide the traffic engineer with a quick assessment of safety at a location. The 

crash data is critical to the overall road safety management process. As a result, it is important for

the traffic engineer to fully understand the crash data processing practices in a jurisdiction. For

example, it is important to know what types of crashes are non-reportable. It is also critical to 

know the methodology for assigning crashes to intersections. In some jurisdictions, intersectionrelated crashes are assigned to the legs of intersections, and in other jurisdictions these crashes

are directly assigned to the intersections.

Once data are available, the most common method of network screening is to compare the 

crash history of each site to other similar locations. For signalized intersections, similar

intersections should 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 crash frequency, with intersections in

urban areas having a different crash profile than intersections in rural areas. Finally, comparisons

with sites that are located in other jurisdictions may be tainted by differing crash 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 crash data to conduct network screening and 

assess safety performance of a site are discussed in the following sections, highlighting their

benefits and drawbacks. The different methods to be discussed are:

• Average annual crash frequency.

• Crash rate.

• Critical rate.

• Equivalent property damage only (EPDO) average crash frequency.

• Excess predicted average crash frequency using safety performance functions

(SPFs).

• Excess expected average crash frequency with empirical Bayes adjustment.

Chapter 4 of the HSM provides details of the above methods. Also, the HSM provides

additional techniques for network screening. However, the techniques provided in this Guide are

the most commonly used techniques in practice.

6.3.1 Average Crash Frequency

Traditionally, traffic engineers used (and many still use) a frequency-based method of

site.(71),(73) identifying and evaluating the safety of a Past average annual observed crash

frequencies at a site over a certain time period may be used to compare and rank the site

against crash frequencies at a reference group (i.e., a group of locations with similar

characteristics). Many jurisdictions produce a top 10 list of the intersections producing the highest

average crash frequency in their jurisdictions and concentrate all of their efforts at reducing

crashes at these sites.

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Chapter 6. Safety Analysis Methods 

The average crash frequency method may also be used to screen candidate sites for

improvements. The average crash frequency at the site may be compared to the average crash 

frequency for the reference population to calculate a potential for improvement.

The study period is often 3 to 5 years in safety analyses. Relatively short periods of time,

such as one year of crash data, are not recommended as the basis for a safety intervention.

Because crashes are relatively rare events, a high crash 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 crash 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 (3 to 5 years)

when evaluating the site. Site selection based on multiple years of crash data will provide a truer

picture of the crash profile of the intersection and avoid errors that can result from looking at

crash history over a short period.

Apart from regression to the mean, there are several other disadvantages to using crash

frequency as the sole means of evaluating safety at a site. First, a high crash 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 crash frequency than sites with lower volumes. Therefore, sites

ranked simply by crash frequency will invariably end up with higher volume sites at the top of the

list. Second, the method does not address the severity of crashes at the site. Failing to consider

severity may result in the identification of sites with high numbers of minor crashes, while ignoring

sites with fewer but more severe crashes. The approach results in a failure to identify sites at

which the public has greater risk of injury or death.

6.3.2 Crash Rate

The crash rate method improves upon the average crash frequency in that it normalizes the

frequency of crashes with the exposure, as measured by traffic. Crash rates are calculated by

dividing the total crash frequency for a period of time by the estimated average annual daily traffic

(AADT) of vehicles entering from all approaches in that time period. Crash rate provides an 

improved yardstick for comparison between sites. As with average crash frequency, a crash rate

for an intersection 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 crash rate will account for the effect that volume has on crash frequency.

However, using a simple crash rate to screen locations has several disadvantages. First,

using a crash rate to rank sites that have different volumes requires the assumption that crash

frequency and volume have a linear relationship, but research suggests that this is not the case.

Lower volume sites tend to experience a higher crash rate. Ignoring this fact means that low

volume sites may appear less safe than their higher volume counterparts. Second, crash rates,

as with crash frequency, do not consider crash severity. Sites with a high crash rate may have

relatively few severe (fatal and injury) crashes. Last, as crash rates are calculated from crash

frequency, which fluctuates around a long-term average and experiences regression to the mean,

a site might be ranked high on a list due to a recent period with an unusually higher number of

crashes. If crash rates are being used to screen out candidate sites for safety improvements, it is

recommended that a study period between 3 to 5 years be selected.

6.3.3 Critical Rate

The critical crash rate method has been widely used among traffic engineers. In this method,

the observed crash rate at a site is compared with a critical crash rate unique to each site. The

critical crash rate for a site is a function of the average crash rate of a reference group associated

with the site, the traffic volume of the site, and a desired level of confidence. In this method, sites

where the crash rates exceed the critical rate require further detailed analysis in the diagnosis

step, which is the next step of the road safety management process.

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Chapter 6. Safety Analysis Methods 

The critical crash rate method is more robust than using average crash frequency or crash 

rate alone, as it provides a means of statistically testing how different the crash rate is at a site

when compared to a reference group. The desired level of confidence may vary depending on the

preference of the user.

Disadvantages of using this method are that it still does not consider the severity of the

crashes and assumes that traffic volume and crashes have a linear relationship. In addition, this

approach does not consider regression to the mean.

6.3.4 Equivalent Property Damage Only (EPDO) Average Crash Frequency

In the above discussion, sites were considered for further analysis if the crash frequency and 

rate were particularly high. As indicated, a weakness with these methods is not considering the

severity of the crashes involved. The crash severity method considers the distribution of crash 

severity for each site under consideration. A typical approach is through the use of the EPDO

score. It attaches greater importance, or weight, to crashes resulting in a serious injury or a 

fatality, lesser importance to crashes resulting in a moderate or slight injury, and the least

importance to property-damage-only crashes.

The HSM suggests using the ratio of the societal cost of crashes over the societal cost of

PDO crashes as weighting factors to calculate an EPDO score for each site. Exhibit 6-2 shows

the suggested societal crash costs and EPDO weight factors by the HSM.

Severity Cost Weight

Fatal (K) $4,008,900 542

Injury (A/B/C) $82,600 11

PDO (O) $7,400 1

Exhibit 6-2. Societal crash costs and EPDO weights.(71)

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 score for similar

sites to the one being considered. The EPDO score will explicitly consider the severity

breakdown of crashes, providing greater weight to fatal and injury crashes over PDO crashes.

The traffic engineer should be aware, however, that because the severity of a crash 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 score than those in urban areas. This may result in a

bias that emphasizes higher speed locations. In addition, as with rankings based on crash 

frequency and rate, regression to the mean will be an issue if the study period chosen is short.

6.3.5 Relative Severity Index

Monetary crash costs are assigned to each crash type and the total cost of all crashes is

calculated for each site. An average crash cost per site is then compared to an overall average

crash cost for the site’s reference population. The overall average crash cost is an average of the

total costs at all sites in the reference population. The resulting Relative Severity Index (RSI)

performance measure shows whether a site experiences higher crash costs than the average for

other sites with similar characteristics. Strengths of this method include the simplicity of the

analysis and the consideration of collision type and crash severity. Weaknesses include lack of

Regression-to-the-Mean bias or traffic volume considerations. This type of analysis can also

overemphasize locations with a small number of severe crashes depending on weighting factors,

and it can prioritize low-volume, low-collision sites.

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Chapter 6. Safety Analysis Methods 

6.3.6 Excess Predicted Average Crash Frequency Using Safety Performance Functions 

In this technique for network screening, average crash frequency at a site is compared with a 

predicted average crash frequency, obtained from an SPF. If the observed average crash

frequency exceeds the predicted average crash frequency at a site, the site is flagged for further

analysis. The SPF equation presents the mathematical relationship between crash frequency and 

volume for a reference group (e.g., 4-leg signalized intersections in a jurisdiction). When crash

frequency and volume are plotted, an equation can be developed that is represented by a curve

that is the best fit possible through the various points. Generally, SPFs demonstrate that the 

expected number of crashes increases as traffic volume increases.

The advantages of this method are more accurately calculating the potential for safety

improvement and acknowledging the complex, non-linear relationship between crash frequency

and volume. Disadvantages are that this method is relatively complex and still does not

acknowledge the random variation of crashes.

As part of the HSM, SPFs for intersections have been developed based on data obtained 

from a number of states in the U.S. Chapter 10, 11, and 12 of the HSM include these SPFs. The

SPFs in the HSM were classified based on the surrounding area land-use (i.e., rural, suburban,

and urban), geometric configuration of intersections (i.e., 3-leg and 4-leg), traffic control device of

intersections (i.e., traffic signal and stop control), and functional classification of the main

roadway.

It is advisable to develop SPFs for intersections in each jurisdiction based on the local

intersection characteristic (e.g., number of approaches, traffic control device, and adjacent landuse). Road agencies require intersection characteristic data, traffic volume in the form of entering

AADT volumes, and crash data. The traffic volume data and crash data need to be available for 3

to 5 years for each location. It should be noted that SPFs can be borrowed from similar

jurisdictions (jurisdictions with the same network characteristics, traffic characteristics, weather

conditions, driver population, and driving behavior).

6.3.7 Excess Expected Average Crash Frequency with Empirical Bayes Adjustment

Each of the above methods only considers past crash history, either by ranking and selecting

a candidate site for further crash analysis or by determining whether a particular intersection

under study has a crash problem. Using crash history alone is flawed because the frequency of

crashes 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 crash frequencies through a combination of observed

and predicted crash frequencies. The predicted crash frequencies are derived through the

development of an SPF.

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 crashes.

In case of a network screening for the entire jurisdiction, excess expected average crash

frequency is calculated for all intersections in the study area. Expected crash frequency is the

difference between the expected collision frequency and the predicted collision frequency, which

is obtained from the SPF. The predicted collision frequency represents the overall safety

performance of similar intersections. If a site has positive excess, it shows that the site has a

potential for safety improvement and merits further detailed investigation. In a network screening 

exercise, sites are ranked based on their excess crash frequency. The same approach can be 

used to identify whether further analysis is warranted for a specific intersection.

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Chapter 6. Safety Analysis Methods 

6.3.8 Summary

The above section detailed various methods of assessing the safety of a location through 

consideration of its crash 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). Methods such as crash frequency and 

crash 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 rate method or

the EPDO average crash frequency 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 site. Given the availability of SPFs in many

jurisdictions in the U.S. and Canada, as well as through the HSM, road agencies are encouraged

to use the excess expected average crash frequency with EB adjustment methodology for

network screening. Exhibit 6-3 presents a summary of the relative merits and drawbacks of each 

method.

Method Advantages Disadvantages

Average crash 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

Crash rates Simple to use

Considers exposure

Biased toward low-volume sites

Requires volume data

Assumes crashes and volume 

have linear relationship

Severity not considered

Regression to the mean not

addressed

Critical rate Relatively simple

Considers exposure

Applies a recognized statistical 

method

Requires volume data

Assumes crashes and volume 

have linear relationship

Severity not considered

Regression to the mean not

addressed

Equivalent property damage

only average crash frequency

Relatively simple

Considers crash severity

Does not account for exposure

May overemphasize sites with a

low frequency of severe 

crashes depending on 

weighting factors used

Regression to the mean not

addressed

Excess predicted average crash

frequency using safety

performance

More accurate

Considers exposure

Acknowledges that crashes and 

volume have a nonlinear

Requires volume data

Regression to the mean not

addressed

Labor intensive

relationship Difficult for public to

conceptualize

Excess expected average crash 

frequency with empirical Bayes

adjustment

Most accurate

Considers exposure

Acknowledges that crashes and 

volume have a nonlinear

Requires volume data

Difficult for public to

conceptualize

relationship

Addresses regression to the 

mean

Exhibit 6-3. Common methods of assessing safety at a location.

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Chapter 6. Safety Analysis Methods 

6.3.9 Case Study

The purpose of this case study is to show the application of the network screening step of the 

road safety management process. This case study will be completed throughout this chapter as

other steps of the road safety management process are described.

A County has conducted network screening using the excess expected average crash

frequency with EB adjustment methodology for all signalized intersections within the county.

Exhibit 6-4 shows the results of the network screening for the top 10 intersections that have been

ranked based on Potential for Safety Improvement (PSI). The PSI is the difference between 

expected crashes (obtained from the EB method) and predicted crashes (obtained from SPFs).

This table is a typical output of a network screening exercise. The county then chooses to

further analyze these intersections to address potential safety issues. As a case study, the first

intersection presented in this exhibit STREET A @ ROAD B will be further analyzed and referred

to throughout this chapter.

Signalized Intersections: Informational Guide 6-12 
 

 

 

1 

2 

3

4

5 

6 

7 

8 

9 

10 

 

Chapter 6. Safety Analysis Methods 

Rank Description

Average Average 

AADT

Minor

Intersection

Type

Traffic

Control

Study 

Period

(Years)

Total

Observed

Crashes

Total

Predicted

Crashes

Total

Expected

Crashes

Potential for

Safety

Improvement

(PSI)

STREET A @ ROAD B 27299 11341 4-legged Signalized 5 90 52.337 87.610 35.273 

STREET G @ ROAD H 30584 2935 4-legged Signalized 5 42 19.599 38.568 18.969 

STREET P @ ROAD Q 27154 3258 4-legged Signalized 5 38 19.672 35.201 15.529 

STREET R @ ROAD S 36966 5045 4-legged Signalized 5 47 33.884 45.757 11.873 

STREET A @ ROAD D 8132 4711 4-legged Signalized 5 26 11.920 22.772 10.852 

STREET E @ ROAD F 39732 8639 4-legged Signalized 5 64 54.090 63.390 9.300 

STREET G @ ROAD Q 52765 18028 4-legged Signalized 5 122 115.747 121.814 6.067 

STREET R @ ROAD H 27815 3773 4-legged Signalized 5 28 22.414 27.237 4.823 

STREET C @ ROAD D 38180 4506 4-legged Signalized 5 37 31.683 36.465 4.782 

STREET C @ ROAD F 32025 25576 4-legged Signalized 5 113 109.720 112.897 3.177 

Exhibit 6-4. Top 10 ranked signalized intersections in a county.

Signalized Intersections: Informational Guide 6-13 

Major

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Chapter 6. Safety Analysis Methods 

6.4 DIAGNOSIS

The previous section discussed different tools used to select a candidate intersection for a safety

evaluation. At a certain point, the traffic engineer will conclude, based on past crash 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:

1. Safety complaints or concerns raised by others (other departments, local politicians, the public).

2. Planned reconstruction that would make it worthwhile to carry out a safety evaluation and

improvements.

3. Identified operational deficiencies.

This section will discuss how the traffic engineer may correctly diagnose what types of safety

problems/issue may be present at an intersection. Diagnosis of a particular safety concern can then lead 

to appropriate countermeasures.

The following four-step process can be used to diagnose safety problems at a site:

• Step 1 – Conduct Safety Data Review.

• Step 2 – Assess Supporting Documentation.

• Step 3 – Assess Field Conditions.

• Step 4 – Define Problem Statement(s).

The above process is consistent with the recommendations of Chapter 5 of the HSM.

6.4.1 Step 1 – Conduct Safety Data Review

In conducting a safety diagnosis at a signalized intersection, the traffic engineer seeks to understand

any patterns in the crash data and identify contributing factors of crashes within the functional boundary

of the intersection.

The safety data review can be conducted in three stages:

1. Assemble crash data.

2. Describe crash statistics.

3. Summarize crashes by location.

Assemble Crash Data

Crash data used for diagnosing safety at a signalized intersection should represent 3 to 5 years of

crash data. It should include all crashes reported as occurring at or related to the intersection’s influence

zone. The relationship of crashes to intersections is often expressed in the Model Minimum Uniform

Crash Criteria (MMUCC) Guideline (74) in “Relation to Junction.”

Most agencies have electronic databases from which the following characteristics of crashes

associated with the subject intersection can be extracted:

• Crash identifiers such as date, time of day, and time.

• Severity: which is often represented in the KABCO scale, defined as follows:

o K-Fatal injury: an injury that results in death.

o A-Incapacitating injury: any injury, other than a fatal injury, that prevents the injured

person from walking, driving, or normally conducting the activities the person was

capable of performing before the injury occurred.

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Chapter 6. Safety Analysis Methods 

o B-Non-incapacitating evident injury: any injury, other than a fatal injury or an

incapacitating injury, that is evident to observers at the scene of the crash in which the

injury occurred.

o C-Possible injury: any injury reported or claimed that is not a fatal injury, incapacitating

injury, or non-incapacitating evident injury and includes claim of injuries not evident.

o O-No Injury/Property Damage Only (PDO).

• Crash Type.

o Rear-end.

o Sideswipe.

o Angle.

o Turning.

o Head-on.

o Fixed object.

• Direction of travel before crash.

• Sequence of events.

• Contributing circumstances:

o Parties involved – vehicle only, pedestrian and vehicle, bicycle and vehicle.

o Road condition at the time of the crash – dry, wet, snow, ice.

o Lighting condition at the time of the crash – dawn, daylight, dusk, dark-lighted, dark-not

lighted.

o Weather condition at the time of the crash – clear, cloudy, fog, rain, snow, ice.

o Impairments of parties involved – alcohol, drugs, fatigue.

If available, the original police reports should be used to gather anecdotal comments written by police

officers at the crash scene and firsthand accounts of the crashes from involved parties and eyewitnesses.

Describe Crash Statistics

Once crash data for the intersection has been extracted from the database, it is important to identify

patterns and potential contributing factors from the historical crash data. Three techniques are often used 

by practitioners to identify crash patterns and contributing factors of crashes in a safety diagnosis

exercise:

1. Develop visualization tools – graphs and charts can assist the traffic engineer in visualizing crash

frequencies in terms of various crash attributes.

2. Conduct a crash cluster analysis – the crash cluster analysis process involves a manual

screening of crash attributes. In this type of analysis, the object is to identify crash clusters for

each crash attribute, such as crash impact type, road surface condition, lighting condition, etc.

3. Conduct over-representation analysis – over-representation analysis is used to determine

whether the proportion of a characteristic found at a specific intersection 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 one of the methods for identifying

over-representation at a site. The HSM refers to this analysis as “Specific Crash Types

Exceeding Threshold Proportion,” and details of this technique can be found in Chapter 4 of the

HSM.

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Chapter 6. Safety Analysis Methods 

The crash characteristics should be reviewed for over-representation through comparison with crash

characteristic information representing the typical experience of a signalized intersection. Examples of

questions that can be answered by the above three techniques to identify over-representations or

patterns in the crash attributes are highlighted below.

An examination of crash pattern 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 crashes 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 attractions. Day of week and time of day patterns should

be examined. Morning/afternoon weekday over-representation may suggest crash 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.

Over-representation in crash severity will highlight a location that has an unusually high proportion of

fatal and/or injury crashes. A higher proportion of fatal and/or injury crashes may suggest a problem with

higher operating speeds.

Summarize Crashes by Location

The end product of the descriptive crash statistics will be a set of characteristics identified as being 

over-represented. The next step is to relate the patterns and over-represented characteristics of crashes

to a particular approach. A crash diagram can be used to create such relationship. A crash diagram is a 

two-dimensional plan view representation of the crashes that have occurred at a site within a given time

period. In a crash diagram, each crash type is represented by combinations of arrows and symbols.

Exhibit 6-6 shows proposed symbols for classification of various crash types.

6.4.2 Step 2 – Assess Supporting Documentation

The main goal of this step is to gather and review documented information or personal opinion about

the site. This information can be gathered from previous studies relevant to the subject intersection,

complaints filed with the road agency by residents, or consultation with the authorities who have local

knowledge about the study area. This is an important step in which the crash patterns can be studied in 

the context of the past changes in the study area. For example, an increase in pedestrian crashes in the

past 3 years can be correlated with the opening of a new school in the vicinity of the subject intersection 3

years ago.

The HSM suggests that the following types of information may be useful as supporting documentation 

to the diagnosis of safety problems at a site:

• Current traffic volumes for all travel modes.

• As-built construction plans.

• Relevant design criteria and pertinent guidelines.

• Inventory of field conditions (e.g. traffic signs, traffic control devices, number of travel lanes,

posted speed limits, etc.).

• Relevant photos.

• Maintenance logs.

• Recent traffic operations or transportation studies conducted in the vicinity of the site.

• Land use mapping and traffic access control characteristics.

• Historic patterns of adverse weather.

• Records of public comments or complaints on transportation issues.

• Roadway improvement plans in the site vicinity.

• Anecdotal information about travel through the site.

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Chapter 6. Safety Analysis Methods 

Appendix 5B of the HSM provides a list of questions and data to consider when reviewing past site

documentations.

6.4.3 Step 3 – Assess Field Conditions

To supplement the analysis and diagnosis using crash 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 crash characteristics were over-represented based on the analysis of crash overrepresentation.

• Which areas within the intersection’s sphere of influence are showing unusual clusters of

crashes.

• 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 crash patterns (Exhibit 6-6). 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 crashes or near-crashes, such as vehicle damage to street

furniture, signs and other objects near the roadway, skid marks on the intersection approaches,

and 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.(9) A positive guidance review uses an in-depth knowledge of human factors and the driving task

to screen roadways for:

• Information deficiencies.

• Expectancy violations.

• Workload issues.

Each of the above may contribute to the occurrence of driver error and crashes.

Information deficiencies occur when information that the driver needs to carry out the driving task

safely is missing. An example may be inadequate signing/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.(75) The key to effective expectancy structuring is uniformity and standardization.

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Chapter 6. Safety Analysis Methods 

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 signing, 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 to 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 treating the roadway, the vehicle, and the driver as a single, integrated system. It recognizes

drivers as the information gatherers and decision-makers 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. 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 crashes.

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 crashes, and

to justify mitigation measures.

Appendix 5C of the HSM provides a process required for preparation for a field assessment

undertaking, and Appendix 5D of the HSM provides a field review checklist for signalized intersections.

It should be noted that an RSA, which was described in the qualitative approach for safety review of

signalized intersections, always includes a field review for existing intersections (obviously a field review

is not possible for intersections in planning and design stages). The process for conducting an RSA field

review described in this section can be followed.

6.4.4 Define Problem Statement(s)

A set of one or more clear problem statements should be developed. The problem statement(s) are

developed on the basis of the crash analysis (i.e., evidence of over-representation among a crash 

subgrouping) and should be supported through the site visit and any further analysis. The problem

statement should correlate crash patterns observed with potential contributing factors.

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.

Example problem statements are given in Exhibit 6-5.

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Chapter 6. Safety Analysis Methods 

Problem Statement #1

Rear-end crashes and crashes occurring between 3 and 6 p.m. are over-represented. The crash 

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 crashes were over-represented, and four fatal or injury crashes involved 

pedestrians. The crash 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.

Exhibit 6-5. Example problem statements.

Signalized Intersections: Informational Guide 6-19 
 

 

 

 

 

 

Chapter 6. Safety Analysis Methods 

Exhibit 6-6. Possible taxonomy for crash type classification.

6.4.5 Case Study

The purpose of this case study is to show the application of the diagnosis step of the road safety

management process.

The intersection of Street A and Road B (shown in Exhibit 6-7) was ranked first in the network

screening exercise of all 4-leg signalized intersection in the county, as shown in the previous section. It

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Chapter 6. Safety Analysis Methods 

was identified that the potential for safety improvement is 35.3 crashes per a 5 year period. The 

intersection characteristics include:

Geometric Characteristics 

Street A (a major east-west arterial roadway), immediately east of Road B, is essentially flat and

straight vertically and horizontally; to the west of Road B, Street A contains a horizontal curve and vertical

curve. The vertical curve exists immediately west and in advance of the intersection, resulting in a vertical

crest for eastbound approaching road users. Road B (a minor north-south arterial roadway) is essentially

flat and straight on the approach to Street A.

Traffic Control

The intersection contains two mast arm-mounted primary signal displays for the through movements

and a secondary signal display for the left-turning movements on all approaches. The signals are both 

horizontally and vertically located within the required mounting field of view, as per the FHWA MUTCD.

The signal displays contain three-section, vertically arranged signal bulbs comprised of circular red,

yellow, and green indications and are positioned over the appropriate lanes based on FHWA MUTCD

2009 guidance.(1)

Signing

Regulatory speed limit signs are present on all approaches to the intersection. Street name signs

both for Street A and Road B are present on the primary signal pole for all approaches (far right quadrant

of the intersection). Advance street name signing is present on both northbound and southbound 

approaches to the intersection Signal ahead warning signs are present on the northbound and

southbound approaches to the intersection. The signs are all located appropriate distances upstream of

the intersection.

Exhibit 6-7. Study intersection.

Source: Google, 2012

Signalized Intersections: Informational Guide 6-21 
 

 

 

 

 

Chapter 6. Safety Analysis Methods 

North

Exhibit 6-8. Lane configuration of the study intersection.

Step 1 – Safety Data Review

Assemble Crash Data

The County has provided crashes for the period of 2006 to 2010 to the traffic engineer. Exhibit 6-9

provides a summary of crashes in terms of severity, and Exhibit 6-10 shows the same crashes in terms of

their impact type.

Crash Severity Year 

Total 2006 2007 2008 2009 2010 

Fatal/Injury 3 10 8 1 3 25 

PDO 10 15 18 14 8 65 

Total 13 25 26 15 11 90 

Exhibit 6-9. Crashes in the study intersection from 2006 to 2010, by severity.

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Chapter 6. Safety Analysis Methods 

Row Labels 2006 2007 2008 2009 2010 Grand 

Total 

Angle 2 2 3 2 1 10 

Rear End 6 14 14 8 5 47 

Sideswipe 1 3 3 1 2 10 

Turning 4 6 6 4 3 23 

Grand Total 13 25 26 15 11 90 

Exhibit 6-10. Crashes at the study intersection from 2006 to 2010, by impact type.

Descriptive crash statistics

Exhibit 6-11 shows crash frequencies in terms of crash types and road surface condition. Based on

this exhibit, a significant number of rear-end and turning movement crashes have been identified at this

intersection. There is also potential concern regarding the number of crashes during wet and slippery

road surface conditions. However, to confirm whether such a problem exists, the proportions of road 

surface condition crashes at this intersection should be compared to similar intersections (overrepresentation analysis).

Slippery 

Angle Rear End Sideswipe Turning 

Crash Impact Type by Road Surface Condition 

Exhibit 6-11. Crash frequencies in terms of crash impact types and road surface conditions.

Exhibit 6-12 shows crash frequencies in terms of crash impact types and light condition. This exhibit

shows that most crashes occur during daylight. There might be some concerns related to turning 

movement crashes during dark hours of days. To be confident about these findings, an overrepresentation analysis should be conducted. Crash Frequency 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

Slippery 

Wet 

Dry 

Slippery 

Wet 

Dry 

Slippery Wet 

Dry 

Wet 

Dry 

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Chapter 6. Safety Analysis Methods 

Exhibit 6-12. Crash frequencies in terms of crash impact types and light conditions.

The results of the proportional analysis (over-representation analysis) showed that the following crash

attributes are over-represented at the study intersection:

• Angle crashes.

• Rear-end crashes.

• Turning movement crashes.

• Wet road surface condition.

Summarizing Crashes by Location

Exhibit 6-13 illustrates the crash diagram associated with the study area. In this diagram the crashes

reviewed in the previous stage are related to each approach of the intersection. Different crash impact

types are shown with different symbols. The number shown beside each crash cluster shows the number

of crashes per each cluster. Red arrows in this diagram represent the at-fault vehicles. The crash diagram

shows that most turning movements have occurred between eastbound left-turning vehicles and

westbound through vehicles. Rear-end crash clusters dominantly exist on east and west approaches of

the intersection. Angle crashes have occurred between southbound through vehicles and westbound

through vehicles.

Signalized Intersections: Informational Guide 6-24 

50

45 Dawn

40 Dusk

35

30

Daylight

25

Dawn

20

Dusk

15 Daylight

10

Dawn Daylight Dark

5

Daylight Dark

0

Angle Rear E nd Sideswipe

Crash Impact Type by Light Condition 

Turning

Crash Frequency 
 

 

 

 

 

 

 

 

Chapter 6. Safety Analysis Methods 

Exhibit 6-13. Crash diagram for the intersection of Street A and Road B.

Step 2 – Assess Supporting Documentation

• Speed limit on all approaches to the intersection is 35 mph.

• Entering AADT of the intersection is 53,866.

• The County has indicated that the following guidelines and manuals are relevant in this study:

o The geometric design guideline pertinent to the study is the AASHTO Green Book – A

Policy on Geometric Design of Highways and Streets.

o All signing and other traffic control devices must conform to the latest edition of the

MUTCD.

• Consultation with the County’s traffic engineer revealed that the westbound left-turning vehicles

have capacity challenges.

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Chapter 6. Safety Analysis Methods 

Step 3 – Assess Field Conditions

Exhibit 6-14 presents the findings of the field investigation. The field visit consisted of peak and offpeak visits as well as visits during day light and dark lighted.

Location Findings

Street A, just west of 

and on approach to 

Road B

• Signal displays are inconspicuous on approach (signal bulbs are dull, and back plates

are inconspicuous at night).

• Vertical crest curve in advance of intersection – stopping sight distance measured and

is inadequate.

• Exclusive eastbound right-turn exit lane exists; however, no exclusive turn lane signs

exist. Due to vertical crest curve, it is difficult to determine the lane configuration on

intersection approach for drivers.

• Polished and worn pavement surface on intersection approach.

• The street name sign at the intersection is being obscured by auxiliary signal pole for

opposing direction.

• No advance street name signs exist on intersection approach.

• No advance intersection ahead warning signs exist on intersection approach

• Road user interactions (eastbound): red light running; high travel speeds (well in excess

of posted speed limit); uncertain maneuvers made by road users, potentially due to nonpresent advance notice (signage); conflicts (near-misses) between eastbound road

users, potentially leading to rear-end type as well as eastbound left-turning with

westbound through-turning movement type crashes.

Street A @ Road B • Road user interactions (westbound): conflicts (near-misses) between westbound leftturning and through-bound road users (potentially leading to rear-end type crashes).

Exhibit 6-14. Field investigation findings.

Step 4: Define Problem Statement

Exhibit 6-15 summarizes problem statements associated with the intersection of Street A and Road 

B. The crash patterns and over-represented crashes identified in Step 1 of the diagnosis process are

correlated with potential contributing factors identified through assessment of supporting documents and

assessment of field conditions.

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Chapter 6. Safety Analysis Methods 

Crash Attributes Problem Statement

Angle: Eastbound through at fault, with 

southbound through movements.

Rear-end: Westbound through at fault,

with westbound left-turn movements.

Turning movement: Eastbound leftturn at fault, with westbound through 

movements.

Rear-end: Westbound through at fault,

with westbound left-turn movements.

Wet Road Surface Conditions:

Westbound through vehicles

contributing to rear-end crashes.

Street A just west of, and on approach to, Road B

• Signal displays are inconspicuous on approach (signal bulbs are dull,

and back plates are inconspicuous at night).

• Vertical crest curve in advance of intersection – stopping sight distance

measured and is inadequate.

• Exclusive eastbound right-turn exit lane exists, however, no exclusive

turn lane signs exist. Due to vertical crest curve, it is difficult to

determine the lane configuration on intersection approach.

• Polished and worn pavement surface on intersection approach.

• The street name sign at the intersection is being obscured by auxiliary

signal pole for opposing direction.

• No advance street name signs exist on intersection approach.

• No advance intersection ahead warning signs exist on intersection

approach.

• Road user interactions (eastbound): red light running; high travel

speeds (well in excess of posted speed limit); uncertain maneuvers

made by road users, potentially due to non-present advance notice

(signing); conflicts (near-misses) between eastbound road users,

potentially leading to rear-end type as well as eastbound left-turning

with westbound through-turning movement type crashes,

Street A @ Road B 

• Road user interactions (westbound): conflicts (near-misses) between

westbound left-turning and through-bound road users (potentially

leading to rear-end type crashes).

Exhibit 6-15. Problem statements.

6.5 SELECTING COUNTERMEASURES

After diagnosis, the next step in the road safety management process is countermeasure selection.

The end product of the diagnosis process is one or more problem statements in which a crash pattern is

related to a number of potential contributing factors. The objective of the countermeasure selection step is

to develop countermeasures to address the contributing factors identified as part of the diagnosis step.

Countermeasures include all measures likely to decrease the frequency or severity of crashes

identified as exhibiting an abnormal pattern (over-representation).

In Part III of this guide, the reader will find countermeasures (treatments) organized into five broad

groups:

• System-wide treatments (Chapter 8).

• Intersection-wide treatments (Chapter 9).

• Approach treatments (Chapter 10).

• Individual movement treatments (Chapter 11).

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Chapter 6. Safety Analysis Methods 

For each treatment, there are references to possible crash groups that are likely to be positively

affected through a treatment’s implementation. At signalized intersections, the following crash patterns

are most commonly identified:

• Rear-end crashes.

• Angle crashes.

• Left-turn or right-turn movement crashes.

• Nighttime crashes.

• Wet pavement crashes.

• Crashes involving pedestrians and bicyclists.

Exhibit 6-16 presents possible contributing factors and countermeasures for each of these types,

along with the appropriate chapter.

The material presented in this section provides a range of options that could be selected, but is not

fully comprehensive. It is not possible to develop a complete list of all potential crash treatments, because

new tools and techniques for improving 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 crash pattern identified represents a unique situation.

Over the course of the above crash diagnostic analysis, site visits, and field analysis, the traffic

engineer may have identified treatments that are of little cost and undoubtedly 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.

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Chapter 6. Safety Analysis Methods 

Possible Treatment Group

Crash Type Possible Contributing Factors (Chapter)

Rear-end 

crashes

• Sudden and unexpected slowing or stopping when

motorists make left turns in and out of driveways

along corridor.

• Median treatments (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.

• Change signal control from

pre-timed to actuated

(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

change and clearance interval.

• Traffic signal not conspicuous or visible to

approaching drivers, causing sudden and

unexpected slowing or stopping movements.

• Change signal control from

pre-timed to actuated

(Chapter 9)

• Red light camera

enforcement (Chapter 10)

• Sudden and unexpected slowing or stopping due

to inadequate intersection capacity.

• Change signal control from

pre-timed to actuated

(Chapter 9)

• Individual movement

treatments (Chapter 11)

Angle crashes • Drivers caught in intersection during red phase

due to inadequate traffic control or inadequate

change and 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.

• Modify change and

clearance intervals (Chapter

9)

• Increase size of signal; Add

supplemental signal heads;

Provide backplates (Chapter

10)

Left-turn 

crashes

• Intersection cannot accommodate left-turn

movements safely.

• Add single or multiple leftturn lane (Chapter 11)

• Restrict turns (Chapter 11)

Nighttime • Poor nighttime visibility or light. • Provide or upgrade

related • Poor sign visibility. illumination (Chapter 9)

Crashes • Inadequate channelization or delineation.

• Inadequate maintenance.

• Excessive speed.

• Inadequate sight distance.

• Add channelizing islands

(Chapter 10)

Wet pavement • Slippery pavement • High visibility crosswalks.

related crashes • Inadequate pavement markings (chapter 9)

• Inadequate maintenance

• Excessive speed

• Improve pavement surface.

(chapter 10)

Crashes or • 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)

conflicts

involving 

bicyclists and 

pedestrians

Exhibit 6-16. Crash types commonly identified, possible causes, and associated treatments.

The practitioner should generate a list of countermeasures (some of which may have been identified

in this guide) that are based on local practice or are representative of a unique situation identified at the

intersection through the diagnosis step. Before conducting the economic appraisal of each 

countermeasure, it is advisable to screen the countermeasures to narrow the options for the economic

appraisal step.

The practitioner should generate a list of countermeasures (some of which may have been identified

in this guide) that are based on local practice or are representative of a unique situation identified at the

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Chapter 6. Safety Analysis Methods 

intersection through the diagnosis step. Before conducting the economic appraisal of each 

countermeasure, it is advisable to screen the countermeasures to narrow the options for the economic

appraisal step.

One method of screening proposed countermeasure 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:

• Overall Feasibility: How feasible would it be to implement the countermeasure? 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-toimplement countermeasures get negative scores.

• Impact on Traffic Operations: Is the countermeasure expected to improve the flow of traffic

within the intersection influence area? Countermeasures that would improve traffic operations

score positive. Countermeasures that would degrade traffic operations score negative.

• Consistency with Local Practice: Is the countermeasure consistent with local practice?

Countermeasures that are familiar to the public and have known benefits score positive.

Countermeasures that are unfamiliar and are largely untested score negative.

Scoring each countermeasure 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

countermeasures then can be reduced to a short list of viable countermeasures. Based on a threshold 

score decided upon among the study team, the countermeasures may then be screened and those

scoring poorly may be discarded.

6.5.1 Case Study

For the case study presented in the diagnosis step, Exhibit 6-17 shows a list of countermeasures

proposed for the study intersection that can potentially address safety problems identified in the problem

statements.

Countermeasure Description

Heighten conspicuity of the signal This countermeasure involves installation of

displays for eastbound intersection- devices to heighten the conspicuity of the signal

approaching road users. displays for road users approaching the intersection 

along Road B. The following treatments are 

recommended:

• Install new signal bulbs and ensure they are

conspicuous to intersection-approaching road

users.

• Install the recommended one signal per lane

over each lane.

• Install yellow retroreflective sheeting border on

the eastbound traffic signal display back

plates.(76)

Address stopping sight distance Low-Cost Solution:

issues on eastbound approach to the

intersection. This countermeasure involves installation of

warning signage to heighten awareness of the sight

distance issue on the intersection approach. The 

following treatments are recommended:

• Install either a “SIGNAL AHEAD” warning sign

or a “BE PREPARED TO STOP” warning sign

to heighten awareness of the presence of the

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Chapter 6. Safety Analysis Methods 

Countermeasure Description

intersection on approach.

High-Cost Solution:

This countermeasure involves re-design and

reconstruction of the vertical curvature of the roadway

to ensure the stopping sight distance on approach to 

the intersection is met.

Enhance presence of lane designation

on eastbound approach to the

intersection.

This countermeasure involves the installation of

lane designation signs and markings for exclusive 

eastbound right-turn lane to ensure lane designation is

evident to intersection-approaching road users.

Pavement friction test and potential

follow-on construction work.

This countermeasure involves conducting a friction

test of the existing pavement surface. An empirical test

of the friction properties of the pavement could 

determine if additional friction should be added to the 

pavement surface. Increasing pavement friction may

assist road users’ ability to maneuver during events

leading up to a potential collision, particularly

eastbound rear-end collisions.

Installation/Relocation of street name 

signs

This countermeasure involves enhancing the

conspicuity of the standard street regulatory name sign 

for Road B by increasing the size of the sign and 

relocating it to a position over the curb-through lane on

the signal mast arm.

Further enhance the presence of Road This countermeasure involves installation of

B on approach along Street A. signage to better inform approaching road users of the 

downstream condition and the subject signalized

intersection so that they can make appropriate

decisions about lanes, etc., and can enter with caution

due to the existing issue with vertical geometry.

Advance street name sign for Road B on eastbound

approach.(77)

Conspicuity enhancement of the standard street

regulatory name sign for Road B through increasing the 

size of the sign and relocating it to a position over the 

curb-through lane on the signal mast arm.

Install INTERSECTION AHEAD

warning sign.

This countermeasure involves the installation of an 

INTERSECTION AHEAD warning sign to provide 

appropriate advance notice of the downstream

condition to eastbound intersection-approaching road 

users.

Install a westbound left-turn lane. This countermeasure involves the installation of a

westbound left-turn lane at the intersection to remove 

westbound left-turning road users from the stream of

through traffic.

Exhibit 6-17. Proposed long list of countermeasures.

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Chapter 6. Safety Analysis Methods 

6.6 ECONOMIC APPRAISAL

Economic appraisals identify whether the countermeasures identified in the previous step of the road 

safety management process have larger benefits than their costs. The economic appraisal quantifies

countermeasures’ benefits in terms of their safety impacts. The ability to evaluate the safety impacts of a

countermeasure is paramount to implementing an intersection improvement plan. Information is needed

on whether the treatment under consideration is effective in reducing crashes. 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.

The economic appraisals include three steps:

• Step 1: Estimate benefits of countermeasures.

• Step 2: Estimate costs of countermeasures.

• Step 3: Evaluate cost effectiveness of countermeasures.

6.6.1 Step 1 – Estimate Benefits of Countermeasures

To estimate the benefits of safety improvement projects (countermeasures), crash modification 

factors (CMF) are utilized. CMF is a term that is widely used in road safety engineering. A CMF is the 

ratio of expected crash frequency at a location with a countermeasure divided by the expected crash

frequency at the location without the countermeasure. If the expected crash frequency with a treatment is

9 and the expected crash frequency without the treatment is 12, then the CMF is 9/12 = 0.75.

Some 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. FHWA has developed the CMF Clearinghouse,(78) which houses a Web-based database of

CMFs along with supporting documentation to help traffic engineers identify the most appropriate

countermeasure for their safety needs. It is a live database in which new CMFs are added as they

become available through research. The CMF clearinghouse has adopted a star rating to represent the

quality of each CMF. A 5-star CMF represents a CMF that has been developed using a valid statistical

methodology.

Part III of this guide reports study findings from a variety of sources. These findings reported a 

change in crash frequency or crash rate as part of a cross-sectional study, a before-after 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 crash data used, methodology, and sample size.

• The country of origin.

In general, findings that appeared unreasonable, 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) were discarded. The results are presented as the expected change in crash

frequency, 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 crashes 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 in 

finding ways 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 in order to determine its applicability

to his or her specific project. Readers may wish to use their own CMFs or the results of another study

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Chapter 6. Safety Analysis Methods 

finding known to them should they believe that it is more accurate or better reflects conditions occurring at

the location in question.

The target benefit of any countermeasure is a reduction in the frequency or severity of crashes.

Assumptions regarding the potential benefit(s) of a countermeasure must be realistic. The crash 

frequency (or crash frequency of a specific group of crashes) cannot be driven below zero. To quantify

the safety benefit of implementing a countermeasure, the estimated crash reduction that will be 

connected with the implementation of the countermeasure must be determined. If a countermeasure is

successful in eliminating or reducing the severity of crashes that would have been expected without the

countermeasure, then the benefits can be attributed to the countermeasure.

When two countermeasures 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, countermeasure A

might have a CMF of 0.90, and countermeasure B might have a CMF of 0.80. Combined, the two

countermeasures should have an expected benefit of 0.72 (CMF A (0.90) x CMF B (0.80)).

Usually, countermeasures will only be effective when applied to a particular target group of crashes.

For example, the installation of protected left-turn phasing on one approach should substantially reduce

left-turn crashes involving that particular approach, but cannot be expected to affect left-turn crashes on

any other approach.

Countermeasures can also have undesirable effects worth considering in evaluating their overall

benefit. For example, the installation of right-turn channelization may reduce crashes involving rightturning vehicles and possibly rear-end crashes on a particular approach, but may increase crashes

involving pedestrians. If the countermeasure is to be applied, both positive and negative consequences

need to be considered.

The potential crash reduction from a countermeasure is determined by multiplying the expected

number of crashes by the percentage reduction that the countermeasure is expected to have. The

expected number of crashes (total or by severity) may be assumed to be the same as in the period before 

the countermeasure, but a much more refined method would be to develop an estimate of the expected

number of crashes based on SPF curves or the EB method.

Placing an economic value on crashes by severity is a common practice in quantifying the safety

benefits of a countermeasure. 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 countermeasure means multiplying the expected crash 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 countermeasure is as follows:

Safety Benefit ($) = ΔnPDO x CPDO + ΔnI x CI + ΔnF x CF (5)

Where: ΔnPDO = Expected reduction in property-damage-only crashes

CPDO = Societal costs of property-damage-only crashes

ΔnI = Expected reduction in injury crashes

CI = Societal costs of injury crashes

ΔnF = Expected reduction in fatal crashes

CF = Societal costs of fatal crashes.

Collision Type Societal Crash Costs

Fatal (K) $4,008,900 

Disabling Injury (A) $216,000

Evident Injury (B) $79,000 

Fatal/Injury (K/A/B) $158,200

Possible Injury (C) $44,900 

PDO (0) $7,400 

Exhibit 6-18. Societal crash cost estimates by crash severity

Source: Table 7-1 of the Highway Safety Manual

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Chapter 6. Safety Analysis Methods 

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 

countermeasure. Calculation of the safety benefit involves determining the product of the yearly average

number of crashes, the societal benefit, and the estimated reduction in crashes grouped by crash type 

(Exhibit 6-19). The total societal benefit is calculated to be $104,948.

Crash

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/ 8 1.6 40% 0.64 $158,200 $101,248

Injury

PDO 25 5.00 10% 0.50 $7,4, 00 $3,700

Total $104,948

Exhibit 6-19. Example calculation of safety benefit of adding a right-turn lane.

6.6.2 Step 2 – Estimate Costs of Countermeasures

The next step of economic appraisal is the estimation of implementation costs of projects

(countermeasures). Similar to other roadway improvement projects, implementation costs of projects may

include right-of-way acquisition, construction cost, utility relocation, environmental impacts, operation

costs, maintenance costs, and the cost associated with planning and engineering.

The most important source for the implementation costs of projects is the local past experience of the

road agency. The SafetyAnalyst software also has costs associated with a number of countermeasures

built-in.

6.6.3 Step 3 – Evaluate Cost Effectiveness of Countermeasures

Once benefits and costs of road safety improvement projects are calculated, various methods for

benefit-cost analysis practiced in engineering economy can be utilized to evaluate whether the projects

are economically viable. In practice, net present worth and benefit-cost ratio are the most commonly used

methods.

The benefits and costs estimated before are likely to occur in the future in different time spans. As a 

result, the present worth of benefits and costs are calculated using an average interest rate (discount

rate). Then, the difference between the discounted costs and discounted benefits at the present year (net

present worth) is calculated. A project with a net present worth greater than zero indicates a projects with 

benefits more than costs. These types of projects are economically viable.

In the benefit-cost ratio (BCR) method, first the present worth of benefits and costs are calculated.

Then the ratio of present worth of benefits over present worth of costs is calculated. If the ratio is greater

than 1.0, the project is economically justified.

The countermeasures which are found economically justified can be implemented to address the 

safety problems identified in the diagnosis step. However, the main challenge is that resources to 

implement all countermeasures are not available. As a result, the road agency needs to make a decision

to identify which countermeasures should be implemented considering the scarce resources. 

6.6.4 Case Study

Exhibit 6-20 summarizes the result of benefit-cost analysis. In this table, the countermeasures

proposed in the countermeasure selection step are listed. CMFs associated with each countermeasure

have been obtained from the CMF Clearinghouse. The original studies through which the CMFs were 

developed are cited as footnotes. No CMF was found for two of the countermeasures in Exhibit 6-20.

Using the CMFs, crash reduction over a 5-year period was calculated. The crash reduction was converted

to benefits using the societal cost of crashes shown in exhibit 6-20. Net present worth of benefits was

calculated using a discount rate of 2%. Net present worth of total costs of projects was calculated. A life

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Chapter 6. Safety Analysis Methods 

cycle of 20 years was assumed for countermeasures. The BCR for countermeasures shows that all

proposed countermeasures are economically justified.

The two countermeasures for which no CMF was found are recommended because both are low cost

countermeasures and potentially have positive operational impacts.

Countermeasure CMF

5-Year Total

Crash Reduction 

After 

Countermeasure

Benefits

($) 

Total Cost

($) BCR

Heighten conspicuity of

the signal displays for

eastbound intersectionapproaching roadusers

0.85 for all

crashes

(all severities) 13.5 627,267 6,000 104.5

Address stopping sight

distance issues on 

eastbound approach to 

the intersection

0.65 for angle 

crashes

(all severities) 3.5 162,625 2,000 81.3

Pavement friction test 

and potential follow-on 

construction work

0.76 for all

crashes

(all severities)

21.6 1,003,627 60,000 16.7

Further enhance the 

presence of Road B,

on approach along 

Street A

0.984 for all

crashes

(all severities) 1.44 66,909 2,000 33.5

Install “Intersection 

Ahead” warning sign

0.65 for all

crashes

(all severities)

3.5 162,625 2,000 81.3

Install a westbound 

left-turn lane

0.9 for all

crashes

(all severities)

9 418,178 280,000 1.5

CMF values developed from a variety of sources, including the Highway Safety Manual and the CMF Clearinghouse 

Exhibit 6-20. Summary of benefit-cost analysis.

6.7 PROJECT PRIORITIZATION

In the previous steps of the road safety management process, one or more countermeasures for one

or more intersections might be selected. One countermeasure or a combination of countermeasures can

be referred to as one project. Now the traffic engineer and the road agency face the important decision of

which project should be implemented first and which projects should be implemented at all, considering

the limited available resources to maximize benefits to the public (i.e., have most safety improvements).

The following two simple methods can help prioritize projects (71):

• Ranking by economic effectiveness measures.

• Incremental benefit-cost analysis ranking.

The ranking by economic effectiveness methods is the simplest method for prioritization of projects.

In this method, economically justified projects are ranking from high to low by any of the following

measures:

• Net present worth.

• Projects costs.

• Monetary value of project benefits.

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Chapter 6. Safety Analysis Methods 

• Total number of crashes reduced.

Next, the agency may start the projects from the top of the list to the bottom. The main challenge

associated with this method is that it ignores resource constraints and potential competing priorities.

In the incremental benefit-cost analysis ranking, the following steps are to be taken (71):

1. Calculate the BCR for each project.

2. Arrange projects with a BCR greater than 1.0 in increasing order based on their estimated cost.

The project with the smallest cost is listed first.

3. Calculate the BCR for the incremental investment by dividing the difference between benefits of

the first two ranked projects by the difference between costs of the first two ranked projects.

4. If the BCR for the incremental investment is greater than 1.0, the project with the higher cost is

compared to the next project in the list. If the BCR for the incremental investment is less than 1.0,

the project with the lower cost is compared to the next project in the list.

5. Repeat this process. The project selected in the last pairing is considered the best economic

investment.

To produce a ranking of projects, the entire evaluation is repeated without the projects previously

determined to be the best economic investment until the ranking of every project is determined.

6.7.1 Case Study

Exhibit 6-21 shows the priority ranking of countermeasures, which were selected as part of the 

countermeasure selection step shown in Exhibit 6-20. In this case study, ranking was performed based 

on the monetary value of project benefits. It should be noted that the road agency has to consider their

budget constraints to identify all or some of the projects that can be implemented. Also, if the criteria for

ranking changes based on the road agency strategic directions, the priority ranking will change. For

example, if the ranking is performed based on total cost of the project, another ranked list is obtained.

Rank Countermeasure CMF

5-Year Total

Crash Reduction 

After 

Countermeasure

Benefits

($) 

Total Cost

($) BCR

1 Pavement friction test and 

potential follow-on 

construction work

0.76 for all

crashes (all

severities)

13.5 627,267 6,000 104.5

2 Heighten conspicuity of the

signal displays for eastbound 

intersection-approaching roadusers

0.85 for all

crashes (all

severities)

3.5 162,625 2,000 81.3

3 Install a westbound left-turn 

lane

0.9 for all

crashes (all

severities)

21.6 1,003,627 60,000 16.7

4 Address stopping sight

distance issues on eastbound 

approach to the intersection

0.65 for all

crashes (all

severities)

1.44 66,909 2,000 33.5

5 Install “Intersection Ahead”

warning sign

0.65 for all

crashes (all

severities)

3.5 162,625 2,000 81.3

6 Further enhance the presence

of Road B, on approach along

Street A

0.984 for all 

crashes (all

severities)

9 418,178 280,000 1.5

Exhibit 6-21. Priority ranking of selected countermeasures.

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Chapter 6. Safety Analysis Methods 

6.8 SAFETY EFFECTIVENESS EVALUATION

Safety effectiveness evaluation is the process of developing quantitative estimates of how a 

countermeasure, project, or a group of projects has affected crash frequencies or severities. The 

effectiveness estimate for a project or treatment is a valuable piece of information for future safety

decision making and policy development.

Safety effectiveness evaluation may include:

• Evaluating a single project at a specific site to document the safety effectiveness of that specific

project.

• Evaluating a group of similar projects to document the safety effectiveness of those projects.

• Evaluating a group of similar projects for the specific purpose of quantifying a CMF for a

countermeasure.

• Assessing the overall safety effectiveness of specific types of projects or countermeasures in

comparison to their costs.

Practitioners should conduct a before-after study to evaluate the safety effectiveness of any project. A

before-after study compares crash frequencies at a site are before and after implementation of a

treatment. The main challenge associated with conducting a before-after study is that a number of factors

change at the subject site from the before to after period, in addition to the treatment. These factors may

include a change in traffic volume, a change in weather conditions, and other unknown factors. As a

result, it is critical to separate the safety changes associated with the treatment from the other factors that

have changed from the before period to the after period through a valid before-after study.

In a before-after study, the collision frequencies at the treated sites in the after period are compared 

with collision frequencies at the same sites had the treatment not been implemented in the after period.

Obviously, the collision frequencies had the treatment not been applied are not known. As a result, there

are a number of techniques in the literature to predict the collision frequencies in the after period had the 

treatment not been applied. The following section identifies the commonly used techniques in road safety:

6.8.1 Before-After Study with Comparison Group

In this type of before-after study, a comparison group is selected comprising sites that have similar

geometric and operational characteristics as the treatment sites. The number of sites in the comparison 

group is more than the treatment group. The rationale behind this technique is that all contributing factors

that affect safety (i.e., traffic volume, weather, etc.) from the before period to the after period impact both

the treatment group and the comparison group in the same way, and the only difference between the

treatment sites and comparison sites is the treatment itself. In this method, collision frequency of the

treatment group had the treatment not been applied is predicted by multiplying crash frequency of the

treatment sites in the after period by the ratio of crash frequency of the comparison sites in the after

period to the crash ratio of the comparison sites in the before period.

This method has been widely used in road safety. The only challenge associated with this method is

that it does not consider the regression-to-the-mean phenomenon.

6.8.2 Before-After Study with Empirical Bayes

In this technique, instead of using a comparison group, the SPF developed for the reference group

associated with the treatment sites is used to predict crash frequency at the treatment sites in the after

period had the treatment not been applied. This technique is the preferred technique because it considers

the regression-to-the-mean phenomenon.

The HSM provides more details on study design and methods for evaluation of safety effectiveness of

countermeasures, and Ezra Hauer provides details on various methods for conducting a valid before-after

study in road safety in his seminal book.(79)

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Chapter 7. Operational Analysis Methods 

CHAPTER 7

OPERATIONAL ANALYSIS METHODS

TABLE OF CONTENTS

7.0 OPERATIONAL ANALYSIS METHODS............................................................................. 7-2

7.1 Operational Performance Measures ......................................................................... 7-5

7.1.1 Automobile Methodology ............................................................................. 7-6

7.1.2 Pedestrian Methodology .............................................................................. 7-9

7.1.3 Bicycle Methodology .................................................................................. 7-10

7.1.4 Multimodal Approach ................................................................................. 7-11

7.2 Traffic Operations Elements ................................................................................... 7-11

7.2.1 Traffic Volume Characteristics ................................................................... 7-11

7.2.2 Intersection Geometry................................................................................ 7-12

7.2.3 Signal Timing and Hardware Capabilities.................................................. 7-12

7.3 General Considerations Sizing an Intersection....................................................... 7-13

7.4 Critical Lane Analysis.............................................................................................. 7-14

7.5 HCM Operational Procedure for Signalized Intersections ...................................... 7-17

7.6 Arterial and Network Signal Timing Models............................................................ 7-18

7.6.1 Introduction ................................................................................................ 7-18

7.6.2 Developing a Macroscopic Simulation Model ............................................ 7-18

7.7 Microscopic Simulation Models............................................................................... 7-19

7.7.1 Introduction ................................................................................................ 7-19

7.7.2 Developing a Microsimulation Model ......................................................... 7-19

7.8 Operational Performance Model Selection ............................................................. 7-20

LIST OF EXHIBITS

7-1 Still reproduction of a graphic from an animated traffic operations model ......................... 7-3

7-2 Overview of intersection traffic analysis models................................................................. 7-4

7-3 Typical lane groups for analysis ......................................................................................... 7-6

7-4 Automobile LOS thresholds at signalized intersections...................................................... 7-8

7-5 Effect of flow rate and detection design on max-out probability ......................................... 7-9

7-6 Evaluation of circulation area based on pedestrian space ................................................. 7-9

7-7 LOS criteria for pedestrian and bicycle modes................................................................. 7-10

7-8 Planning-level guidelines for sizing an intersection.......................................................... 7-14

7-9 Graphical summary of the quick estimation method......................................................... 7-15

7-10 V/C ratio threshold descriptions for the quick estimation method .................................... 7-16

7-11 Criteria for selecting a traffic analysis tool category ......................................................... 7-21

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Chapter 7. Operational Analysis Methods 

7.0 OPERATIONAL ANALYSIS METHODS

Chapter 6 described tools that can be used to assess safety performance at a signalized

intersection. Evaluating a candidate treatment also usually requires assessing its performance 

from the perspective of traffic operations. This chapter will 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 softwarebased, are available. Selection of 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 site-specific 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. Most can generate animated graphics displays

depicting the movement of individual vehicles and pedestrians in an intersection (see Exhibit 7-1)

and some allow for three-dimensional rendering. These enhancements have caused an 

increasing trend toward the use and acceptance of advanced traffic modeling techniques.

While the range of operational performance models is more or less continuous, it will be

categorized into the following analysis levels for purposes of this discussion:

• Rules of thumb for intersection sizing.

• Critical lane analysis.

• The HCM 2010 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.

Each analysis level 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. Additional guidance for each level

above can be found in the FHWA Traffic Analysis Tools Program website at

http://ops.fhwa.dot.gov/trafficanalysistools/.

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Chapter 7. Operational Analysis Methods 

Exhibit 7-1. Still reproduction of a graphic from an animated traffic operations model.

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Chapter 7. Operational Analysis Methods 

Exhibit 7-2. Overview of intersection traffic analysis models.

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.

In all analysis methods, especially those that involve modeling, it is important that any tools

used are calibrated and validated for real-life field conditions to ensure credible analysis results.

Data collected include entering traffic volume, turning movements, queue lengths, vehicle speed,

and lane capacity. Modifications to the software tools may be necessary to accurately reflect field

conditions. It is necessary to document all calibration adjustments to support credibility.

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Chapter 7. Operational Analysis Methods 

7.1 OPERATIONAL PERFORMANCE MEASURES

A signalized intersection’s performance is described by the use of one or more quantitative

measures that characterize some aspects of the service provided to specific road user groups.

The HCM 2010 introduces four road user groups: automobile, pedestrian, bicycle, and transit. In

order to encourage users to consider all travelers on a facility when they perform analyses and

make decisions, the HCM 2010 integrates material on automobile and non-automobile modes.

Generally, three methodologies are used to evaluate the performance measures of signalized

intersection operations. They are referred to as the automobile methodology, the pedestrian 

methodology, and the bicycle methodology. Each methodology addresses one possible travel

mode through the intersection. A complete evaluation of intersection operation includes the

separate examination of performance for all relevant travel modes. The performance measures

associated with each travel mode are as follows:

a) Automobile mode

• Capacity and volume-to-capacity ratio.

• Delay and Level of Service (LOS).

• The back-of-queue and queue storage ratio.

• Probability of phase termination by max out or force-off.

b) Pedestrian mode

• Corner and crosswalk circulation area.

• Pedestrian delay.

• Pedestrian LOS score.

c) Bicycle mode

• Bicycle delay.

• Bicycle LOS score.

The HCM 2010 evaluates the intersection operation by the concept of movement groups and 

lane groups.(2) A separate movement group is established for (a) each turn movement with one 

or more exclusive turn lanes with no shared movements, and (b) the through movement inclusive

of any turn movements that share a lane.

The movement group and lane group designations are very similar in meaning. In fact, their

differences emerge only when a shared lane (such as a through lane that is also serving right

turns) is present on an approach with two or more lanes. (2) Thus, any shared lane is considered 

as a separate lane group, while an exclusive turn lane or lanes should be designated as another

separate lane group. Similar to movement group definition, any lanes that are not exclusive turn 

lanes or shared lanes are combined into one lane group. These rules for movement group and

lane group result in designation of different group possibilities for an intersection approach.

Exhibit 7-3 presents some common movement groups and lane groups.(2)

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Chapter 7. Operational Analysis Methods 

Exhibit 7-3. Typical lane groups for analysis.

(2)

7.1.1 Automobile Methodology

The automobile methodology described in the HCM 2010 is originally based on the results of

NCHRP Project 3-28(2) study that formulized (a) the critical movement analysis procedure 

developed in the United States, Australia, Great Britain, and Sweden, and (b) the automobile

delay estimation procedure, developed in Great Britain, Australia, and the United States. The

updated procedures described in the HCM 2010 are used to evaluate the associated automobile

performance measures for signalized intersection.

7.1.1.1 Capacity and volume-to-capacity ratio

Capacity is defined as the maximum sustainable flow 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, and width of lanes, grades, and lane use allocations, as well as

signalization conditions. Under the HCM 2010 procedure, intersection capacity is measured for

critical lane groups (those lane groups that have the highest volume-to-capacity ratios). Critical

intersection volume-to-capacity ratios are based on flow ratio for the critical phase. A critical

phase is one phase of a set of phases that occur in sequence and whose combined flow ratio is

the largest for the signal cycle. Rules for determining critical flow ratio and critical path are further

explained in HCM 2010.

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.(80) 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. (81)

The volume-to-capacity (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

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Chapter 7. Operational Analysis Methods 

capacity (a v/c ratio greater than 1.0), traffic flow is unstable and excessive delay and queuing is

expected. Aside from the excessive demand, there are other factors that may contribute to cycle 

failure as well (e.g., influence of pedestrians, poor signal timing, incidents, etc.). 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). Over-designing an

intersection should be avoided due to negative impacts to all users associated with wider street

crossings, the potential for speeding, land use impacts, and cost.

Delay

Delay is defined in the HCM 2010 as “the additional travel time experienced by a driver,

passenger, bicyclist, or pedestrian beyond that is required to travel at the desired speed.”(2) The

signalized intersection chapter (Chapter 18) of the HCM 2010 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 the queue, and 

accelerating. Expectation of delay at a signalized intersection is different than at an unsignalized 

intersection.

The control delay equation comprises three elements: uniform delay, incremental delay, and 

initial queue delay. The primary factors that affect uniform delay are lane group volume, lane 

group capacity, cycle length, and effective green time. Two factors that account for incremental

delay are (a) the effect of random and cycle-by-cycle fluctuations in demand that occasionally

exceed capacity, and (b) a sustained oversaturation during the analysis period, when the

aggregate demand exceeds the aggregate capacity. The third component of the control delay

illustrates the delay due to an initial queue, as a result of unmet demand in the previous time 

period.

The Back-of-queue and Queue Storage Ratio

Practitioners should evaluate vehicle queuing, an important performance measure, as part of

all signalized intersections analyses. Vehicle queue estimates help determine the amount of

storage required for turn lanes and whether spillover occurs at upstream facilities (driveways,

unsignalized intersections, signalized intersections, etc.). Queues that extend upstream from an

intersection can spill back into and block upstream intersections, causing side streets to begin to

queue back. The back-of-queue is the maximum backward extent of queued vehicles during a

typical cycle. This back-of-queue length depends on the arrival pattern of vehicles and the 

number of vehicles that do not clear the intersection during the previous cycle.(2) Approaches that

experience extensive queues also may experience an over-representation 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. This is the length at which 95 percent of lane queues

are less than in a given study period.

The queue storage ratio represents the proportion of the available queue storage distance 

that is occupied at the point in the cycle when the back-of-queue position is reached.(2) If this ratio

exceeds 1.0, then the storage space will overflow and queued vehicles may block other vehicles

from moving forward.

Volume 3 of the HCM 2010 provides procedures for calculating back-of-queue length and the

queue storage ratio. In addition, all known simulation models provide ways of obtaining queue 

estimates.

Level of Service (LOS)

Level of Service (LOS) is a grading-scale based descriptor that attempts to relate relative

operational quality (based on certain measures of effectiveness) to that of driver perception in a 

simple fashion. Control delay is used as the basis for determining LOS for an intersection or a

single approach. Delay thresholds for the various LOS are given in Exhibit 7-4.

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Chapter 7. Operational Analysis Methods 

Typically LOS is reported on an A through F scale, with Level A being the best LOS and

Level F being the worst. While the A through F scale seems fairly straightforward, the

quantifiable measures of effectiveness (MOEs) used to derive the “grading scale” are derived

from empirical data.

For signalized intersections, control delay (in seconds) is the MOE for the LOS scale (note

that the grade thresholds for signalized intersections are different than for stop-controlled 

intersections). However, there are other MOEs that are important in characterizing the operations

of signalized intersections, including v/c ratio and intersection utilization. Furthermore, while it is

common for weighted averages to be used in describing overall intersection operation, it is often 

the case where one or more specific movements, lane groups, or approaches may be operating 

poorly, but be masked by the overall average. Also, when intersections are operating at capacity

(i.e., LOS F) and beyond, only close analysis of the various MOEs will allow for distinctions to be 

made among different alternatives. Finally, it should be noted that safety is not reflected or

implied in LOS.

Exhibit 7-4. Automobile LOS thresholds at signalized intersections.

(2)

Control Delay per Vehicle

(seconds per vehicle)

LOS by V/C Ratio

≤1 >1

≤ 10 A F

> 10-20 B F

> 20-35 C F

> 35-55 D F

> 55-80 E F

> 80 F F

LOS has historically been given high emphasis by practitioners due to its relative ease of

explanation, but it is a crude measure at best. The language of LOS (A-F scale) is easily

understood, regardless of the background MOEs used or their accuracy in actually determining

the operation of the intersection.

Probability of Phase Termination by Max-out or Force-off

For actuated and semi-actuated operation, 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 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. However, the safety benefit of green extension

can be negated if the phase is extended to its maximum duration (i.e., maximum-green setting).

The probability of termination by “max-out” is dependent on flow rate in the subject phase and the

“maximum allowable headway.” Exhibit 7-5 illustrates the relationship between max-out

probability, maximum allowable headway, maximum green, and flow rate for actuated and semiactuated operation. For coordinated operation, the main street phase will receive its entire split

time (effectively a force-off) regardless of calls on conflicting phases.

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Chapter 7. Operational Analysis Methods 

Exhibit 7-5. Effect of flow rate and detection design on max-out probability.

Source: Bonneson, J. et al, Intelligent Detection-Control System for Rural Signalized

Intersections, FHWA/TX-03/4022-2, 2002.

7.1.2 Pedestrian Methodology

This section describes the methodology for evaluating the performance of a signalized

intersection in terms of its service to pedestrians.

Corner and Crosswalk Circulation Area 

The corner and crosswalk circulation area are used to evaluate the circulation area provided 

to pedestrians while they are waiting at the corner or crossing the crosswalk, respectively. Exhibit

7-6 can be used to evaluate intersection performance from a circulation-area prospective in terms

of space available to the average pedestrian.(2)

Exhibit 7-6. Evaluation of circulation area based on pedestrian space.

(2)

Pedestrian

Space (ft2 per

pedestrian)

Description

>60 Ability to move in desired path, no need to alter movements

> 40-60 Occasional need to adjust path to avoid conflicts

> 24-40 Frequent need to adjust path to avoid conflicts

> 15-24 Speed and ability to pass slower pedestrian restricted

> 8-15 Speed restricted, very limited ability to pass slower pedestrian

≤ 8 Speed severely restricted, frequent contact with other users

The critical parameter for the analysis of circulation area at the street corner and crosswalk is

the product of available time and space with pedestrian demand, which combines the physical

design constrains (i.e., available space) and signal operation (i.e., available time). This parameter

is referred to as the “time-space” available for pedestrian circulation.

(2) Circulation time-space and

pedestrian circulation area are estimated based on intersection and pedestrian signal phasing

settings, pedestrian flow rates in different directions, and physical characteristics of the sidewalks.

Chapter 18 of the HCM 2010 provides the detailed procedure for calculating street corner and

crosswalk circulation area.

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Chapter 7. Operational Analysis Methods 

Pedestrian Delay

In the HCM 2010 (Chapter 18), pedestrian delay at a signalized intersection while crossing 

the major street is determined based on effective walk time and cycle length. The delay computed

in this step can be used to make judgments about pedestrian compliance. Research indicates

that pedestrians become impatient when they experienced delay in excess of 30 seconds per

pedestrian. In contrast, it is reported that pedestrians are very likely to comply with signal

indicators if their expected delay is less than 10 seconds per pedestrian.

(2)

Pedestrian LOS Score

Historically, the HCM has used a single performance measure as the basis for defining LOS.

However, in the HCM 2010, the LOS is separated for automobile and non-automobile modes.

Based on traveler perception research for pedestrians and bicyclists, it was found that a wide 

variety of factors should be considered in assessing the quality of service for non-automobile road

users. Therefore, a methodology for evaluating each mode was developed to mathematically

combine various factors into a score. Exhibit 7-7 presents the range of scores associated with 

each LOS for pedestrian and bicycle travel modes.

Exhibit 7-7. LOS criteria for pedestrian and bicycle modes.

(2)

LOS Score LOS

≤ 2.00 A

> 2.00 – 2.75 B

> 2.75 – 3.50 C

> 3.50 – 4.25 D

> 4.25 – 5.00 E

> 5.00 F

The pedestrian LOS score for the intersection is calculated based on a number of factors,

such as traffic counts during a 15-min period, 85th percentile speed on the major street,

pedestrian delay when traversing, and number of right-turn channelizing islands along crosswalk.

The detailed calculations of pedestrian LOS score are presented in the HCM 2010 (Chapter 18).

Finally, the pedestrian LOS is determined from Exhibit 7-7 by using the calculated pedestrian 

LOS score. As discussed above, LOS is a crude measure of pedestrian operational efficiency

and is often overused by designers.

7.1.3 Bicycle Methodology

This section describes the methodology for evaluating the performance of a signalized

intersection in terms of its service to bicyclists. This section replicates the procedure from Chapter

18 of the HCM 2010.

Bicycle Delay

The HCM 2010 provides an analysis procedure for assessing the delay for bicycles at

signalized intersections where there is a designated on-street bicycle lane on at least one

approach or a shoulder that can be used by bicyclists as a bicycle lane.

Many countries have reported a wide range of capacities and saturation flow rates for bicycle

lanes at signalized intersections. The HCM 2010 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.

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Chapter 7. Operational Analysis Methods 

Using the default saturation flow rate of 2,000 bicycles per hour, the capacity of the bicycle

lane and control delay at a signalized intersection can be computed, based on effective green 

time for the bicycle lane, and cycle length.

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. Bicyclists tend to have about the same tolerance for delay as 

pedestrians.

Bicycle LOS Score 

Following the same methodology as pedestrian mode, bicycle LOS score is first calculated

based on physical characteristics of the intersection, traffic flow rate, and the proportion of onstreet occupied parking. The detailed calculations of bicycle LOS score are presented in the HCM 

2010 (Chapter 18). Finally, the bicycle LOS is determined from Exhibit 7-7 by using the calculated 

bicycle LOS score. As discussed above, LOS is a crude measure of pedestrian operational

efficiency and is often overused by designers.

7.1.4 Multimodal Approach

In the HCM 2010, there are no stand-alone analyses for pedestrians, bicyclists, and transit

users. Instead, the HCM encourages performing multimodal analysis of non-automobile modes

on a specific facility of urban streets, such as a signalized intersection, in addition to automobile

analysis. The Transit Capacity and Quality of Service Manual (TCQSM), recognized as the

companion of HCM 2010, extensively covers the analysis of the transit mode. Therefore, the

HCM 2010 now addresses the transit mode only with respect to multimodal analysis of urban 

streets.(2) 

7.2 TRAFFIC OPERATIONS ELEMENTS

The following sections will describe signalized intersection operations as a function of the

following three elements and discuss their effects on operations.

1. Traffic volume characteristics.

2. Roadway geometry.

3. Signal timing and hardware capabilities.

7.2.1 Traffic Volume Characteristics

The traffic characteristics used in an analysis can play a critical role in determining

intersection treatments. Over-conservative judgment may result in economic inefficiencies due to

the construction of unnecessary treatments or an oversized intersection, 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 as the number of vehicles that

pass through the intersection over a specific period of time. In the case of overcapacity or

constrained situations, the traffic volume typically does not reflect the true demand on an

intersection because vehicles are queued upstream. In these cases, the user should develop a

demand profile 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. If the constraint is upstream, traffic

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Chapter 7. Operational Analysis Methods 

volumes would be metered at that location and “starve” the demand at the subject intersection; if

the constraint is downstream, traffic could spill back to the subject intersection and impede traffic

flow. These effects are 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 2010 uses a

default ideal saturation flow rate of 1,900 vehicles per hour. Ideal saturation flow assumes the 

following:

• 12-ft wide travel lanes.

• Through movements only.

• Even lane utilization,

• Level grades.

• No curbside impedances

• No pedestrians/bicyclists.

• No central business district influences.

The HCM 2010 provides adjustment factors for non-ideal conditions to estimate the prevailing 

saturation flow rate. Saturation flow rate can vary in time and location and has 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 improve the 

accuracy of the analysis.

Practitioners should evaluate existing or planned intersection geometry to determine features

that may impact operations and that require special consideration.

7.2.3 Signal Timing and Hardware Capabilities

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 lost time. 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.

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Chapter 7. Operational Analysis Methods 

• Change and clearance interval. The change and clearance interval represents the

amount of time needed for vehicles to safely clear the intersection. It includes the yellow

change and red clearance intervals and is primarily set based on the speed of

approaching vehicles and the width of the intersection. The effect of the change and

clearance interval on capacity is dependent upon the lost time.

• Lost time. Lost time represents the unused portion of a vehicle phase. Lost time occurs

twice during a phase: at the beginning when vehicles are accelerating from a stopped

position, and at the end when vehicles decelerate in anticipation of the red indication.

Longer lost 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 lost times than

conventional intersections.

• Cycle length. Cycle length determines how frequently during the hour each movement is

served. It is a direct input, in the case of pre-timed or coordinated signal systems running

on 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 can

result in increased delay and queues for all users, and may result in disobedience of the

traffic signal and other aggressive driving behavior.

• Phasing. The phasing plan is based on the treatment of each left turn (protected,

permitted, or protected-permitted). The number of phases at a signalized intersection,

which is directly correlated with its treatment of left turns, impacts the operating capacity

of the intersection as it affects effective green time for each movement.

• Signal Technology. Technology can play a significant role in the operating capacity of a

signalized intersection. A pre-timed signal, which provides a fixed amount of green time

to each intersection approach independent of actual traffic demand, is the simplest form

of operation. Actuated signals rely on vehicle detection technology and generally operate

more efficiently by extending signal phases when continuous demand is present and

skipping phases that would not be servicing any vehicles. The most advanced signal

technology, called adaptive signal control, uses sensors to read current traffic conditions

and modify signal timings based on real-time information.

• 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 delays, queues, and stops 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.

• Detector Technology. Use of detector features and settings can impact operations

positively or negatively. Employing features such as delay, lock, or switch can improve

service to waiting or approaching vehicles and streamline intersection operations.

Factors such as volumes, phasing, geometry, and driver characteristics (aggressive or

passive) will help influence if and how detector settings are used, and how the controller

receives those inputs.

7.3 GENERAL CONSIDERATIONS FOR SIZING AN INTERSECTION

This first level of analysis does not use formal models or procedures; instead, it relies on past

experience and rules of thumb to offer a very coarse approximation. In spite of its obvious

limitations, this approach can be used to size an intersection and determine appropriate lane

configurations. Guidelines for determining intersection geometry at the planning level are shown

in Exhibit 7-8.

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Chapter 7. Operational Analysis Methods 

Exhibit 7-8. 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 or through

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(3) Storage bays should accommodate one and one-half to two times the 

average number of left-turn arrivals during a cycle.

7.4 CRITICAL LANE ANALYSIS

Critical lane analysis (CLA) is usually applied at the planning stage and represents the 

highest of the four levels of operational performance models.

The Quick Estimation Method (QEM) 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)

allows the QEM to remain 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 the 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. Exhibit 7-9 illustrates the various steps involved in

conducting a QEM analysis, and Exhibit 7-10 identifies the various thresholds for the v/c ratio.

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Chapter 7. Operational Analysis Methods 

Exhibit 7-9. 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 non-conflicting movements. This step determines which 

movements are critical. The critical lane 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.

Step 6 – Determine the critical v/c 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 Exhibit 7-10.

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Chapter 7. Operational Analysis Methods 

Exhibit 7-10. V/C ratio threshold descriptions for the quick estimation method.(2)

Critical Volume-toCapacity 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 CLA 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 CLA

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 CLA procedures in general, and the QEM in particular:

• No provision exists for the situation in which 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 CLA 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 leftturn 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.

• Lost time is not directly accounted for in the CLA 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 will be often necessary to examine the intersection using a more

detailed level of operational performance modeling.

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Chapter 7. 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 CLA 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 Exhibit 7-2

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 shared movements 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 CLA 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 Exhibit 7-2, 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.

The HCM 2010 provides a more detailed analysis procedure than previous editions as it now

has improved methods for calculating delays and queues as well as for analyzing intersections

with actuated signals.

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 analysis does not explicitly account for travel lanes added just upstream or dropped

just downstream of the intersection.

• 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.

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Chapter 7. Operational Analysis Methods 

7.6 ARTERIAL AND NETWORK SIGNAL TIMING MODELS

7.6.1 Introduction

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 the HCM. Most

of the macroscopic simulation models for signalized intersections are designed to develop

optimum signal timing along an arterial. These models are usually used to improve progression

between intersections. 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.

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 Exhibit 7-2, 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 in Exhibit 7-2 as a part of the data flow between the

various analysis levels.

7.6.2 Developing a Macroscopic Simulation Model

Arterial and network models represent traffic flow by considering traffic stream characteristics

like speed, flow and density and their relationship to each other. These macroscopic models do

not track individual vehicles and their interactions, but rather employ equations of known traffic

flow behavior on the roadway facility being analyzed. Versions of these models have been

designed for specific types of facilities, but their application is usually limited to those unique 

applications (such as unconventional or alternate design configurations). Macroscopic analysis

models are also limited by the inability of the embedded models to accurately model

oversaturated conditions. Specifically, signalized intersection models have some limitations in 

estimating the delay experienced, number of stops, and queue length in oversaturated conditions.

Some arterial and network model developers have attempted to overcome these issues by

varying flow levels and performing input/output flow checks at intersections. However, the typical 

practice is to apply microscopic simulation models if the effects and extent of arterial or network

congestion need to be analyzed.

Macroscopic models require the following four types of data to be collected.

• Traffic data comprising traffic volumes and turning movement counts are typically

collected in 15-minute increments and usually the peak one hour count and the peak 15-

minute count within that one hour will be identified as input data into the model. These

counts are made for periods of interest within a day, which typically includes the AM

peak, PM peak, and off-peak periods.

• Geometric data such as the number of lanes and lane assignment at the intersection, as

well as turn bay presence and length.

• Phasing data that can be implemented will depend on existing geometry, signal head

locations and configurations, and the signal controller’s capabilities.

• Requirements of pedestrians and other intersection users like rail and transit will have a

significant impact on signal timing.

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Chapter 7. Operational Analysis Methods 

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

7.7.1 Introduction

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 an 

increasing range of available microsimulation software products. Microsimulation analysis tools

are based on a set of rules used to propagate the position of vehicles from one time step (usually

each second) to the next. Rules such as car following, lane changing, 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 multiple aspects

of driver decision-making in the simulated environment. Some simulation models can explicitly

model pedestrians, enabling the analyst to study the impedance effects of vehicles on

pedestrians and vice versa.

Microscopic models produce similar measures of effectiveness as their macroscopic

counterparts, although minor differences exist in the definition of some measures. Microscopic

model results typically include pollutant discharge measures. 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. Rather than being a model

input, capacity is an outcome produced by the driver behavior rules intrinsic to the model and the

modeler’s calibration adjustments to realistically replicate field conditions.

Microscopic simulation models also can be used to identify a condition’s duration, and can

account for the capacity and delay effects associated with known system-wide travel patterns.

Because microscopic models track the behavior of individual vehicles within a given roadway

environment, they are often more realistic in representing traffic flow and queuing propagation

under congested conditions than macroscopic tools. As a result, output measures of

effectiveness for congested networks from microsimulation models are often more representative

than those produced by macroscopic methods or tools.

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. Several modern simulation tools allow analysts to render their roadway network

simulation in two or three dimensions, allowing the model to serve not only its analytical purpose 

but also as a demonstration and public involvement tool.

7.7.2 Developing a Microsimulation Model

In the past, the level of effort involved with developing a microscopic simulation network was

greater than that of a macroscopic analysis, and significantly greater than a CLA. However,

recently there have been significant strides in modeling tool integration and user interface 

development. Some macroscopic intersection analysis tools currently feature conversion utilities

to generate a draft input file for a microsimulation model, or even feature the developer’s own

microsimulation model as part of an integrated traffic analysis and modeling suite. Like the HCM

operational procedure, microscopic simulation tools require a fully specified signal-timing plan

that must be generated externally; however, in the case of an integrated signal optimization and 

microsimulation modeling suite of tools, alternative timing plans can be developed and modeled

at the microscopic level with the literal “press of a button.” Unlike the HCM, calibration effort

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Chapter 7. Operational Analysis Methods 

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. The typical steps in a 

successful microsimulation modeling effort include:

Step 1—Identify the scope of the model. For signalized intersections or arterials, this will include

the subject intersection or roadway corridor and adequate length of roadway segments at the 

model boundaries to permit lane changing and full queue storage for signalized and unsignalized 

intersections (including driveways, etc.) in the model.

Step 2—Collect and organize field data. Data requirements include traffic volume data (either

roadway directional counts and intersection turning movements counts, or roadway counts and

origin-destination routing data, depending on model type), geometric data (road segment lengths

and number of lanes, length and number of turn bays, etc.) and traffic control data (lane 

markings, signing, signals and their timing plans). Field performance measures such as arterial

average speed or average queue lengths should also be collected, as these measures are

commonly used for model calibration and validation.

Step 3—Develop the current condition, or base, model in the microsimulation tool. Note that

almost all modern microsimulation models allow analysts to create their networks by “drawing”

them over scaled background aerial photography, greatly reducing model development time.

Step 4—Verify that the model performs as observed in the field, correcting any logical or coding 

errors where present and re-running the model. Calibration adjustments to aspects of the driver

behavior model(s) may be necessary to accurately reflect field conditions; all such adjustments

must be documented.

Step 5—Validate the model. Microsimulation model validation is an essential step in producing

credible results. Validation typically takes the form of statistical tests comparing average output

from multiple runs of the microsimulation model and the same output measures collected in the

field (see Step 2).

Step 6—Perform final current condition model runs and summarize output. The number of runs

to perform in generating the final performance measures are affected by network size and 

performance variability, with larger networks and congested networks requiring more modeling

runs to ensure statistically valid results. At least five (5) microsimulation modeling runs should be

performed as a general rule, and the results averaged for presentation.

Step 7—Develop alternatives. Using the current/base model as a departure point, create a new

version of the network for each set of alternative conditions requiring analysis. Ensure that the

same calibration settings used in the validated, current condition model are used for all

alternatives.

Step 8—Perform final runs of alternative model(s) and summarize output. As in Step 6, the

number of final runs for each alternative is dependent on network size and performance

variability. Typical practice is to perform the same number of runs of each alternative model as

were conducted for the base model.

Step 9—Presentation and reporting. As with any analysis process, the final step in using

microsimulation models is the presentation of output measures of performance and the 

assessment of alternatives based on those measures. The two- or three-dimensional renderings

of the modeled network possible with modern microsimulation tools can be a valuable method for

familiarizing professionals and the public with the modeling process and increasing audience 

confidence in both the tool and its results.

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Chapter 7. Operational Analysis Methods 

7.8 OPERATIONAL PERFORMANCE MODEL SELECTION

Situations vary widely based on a multitude of factors. Practitioners should strive to choose 

the right tool for their intersection needs. Often models can be combined in some way by

practitioners to address their particular situation.

The first step is identification of the analytical context for the task: planning, design, or

operations/construction. Seven additional criteria are necessary to help identify the analytical

tools that are most appropriate for a particular project. Depending on the analytical context and

the project's goals and objectives, the relevance of each criterion may differ. The criteria include:

1. Ability to analyze the appropriate geographic scope or study area for the analysis,

including isolated intersection, single roadway, corridor, or network.

2. Capability of modeling various facility types, such as freeways, high-occupancy vehicle

(HOV) lanes, ramps, arterials, toll plazas, etc.

3. Ability to analyze various travel modes, such as single-occupancy vehicle (SOV), HOV,

bus, train, truck, bicycle, and pedestrian traffic.

4. Ability to analyze various traffic management strategies and applications, such as

ramp metering, signal coordination, incident management, etc.

5. Capability of estimating traveler responses to traffic management strategies, including

route diversion, departure time choice, mode shift, destination choice, and

induced/foregone demand.

6. Ability to directly produce and output performance measures, such as safety measures

(crashes, fatalities), efficiency (throughput, volumes, vehicle-miles of travel (VMT)),

mobility (travel time, speed, vehicle-hours of travel (VHT)), productivity (cost savings),

and environmental measures (emissions, fuel consumption, noise).

7. Tool/cost-effectiveness for the task, mainly from a management or operational

perspective. Parameters that influence cost-effectiveness include tool capital cost, level

of effort required, ease of use, hardware requirements, data requirements, animation, etc.

Exhibit 7-11 summarizes the criteria that may be considered for the selection of a tool category.

Signalized Intersections: Informational Guide 7-21 
 

 

 

Chapter 7. Operational Analysis Methods 

Exhibit 7-11. Criteria for selecting a traffic analysis tool category.

Source: FHWA Traffic Analysis Tools, Volume 2, 2004.

Situations vary widely based on a multitude of factors. Practitioners should strive to choose

the right tool for their intersection needs. Additional guidance is available from the FHWA Traffic

Analysis Tools website at http://ops.fhwa.dot.gov/trafficanalysistools/tat_vol2/index.htm.

Signalized Intersections: Informational Guide 7-22 
 

 

 

 

 

 

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: System-Wide 

Treatments (Chapter 8), Intersection-Wide Treatments (Chapter 9), Approach Treatments (Chapter 10), 

and Individual Movement Treatments (Chapter 11). 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.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 8. System-Wide Treatments 

CHAPTER 8

SYSTEM-WIDE TREATMENTS

TABLE OF CONTENTS

8.0 SYSTEM-WIDE TREATMENTS......................................................................................... 8-3

8.1 Median Treatments ................................................................................................... 8-3

8.1.1 Description ................................................................................................... 8-3

8.1.2 Applicability .................................................................................................. 8-3

8.1.3 Key Design Features ................................................................................... 8-3

8.1.4 Safety Performance ..................................................................................... 8-9

8.1.5 Operational Performance............................................................................. 8-9

8.1.6 Multimodal Impacts ...................................................................................... 8-9

8.1.7 Physical Impacts ........................................................................................ 8-10

8.1.8 Socioeconomic Impacts ............................................................................. 8-10

8.1.9 Enforcement, Education, and Maintenance............................................... 8-10

8.1.10 Summary.................................................................................................... 8-11

8.2 Access Management............................................................................................... 8-13

8.2.1 Description ................................................................................................. 8-13

8.2.2 Applicability ................................................................................................ 8-14

8.2.3 Design Features......................................................................................... 8-14

8.2.4 Safety Performance ................................................................................... 8-19

8.2.5 Operational Performance........................................................................... 8-20

8.2.6 Multimodal Impacts .................................................................................... 8-20

8.2.7 Physical Impacts ........................................................................................ 8-20

8.2.8 Socioeconomic Impacts ............................................................................. 8-20

8.2.9 Enforcement, Education, and Maintenance............................................... 8-21

8.2.10 Summary.................................................................................................... 8-21

8.3 Signal Coordination................................................................................................. 8-22

8.3.1 Description ................................................................................................. 8-22

8.3.2 Applicability ................................................................................................ 8-23

8.3.3 Safety Performance ................................................................................... 8-23

8.3.4 Operational Performance........................................................................... 8-23

8.3.5 Multimodal Impacts .................................................................................... 8-24

8.3.6 Physical Impacts ........................................................................................ 8-24

8.3.7 Socioeconomic Impacts ............................................................................. 8-24

8.3.8 Enforcement, Education, and Maintenance............................................... 8-25

8.3.9 Summary.................................................................................................... 8-25

8.4 Signal Preemption and/or Priority ........................................................................... 8-25

8.4.1 Description ................................................................................................. 8-25

8.4.2 Emergency Vehicle Preemption................................................................. 8-25

8.4.3 Railroad Preemption .................................................................................. 8-26

8.4.3 Transit Vehicle Preemption........................................................................ 8-26

8.4.5 Applicability ................................................................................................ 8-27

8.4.6 Safety Performance ................................................................................... 8-27

8.4.7 Operational Performance........................................................................... 8-27

8.4.8 Multimodal Impacts .................................................................................... 8-27

8.4.9 Physical Impacts ........................................................................................ 8-27

8.4.10 Socioeconomic Impacts ............................................................................. 8-28

8.4.11 Enforcement, Education, and Maintenance............................................... 8-28

8.4.12 Summary.................................................................................................... 8-28

Signalized Intersections: Informational Guide 8-1 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 8. System-Wide Treatments 

LIST OF EXHIBITS

8-1 Issues associated with intersections with a narrow median ............................................... 8-4

8-2 Issues associated with intersections with a wide median................................................... 8-5

8-3 Median pedestrian treatments ............................................................................................ 8-7

8-4 Pedestrian signal treatments where medians are present ................................................. 8-8

8-5 This refuge island enables two-stage pedestrian crossings............................................... 8-9

8-6 Summary of issues for providing median treatments ....................................................... 8-12

8-7 Comparison of physical and functional areas of an intersection ...................................... 8-14

8-8 Diagram of the upstream functional area of an intersection............................................. 8-15

8-9 Access points near signalized intersections ..................................................................... 8-17

8-10 Access management requiring U-turns at a downstream signalized intersection............ 8-18

8-11 Access management requiring U-turns at an unsignalized, directional median opening. 8-18

8-12 Relative crash rates for unsignalized intersection access spacing .................................. 8-19

8-13 Summary of issues for providing access management.................................................... 8-22

8-14 Selected findings of safety effects associated with signal coordination or progression ... 8-23

8-15 Summary of issues for providing signal coordination ....................................................... 8-25

8-16 Summary of issues for providing signal preemption and/or priority.................................. 8-28

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Chapter 8. System-Wide Treatments 

8.0 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. These 

treatments 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. The following specific treatments are examined:

1. Median treatments.

2. Access management.

3. Signal coordination.

4. Signal preemption and/or priority.

5. Automated enforcement.

8.1 MEDIAN TREATMENTS

The median of a roadway is used for left turns, pedestrian refuge, restriction of or 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.

Medians can be either flush or raised, each having specific operational and safety characteristics

that may lead to tradeoffs in either.

8.1.1 Description

Median design contributes to safe and efficient operation of corridors and intersections,

especially left-turn and pedestrian movements. Specifically, width, height, length, 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. Medians

may also provide a refuge for pedestrians. 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 and public or private entrances.

8.1.2 Applicability

Operational or safety issues that could be addressed by median design changes include 

spillover of left-turn lanes into the through traffic stream, rear-end or side-swipe 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, height, length, 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 negated by operational or safety problems created by an

inappropriate width, as shown in Exhibits 8-1 and 8-2. 

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Chapter 8. System-Wide Treatments 

• Narrow medians: Many 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. Additionally, pedestrians can have difficulty at signalized

intersections with medians that are too narrow. At large intersections with medians,

pedestrians commonly cross the street in two stages. If the median width is too narrow,

pedestrians may not have sufficient room to wait safely and comfortably. Also, 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, wide medians increase

motor vehicle and bicycle clearance time, thus adding lost time and delay to the

intersection. If pedestrians are expected to cross the entire intersection 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 result in

the use of two sets of signal indications: one mid-intersection, and one on the far side.

Extremely wide medians can also cause driver confusion with respect to how motorists

are to maneuver turns. Extra pavement marking, island delineation and/or signing may

be needed to guide motorists. These factors increase the cost of construction and

operation of the intersection.

Exhibit 8-1. Issues associated with intersections with a narrow median.

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Chapter 8. System-Wide Treatments 

Exhibit 8-2. 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 may be delineated with reflectors, tape, or paint, in addition to 

the presence of lighting.

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.

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Chapter 8. System-Wide Treatments 

Where left-turn lanes are provided in the median, raised medians should be used to separate 

left-turn and opposing through traffic on medians 14 to 16 ft wide or less. These raised medians

should be 4 ft wide. Medians 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 11.

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 4 ft wide.

• Bullet-nose median ends are preferred for medians 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 14 ft wide with a control radius of 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, bicyclists, and through traffic on the opposing approach if

permissive left turns are allowed. 

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. Exhibit 8-3 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.

Cut-through and ramped medians both provide pedestrian refuge, but cut-through medians

are susceptible to hold roadway drainage and resulting debris. If space allows for ramped 

medians, they can provide extra visibility to pedestrians by being vertically separated from the

roadway. Both cut-through and ramped medians should be designed and operated in a way that

provides visibility and conspicuity of pedestrians located in the median, as well as a line-of-sight

from the median to roadway users. This is especially important when median landscaping is

present. The landscaping must be maintained to provide pedestrians a line-of-sight over and

around the landscaping and give motorists the opportunity to detect pedestrians in 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.

(37)

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Chapter 8. System-Wide Treatments 

Exhibit 8-3. Median pedestrian treatments.(37) 

Exhibit 8-4 summarizes pedestrian signal treatments, which also depend on the width of the 

median. 

• Narrow crossings providing no refuge require a one-stage crossing using a single set of

pedestrian signal displays and detectors. For this option, pedestrian clearance time

needs to accommodate crossing the entire roadway.

• Wide intersection crossings with ample room for pedestrians to wait in the median (and

where it is advantageous to all users to cross in two stages) require separate pedestrian

signal displays and detectors for each half of the roadway. Pedestrian clearance times

are set independently for each half of the roadway, as shown in Exhibit 8-5.

• 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.

Signalized Intersections: Informational Guide 8-7 
 

Chapter 8. System-Wide Treatments 

(a) One-stage pedestrian crossing.

(b) Two-stage pedestrian crossing.

(c) One-stage pedestrian crossing with optional two-stage crossing.

Exhibit 8-4. Pedestrian signal treatments where medians are present.

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Chapter 8. System-Wide Treatments 

Exhibit 8-5. This refuge island enables two-stage pedestrian crossings.

Source: Michael Ronkin (Safety Benefits of Raised Medians and Pedestrian Refuge Areas, 

FHWA, 2010)

8.1.4 Safety Performance 

Medians at intersections can provide safety benefits similar to medians between

intersections. Introducing distance between opposing flows can decrease the frequency and

severity of crashes. The presence of a raised median impacts motorists’ ability to cross the 

opposing lanes, which can reduce head-on collisions. One report has shown that at urban and 

suburban intersections, multiple-vehicle crash frequency increases as median width increases for

widths between 14 ft and 80 ft, unlike in rural areas where multiple-vehicle crash rates tend to be 

lower for wider medians.(82) 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

30 ft and 60 ft wide.(83)

One study found decreasing crash rates with increasing median widths.(84) A Michigan State

University study found that Michigan’s boulevard roadways experienced a crash rate half that of

roadways with continuous center left-turn lanes.(85) A median width of 30 ft to 60 ft was found to

be the most effective in providing a safe method for turning left.

The frequency of minor collisions and vehicle damage claims may increase when raised 

medians are present as a result of drivers misinterpreting their distance from the raised median.

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, 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.(86) 

Depending on the radius design, the presence of a raised median may impact the speed at

which motorists can maneuver left turning movements. A less severe radius will allow for higher

speeds of left-turning traffic, which can help clear intersections of traffic more quickly and reduce

cycle lengths and delay, but may have adverse effects on pedestrian and bicycle users.

8.1.6 Multimodal Impacts

As noted previously, the width of the median (and the roadway in general) directly impacts

the amount of time needed for pedestrians and bicycles to cross the roadway. Large intersections

with no median or a median too narrow to provide a refuge force pedestrians to cross the entire 

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Chapter 8. System-Wide Treatments 

street in one stage. Therefore, provision of a median with at least enough width to accommodate 

a pedestrian can provide 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 4 ft/s used to

time pedestrian clearance intervals.

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 in the median should not affect 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.

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, discussed in Section 8.2. The frequency of

minor collisions and vehicle damage claims will likely increase when raised medians are installed;

sometimes drivers misinterpret their vehicle’s distance from the raised median.

Landscaping can play an important esthetic 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 signals and signs, pedestrian crossings, nearby railroad

crossings, and school zones are not obstructed. Median planting of trees or shrubs greater than 2 

ft in height should be well away from the intersection (more than 50 ft). No plantings having

foliage between 2 ft and 8 ft in height should be present within sight distance triangles.

Low shrubs or plants not exceeding a height of 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 plantings should have adequate watering and drainage systems or be drought

resistant. FHWA’s report Vegetation Control for Safety provides additional guidelines and

insight.(87)

In addition to landscaping height considerations, AASHTO’s Roadside Design Guide provides

guidance to establish an enhanced lateral offset distance to signs, poles, trees, plants, and

shrubbery located within the median. Specifically, the enhanced lateral offset is intended to 

provide an additional level of protection for roadway users at high-risk locations, such as at

locations where lanes merge or at driveways and medians are present. The recommended

enhanced lateral offset distance is 4 to 6 ft.

8.1.9 Enforcement, Education, and Maintenance

Flush medians introduce little in the way of unique enforcement or education issues for motor

vehicles. However, the enforcement of signalized corridors with continuous raised medians will 

vary from corridors with median breaks or flush medians that allow enforcement to access both

directions of traffic. Practitioners should coordinate with enforcement to discuss these concerns

or find locations for median opening turnarounds or flush medians. Pedestrians may need

assistance through the use of signs or other methods to make them aware of one-stage versus

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Chapter 8. System-Wide Treatments 

two-stage crossings, particularly in communities that have both types of crossings at signalized

intersections.

Typical maintenance procedures will apply to medians. However, consideration should be

given for providing vertical guidance for snow removal operations on raised medians using

delineation. The addition of a raised median will also result in a treatment located among

roadway users that will require intermittent maintenance. Landscaping should be maintained so

as not to obstruct sight distance.

8.1.10 Summary

Exhibit 8-6 summarizes issues associated with providing median treatments.

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Chapter 8. System-Wide Treatments 

Exhibit 8-6. Summary of issues for providing median treatments.

Characteristic Potential Benefits Potential Liabilities

Safety Introducing distance between 

opposing flows may allow for a

reduction in the frequency and 

severity of certain crash types.

The frequency of minor

collisions may increase when 

raised medians are present.

Operations Signalized directional crossovers

can operate more efficiently than 

unsignalized directional

crossovers.

Appropriately designed median 

radii can help raise speeds in 

turning movements and 

decrease intersection delay.

Narrow medians may create

storage problems.

For intersections where high 

pedestrian volumes are 

present, increased motorist

speeds could negatively

impact pedestrian safety.

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 None identified. Changes to median width may

have a substantial physical

impact upstream and 

downstream of the 

intersection.

Presence of a raised median

requires additional roadway

maintenance.

Socioeconomic Landscaping may provide visual 

appeal.

Access control upstream or

downstream of the intersection

may create challenges.

The frequency of vehicle 

damage claims may increase.

Potential safety concern if the 

landscaping becomes a fixed 

object hazard or impedes sight

distance.

Enforcement,

Education, and

Maintenance

None identified. Education on the use of

pedestrian push buttons in the 

median may be considered.

Presence of a raised median

and landscaping in the median 

will require maintenance.

Enforcement methods may

need to be addressed,

depending on the presence of

raised median between 

signals.

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Chapter 8. System-Wide Treatments 

8.2 ACCESS MANAGEMENT

Practical experience and recent research indicate that

controlling access on a roadway can positively impact traffic flow

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(88); ITE’s Transportation and Land Development(89)

; and 

TRB’s Access Management Manual.(90) Many States 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 needing both mobility of through traffic

and access to adjacent properties. 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 250 ft upstream or downstream) include

changes in infrastructure, geometry, or signing to close or combine

driveways, provide turn lanes, or restrict or relocate turn

movements.

TRB’s Access Management Manual states that access

management programs seek to limit and consolidate access along 

major roadways, while promoting a supporting street system and 

unified access and circulation systems for development. The result

is a roadway that functions safely and efficiently for its useful life,

and a more attractive corridor. The goals of access management

are accomplished by applying the following principles (90)

:

• Provide a specialized roadway system.

• Limit direct access to major roadways.

• Promote intersection hierarchy.

• Locate signals to favor through movements.

• Preserve the functional area of intersections and

interchanges.

• Limit the number of conflict points.

• Separate conflict areas.

• Remove turning vehicles from through-traffic lanes.

• Use non-traversable medians to manage left-turn

movements.

• Provide a supporting street and circulation system.

For more information on Access 

Management, consider the following 

resources: 

o AASHTO A Policy on 

Geometric Design of 

Highways and Streets 

o ITE Transportation and Land 

Development 

o Transportation Research 

Board’s Access Management 

Manual 

o FHWA’s 2007 Compendium of 

Access Management Tools 

o NCHRP 420: Impacts of 

Access Management 

Techniques 

o NCHRP Synthesis 304: 

Driveway Regulation 

Practices 

o NCHRP Synthesis 337: 

Cooperative Agreements for 

Corridor Management 

o NCHRP Report 348: Access 

Management Guidelines for 

Activity Centers 

o NCHRP Synthesis 351: Access 

Rights 

o NCHRP Report 395: Capacity 

and Operational Effects of 

Midblock Left-Turn Lanes 

o NCHRP Report 524: Safety of 

U-Turns at Unsignalized 

Median Openings 

o NCHRP Report 548: Median 

Intersection Design for Rural 

High-Speed Divided Highways 

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Chapter 8. System-Wide Treatments 

Access management works best when combined with land use and zoning policies. Agencies

can also regulate aspects of access management through geometric design and ingress/egress

spacing.

8.2.2 Applicability

Examples of when to improve access management at an intersection include situations

where through vehicles experience delay due to vehicles turning left or right into intersections,

such as from major and minor streets (signalized and unsignalized) and from driveways, and

when rear-end or angle crashes occur involving vehicles entering or leaving driveways.

8.2.3 Design Features

Practitioners should determine the functional area of the signalized intersection, as shown in

Exhibit 8-7, to understand the upstream and downstream effects of a signalized intersection on

access management. The functional area is larger than the physical area of the intersection 

because it includes several items, as shown in Exhibit 8-8.(90)

• 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).

Exhibit 8-7. Comparison of physical and functional areas of an intersection.(90)

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Chapter 8. System-Wide Treatments 

Exhibit 8-8. Diagram of the upstream functional area of an intersection.(90)

Consider overlapping functional areas’ varying levels of access when addressing two

proximal signalized intersections. Exhibit 8-9 shows how the functional areas of nearby signalized

intersections affect the location and extent of feasible access. Ideally, driveways with full access

should be located outside of the functional areas of both signalized intersections. However,

signalized intersections are often located close enough to each other that the downstream

functional area of one intersection 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,

practitioners should apply sound engineering judgment regarding where and if to allow a 

driveway. Some important considerations in the evaluation include:

• The volume and type of traffic using the driveway.

• The type of turning maneuvers that will be most prominent.

• The type of median present and potential conflicts with and proximity to other

driveways.

• The types and severity of existing crashes in the vicinity.

• The volume of traffic on the major street.

Access points 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 intersections. These situations are likely candidates for either partial or full access

restriction. It is important to note that driveways should not be simply eliminated based on

general 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 (45 mph or greater) and whose primary purpose is mobility. If the corridor has a two-way 

left-turn lane design and driveways are placed indiscriminately, there is a high likelihood for angle

crashes, and safety becomes the driving factor.

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Chapter 8. System-Wide Treatments 

Improvements to the current access to properties adjacent to an intersection area can be

implemented by:

• Closing, relocating, or combining driveways.

• Restricting turning movements through the use of median treatments, using driveway

treatments, and/or the installation of 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 (Exhibit 8-10).

This requires adequate cross-section width to allow the U-turn and sufficient distance to the

downstream intersection 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 left-turn 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 (Exhibit 8-11). 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.(91) 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 8-16 
Chapter 8. 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.

Exhibit 8-9. Access points near signalized intersections.(adapted from 90, figure 8-15)

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Chapter 8. System-Wide Treatments 

Exhibit 8-10. Access management requiring U-turns at a downstream signalized intersection.

Exhibit 8-11. 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

discord in driver maneuvers.

• Better operation for the driveway. Eliminating left turns out of the driveway generally

reduces delays for the driveway movements.

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Chapter 8. System-Wide Treatments 

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.

• 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 

decision-making 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, sight distance, etc.) and traffic characteristics.

Exhibit 8-12 presents a summary of the relative crash rates for a range of unsignalized 

intersection access spacing. As can be seen, doubling access frequency from 10 to 20 access

points per mile increases crash rates by about 40 percent. An increase from 10 to 60 access

points per mile 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 92 and 93).

Exhibit 8-12. Relative crash rates for unsignalized intersection access spacing.*

Unsignalized Access Points Spacing** Average Spacing*** Relative Crash Rate****

10 per mi 1056 ft 1.0

20 per mi 528 ft 1.4

30 per mi 352 ft 1.8

40 per mi 264 ft 2.1

50 per mi 211 ft 2.4

60 per mi 176 ft 3.0

70 per mi 151 ft 3.5

*Source: Reference 90, as adapted from 88.

**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 10 access points per mi.

Removing or limiting access to restrict specific movements, such as right-in/right-out access,

both have positive impacts to crash severity, congestion, and operational speeds. In Safe Access 

is Good for Business, FHWA states that where access is well-managed operating speeds are 15-

20 mph higher. Restricting movements may require adding horizontal and vertical features, such 

as raised islands, which may contribute to an increase in fixed object crashes.

(199)

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Chapter 8. System-Wide Treatments 

8.2.5 Operational Performance

Reducing access along an arterial street can 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.(94) Improved access management also has been shown to improve

LOS.(95) Controlling the flow of traffic through restricting and managing accesses can reduce 

delay.

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.(96)

However, as indicated earlier, practitioners should evaluate the impact of access control on

the upstream and downstream intersections, which may experience a significant increase in Uturns or other types of turning movements. For example, eliminating left-turn movements and

converting them to U-turns at signalized intersections could degrade arterial operational

performance if adequate capacity to accommodate the turning movements at midblock access

driveways exists, because less green time will be available for through traffic. This could 

substantially reduce capacity and increase delay at the signalized intersection.

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 also provides the opportunity for a midblock signalized or unsignalized

pedestrian crossing. Practitioners should evaluate whether the considered access treatments

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

Several solutions exist for access management that can affect the footprint of the intersection

area. The addition of U-turn lanes for property access will increase the roadway width of the

intersection area. Turn restrictions may affect the physical size of an area if a vertical element is

added to the intersection (for example a raised curb, median barrier, or flexible delineators used

to prohibit left turns). In order for these not to present difficulties for pedestrians with mobility

impairments, it may be necessary to provide a cut through.

8.2.8 Socioeconomic Impacts

Literature review 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.(97) 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.(95) In Safe Access is Good for Business, FHWA states that, where access is managed 

properly, operating speeds are 15 to 20 mph higher, which yields an increased exposure to more

potential customers. The publication also states that "before and after" studies of businesses in

Florida, Iowa, Minnesota, and Texas along highways where access has been managed found 

that the vast majority of businesses do as well or better after the access management projects

are completed.

The reactions of drivers, property owners, pedestrians, and others concerned with access to 

properties adjacent to intersections vary widely. Access management strategies should be

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Chapter 8. System-Wide Treatments 

considered in the context of a roadway corridor with the approval and backing of those affected or

if significant safety and operational enhancements can be achieved. A decrease in crashes and 

traveler delay from applying access management principles can result in considerable societal

savings.

Redesign, relocation or closing of driveways should be part of a comprehensive corridor

access-management 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 should also understand 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. If raised channelization is used corridor-wide, it may be necessary to team

with enforcement to provide openings for emergency turnarounds.

Education other than appropriate signing should not be needed when implementing changes

to access unless major changes to access management are made along a corridor, requiring a 

fundamental shift in driver behavior.

8.2.10 Summary

Exhibit 8-13 summarizes issues associated with providing access management.

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Exhibit 8-13. 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.

Physical segregation of opposing traffic flows

if barrier or curb is used as an access

Turn restrictions may require adding 

horizontal and vertical features to driveways,

which may contribute to an increase in fixed 

object crashes.

management strategy.

Operations Fewer access points generally result in an 

increase in LOS and capacity.

An increased number of U-turns at a 

signalized intersection due to access

management may reduce the overall

capacity of the intersection.

An increase in weaving as vehicles entering

the highway attempt to turn left at signalized 

intersections.

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.

Societal cost savings attributed to decreased 

crashes and travel delay.

Enforcement,

Education, and

Maintenance

None identified when raised channelization is

used.

Periodic enforcement may be needed where 

signs are used instead of raised 

channelization.

May be necessary to educate motorists on

access options if corridor wide improvements

are made, and provide emergency

turnarounds for enforcement.

Additional costs may be incurred for

maintenance with the installation of physical

barriers preventing access.

8.3 SIGNAL COORDINATION

8.3.1 Description

The primary objective of signal coordination is smooth flow of traffic along an arterial, street,

or a highway to improve mobility, safety, and fuel consumption. This can be achieved by

synchronizing the signal timings at multiple intersections along a major street to improve traffic

flow in one or more directional movements. Examples include arterial streets, downtown

networks, and closely spaced intersections like diamond interchanges. Intersections should be

coordinated when they are in close proximity to each other (i.e., 0.5 miles or less) and there is a 

significant amount of traffic on the street being coordinated.(66) Coordination can also improve 

travel time reliability; reduce travel time, stops and delay; and improve air quality.

(201)

Coordination also has other benefits. Drivers may have occasional difficulty making permissive

turns at signalized intersections because of lack of acceptable gaps in the opposing through

traffic. This can contribute to both operational and safety problems. Providing coordination can

create platooning of through traffic, resulting in availability of more acceptable gaps to left-turning

traffic. Increasing acceptable gaps can improve intersection capacity and safety.

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Chapter 8. System-Wide Treatments 

8.3.2 Applicability

Signal coordination may be applicable for intersections where:

• 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.

• Rear-end conflicts/collisions are occurring due to the higher probability of having to stop

at each light.

8.3.3 Safety Performance

Apart from its operational benefits, signal coordination reduces vehicle conflicts along

corridors with coordinated traffic signals. This 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.(98) 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.(99) 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.(100)

Exhibit 8-14 shows selected findings of safety benefits associated with signal coordination.

Treatment Finding

Signal Coordination(100) 3 to 18% estimated reduction in all collisions along corridor

14 to 43% estimated reduction in rear-end collisions along corridor

Provide Signal Progression (101) 10 to 20% estimated reduction in all collisions along corridor

Exhibit 8-14. Selected findings of safety effects associated with signal coordination or

progression.

8.3.4 Operational Performance

The potential benefits of coordination directly relate 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 or end times for the through green

at adjacent intersections.

The primary parameters to implement coordination are cycle lengths, splits, offsets and

phasing sequences. Coordination requires a fixed background cycle length for all intersections

within a specific coordination plan. Selection of an appropriate cycle length for a system is crucial

for two reasons. First, the cycle length should be able to service the expected vehicle and

pedestrian demand on all movements by selecting the appropriate split (time allocated to service 

each movement). Second, the cycle length should facilitate good progression along the major

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Chapter 8. System-Wide Treatments 

street. Coordination is then achieved by adjusting the offsets (a function of start or end of a major

street green with respect to the start or end of major street green for the adjacent intersection).

These offsets are fine-tuned in the field to ensure that any residual queues are cleared before the 

arrival of platoons for smooth progression. Finally, progression can sometimes be further

improved by modifying the signal phasing for left turns (e.g., implementing a lead-lag sequence).

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. 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

0.5-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.

(90, adapted from reference 102)

Grouping the signals into a system to be coordinated is an important aspect of the design of a

progressive system. Factors that should be considered include geographic barriers, v/c ratios,

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.

Coordination is effective in improving throughput along a major thoroughfare. However,

during oversaturated conditions the objective typically changes from providing progression to

managing queues. The traffic engineer needs to identify the period of oversaturated conditions

and select the appropriate cycle length, splits, offsets, and phasing sequences to ensure smooth 

movement of traffic under such conditions by management of queues.

Dependent on the spacing between signalized intersections, prevalence of certain

movements, or a disparity in ideal cycle lengths of each signalized intersection, it may be

beneficial to consider half or double cycles, respective of other cycle lengths that appear on the 

corridor. Double cycles allow an intersection to cycle twice as frequently as a major intersection,

while half cycles have half the cycle length of a major intersection along the corridor. According 

to FHWA’s Traffic Signal Timing Manual,

(66) half cycles can often produce substantially lower

delays at the minor intersections where double cycling is employed. However, it may become

more difficult to achieve progression in both directions along the major arterial, which may result

in more arterial stops than desired. 

8.3.5 Multimodal Impacts

Progression along a transit route can reduce travel time and improve travel time reliability of

transit vehicles. The transit agency should also play a role. They can design their stops

appropriately with respect to traffic signals to take advantage of the progression being provided 

along the corridor.

8.3.6 Physical Impacts

Signal coordination may require overhead or underground installation of wire, fiber, or radio 

equipment if direct connection type of coordination is employed.

8.3.7 Socioeconomic Impacts

Signal coordination will also reduce fuel consumption, noise, and air pollution, by reducing the 

number of stops and delays. If traffic signals are retimed and maintained properly, we would see 

a reduction in harmful emissions (carbon monoxide, nitrogen oxides, and volatile organic

compounds) of up to 22 percent.(202) According to the Surface Transportation Policy Project,

motor vehicles are the largest source of urban air pollution.(203)

In addition, the EPA estimates that

vehicles generate 3 billion pounds of air pollutants annually.(204)

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Chapter 8. System-Wide Treatments 

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

Exhibit 8-15 summarizes the issues associated with 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 None identified.

air pollution.

Enforcement, May result in less need for speed Signal timing plans need periodic

Education, and

Maintenance

enforcement. updating.

Exhibit 8-15. Summary of issues for providing signal coordination.

8.4 SIGNAL PREEMPTION AND/OR PRIORITY

8.4.1 Description

Signal preemption and signal priority are terms describing treatments for special needs (e.g.,

drawbridge, railroad crossing), special vehicle classes or vehicles with multiple users, relative to

automobile traffic at the intersection. Signal preemption is the higher order of the two treatments

and involves transferring the intersection’s signal controller into a special operating mode 

designed to clear the intersection, if necessary, and then service the special vehicle type or need.

The two most common types of signal preemption are emergency vehicle preemption and

railroad preemption.

Priority is defined as 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)

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Several types of emergency vehicle detection technologies are available. These 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 of a police

pursuit in progress.

8.4.3 Railroad Preemption

When located in close proximity to rail-highway grade crossings, signalized intersections can

use railroad preemption to ensure that vehicles safely clear the crossing prior to train arrival.

Operation of the grade crossing’s active warning devices (flashing lights or flashing lights with

gates) can be synchronized with the traffic signal display such that any active vehicular or

pedestrian phases that conflict with the phase(s) servicing the intersection leg with the grade 

crossing are safely terminated, and then the phase(s) clearing vehicles from the grade crossing

are activated with sufficient time to clear the crossing before train arrival.

The signal initiating railroad preemption originates from the track circuit and train detection

equipment provided by the railroad for actively-controlled grade crossings. Variations exist in the

design of the preemption interconnect circuit and track detection and warning system, but all

share the purpose of providing adequate warning time of train arrival to both approaching 

motorists and the traffic signal controller. In special cases, advance preemption is used to alert

the traffic signal controller about the impending arrival of a train before the grade crossing’s active 

warning system (i.e., flashing lights with or without gates) begins operation. Proper design of

signal timing for preemption operation is covered in the ITE Preemption of Traffic Signals Near

(205) Railroad Crossings: An ITE Recommended Practice.

8.4.4 Transit Vehicle Priority

Unlike preemption, traffic signal priority operates within the context of a signal’s routine 

operational mode. Also, while the immediacy of preemption requests allows the shortening of

pedestrian walk and clearance intervals, these changes to routine signal operation are not

allowed with signal priority. A variety of methods can be used to provide priority to buses or light

rail vehicles, including extending green on identified phases, altering phase sequences and 

including special phases without interrupting the coordination of green lights between adjacent

intersections.(66)

Several different technologies are available for generating a priority request for the transit

vehicle on approach to a signalized intersection. Pavement loops and radio (which can also be 

used for emergency vehicle preemption) can be employed in transit detection and signal

interconnection, and even train detection circuits for light rail transit can be used. One emerging

technology uses global positioning system (GPS) technology in accordance with the transit

agency’s automatic vehicle location (AVL) system to transmit a priority request signal in

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Chapter 8. System-Wide Treatments 

conjunction with a roadside reader near the signal controller or remotely using the Internet and 

communication between the transit and road authority. Whether a priority request is granted and 

can be accommodated by the traffic signal controller can be affected by the current controller

state and whether or not the transit vehicle is behind schedule at the time the priority request is

received.

8.4.5 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.

8.4.6 Safety Performance

No known research addresses the safety implications of emergency vehicle preemption,

although it is expected that the number of conflicting movements associated with an emergency

vehicle having to run a red light would be reduced.

Installation of signal preemption systems for emergency vehicles decreases 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

deploying the system.(103)

Signal preemption has also been considered for intersections at the base of a steep and/or

long grade. These grades create a potentially dangerous situation if large trucks lose control and

enter the intersection at a high speed. Preemption can reduce the likelihood of conflicts between 

runaway trucks and other vehicles.

8.4.7 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.(103)

8.4.8 Multimodal Impacts

Priority for transit vehicles can enhance transit operations, reducing delays and allowing for a

tighter schedule, with minimal impacts to pedestrians and bicyclists. A study in King County,

Washington showed that transit signal priority coupled with signal timing optimization resulted in a 

40 percent reduction in transit signal delay and a 35 to 40 percent reduction in travel time 

variability. In Portland, Oregon, transit signal priority improved travel time by 10 percent and

reduced travel time variability by 19 percent.(206)

8.4.9 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, practitioners should ensure 

that vehicles from a variety of jurisdictions can 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

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Chapter 8. System-Wide Treatments 

different vendors may not interact well together. Other alarms, such as from nearby buildings,

may be detected by a sound-based system.

8.4.10 Socioeconomic Impacts

Reduction in response time by emergency services and more predictable transit services

benefit society. However, the costs, particularly when applied to an entire road network, can be

significant.

8.4.11 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.

8.4.12 Summary

Exhibit 8-16 summarizes the issues associated with providing signal preemption and/or

priority.

Characteristic Potential Benefits Potential Liabilities

Safety Quicker response time for emergency

vehicles.

None identified.

On steep grades, preemption could be 

used to minimize conflicts between 

runaway trucks and other vehicles.

Operations None identified. Can be disruptive to traffic flow,

particularly during peak hours.

Multimodal Delay to transit vehicles and travel time None identified.

variability is reduced.

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. Can be costly.

More reliable transit service.

Enforcement, Improves emergency vehicle response None identified.

Education, and time.

Maintenance

Exhibit 8-16. Summary of issues for providing signal preemption and/or priority.

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Chapter 9. Intersection-Wide Treatments 

CHAPTER 9

INTERSECTION-WIDE TREATMENTS

TABLE OF CONTENTS

9.0 INTERSECTION-WIDE TREATMENTS............................................................................. 9-3

9.1 Pedestrian Treatments.............................................................................................. 9-3

9.1.1 Reduce Curb Radius.................................................................................... 9-4

9.1.2 Provide Curb Extensions ............................................................................. 9-6

9.1.3 Modify Stop Line Location............................................................................ 9-8

9.1.4 Improve Pedestrian Signal Displays .......................................................... 9-10

9.1.5 Modify Pedestrian Signal Phasing ............................................................. 9-13

9.1.6 Grade-Separate Pedestrian Movements ................................................... 9-15

9.1.7 High Visibility Crosswalks .......................................................................... 9-17

9.2 Bicycle Treatments.................................................................................................. 9-18

9.2.1 Provide Bicycle Box ................................................................................... 9-18

9.2.2 Provide Bike Lanes .................................................................................... 9-19

9.3 Transit Treatments.................................................................................................. 9-21

9.3.1 Relocate Transit Stop ................................................................................ 9-21

9.4 Traffic Control Treatments ...................................................................................... 9-23

9.4.1 Change Signal Control from Pre-Timed to Actuated ................................. 9-23

9.4.2 Modify Change and Clearance Intervals (Yellow and All-Red).................. 9-26

9.4.3 Modify Cycle Length .................................................................................. 9-29

9.4.4 Late Night/Early Morning Flash Removal .................................................. 9-30

9.5 Street Lighting and Illumination............................................................................... 9-32

9.5.1 Provide or Upgrade Illumination................................................................. 9-32

9.6 Remove Traffic Signal............................................................................................. 9-35

9.6.1 Convert Signalized Intersection to a Roundabout ..................................... 9-35

9.6.2 Convert Signalized Intersection to All-Way Stop Control .......................... 9-37

LIST OF EXHIBITS

9-1 A curb radius increase from 15 ft to 50 ft increases the pedestrian crossing distance

from 62 ft to 100 ft, all else being equal ....................................................................... 9-4

9-2 Summary of issues for curb radius reduction ..................................................................... 9-6

9-3 Intersection with curb extension in South Haven, Michigan ............................................... 9-7

9-4 Summary of issues for curb extensions.............................................................................. 9-8

9-5 Benefits of Modifying Stop Line Location ........................................................................... 9-9

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Chapter 9. Intersection-Wide Treatments 

9-6 Summary of issues for stop line alterations...................................................................... 9-10

9-7 Examples of countdown and animated eyes pedestrian signal displays.......................... 9-11

9-8 Safety effects associated with addition of pedestrian signals: selected findings ............. 9-12

9-9 Summary of issues for pedestrian signal display improvements...................................... 9-12

9-10 Summary of issues for pedestrian signal phasing modifications...................................... 9-15

9-11 Summary of issues for pedestrian grade separation........................................................ 9-17

9-12 Summary of issues for high visibility crosswalks .............................................................. 9-18

9-13 Summary of issues for providing a bicycle box ................................................................ 9-19

9-14 Summary of issues for providing bicycle lanes................................................................. 9-20

9-15 Summary of issues for near-side/far-side transit stops .................................................... 9-23

9-16 Summary of issues for providing signal actuation ............................................................ 9-25

9-17 Safety effects associated with modifying clearance intervals: selected findings.............. 9-27

9-18 Summary of issues for modifying yellow/red clearance intervals ..................................... 9-28

9-19 Summary of issues for cycle length modifications............................................................ 9-30

9-20 Safety effects associated with removal of signal from late night/early morning flash mode:

selected findings............................................................................................................ 9-31

9-21 Summary of issues for flash mode removal ..................................................................... 9-31

9-22 Safety effects associated with providing illumination: Selected findings .......................... 9-33

9-23 Summary of issues for providing illumination ................................................................... 9-34

9-24 Safety effects associated with converting traffic signals to roundabouts: selected

findings .......................................................................................................................... 9-35

9-25 Summary of issues for converting traffic signals to roundabouts ..................................... 9-37

9-26 Safety effects associated with converting traffic signals to multi-way stop ...................... 9-37

9-27 Summary of issues for converting traffic signals to all-way stop control .......................... 9-38

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Chapter 9. Intersection-Wide Treatments 

9.0 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

Accommodating pedestrians significantly affects the design and operations of a signalized

intersection and should therefore be an integral part of the design process. Key actions to 

consider are:

• Protect crossing locations with a high number of pedestrians (where possible) from

conflicting through traffic.

• Minimize crossing distances.

• Provide adequate crossing times.

• Locate pedestrian ramps within the crosswalk.

• Ensure pedestrian ramp location and design meet ADA requirements.

• Consider high visibility cross walk markings.

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:

• Reducing curb radius

• Extending curbs.

• Providing median crossing islands.

Traffic engineers have also modified the location of the stop line 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.

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Chapter 9. Intersection-Wide Treatments 

9.1.1 Reduce Curb Radius

Description

A wide curb radius typically results in high-speed turning movements by motorists, increasing 

the opportunity for right-turning vehicle conflicts with pedestrians. 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. Exhibit

9-1 demonstrates that increasing the curb radius increases pedestrian crossing distance. Tighter

turning radii are even more important where street intersections are not at right angles.(104)

Exhibit 9-1. A curb radius increase from 15 ft to 50 ft increases the pedestrian crossing distance

from 62 ft to 100 ft, all else being equal.

Applicability

Consider reducing the curb radii at any signalized intersection with pedestrian activity. Note

that the need to accommodate the design vehicle may limit how much the curb radius can be

reduced.

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Chapter 9. Intersection-Wide Treatments 

Safety Performance

Reducing the curb radius lowers the speed of right-turning vehicles and should reduce the

frequency of pedestrian-vehicle collisions. Any remaining collisions will be less severe due to the

lower speeds involved. Crash severity increases significantly between 20 and 40 mph.(105)

However, vehicles turning right will be forced to decelerate more rapidly in attempting the

right turn. This could 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 via 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 encroach 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 stop line 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

Exhibit 9-2 summarizes issues associated with curb radius reduction.

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Chapter 9. Intersection-Wide Treatments 

Exhibit 9-2. Summary of issues for curb radius reduction.

Characteristic Potential Benefits Potential Concerns

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 Curb extensions provide multiple benefits:

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 Exhibit 9-3.

- Improve crosswalk visibility

- Reduce pavement for high-speed turns

and passing on right.

- Motorists are more likely to stop.

- Pedestrians are more likely to wait.

Application

This treatment applies to urban intersections with moderate to heavy pedestrian traffic and/or

a history 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.

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Chapter 9. Intersection-Wide Treatments 

Exhibit 9-3. Intersection with curb extension in South Haven, Michigan.

Photo credit: Jeff Shaw, Federal Highway Administration

Safety Performance

Reducing the pedestrian crossing distance and subsequent exposure of pedestrians to traffic

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.(106)

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 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.

Practitioners should use caution when considering this treatment along heavy truck routes.

All types of trucks and transit vehicles, in particular those needing to turn right at the intersection,

would be negatively affected by this treatment.

Physical Impacts

Drainage should be evaluated whenever curb extensions are being considered, as the curb 

extension may interrupt the existing flow line.

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Chapter 9. Intersection-Wide Treatments 

Socioeconomic Impacts

Costs associated with this improvement would be low to moderate.

Enforcement, Education, and Maintenance

No specific effects have been identified.

Summary

Exhibit 9-4 provides a summary of the issues associated with curb extensions.

Characteristic Potential Benefits Potential Concerns

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 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.

Exhibit 9-4. Summary of issues for curb extensions.

9.1.3 Modify Stop Line Location

Description

Visibility is a key consideration for determining the location of stop lines. The FHWA

Pedestrian Facilities Users Guide—Providing Safety and Mobility suggests advance stop lines as

a possible countermeasure.(38) At signalized pedestrian crossing locations, the vehicle stop line

can be moved 15 to 30 ft further back from the pedestrian crossing than the standard 4 ft distance

to improve visibility of through bicyclists 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, as shown in Exhibit 9-5.

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Chapter 9. Intersection-Wide Treatments 

Exhibit 9-5. Benefits of Modifying Stop Line Location

Source: Crossing Enhancements, Pedestrian and Bicycle Information Center,

www.walkinfo.org.

Applicability

Relocated stop lines may apply to intersections with frequent conflicts between pedestrians

and adjacent right-turning vehicles, or a history of right-turn-on-red vehicle/pedestrian collisions.

Safety Performance

One evaluation study found that advance stop lines resulted in reduced right-turn-on-red 

conflicts with cross traffic; more right-turn-on-red vehicles also made complete stops 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.(104),(108),(109) However,

placing the crosswalk at least 10 ft or more from the cross-street flow line or curb also provides

more time for drivers to react for the presence of pedestrian crossing on the street they are about

to enter.(110)

Operational Performance

Advance stop lines increase the clearance time for vehicles passing through the intersection.

As a result, there may be an increase in lost time. If in-pavement stop line vehicle detectors are

already installed at this signalized intersection, they may need to be replaced or modified.

Multimodal Impacts

Advance stop lines can better allow trucks entering the intersection from the side street to

turn wide, thereby allowing smaller curb radii that are more pedestrian friendly.

Physical Impacts

No physical needs have been identified.

Socioeconomic Impacts

Minimal costs associated with stop line alterations.

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Chapter 9. Intersection-Wide Treatments 

Enforcement, Education, and Maintenance

Supplemental signing (e.g., STOP HERE with appropriately oriented downward pointing

arrow) and enforcement of the relocated stop lines may be necessary.

Summary

Exhibit 9-6 summarizes the issues associated with stop line alterations.

Characteristic Potential Benefits Potential Concerns

Safety Decreased risk of pedestrian collisions. None identified.

Operations None identified. Increase in vehicular clearance time and 

lost time.

Multimodal Facilitates turning movements of heavy None identified.

trucks.

Physical No physical needs identified. None identified.

Socioeconomic None identified. None identified.

Enforcement,

Education, and

Improved compliance. None identified.

Maintenance

Exhibit 9-6. Summary of issues for stop line alterations.

9.1.4 Improve Pedestrian Signal Displays

Traffic signals should allow adequate crossing time for pedestrians and an adequate change 

and clearance interval based on walking speed. Pedestrian signal enhancements include:

• Separate pedestrian signals (WALK/DON’T WALK)

• Accessible pedestrian signals.

• Countdown displays.

• Animated eyes display.

Application

Chapter 5 provided guidance on the use of pedestrian signals and accessible pedestrian

signals. Current thinking suggests that redundancy in information 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 Exhibit 9-7(a), display the number of seconds remaining before 

the end of the flashing 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. All pedestrian signal heads used at crosswalks where the pedestrian change interval

is more than 7 seconds shall include a pedestrian change interval countdown display in order to

inform pedestrians of the number of seconds remaining in the pedestrian change interval.(1)

Another innovative pedestrian signal treatment is an animated eyes display, shown in Exhibit

9-7(b). The animated, 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.

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Chapter 9. Intersection-Wide Treatments 

Animated eyes are included in the MUTCD for optional use with the pedestrian signal WALK

indication.(1)

(a) Countdown display.(111) (b) Animated eyes display.

Exhibit 9-7. Examples of countdown and animated eyes pedestrian signal displays.

Safety Performance

The available research does not provide a clear indication of the safety effects of installing

pedestrian signals. One report suggests that installing pedestrian signals is associated with a 15 

to 17 percent reduction in pedestrian collisions.(112) However, a number of older studies found 

that pedestrian signalization does not improve safety.(113),(114) Larger pedestrian signal heads

were described in the literature as a treatment to enhance conspicuity, though 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

(115) push button, and transmitted messages are in use. 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.(116)

Countdown displays may reduce vehicle-pedestrian conflicts resulting from pedestrians

attempting to cross the intersection at inappropriate times. Some 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).(110),(117),(118) A 2005 study in San 

Francisco, California, indicated a reduction of up to 52 percent by converting to countdown

signals.(119)

Results from studies of the use of animated-eye displays show increased pedestrian

observation of traffic behavior and reductions in pedestrian/vehicle conflicts at a variety of

intersection configurations.

(116),(120) The 2009 MUTCD allows for and provides a standard for its

design (Section 4E.04).

Exhibit 9-8 presents the results of selected references involving the addition of pedestrian 

signals.

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Chapter 9. Intersection-Wide Treatments 

Treatment Implication

Convert WALK / DON’T WALK pedestrian signals

to countdown signals

52% reduction in pedestrian-related crashes.

Exhibit 9-8. Safety effects associated with addition of pedestrian signals: selected findings.(147)

Operational Performance

These treatments should have a negligible effect on vehicle operations. 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 on the meaning of the devices should be considered 

upon their introduction to the public.

Summary

Exhibit 9-9 summarizes the issues associated with pedestrian signal display improvements.

Characteristic Potential Benefits Potential Concerns

Safety Give pedestrians improved awareness

of traffic.

None identified.

Operations None identified. None identified.

Multimodal All pedestrians, but especially visually None identified.

impaired pedestrians, are likely to 

benefit.

Physical None identified. None identified.

Socioeconomic None identified. Some enhancements are expensive.

Enforcement,

Education, and

None identified. Education may be necessary.

Maintenance

Exhibit 9-9. Summary of issues for pedestrian signal display improvements.

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Chapter 9. Intersection-Wide Treatments 

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. Pedestrian walking speeds generally

range between 2.5 to 6.0 ft/s.(3) The MUTCD uses a walk speed of 3.5 ft/s for determining 

crossing times (Page 497, Sect. 4E.06-07).(1) However, FHWA pedestrian design guidance

recommends a lower speed 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.(37),(38) The HCM 2000 indicates that if elderly persons constitute more than 20 

percent of the total pedestrians, the average walking speed should be decreased to 3.0 ft/s.(2)

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. While the vehicle signals are in “All 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.(110) 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 “Barnes 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.(110)

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.

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Chapter 9. Intersection-Wide Treatments 

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, practitioners should use accessible pedestrian

signals to give people with visual disabilities information regarding the walk phase in the absence

of predictable surging traffic.

Safety Performance

Several studies have demonstrated that imposing leading pedestrian intervals significantly

reduces conflicts for pedestrians.(106),(110),(121) Crash analysis conducted at 26 locations with

leading 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).(104),(122)

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. This causes all movements to receive less green time, but

optimizes that time. However, this timing was not investigated empirically.(106)

A main operational disadvantage of lagging pedestrian intervals is 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.(104),(122) 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 (2009 MUTCD, Section 3B.18).(1)

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Description

 

 

 

 

 

 

 

 

 

 

 

Chapter 9. Intersection-Wide Treatments 

Enforcement, Education, and Maintenance

Leading or lagging pedestrian phases should be accompanied by police enforcement to

ensure that vehicles and pedestrians obey traffic signals.

Summary

Exhibit 9-10 summarizes the issues associated with pedestrian signal phasing modifications.

Characteristic Potential Benefits Potential Concerns

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

Enforcement,

Education, and

Maintenance

Lead or lag phases: little or no cost.

None identified.

Exclusive phase: low cost to implement;

moderate costs associated with vehicle delays.

Enforcement may be necessary.

Exhibit 9-10. Summary of issues for pedestrian signal phasing modifications.

9.1.6 Grade-Separated Pedestrian Treatment

In some situations, it may be feasible to separate 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 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. The first case provides greater opportunities for grade separation. In some

cases, safety can be a major factor; for example, 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.(123) 

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Chapter 9. Intersection-Wide Treatments 

Safety Performance

Ideally, pedestrian grade separations 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 will not likely be used if it is too inconvenient. Use of a median pedestrian 

barrier or landscaping treatments 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.(104)

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.

Summary

Exhibit 9-11 summarizes the issues associated with pedestrian grade separation.

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Description

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 9. Intersection-Wide Treatments 

Characteristic Potential Benefits Potential Concerns

Safety Reduced pedestrian-vehicle 

collisions. Converting at-grade 

intersections to grade-separated 

interchanges is associated with a 

57 percent reduction in injury

crashes, although this finding is

for all road users.

(124)

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.

Exhibit 9-11. Summary of issues for pedestrian grade separation.

9.1.7 High Visibility Crosswalks

In some situations, increasing the conspicuity of crosswalks can provide a safety benefit to

pedestrians at signalized intersections. Designs and product application vary around the country

based on State and local needs. The crosswalk should include retroreflective pavement

markings (versus only using a different material like brick for the crosswalk).

Applicability

The addition of high visibility crosswalks may apply to intersections with frequent conflicts

between pedestrians and vehicles. Due to the low cost of this treatment, it could also serve as a

systemic treatment on a series of intersections or jurisdiction-wide as a policy.

Safety Performance

Anecdotal evidence has shown a safety benefit to the installation of high visibility crosswalks.

A case study in New York City in 1995 indicated reductions at a small number of installations at

locations with a high number of pedestrian-vehicle crashes.

Additionally, a ladder-style, also referred to as a continental style, crosswalk (longitudinal

versus lateral) was shown to be effective for keeping vehicles out of the crosswalk area.(125)

Operational Performance

None identified. The high visibility crosswalks typically have the same footprint as existing 

crosswalks.

Multimodal Impacts

High visibility crosswalks provide an enhanced space for pedestrian and bicycles to cross the 

intersection safely.

Physical Impacts

None identified. High visibility crosswalks typically have the same footprint as existing

crosswalks.

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Chapter 9. Intersection-Wide Treatments 

Socioeconomic Impacts

Minimal costs are associated with high visibility pavement markings.

Enforcement, Education, and Maintenance

Because the high visibility pavement marking is installed in the travel lane, it will be

necessary to maintain the markings. In some cases the markings (e.g., “ladder style” markings)

can be designed so there is little or no pavement marking in the typical motor vehicle wheel

paths.

Summary

Exhibit 9-12 summarizes the issues associated with high visibility crosswalks.

Characteristic Potential Benefits Potential Concerns

Safety Decreased risk of pedestrian collisions. None identified.

Operations None identified. None identified.

Multimodal Enhanced space for pedestrian and None identified.

bicyclists to cross.

Physical Installation can occur in the same 

footprint as standard crosswalks.

None identified.

Socioeconomic None identified. None identified.

Enforcement,

Education, and

Improved compliance. Enhanced crosswalks may require

additional effort to maintain pavement

Maintenance markings.

Exhibit 9-12. Summary of issues for high visibility crosswalks.

9.2 BICYCLE TREATMENTS

9.2.1 Provide Bicycle Box

Description

A bicycle box uses advance stop lines placed on the approach to a signalized intersection,

typically in the rightmost lane, at a location upstream from the normal stop line location. These 

create a dedicated space for bicyclists—a bicycle box—to occupy while waiting for a green

indication. Advance stop lines are used in conjunction with bicycle lanes or other similar bicycle

provisions.

Note that this treatment is considered experimental; it is not currently identified in the

MUTCD.

Applicability

This treatment may apply 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 motor vehicle traffic, use of this treatment may

be beneficial.

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Chapter 9. Intersection-Wide Treatments 

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.(126)

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.

Enforcement, Education, and Maintenance

Concerns with providing a bicycle box include motorist violation of existing stop line, a lack of

uniformity with other intersections, and a need for right-turn-on-red prohibitions. Users are not yet

familiar with this application, so heavy education may be required.

Summary

Exhibit 9-13 summarizes the issues associated with providing a bicycle box.

Characteristic Potential Benefits Potential Concerns

Safety Potential reduction in collisions between 

through bicycles and right-turning 

None identified.

vehicles.

Operations None identified. None identified.

Multimodal Bicyclists can bypass queued traffic, None identified.

thus reducing delay.

Physical None identified. None identified.

Socioeconomic None identified. None identified.

Enforcement,

Education, and

None identified. Enforcement of the box may be necessary.

Maintenance

Exhibit 9-13. Summary of issues for providing a bicycle box.

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.

(26) 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, bicyclists are encouraged to stay right. Installation of bike lanes at signalized 

intersections is associated with a range of vehicle-bicycle crash effects – both increases and 

decreases.

(127)

The bike lane shall be positioned 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

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Chapter 9. Intersection-Wide Treatments 

traffic law requires). A bicyclist going straight can easily avoid a conflict with a right-turning car by

staying to the left 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. The MUTCD requires through

bicycle lanes to be positioned only to the left of a right-turn-only lane and to the right of a left-turnonly lane.

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.(128) Other research concludes that bicycle paths along arterials typically

increase bicyclists’ 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) Installation of colored bike lanes at signalized intersections has been associated with a

39 percent reduction in vehicle/bicycle crashes.

(127)

Multimodal Impacts

Bicycle lanes delineate roadway space between motor vehicles and bicycles and provide for

more predictable movements by each.(26)

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

Exhibit 9-14 summarizes of the issues associated with providing bicycle lanes.

Characteristic Potential Benefits Potential Concerns

Safety Potential reduction in vehicle/bicycle 

collisions.

Potential increase in vehicle/bicycle 

collisions.

Operations None identified. None identified.

Multimodal Bicycle lanes delineate roadway space None identified.

between motor vehicles and bicycles and 

provide for more predictable movements by

each.

Physical None identified. Bicycle lanes may require additional rightof-way unless width is taken from existing 

lanes.

Socioeconomic None identified. None identified.

Enforcement, None identified. None identified.

Education, and

Maintenance

Exhibit 9-14. Summary of issues for providing bicycle lanes.

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Chapter 9. Intersection-Wide Treatments 

9.3 TRANSIT TREATMENTS

9.3.1 Relocate Transit Stop

Placement of bus stops in the vicinity of intersections can significantly influence safety and

operational performance. Approximately 2 percent of pedestrian accidents in urban areas and 3

percent in rural areas are related to bus stops.(129) 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.(129)

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 one or more of the following exist:

• Heavy right-turn movement.

• Conflicts between vehicles trying to turn right, through vehicles, and stationary near-side

buses, resulting in rear-end and sideswipe collisions.

• 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 increase conflicts

between right-turning vehicles, through traffic, and the bus itself. When the bus is stopped at the

bus stop, traffic control devices, signing, 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 by eliminating

the sight distance restriction caused by the bus and encouraging pedestrians to cross the street

from behind the bus instead of in front of it.(130) The presence of a far-side transit bus stop is

associated with a 45 percent reduction in transit-related crashes.

(131) The 1996 TCRP report

recommends a minimum clearance distance of 5 ft between a pedestrian crosswalk and the front

or rear of a bus stop.(129) 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.

Far-side bus stops appear to 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 services 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

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Chapter 9. Intersection-Wide Treatments 

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 allow 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.(104) 

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.

Far-side bus bays provide a location for police officers to conduct 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

Exhibit 9-15 summarizes of the issues associated with providing near-side or far-side transit

stops.

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Chapter 9. Intersection-Wide Treatments 

Characteristic Potential Benefits Potential Concerns

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.

Exhibit 9-15. Summary of issues for near-side/far-side transit stops.

9.4 TRAFFIC CONTROL TREATMENTS

Intersection-wide traffic control treatments can provide operational and/or safety benefits on

all approaches and for 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. Change and 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, semi-actuated, actuated, adaptive

or traffic responsive. A pre-timed mode of control could simply 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 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.

Traffic engineers should consider upgrading intersections from pre-timed to more efficient

types of control. Semi-actuated traffic signals have detectors located on the minor approaches

and oftentimes in the left-turn lanes of the major approaches. Fully actuated traffic signals have

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Chapter 9. Intersection-Wide Treatments 

detection on all approaches, have varying cycle lengths, and ensure acceptable servicing through

basic controller timings.

Traffic responsive control uses system and presence detection to select one of a set of

timing plans (pre-timed) based upon the traffic demand. This type of control further optimizes the

operation by using the presence detection on the side streets and left turns to allocate unused

green time to other phases as needed. Adaptive control dynamically assigns green time for each

phase based upon system detection.

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.

• Capabilities of existing traffic control equipment.

• Locations where main or side street traffic could benefit from progression or platooning.

Applicability

Converting a signal from pre-timed to a more efficient type of control may be considered in

the following 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 pretimed traffic signals.

• To minimize delay in periods of light traffic.

Safety Performance

Actuated traffic signals and traffic signal systems control (intelligent signal systems) provide

better service to all movements at an intersection, reducing driver frustration and the likelihood of

red-light running. However, they can also make it more difficult for pedestrians with visual

impairments to predict when changes in signal phasing will occur. There is little research on the

safety effects of changing signal control from pre-timed to actuated, but the possibility of reduced

rear-end and red-light running crashes due to fewer stops makes actuation a potential safety

measure.

Operational Performance

Intelligent signal systems, used in appropriate situations, can reduce delays to vehicles,

particularly in light traffic situations and for movements from minor approaches.

Benefits of intelligent signal systems may be less significant in situations where traffic

patterns and volumes are predictable and do not vary significantly. Actuated control only 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 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. To a lesser degree, other types of intelligent

signal control operation could be impacted by malfunction or loss of system detectors. Most

intelligent signal systems rely upon fail-safe timing plans when one or more groups of detectors

fail.

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Chapter 9. Intersection-Wide Treatments 

Multimodal Impacts

Pre-timed traffic signals may be more acceptable to the unfamiliar pedestrian than trafficactuated signals in areas where there is large and fairly consistent pedestrian traffic crossing the

road. Intelligent signal systems may cause confusion to the pedestrian with the operation of

pedestrian push buttons where long cycle lengths or adaptive control is present. Actuated

pedestrian push buttons must be located in appropriate locations and be accessible to be ADA

compliant.

Physical Impacts

Approaches needing actuation require detectors. Depending on the type of detector, this may 

create physical impacts (see Chapter 5 for further discussion of detector types).

Socioeconomic Impacts

Generally speaking, intelligent signal system equipment costs more to purchase and install

than pre-timed traffic controllers, although almost all traffic controllers purchased today are 

capable of actuated operation. Depending on the geometry, number of lanes, and traffic

characteristics, detection can be a significant percentage of the cost of a signalized intersection, 

but many of the more advanced, newer types of detection can cover an entire approach (lefts and

throughs) per unit.

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 waits for the signal to change green while no other

vehicles are present on the other approaches. This may lead to red-light running. 

Intelligent signal systems require more equipment and components, and can be more costly

to maintain. Detector and/or signal indication (bulb, lens, LED) failure are the most common

public complaints.

Summary

Exhibit 9-16 summarizes the issues associated with providing signal actuation.

Characteristic Potential Benefits Potential Concerns

Safety Improves safety. None identified.

Reduces driver frustration, red-light

running.

Operations Provides better service to minor

approaches.

Can sometimes reduce smooth platooning 

in coordinated systems.

Accommodates widely fluctuating Requires proper operation of detectors.

volumes.

Multimodal None identified. May be problematic for unfamiliar

pedestrians due to variations to cycle

lengths or longer cycle lengths.

Physical None identified. Detectors required.

Socioeconomic None identified. Can be costly.

Enforcement,

Education, and

Enforcement needs may decrease. Maintenance costs will likely increase to

maintain detection.

Maintenance

Exhibit 9-16. Summary of issues for providing signal actuation.

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V W + L CP = t + + (U.S. Customary) 2a + 64.4g V 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chapter 9. Intersection-Wide Treatments 

9.4.2 Modify Change and Clearance Intervals (Yellow and All-Red)

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 seconds. Since long yellow

change intervals may encourage drivers to use it as a part of the green interval, a maximum of

5 seconds is commonly employed. Longer yellow intervals are generally associated with higher

approach speeds. Local practice dictates the length of the change interval.

The ITE standard formula for change intervals is a follows:

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

Intersections where the existing yellow change interval time is less than the time needed for a

motorist traveling at the prevailing speed of traffic to reach the intersection or stop comfortably

before the signal turns red will require a longer yellow change interval. The minimum length of

yellow should be determined using the kinematics formula in the 1985 ITE proposed practice 

assuming an average deceleration of 10 ft/s or less, a reaction time of 1 second or more, and an

85th percentile approach speed. An additional 0.5 seconds of yellow time should be considered

for locations with significant truck traffic, significant population of older drivers, or more than 3

percent of the traffic entering on red.(133)

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 releasing conflicting traffic. 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 typically 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 (134) (and Chapter 5). 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.

Applicability

Modifying the yellow or red clearance interval may be considered where:

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Chapter 9. Intersection-Wide Treatments 

• 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 number of red-light violations are recorded.

Safety Performance

At intersection approaches where yellow signal timing duration is set below values associated

with ITE guidelines or similar kinematic-based formulae, increasing yellow change interval

duration to achieve ITE guidelines can significantly reduce red-light running. Increasing yellow

change and/or red clearance interval timing to achieve values associated with ITE guidelines or

similar kinematic formulae can significantly reduce motorists entering the intersection at the end

of the yellow phase.

The best estimate of the crash effects associated with implement improved change interval

timing, based on before-after studies, is about 8 to 14 percent reduction in total crashes, and

about a 12 percent decrease in injury crashes.

(135)

Research shows that yellow interval duration is a significant factor affecting the frequency of

red-light running and that increasing yellow time to meet the needs of traffic can dramatically

reduce red-light running. Bonneson and Son (2003) and Zador et al. (1985) found that longer

yellow interval durations consistent with the ITE Proposed Recommended Practice (1985) of

using 85th percentile approach speeds are associated with fewer red-light violations, all other

factors being equal. Bonneson and Zimmerman (2004) found that increasing yellow time in 

accordance with the ITE guideline or longer reduced red light violations more than 50 percent. 

Van Der Host found that red light violations were reduced by 50 percent one year after yellow

intervals were increased by 1 seconds.

(140) Retting et al (2007) found increasing yellow time in 

accordance with the guideline reduced red-light violations by 36 percent on average. Retting,

Chapline & Williams (2002) found that adjusting the yellow change interval in accordance with the 

ITE guidelines reduced total crashes by 8 percent, right-angle crashes by 4 percent, and

pedestrian and bicycle crashes by 37 percent.

(78)

One study conducted by Souleyrette et al. (2004), suggests modest short-term crash

reductions, but no longer-term effects associated with installing red clearance intervals.(136)

Exhibit 9-17 presents selected findings associated with signal clearance modifications.

Treatment Finding

Retiming to ITE standards. (137) Reduced red-light violations by 50 percent.

Add all-red clearance interval.

(136) Modest short-term crash reductions, but no longer-term

effects.

Retiming signal change intervals to ITE

standards.

(138)

8 percent estimated reduction in all collisions.

12 percent estimated increase in rear-end collisions.

39 percent estimated reduction in vehicle-bicycle and 

vehicle-pedestrian collisions.

Retiming signal change intervals to ITE

standards.

(139)

5 percent estimated reduction in all collisions.

9 percent estimate reduction in fatal and injury collisions.

Exhibit 9-17. Safety effects associated with modifying change and clearance intervals: selected 

findings.

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Chapter 9. Intersection-Wide Treatments 

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, giving 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.

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

Exhibit 9-18 summarizes the issues associated with modifying yellow and/or red clearance

intervals at signalized intersections.

Characteristic Potential Benefits Potential Concerns

Safety Angle collisions are reduced. None identified.

Left-turn collisions are reduced.

Rear-end collisions are reduced.

Operations None identified. Increased lost time.

Multimodal The elderly and people with mobility disabilities have None identified.

more time to cross.

Physical No physical requirements. None identified.

Socioeconomic Low-cost alternative to police and automated None identified.

enforcement.

Enforcement,

Education, and

Red-light enforcement may become less necessary. None identified.

Maintenance

Exhibit 9-18. Summary of issues for modifying yellow/red clearance intervals.

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Chapter 9. Intersection-Wide Treatments 

9.4.3 Modify Cycle Length

Description

Calculating and selecting cycle length requires judgment on the part of the traffic engineer or

analyst. General practice suggests a cycle length between 50 and 120 seconds. For low-speed

urban roads, a shorter cycle length is preferable (50 to 70 seconds). For wider roadways (greater

than 50 ft) with longer pedestrian crossing times (greater than 20 s seconds), or in situations

where heavier traffic is present and left-turning vehicles are not effectively accommodated, a

cycle length of 60 to 90 seconds may be preferable. At high-volume intersections, multiple

phases to accommodate heavy turning movements may necessitate a cycle length of 90 to 120

seconds.

(140) In addition, cycle lengths longer than 120 seconds may be needed at large

intersections to accommodate multiple long pedestrian crossings in combination with heavy

turning movements, especially during peak periods. Typically, system cycle lengths are governed

by the higher volume intersections within the system and limit the flexibility of the traffic engineer

in choosing a cycle length that may otherwise work better for a specific location.

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. However, because an increase in cycle length reduces driver

exposure to the yellow indication (e.g., a cycle length change from 60 to 120 seconds reduces the

number of times that the yellow is presented by 50 percent), there is an inverse relationship

between a change in cycle length and the frequency of red-light-running. That is, an increase in 

cycle length corresponds to a decrease in the frequency of red-light-running.

(141)

No known research or specific collision modification factors exist for modifying cycle length.

Operational Performance

A cycle length of 90 seconds is often considered optimum, since lost time is approaching a

maximum, capacity is approaching a minimum, and delay is not too great.(140) 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 seconds, 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.

Physical Impacts 

No physical impacts are associated with the modification of cycle length.

Enforcement, Education, and Maintenance

As part of regular traffic signal observations (recommended every 3 to 5 years, or as

needed), consider modifying cycle lengths and splits (and offsets in coordinated systems) to

accommodate emerging operational needs.

Socioeconomic Impacts

No significant costs are associated with this treatment, apart from labor.

Summary

Exhibit 9-19 summarizes the issues associated with cycle length modification.

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Chapter 9. Intersection-Wide Treatments 

Characteristics Potential Benefits Potential Concerns

Safety

Operations

Increase in cycle length

corresponds to a decrease in the

frequency of red-light running.

Reduction in delay optimized at

90 seconds.

Longer cycle lengths could induce some drivers

to run red lights.

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. Increased maintenance cost of regular signal

observations and retiming.

Exhibit 9-19. Summary of issues for cycle length modifications.

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 can benefit traffic flow, particularly with pretimed 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 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 as a two-way stop.

Safety Performance

One study examined safety impacts associated with converting 12 intersections from

nighttime flashing operation to steady operation in Winston-Salem, NC. The analysis indicated

that flashing operation reduced nighttime angle crashes (the ones most likely to be positively

affected) by approximately 34 percent. Total nighttime crashes also saw a significant reduction of

approximately 35 percent. (142)

A separate study evaluated safety impacts associated with a change in statewide late night

flash policy by the North Carolina DOT making it standard practice to operate signals in steady

mode at all times. Before this policy, it was standard practice to allow traffic signals to operate in

late night flash mode unless directed otherwise by the division traffic engineer. The policy also

changed the standard operating times for late night flash operations. As a result of this policy,

many signals were either removed from late night flash operations or had their late night flash

operating times modified to conform to the new policy. Replacing nighttime flash with steady

operation was associated with an estimated 48 percent reduction in nighttime frontal and

opposing direction sideswipe collisions and head-on collisions, and an estimated 27 percent

reduction in all nighttime collisions.

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 Exhibit 9-20.

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Chapter 9. Intersection-Wide Treatments 

Treatment Finding

Remove signal from late 34 percent estimated reduction in nighttime angle collisions.

night/early morning flash 35 percent estimated reduction in all nighttime collisions.

mode.

(142),(143)

48 percent estimated reduction in nighttime frontal and opposing direction

sideswipe collisions and head-on collisions

27 percent estimated reduction in all nighttime collisions

Exhibit 9-20. Safety effects associated with removal of signal from late night/early morning flash 

mode: selected findings.

Operational Performance

If the signalized intersection removed from flashing operation is not fully actuated and 

responsive to traffic demand, increased red-light violations and/or complaints about unnecessary

long waits on red signals may occur. 

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 habituated drivers do not proceed through the intersection as if the signal

were still operating in flashing mode. The traffic engineer may consider temporary

signing/publicity to inform motorists of the change in operations and to explain the safety benefits.

Summary

Exhibit 9-21 summarizes the issues associated with flash mode removal.

Characteristic Potential Benefits Potential Concerns

Safety Angle collisions are reduced. Could induce red-light running on minor legs if

controller is not sufficiently sensitive to minor

road demand.

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, None identified. Enforcement and temporary signing may be 

Education, and

Maintenance

needed for a period after conversion.

Exhibit 9-21. Summary of issues for flash mode removal.

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Chapter 9. Intersection-Wide Treatments 

9.5 STREET LIGHTING AND ILLUMINATION

9.5.1 Provide or Upgrade Illumination

Description

The purpose of roadway lighting is to enhance visibility and conspicuity 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 drops below a certain level, either at night or during bad weather.

Applicability

Consider intersection lighting at all signalized intersections. More nighttime collisions than 

expected may justify upgrades, 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.(70) The basic principles and design values for

intersections have been presented previously (Chapter 5) 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. 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. The first is safety.

Most important is to place the pole at an offset distance that can assist in preventing crashes

(vehicles and pedestrians). Second, determine the pole spacing most efficacious for initial and

long-term maintenance costs, yet still meeting the lighting requirement. At intersections, shared

use of poles for signal equipment and illumination is recommended. Exhibit 9-22 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 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. This may

require separate poles for signal equipment and luminaires.(144) For intersections providing 

separate pedestrian pedestals at the crosswalk, the mast arm poles for vehicle signal heads

should be located for optimal illumination as well. Intersection lighting, when crosswalks are 

present, should account for the presence of pedestrians and attempt to achieve positive contrast.

Signalized Intersections: Informational Guide 9-32 
 

 

 

 

 

Chapter 9. Intersection-Wide Treatments 

(a) Typical lighting layout for intersection without right-turn bypass lane.

(b) Typical lighting layout for intersection with right-turn bypass lane.

Exhibit 9-22. Typical lighting layouts.(70, figure D3)

Safety Performance

Optimal illumination and visibility reduces the chance of nighttime accidents and enhances

traffic flow. Roadway lighting also increases sight distance, security, and the use of surrounding 

facilities. Installation of lighting at intersections is associated with a 38 percent reduction in all

dark condition collisions and a 42 to 59 percent reduction in vehicle/pedestrian collisions in dark

conditions.

(145)

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Chapter 9. Intersection-Wide Treatments 

Operational Performance

No documented relationship exists between illumination and operational intersection 

performance. The authors believe that illumination likely has little effect on traffic flow, delay, and

queuing.

Multimodal Impacts

As noted above, illumination demonstrably reduces pedestrian crashes and provides a more 

secure nighttime environment for all intersection users.

Physical Impacts

Illumination typically has little effect on the overall footprint of an intersection. Commonly,

combination poles 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 also reduces the fear of crime at night, and it promotes business and the use of

public streets at night.(70)

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.(70) Judicious design 

of luminaire types, wattages, mounting height, and pole spacing may increase visibility at the

intersection without significantly increasing energy costs.

Summary

Exhibit 9-23 summarizes the issues associated with providing illumination.

Characteristic

Safety

Potential Benefits

Reported reductions in nighttime collisions.

Potential Disbenefits

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.

Exhibit 9-23. Summary of issues for providing illumination.

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Chapter 9. Intersection-Wide Treatments 

9.6 REMOVE TRAFFIC SIGNAL

As indicated in Section 4B.03 of the MUTCD, improper or unjustified traffic control signals

can result in one or more of the following disadvantages:

• Excessive delay.

• Excessive disobedience of the signal indications.

• Increased use of less adequate routes as road users attempt to avoid the traffic control

signals.

• Significant increases in the frequency of collisions (especially rear-end collisions).

Converting traffic signals to roundabouts or multi-way stop controls at appropriate settings

and under appropriate traffic conditions can provide a range of safety, operational, environmental,

and economic benefits.

9.6.1 Convert Signalized Intersection to a Roundabout 

Description

The modern roundabout is a circular intersection with design features promoting safe and 

efficient traffic flow. At roundabouts in the United States, vehicles travel counterclockwise around

a raised center island, with entering traffic yielding the right-of-way to circulating traffic. In urban

settings, entering vehicles negotiate a curve sharp enough to slow speeds to about 15 to 20 mph;

in rural and suburban settings, entering vehicles may be held to somewhat higher speeds (30 to 

35 mph). Within the roundabout and as vehicles exit, slow speeds are maintained by the

deflection of traffic around the center island and the relatively tight radius of the roundabout and

exit lanes. Roundabouts have replaced many formerly signalized intersections.

Applicability

Converting a signalized intersection to a roundabout requires sufficient right-of-way to

accommodate the circumference of the roundabout, which may include one, two, or three

circulating lanes, depending on the volume of traffic. Mini roundabouts can be installed with less

right-of-way, including some cases where no additional right-of-way is needed.

Safety Performance

Conversion of signalized intersections to roundabouts is associated with substantial safety

benefits. Before-after analysis conducted for nine such conversions as part of NCHRP Report

672 estimated a 48 percent reduction in all crashes, and a 78 percent reduction in injury crashes. (146)

Treatment Finding

Convert signalized 48 percent estimated reduction in all collisions.

intersection to 78 percent estimated reduction in injury collisions.

(146) roundabout.

Exhibit 9-24. Safety effects associated with converting traffic signals to roundabouts: selected 

findings.

Operational Performance

In addition to providing safety effects, converting signalized intersections to roundabouts is

associated with substantial reductions in vehicle delay. Several studies have reported significant

improvements in traffic flow following conversion of traditional intersections to roundabouts. A

study of three locations in New Hampshire, New York, and Washington, where roundabouts

replaced traffic signals or stop signs, found an 89 percent average reduction in vehicle delays and 

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Chapter 9. Intersection-Wide Treatments 

a 56 percent average reduction in vehicle stops.(148) A study of 11 intersections in Kansas found a 

65 percent average reduction in delays and a 52 percent average reduction in vehicle stops after

roundabouts were installed.(149)

Multimodal Impacts

Conversion of signalized intersections to roundabouts can benefit pedestrians. Roundabouts

generally are safer for pedestrians than traditional intersections. In a roundabout, pedestrians

walk on sidewalks around the perimeter of the circular roadway. If they need to cross the 

roadway, they cross only one direction of traffic at a time. In addition, crossing distances are

relatively short, and traffic speeds are lower than at traditional intersections. Studies in Europe

indicate that, on average, converting conventional intersections to roundabouts can reduce

pedestrian crashes by about 75 percent.(150),(151) Single-lane roundabouts in particular have been

reported to involve substantially lower pedestrian crash rates than comparable intersections with

traffic signals. Safety studies on bicyclists at roundabouts have mixed findings, with some

European studies showing higher crash rates for bicycles at roundabouts compared with traffic

signals.(146)

Physical Impacts

Converting a signalized intersection to a roundabout requires sufficient right-of-way to

accommodate the circumference of the roundabout. In many cases, construction of a roundabout

in place of a traffic signal will require the acquisition of small amounts of right-of-way at the

intersection. However, because roundabouts generally require fewer approach lanes than

signalized intersections, in some cases existing travel lanes approaching the intersection can be 

converted to parking, bike lanes, or other uses. Roundabouts can also improve the esthetics of

existing signalized intersections, including the addition of landscaping.

Socioeconomic Impacts

Converting a signalized intersection to a roundabout requires significant capital investment.

However, roundabouts offer lower lifecycle costs compared with traffic signals, which require 

electrical power and maintenance of signal hardware (including detectors). Reduced vehicle 

delays and other operational benefits associated with roundabouts can lower vehicle operating 

costs (including fuel consumption) for motorists and transit agencies.

Summary

Exhibit 9-25 summarizes the issues associated with converting traffic signals to roundabouts.

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Chapter 9. Intersection-Wide Treatments 

Characteristic Potential Benefits Potential Disbenefits

Safety Substantial reductions in all collisions and 

injury collisions.

None identified.

Operations Substantial reductions in traffic delays and 

vehicle stops.

None identified.

Multimodal Roundabouts generally are safer for

pedestrians than traditional intersections.

Multi-lane roundabouts can be

challenging for visually impaired 

pedestrians. Safety studies on bicyclists

at roundabouts have mixed findings.

Physical Esthetic improvement, including 

landscaping.

May require additional right-of-way.

Socioeconomic Lower life cycle costs, vehicle operating 

costs (including fuel consumption) for

motorists.

Requires significant capital investment.

Enforcement,

Education, and

Maintenance

Roundabouts require less maintenance than

traffic signals.

Public information may be needed.

Exhibit 9-25. Summary of issues for converting traffic signals to roundabouts.

9.6.2 Convert Signalized Intersection to All-Way Stop Control

Description

All-way stop control requires vehicles approaching the intersection from all directions to stop 

prior to entering the intersection. Because of the large number of vehicle stops and delays

associated with this form of control, its use is generally limited to residential areas and low-speed

settings. 

Applicability

Converting a signal to all-way stop control requires thoughtful analysis and consideration, as

it is not a common practice. Before converting a signal to all-way stop control, the engineer

should review the guidance in the MUTCD Part 2B.07.

Safety Performance

Researchers identified the effect on intersection crashes of converting nearly 200 one-way

street intersections in Philadelphia from signal to all-way stop sign control.

(152) Using crash and 

traffic volume data for a comparison group, regression models were computed to represent the

normal crash experience of signal controlled intersections of one-way streets, by impact type, as

a function of traffic volume. Estimates were obtained for different classes of crashes categorized 

by impact type, day/night condition, and impact severity. Aggregate results indicate that replacing 

signals by all-way stop signs on one-way streets is associated with a reduction in crashes of

approximately 24 percent, combining all severities, light conditions, and impact types.

Treatment Finding

Convert signalized 24 percent estimated reduction in all collisions.

intersection to multi-way 25 percent estimated reduction in right-angle collisions.

stop.

(152)

17 percent estimated reduction in pedestrian collisions (46 percent reduction 

at night)

Exhibit 9-26. Safety effects associated with converting traffic signals to multi-way stop.

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Chapter 9. Intersection-Wide Treatments 

Operational Performance

By design, all-way-stop control generates considerable vehicle delay compared with traffic

signal operation because all vehicles are required to stop before entering the intersection.

Multimodal Impacts

Conversion of signalized intersections to all-way stop control benefits pedestrians and

bicyclists because of the low traffic speeds of motor vehicles in the vicinity of the intersection.

Physical Impacts

Conversion of signalized intersections to all-way stop control eliminates traffic signal poles,

but introduces sign supports. Intersection sight distance differs depending on the type of

intersection and maneuver involved. Signalized intersections require that drivers be provide with

an unobstructed view of both the approach triangle and the departure triangle, whereas

intersections controlled by all-way stop signs have no such requirements.

(153)

Socioeconomic Impacts

Conversion of signalized intersections to all-way stop control reduces costs required to

electrify and maintain traffic signals. The cost of installing and maintaining multi-way stop signs is 

relatively low.

Summary

Exhibit 9-27 summarizes the issues associated with converting traffic signals to all-way stop

control.

Characteristic Potential Benefits Potential Disbenefits

Safety Reduced crashes. None identified.

Operations None identified. Increased vehicle delay.

Multimodal Benefits pedestrians and bicyclists because None identified.

of the low traffic speeds of motor vehicles in

the vicinity of the intersection.

Physical Eliminates traffic signal poles. Requires installation of sign poles.

Socioeconomic Reduces costs required to electrify and None identified.

maintain traffic signals.

Enforcement,

Education, and

Eliminates traffic signal maintenance. Significant education will be required to 

share the signal removal decision with 

Maintenance the public and public officials. The

location may require periodic police 

enforcement of stop signs.

Exhibit 9-27. Summary of issues for converting traffic signals to all-way stop control.

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Chapter 10. Approach Treatments 

CHAPTER 10

APPROACH TREATMENTS

TABLE OF CONTENTS

10.0 APPROACH TREATMENTS ............................................................................................ 10-2

10.1 Signal Head Placement and Visibility ..................................................................... 10-2

10.1.1 Convert to Over-the-Road Signal Heads ................................................... 10-3

10.1.2 Add Supplemental Signal Heads ............................................................... 10-4

10.1.3 Increase Size of Signal Heads................................................................... 10-5

10.1.4 Increase Number of Signal Heads ............................................................. 10-7

10.1.5 Provide Backplates .................................................................................... 10-9

10.1.6 Provide Advance Warning ....................................................................... 10-10

10.2 Signing and Speed Control Treatments................................................................ 10-12

10.2.1 Improve Lane Use and Street Name Signing .......................................... 10-12

10.2.2 Reduce Operating Speed ........................................................................ 10-14

10.3 Roadway Surface Improvements.......................................................................... 10-14

10.3.1 Improve Pavement Surface ..................................................................... 10-14

10.3.2 Improve Cross Section............................................................................. 10-17

10.3.3 Remove Obstacles from Clear Zone ....................................................... 10-19

10.4 Sight Distance Treatments.................................................................................... 10-20

10.4.1 Improve Sight Lines ................................................................................. 10-20

10.5 Dilemma Zone Detection ...................................................................................... 10-23

10.6 Red Light Camera Enforcement ........................................................................... 10-25

LIST OF EXHIBITS

10-1 Summary of approach treatments .................................................................................... 10-2

10-11 Safety benefits associated with advance warning signs and flashers: selected findings10-11

10-15 Safety benefits associated with nonskid treatments, drainage improvements, or

10-2 Safety benefits associated with using mast arms: selected findings................................ 10-3

10-3 Summary of issues for using mast arm/span wire-mounted signal heads ....................... 10-4

10-4 Summary of issues for supplemental near-side traffic signal heads ................................ 10-5

10-5 Safety benefits associated with using 12-inch signal lenses: selected findings............... 10-6

10-6 Summary of issues for increasing the size of signal heads.............................................. 10-7

10-7 Lane-aligned signal heads................................................................................................ 10-7

10-8 Safety benefits associated with the addition of a signal head: selected findings ............. 10-8

10-9 Summary of issues for adding a signal head.................................................................... 10-8

10-10 Summary of issues for using signal head backplates.................................................... 10-10

10-12 Summary of issues related to advance warning treatments .......................................... 10-12

10-13 Safety benefits associated with advance lane-use signs: selected findings.................. 10-13

10-14 Summary of issues for improving signing..................................................................... 10-14

resurfacing: selected findings ...................................................................................... 10-16

10-16 Summary of issues for pavement treatments ................................................................ 10-17

10-17 Summary of issues for cross section improvements................................................... 10-19

10-18 Summary of issues for removing obstacles from the clear zone................................... 10-20

10-19 Expected reduction in number of crashes per intersection per year by increased sight

distance ....................................................................................................................... 10-21

10-20 Safety benefits associated with sight distance improvements: selected findings. ........ 10-22

10-21 Summary of issues for visibility improvements.............................................................. 10-23

10-22 Dilemma zone and detector placement ......................................................................... 10-24

10-23 Vehicular distances traveled by speed .......................................................................... 10-24

10-24 Summary of issues for dilemma zone detection............................................................ 10-25

10-25 Summary of issues for red light cameras ...................................................................... 10-27

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Chapter 10. Approach Treatments 

10.0 APPROACH TREATMENTS

Approaches are critical signalized intersection components. Intersections and traffic control

devices should be obvious to approaching motorists, bicyclist, and pedestrians. Adequate signing

and pavement marking must provide the driver with sufficient information to determine the

appropriate lane and direction to travel. The pavement on the approaches should provide the 

needed degree of friction for a turning maneuver or stop and 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 permissive left turn.

This chapter will discuss various treatments related to signalized intersection approaches, as

summarized in Exhibit 10-1.

Approach Treatment Type Treatment

Traffic control Mast arm and span wire mounts

Advanced warning flashers

Dilemma zone protection

Operating speed

Extended lane line markings

Pavement/cross section improvements Skid resistance

Rumble strips

Improved cross section

Removal of obstacles

Reduce intersection skew

Visibility Near-side traffic signal heads

Larger traffic signal heads

Increase number of signal heads

Backplates

Adequate sight distance for conflicting 

turning movements, pedestrian 

crossings

Exhibit 10-1. Summary of approach treatments.

10.1 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 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. Some red-light

runners claim they did not see the traffic signal, and one reason could be suboptimal placement

of traffic signal heads or a failure to make the traffic signal head visually prominent.

Approach treatments that improve signal visibility help drivers make decisions at the

intersection and alert them to the presence 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.

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Chapter 10. Approach Treatments 

10.1.1 Convert to Over-the-Road Signal Heads

Description

Three major types of signal head placement are in popular use today: pedestal, span wire, or

mast arm mounted. Chapter 5 discussed the merits and drawbacks of each. For a signalized

intersection experiencing safety problems related to the placement or visibility of a pedestalmounted signal head, the traffic engineer should consider either replacing signal heads or

supplementing signal heads. Replacing or supplementing signal heads should 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 angle collisions occur that may be attributable to

unintentional red-light runners.

Safety Performance

The safety impact of mast arm mounted signal heads relates to the conspicuity of the signal

indications, especially in areas where there are competing visual distractions like on-site signing

and lighting near the pedestal-mounted heads. Safety effects of signal upgrades from pedestal to 

mast arm are shown in Exhibit 10-2.

Treatment Finding

(155) Replace pedestals with mast arms, 36 percent reduction for all crash types and severities.

47 percent reduction for severe injuries (all crash types)

13 percent reduction for minor injuries (all crash types)

72 percent reduction for right angle crashes (all severities)

20 percent increase in rear-end crashes (all severities)

2 percent increase in left turn crashes (all severities)

Exhibit 10-2. Safety benefits associated with using mast arms: selected findings.

Operational Performance

Signal head placement has a negligible effect on intersection capacity. However, centering 

signal heads over lanes can help drivers chose the proper lane to navigate through the 

intersection.

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.

Physical Impacts

Span wire mounted signal heads have a constructability advantage over mast arm mounted 

signal heads. At larger intersections, the length of the mast arm may limit its use.

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Chapter 10. Approach Treatments 

Socioeconomic Impacts

Span wire installations are generally considered less esthetically pleasing than mast arms

because of overhead wires.

Enforcement, Education, and Maintenance

Span wire installations generally have higher ongoing maintenance costs than mast arms.

Both types may need additional reinforcements if installed in a location known for strong winds.

Summary

Exhibit 10-3 summarizes the issues associated with using mast arm or span wire mounts for

signal heads.

Characteristic Potential Benefits Potential Concerns

Safety Increases signal visibility. None identified.

Decreases collisions.

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, None identified. Span wires typically require more

Education, and maintenance than mast arms.

Maintenance

Exhibit 10-3. Summary of issues for using mast arm/span wire-mounted signal heads.

10.1.2 Add Supplemental Signal Heads

Description

Supplemental traffic signals may also be placed on the near side of the intersection, far-left, 

far-right, or very high. This may be particularly useful if:

• Sight distance is an issue, such as on approaches to intersections on horizontal and

vertical curves.

• The intersection is particularly wide, so that a far-side signal cannot be placed within

MUTCD sight distance requirements for approaching drivers.(1)

• Auxiliary turn lanes are present.

Applicability

Supplemental head placements may be considered where there may be limited sight

distance or at a particularly wide intersection where visibility of the signal indications could be a

problem. Refer to the MUTCD for guidance on the location of signal heads.

(1)

Safety Performance

Supplemental traffic signal heads 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.

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Chapter 10. Approach Treatments 

Operational Performance

When placed on the near side of an intersection, additional signal poles have a negligible

effect on intersection capacity.

Multimodal Impacts

Near-side traffic signal placement 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. This will likely incur additional costs to provide electricity and conduit to

connect to the traffic controller. In other cases (far-left, far-right, or very high-mounted), the signal

head can often be placed on an existing pole with access to conduit and power.

Summary

Exhibit 10-4 summarizes the issues associated with supplemental near-side traffic signal

poles.

Characteristic Potential Benefits Potential Concerns

Safety Increases signal visibility. None identified.

Decreases angle collisions.

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, None identified. None identified.

Education, and

Maintenance

Exhibit 10-4. Summary of issues for supplemental near-side traffic signal heads.

10.1.3 Increase Size of Signal Heads

Description

Two diameter sizes are currently used for signal lenses: 8 inches and 12 inches. Of these,

12-inch signal faces for red, amber, and green indications are commonly used at medium- and

high-volume intersections. Many jurisdictions are working to limit the use of 8-inch signal heads to

only low-speed locations without confusing/complex backgrounds. The MUTCD indicates 12-inch

signal faces shall be used for all signal sections in all new signal faces, with the following

exceptions:(1)

Eight-inch circular signal indications may be used in new signal faces only for:

A. The green or flashing yellow signal indications in an emergency-vehicle traffic control

signal;

B. The circular indications in signal faces controlling the approach to the downstream location

where two adjacent signalized locations are close to each other and it is not practical

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Chapter 10. Approach Treatments 

because of factors such as high approach speeds, horizontal or vertical curves, or other

geometric factors to install visibility-limited signal faces for the downstream approach;

C. The circular indications in a signal face located less than 120 feet from the stop line on a

roadway with a posted or statutory speed limit of 30 mph or less;

D. The circular indications in a supplemental near-side signal face;

E. The circular indications in a supplemental signal face installed for the sole purpose of

controlling pedestrian movements rather than vehicular movements; and

F. The circular indications in a signal face installed for the sole purpose of controlling a

bikeway or a bicycle movement.

Existing 8-inch circular signal indications not included in items A through F may be retained 

for the remainder of their useful service life.

Application

Using 12-inch lenses should improve visibility for the driver, and as such may reduce red-light

running and associated angle collisions.

Safety Performance

Srinivasan et al. (2008) conducted a before-after evaluation for four types of treatments at

signalized intersections using data from Winston-Salem, NC. The result was an estimated 42

percent reduction in right-angle collisions and a 3 percent reduction in total collisions.(156) Another

before-and-after study was undertaken to assess the effectiveness of larger (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.(157)

References regarding the safety benefits of installing 12-inch signal lenses are shown in 

Exhibit 10-5.

Treatment Finding

Install 12-inch signal lenses, use higher wattage 

bulbs.

(157)

24 percent estimated reduction in all collisions.

Install 12-inch signal lenses.

(156) 42 percent estimated reduction in right angle collisions.

3 percent estimated reduction in all collisions.

Exhibit 10-5. Safety benefits associated with using 12-inch signal lenses: selected findings.

Operational Performance

None identified.

Socioeconomic Impacts

Using 12-inch lenses costs nominally more than using 8-inch lenses.

Summary

Exhibit 10-6 summarizes the issues associated with increasing the size of signal heads.

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Chapter 10. Approach Treatments 

Characteristic

Safety

Potential Benefits

Reduction in collisions – particularly

angle collisions.

Potential Concerns

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.

Exhibit 10-6. Summary of issues for increasing the size of signal heads.

10.1.4 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.”(1) In addition, at least one signal head must be not less than

40 ft beyond the stop line and not more than 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.

Traffic signal heads on a mast arm typically located above each. Exhibit 10-7 shows an

example of an approach with dual left-turn lanes, two through lanes, and a right-turn lane with 

lane-aligned signal heads.

Exhibit 10-7. Lane-aligned signal heads.

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Chapter 10. Approach Treatments 

Application

Consider this treatment in situations where unusually high numbers of angle collisions occur

because a vehicle runs a red light. Also, consider it at high speed intersections with fewer signal 

heads than approach lanes. This application may be a local or spot treatment, or may be part of a 

systematic improvement plan.

Safety Performance

A Canadian study evaluated the crash effects associated with additional primary signal heads

and found a 28 percent decrease in all collisions, a 28 percent decrease in rear-end collisions,

and a 35 percent reduction in angle collisions. (158)

Exhibit 10-8 summarizes selected findings relating to the safety benefits of adding a signal

head.

Treatment Finding

Add a primary signal

head.

(158)

28 percent estimated reduction in all collisions.

28 percent estimated reduction in rear-end collisions.

35 percent estimated reduction in angle collisions.

Exhibit 10-8. Safety benefits associated with addition of a signal head: selected findings.

Operational Performance

None identified.

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

Exhibit 10-9 summarizes the issues associated with adding a signal head.

Characteristic

Safety

Potential Benefits

Reduction in collisions.

Potential Concerns

None identified

Operations None identified. 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.

Exhibit 10-9. Summary of issues for adding a signal head.

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Chapter 10. Approach Treatments 

10.1.5 Provide Backplates

Description

Backplates are a common treatment for enhancing the signal head visibility. Backplates have

a dull black finish to enhance the contrast between the signal head and its surroundings, and can

include a strip of yellow retroreflective tape around the perimeter of the backplate.

Applicability

The MUTCD contains guidance pertaining to the use of backplates in Section 4D.12,

Visibility, Aiming, and Shielding of Signal Faces. Backplates should be provided for the following

situations

• Intersections with approach speeds 45 mph or higher.

• Sun glare, bright sky, and/or complex or confusing backgrounds indicate a need for

enhanced signal face target value.

Backplates serve to increase the contrast between the signal head and its surroundings,

drawing the attention of approaching drivers and therefore increasing the likelihood that they will

stop on a red indication. They should be considered in situations where a high number of angle

collisions occur.

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, and provides an

additional benefit to drivers with a color vision deficiency (the shape of the signal is clear, helping

a color deficient driver identify red-yellow-green by placement rather than color).

Safety Performance

A British Columbia study evaluated crash effects of installing yellow micro-prismatic

retroreflective sheeting along the outer edge of backplates in an attempt to frame the signal

heads and make them more visible to motorists.

(159) The study found an estimated 15 percent

reduction in all crashes.

Operational Performance

The use of backplates enhances the contrast between the traffic signal indications and their

surroundings for both day and night conditions, which is also helpful to older drivers (MUTCD 

Section 4D.12).

(1)

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, and Maintenance

Due to their larger size, signal heads with backplates may be more prone to movement

during high winds. This may pose a problem if they are mounted on a span wire, leading to

maintenance issues; however, there are designs available (e.g., vented backplates) to mitigate

potential problems. 

Summary

Exhibit 10-10 summarizes the issues associated with using signal head backplates.

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Chapter 10. Approach Treatments 

Characteristic

Safety

Potential Benefits

Reduction in angle collisions.

Potential Concerns

None identified.

Operations Benefit to Older Drivers None identified.

Multimodal None identified. None identified.

Physical None identified. None identified.

Socioeconomic None identified. Minor cost for backplates and reflective 

tape. Possible increased pole cost for

increased wind loads.

Enforcement,

Education, and

Maintenance

None identified. None identified.

Exhibit 10-10. Summary of issues for using signal head backplates.

10.1.6 Provide Advance Warning 

Description

These two treatments provide advance warning to motorists:

1. Provide a general warning of a signalized intersection ahead.

2. Provide a specific advance 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 a

yellow 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.” 

The sign and the flashers are placed a certain distance from the stop line as determined by

the speed limit on the approach.

Applicability

A SIGNAL AHEAD sign (possibly with an optional warning flasher) is required 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. 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 higher-speed, isolated intersections where the

signalized intersection may be unexpected or where there may be sight distance issues. They

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Chapter 10. Approach Treatments 

appear to be most beneficial in situations where the minor approach volumes exceed 13,000

AADT or greater.(160)

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 line. 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.

Angle collisions were reduced by 35 percent at 11 signalized intersections where a SIGNAL

AHEAD sign was installed on one or more approaches.(161)

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.(162) 

Results from a study of 106 signalized intersections in British Columbia showed 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 percentile

confidence level. Benefits were found primarily for moderate-to-high traffic volumes on the minor

approach.(160)

Exhibit 10-11 shows selected references to safety benefits of advance-warning devices.

Treatment

Post SIGNAL AHEAD signs.

(161)

Finding

35 percent estimated decrease in angle collisions.

Advance-warning flasher (163) 8 percent estimated decrease in all crash types, all severities.

11 percent estimated decrease in injury crashes (all crash types)

43 percent estimated decrease in right angle crashes (all

severities)

1 percent estimated decrease in rear-end crashes (all severities)

Exhibit 10-11. Safety benefits associated with advance warning signs and flashers: selected 

findings.

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.

Socioeconomic Impacts

Advance-warning flashers that activate before the onset of the yellow phase may be costly to

install.

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Chapter 10. Approach Treatments 

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.(164)

Summary

Exhibit 10-12 summarizes the issues associated with advance warning treatments.

Characteristics

Safety

Potential Benefits

Decreases angle collisions.

Potential Concerns

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 Signing and continuous advancewarning flashers have low cost.

Activated advance-warning flashers have 

moderate costs.

Enforcement,

Education, and

Maintenance

None identified. Enforcement may be needed to ensure 

compliance with the signal indications.

Exhibit 10-12. Summary of issues related to advance warning treatments.

10.2 SIGNING AND SPEED CONTROL TREATMENTS

10.2.1 Improve Lane Use and Street Name Signing

Description

For some intersections, the use of signs beyond the minimum required by the MUTCD may 

improve safety and/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, and signs located overhead appear smaller to drivers and therefore need to

be substantially larger than ground-mounted signs to have the same visibility.(69)

• 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 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.

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Chapter 10. Approach Treatments 

• Use advance street name signs.

Safety Performance

Advance lane-use signs may improve safety by reducing last-minute lane changes and better

preparing drivers to watch for potential conflicts. One study in Winston Salem, NC based on

limited data reported that advance signing reduced angle collisions by 35 percent.

(161) An

evaluation of advance street name signs estimated these devices were associated with a 10

percent reduction in sideswipe crashes.

(165)

Selected findings of safety benefits of other types of improved signing at signalized

intersections are shown in Exhibit 10-13.

Treatment

Install larger signs.

(101)

Finding

15 percent decrease in all collisions.

Overhead lane-use signs.

(166) 10 percent decrease in rear-end collisions.

20 percent decrease in sideswipe collisions.

Install advance warning signs. (161) 35 percent estimated reduction in angle crashes.

(165) Install advance street name signs. 10 percent estimated reduction in sideswipe crashes.

Exhibit 10-13. Safety benefits associated with advance lane-use signs: selected findings.

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

vehicle occupants.

(69) 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

Low to moderate cost. 

Summary

Exhibit 10-14 summarizes the issues associated with improving signing.

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Chapter 10. Approach Treatments 

Characteristic

Safety

Potential Benefits

Various types of improved 

informational signing can reduce

crashes.

Potential Concerns

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. Low to moderate cost.

Enforcement,

Education, and

Maintenance

None identified. Added sign inventory to manage/maintain.

Exhibit 10-14. Summary of issues for improving signing.

10.2.2 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 to reduce vehicles’ operating speed include landscaping, rumble

strips, medians, narrow travel lanes, bike lanes, on-street parking, curb radii reductions, and 

automated speed enforcement. Several of these treatments are discussed elsewhere in the

guide; the reader is encouraged to refer to those sections for more information.

10.3 ROADWAY SURFACE IMPROVEMENTS

10.3.1 Improve Pavement Surface

Description

An important objective of highway design objective is ensuring that pavement provides

sufficient friction 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 crowns, 

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

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Chapter 10. Approach Treatments 

when frictional demand exceeds the friction force that can be developed between the tire and the

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.(167) 

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 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.

• Change in type of control.

Safety Performance

Several pavement treatments appear to reduce collisions, although the study locations for the 

following findings of effectiveness were not necessarily signalized intersections. A 2010 California 

study reported that resurfacing with grooved pavement reduced wet road crashes by 50 percent,

but results were not significant due to the lack of sufficient data.

(168) Grooves carry off water from

the road surface and increase the coefficient of friction between tires and pavement. The same

study found that resurfacing with open-graded asphalt concrete significantly decreased the

number of wet-related collisions by 42 percent. Another paper describes a non-carbonate 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.(169) 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.

Exhibit 10-15 shows the safety benefits associated with nonskid treatments, drainage 

improvements or resurfacing.

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Chapter 10. Approach Treatments 

Treatment Finding

Groove pavement.

(168) 50 percent estimated reduction in wet pavement collisions.

Resurface with open-graded asphalt 42 percent estimated reduction in wet pavement collisions.

concrete.

(168)

Overlay pavement.

(170) 27 percent estimated reduction in all collisions.

29 percent estimated reduction in fatal collisions.

16 percent estimated reduction in injury collisions.

32 percent estimated reduction in PDO collisions.

Resurface.(171) 5 percent estimated reduction in fatal/serious injury collisions.

1 percent estimated increase in all collisions.

Improve pavement friction (increase 40 to 78 percent estimated reduction in wet road crashes

skid resistance).

Improve pavement texture.

(172) 5 percent estimated reduction in all collisions.

Noncarbonate surface treatment.

(169) 61 to 82 percent estimated reduction in wet pavement collisions.

73 to 82 percent estimated reduction in fatal/injury collisions on

wet pavement.

(101) Drainage improvement. 20 percent estimated reduction in all collisions.

Exhibit 10-15. Safety benefits associated with nonskid treatments, drainage improvements, or

resurfacing: selected findings.

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, speed enforcement should be considered.

Summary

Exhibit 10-16 summarizes the issues associated with pavement treatments.

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Chapter 10. Approach Treatments 

Characteristic Potential Benefits Potential Concerns

Safety Wet-weather collisions reduced.

Angle collisions due to skidding 

reduced.

Rear-end/sideswipe collisions due to 

swerving/braking reduced.

Higher speed profile is a possible 

byproduct.

Operations Improved traffic flow, less swerving. None identified.

Multimodal None identified. None identified.

Physical No additional requirements. None identified.

Socioeconomic

Enforcement,

Education, and

Maintenance

None identified

None identified.

Moderate to high costs associated with 

improvements.

Enforcement may be needed to control

speeds.

Exhibit 10-16. Summary of issues for pavement treatments.

10.3.2 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. Practitioners

should examine roadway profiles and crowns 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, flat roadway 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.(36)

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:

• 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.

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Chapter 10. Approach Treatments 

Safety Performance

The 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

The 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. During any intersection reconstructing, the engineer should

consider improvements to the adjacent sidewalks if pedestrian facilities exist and are being used.

Socioeconomic 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, and 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 leads to safety problems, consider police speed enforcement.

Note that cross section improvements on hilly roadways may actually result in reduced 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

Exhibit 10-17 summarizes the issues associated with cross section improvements.

Characteristic Potential Benefits Potential Concerns

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.

Exhibit 10-17. Summary of issues for cross section improvements.

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Chapter 10. Approach Treatments 

10.3.3 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. 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

For high speed approaches at rural intersections, obstacles should be routinely removed from 

the clear zone on intersection approaches. Removing objects should be considered an 

immediate priority when:

• An unusually high number of run-off-the-road injury and fatal collisions involving roadside

obstacles occurs.

• There is evidence in the collision police report that drivers claim distraction by

unnecessary or illegally placed signing or other visual clutter.

Poles and other hardware that cannot be removed could be shielded from impact by errant

vehicles.

For urban, low-speed environments, the right-of-way is often limited. It may not be practical to 

establish a full-width clear zone. Types of obstructions that may be located near signals could be

fire hydrants, signs, utility poles, transit facilities, and luminaire supports. Obstacles should be

located far enough away from the shoulder and curb to accomplish the following:

• Avoid adverse impacts on vehicle lane position and encroachments into other lanes.

• Improve sight distance for all users at the signal.

• Reduce the travel lane encroachments from occasional parked and disabled vehicles.

• Minimize contact between obstacles and vehicles.

The practitioner should relocate objects a minimum of 4 feet and at least 6 feet where

feasible under these conditions. Other considerations can be found in the Roadside Design

Guide.(62)

Safety Performance

This treatment should decrease the frequency and severity of run-off-the-road collisions

involving roadside obstacles. An Ohio study on roadside safety treatments estimated that

removing or relocating fixed objects outside of the clear zone was associated with a 38 percent

reduction in fatal and injury crashes.

(173)

This study was not limited to intersections.

Physical Impacts

Moving objects further away from the roadside may be difficult to implement in built-up areas

where right-of-way is limited. Studies have shown under urban conditions that a minimum offset

from curbs of 4 ft and, if possible, a distance of 6 ft can reduce fixed object crashes. For buffer

areas between sidewalks and curbs, the practitioner should only allow posts with frangible 

bases.(174)

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 signing.

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Chapter 10. Approach Treatments 

Summary

Exhibit 10-18 summarizes the issues associated with removing obstacles from the clear

zone.

Characteristic

Safety

Potential Benefits

Reduction in the number and 

severity of single-vehicle collisions.

Potential Concerns

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.

Exhibit 10-18. Summary of issues for removing obstacles from the clear zone.

10.4 SIGHT DISTANCE TREATMENTS

10.4.1 Improve Sight Lines

Description

Adequate sight distance for drivers contributes to the safety of the intersection. In general,

left-turning vehicles need sight distance 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)

Sight distance at signalized intersections should:

• Provide drivers making permissive left-turning movements need enough sight distance to

judge on-coming traffic.

• Provide clear sight lines to all signal faces.

• Provide clear sight lines at pedestrian crosswalks.

• Provide clear sight lines at bike lanes and other bicycle facilities or treatments.

• Have sight distance at or above the above the minimums used in the AASHTO Green

Book when placed on flash for emergencies.

Carefully consider landscaping at signalized intersections; it could prevent motorists from

making left and right turns safely due to inadequate sight distances. Practitioners should ensure 

that traffic signs, pedestrian crossings, and nearby railroad crossing and school zones are not

obstructed. Median planting of trees or shrubs greater than 2 ft in height should be well away

from the intersection (more than 50 ft). No plantings having foliage between 2 ft and 8 ft in height

should be present within sight triangles. Low shrubs or plants not exceeding a height of 2 ft are 

appropriate on the approaches to a signalized intersection, either on the median, or along the 

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Chapter 10. Approach Treatments 

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.

(87)

Application

Visibility improvements at signalized intersections should be considered when:

• Inadequate sight distance exists between vehicles and/or pedestrian. Any obstructions

that limit sight distance of any types of users should be removed or relocated. A high

number of left- and right-turn collisions are occurring.

Safety Performance

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.(157) 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. Exhibit

10-19 shows the expected reduction in number of collisions per intersection per year, based on

an FHWA report.(175) 

AADT* Increased Sight Distance

(1000s)

20 ft–49 ft 50 ft–99 ft > 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

Exhibit 10-19. Expected reduction in number of crashes per intersection per year by

increased sight distance.(175)

A report by FHWA cites sight distance improvements as being one of the most cost-effective 

treatments (see Exhibit 10-20). Fatal collisions were reduced by 56 percent and nonfatal injury

collisions were reduced by 37 percent at intersections having sight distance improvements.(176)

The Handbook of Road Safety measures estimates that increasing triangle sight distance is

associated with a 48 percent reduction in injury crashes, and an 11 percent reduction in property

damage crashes.

(145) However, these results include both signalized and unsignalized

intersections.

Treatment Implication

(176) Sight distance improvements. 56 percent estimated reduction in fatal collisions.

37 percent estimated reduction in injury collisions.

Sight distance improvements.

(145) 48 percent estimated reduction in injury crashes.

11 percent estimated reduction in property damage crashes.

* Note: these crash results include both signalized and unsignalized intersections

Exhibit 10-20. Safety benefits associated with sight distance improvements: selected findings.

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

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Chapter 10. Approach Treatments 

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. Consider

other alternatives in these situations.

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.

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

Exhibit 10-21 summarizes the issues associated with visibility treatments.

Characteristics Potential Benefits Potential Concerns

Safety Left- and right-turning collisions involving 

inadequate sight distance.

None identified.

Operations Negligible. None identified.

Multimodal Provides additional warning for heavy None identified.

vehicles making left and right turns.

Appropriate landscaping will provide a 

more pleasant environment for

pedestrians.

Physical None identified. May be significant right-of-way

requirements.

Socioeconomic Appropriate landscaping will visually None identified.

enhance intersection and surroundings.

Enforcement, None identified. Landscaping may require extensive 

Education, and maintenance.

Maintenance

Exhibit 10-21. Summary of issues for visibility improvements.

10.5 DILEMMA ZONE DETECTION 

Description

On a high-speed approach to a signalized intersection there is a length of roadway in 

advance of the intersection, commonly referred to as the “dilemma zone,” wherein drivers may be

indecisive and respond differently to the onset of the yellow signal. When in the dilemma zone at

the onset of yellow, some drivers may stop abruptly, while others may decide not to stop and

perhaps even accelerate through the intersection. Such variation in driver behavior is conducive 

to the occurrence of rear-end, right-angle, and left-turn collisions. A dilemma zone detection 

system uses pulse (or advanced) detectors placed at one or more locations on the intersection 

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Chapter 10. Approach Treatments 

approach to extend the green and prevent the onset of yellow while approaching vehicles are in 

the dilemma zone (see Section 5.5.1).

The current state of the practice includes two typical installations:

1. Basic detection/actuation to increase the probability of gap-outs and reduce max-outs to

improve both safety and operations.

2. Detection systems that take more dynamic control, extending all-red time if the system

detects that a driver will likely run the red light.

As shown in Exhibit 10-22, some States use a rule of thumb of 5 seconds in advance of the

stop line to provide dilemma zone protection. On very high speed routes, an additional set of

detectors may be placed 8 seconds from the stop line. Exhibit 10-23 illustrates the distance 

traveled by vehicles at various speeds.

Exhibit 10-22. Dilemma Zone and detector placement.

(63)

Exhibit 10-23. Vehicular distances traveled by speed.(Adapted from 63)

Speed (mph) Time (s)

mph fps

5 8

Distance Traveled

(ft)

5 7.3 37 59

10 14.7 73 117

15 22.0 110 176

20 29.3 147 235

25 36.7 183 293

30 44.0 220 352

35 51.3 257 411

40 58.7 293 469

45 66.0 330 528

50 73.3 367 587

55 80.7 403 645

60 88.0 440 704

65 95.3 477 763

70 102.7 513 821

75 110.0 550 880

80 117.3 587 939

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Chapter 10. Approach Treatments 

Application

Dilemma zone detection systems apply to high-speed signalized intersections, often located

in rural or suburban areas. This treatment (more specifically, a dynamic type control) is especially

useful on high-speed approaches with heavy volumes of large trucks.

Safety Performance

An evaluation of a dilemma zone detection system developed for the Texas Department of

Transportation estimated that red light violations were reduced by 58 percent, heavy vehicle red 

light violations were reduced by 80 percent, and severe crash frequency was reduced by 39 

percent.

(177)

Operational Performance

The dilemma zone detection system developed for the Texas Department of Transportation

was associated with a 14 percent reduction in approach delay and a 9 percent reduction in stop

frequency. Other dynamic detection system designs for protection achieve similar operational

improvements.

Multimodal Impacts

Large trucks and tour buses, which require longer stopping distances than passenger

vehicles, especially benefit from the use of dilemma zone detection.

Socioeconomic impacts

Reductions in approach delay, heavy vehicle braking, and injury crashes provide economic

benefits. Significant initial costs are associated with design and implementation of dilemma zone 

detection systems.

Education, Enforcement, and Maintenance

Traffic signal maintenance technicians may require additional training on technical aspects of

dilemma zone detection systems.

Summary

Exhibit 10-24 summarizes the issues associated with the application of dilemma zone 

detection.

Characteristics Potential Benefits Potential Concerns

Safety Reduced red-light running and injury

crashes.

None identified.

Operations Reduced approach delay and stop 

frequency.

None identified.

Multimodal Especially useful for large trucks. None identified.

Physical None identified. Possible disturbance to ROW and/or

pavement surface.

Socioeconomic Economic benefits from reductions in 

approach delay, heavy vehicle braking,

Significant initial costs for design and 

implementation.

and injury crashes.

Enforcement, None identified. Traffic signal technicians may require 

Education, and additional training for maintenance of

Maintenance installed equipment.

Exhibit 10-24. Summary of issues for dilemma zone detection

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Chapter 10. Approach Treatments 

10.6 RED LIGHT CAMERA ENFORCEMENT

Description

Red light cameras automatically photograph vehicles whose drivers run red lights. The 

cameras are connected to the traffic signal and to sensors monitoring traffic flow just before the

crosswalk or stop line. Vehicles that do not stop during the red phase are photographed.

Depending on the particular technology, the system captures a series of photographs and/or a

video clip showing the red light violator prior to entering the intersection on a red signal, as well

as the vehicle's progression through the intersection. Cameras record the date, time of day, time 

elapsed since the beginning of the red signal, vehicle speed, and license plate. Tickets typically

are mailed to owners of violating vehicles, based on a review of photographic evidence.

Application

Red light cameras are typically deployed at specific approaches to urban and suburban

intersections with histories of red-light running crashes. Red light cameras may be especially

useful on approaches where police officers have difficulty conducting traditional red light

enforcement due to constrained environments and/or high traffic speeds.

It is vital to put public safety first in decisions regarding enforcement of traffic laws, including

an emphasis on non-automated enforcement alternatives where applicable.

(178) Note that other

infrastructure treatments should be considered before automated red light enforcement, including

the following:

• Updating signal timing to reflect current traffic conditions.

• Updating clearance timing per recommended practice.

o Ensuring that clearance timing practice does not vary between State and local

agencies in a region.

• Clearing sight lines to signal heads.

• Signing in advance of the intersection.

• Installing advance, signal-activated warning flashers.

• Installing reflectorized backplates.

Safety Performance

In NCHRP Report 729: Automated Enforcement for Speeding and Red Light Running three of

the four case studies included information on safety performance:

(179)

• The program in the city of Portland, Oregon, resulted in a 69 to 93 percent reduction in

red-light running violations.

• The program in the city of Virginia Beach, Virginia, reduced red light violations more than

69 percent over a 13 month period since the activation of the red light cameras.

• An audit of the program in the city of San Diego, California, found an 8 percent reduction

in crashes from red-light running and a 16 percent reduction in red-light running related

crashes at the specific signals with cameras. The city has initiated many changes to the

program since completion of the audit.

Some studies, including FHWA’s Safety Evaluation of Red Light Cameras, (207) have reported 

reductions in angle crashes along with increases in rear end crashes, resulting in a net decrease

in aggregate crash severity. The Highway Safety Manual (11) (Chapter 14) includes crash 

modification factors for red light cameras that indicate a 26 percent reduction in angle crashes

and an 18 percent increase in rear-end crashes. However, NCHRP Report 729 concluded that

the overall impact on violations and crashes related to a red light enforcement program needs

further study.

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Chapter 10. Approach Treatments 

Operational Performance

No operational performance measures have been reported for this treatment. However,

changes to signal timing, detector settings, and other components of the intersection must be

communicated to the division responsible for overseeing the red light program. As these 

adjustments are made, changes to the red light cameras can be made to ensure proper

operation.

Multimodal Impacts

Pedestrians and bicyclists are vulnerable to impacts from motor vehicles that run red lights,

and thus stand to benefit from reductions in red-light running behavior.

Socioeconomic impacts

A successful red light camera program will modify driver behavior in order to achieve a

decrease in severe crashes associated with red-light running. The citations generated from red

light cameras will result in fines and fees, which should be distributed in accordance with the state 

laws and/or local ordinances. In most cases, the citation fines and fees may be used to offset the 

cost of the red light camera program, with any excess monies used expressly for other road

safety purposes.

The judiciary is critical to a successful red light camera program from the development of

legislation to the choice of camera right down to the processing of violations. It is therefore 

important to get them involved as early on in the process as possible and for the judiciary to 

champion the effort. Another reason to involve them is to ensure that they are prepared to

support the prosecution of the issued tickets when the red light camera system is activated.

(180)

Education, Enforcement, and Maintenance

A key component in developing a new enforcement program is informing and educating the

public about the program, especially the purpose, the camera locations, the process for

adjudication of citations, the use of revenue, and results of program evaluation in terms of effect

on violations and crashes. In addition to conducting a public information campaign, a jurisdiction

should consider assessing public support prior to, and during, implementation of the program.

Summary

Exhibit 10-25 summarizes the issues associated with red light cameras

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Chapter 10. Approach Treatments 

Characteristics Potential Benefits Potential Concerns

Safety Reduced red-light running and angle 

crashes.

Increased rear-end crashes.

Operations None identified. Changes to signal timing must be

addressed when an agency installs

red light cameras.

Multimodal Pedestrians and bicyclists benefit from

reduced red-light running.

None identified.

Physical None identified. Additional equipment installed along 

the roadside.

Socioeconomic Fines generated by citations typically cover

the cost of camera installation and

operation

Fine revenue in excess of program

operating costs can be a source of

controversy.

Enforcement,

Education, and

Maintenance

Enforcement should be accompanied by

public information and education.

Maintenance of installed equipment.

Exhibit 10-25. Summary of issues for red light cameras.

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Chapter 11. Individual Movement Treatments 

Chapter 11

INDIVIDUAL MOVEMENT TREATMENTS

TABLE OF CONTENTS

11.0 Individual Movement Treatments...................................................................................... 11-3

11.1 Left-Turn Treatments .............................................................................................. 11-3

11.1.1 Add Single Left-Turn Lane ......................................................................... 11-3

11.1.2 Multiple Left-Turn Lanes .......................................................................... 11-15

11.2 Right-Turn Treatments.......................................................................................... 11-18

11.1.1 Channelizing Islands................................................................................ 11-18

11.2.2 Right-Turn Lanes ..................................................................................... 11-23

11.2.3 Provide Double Right-Turn Lanes............................................................ 11-28

11.2.4 Restricting Turns, U-Turns....................................................................... 11-30

11.2.5 Provide Auxiliary Through Lanes ............................................................. 11-31

11.2.6 Delineate Through Path ........................................................................... 11-34

11.3 Variable Lane Use Treatments ............................................................................. 11-36

11.3.1 Provide Reversible Lanes ........................................................................ 11-36

11.3.2 Provide Variable Lane Use Assignments ................................................ 11-37

LIST OF EXHIBITS

11-1 Diagram of a single left-turn lane...................................................................................... 11-4

11-2 Rule-of-thumb intersection capacities assuming various exclusive left-turn treatments .. 11-5

11-3 Narrow left-turn lanes may be used effectively in retrofit situations ................................. 11-6

11-4 Illustration of negative, no, and positive offset left-turn lanes........................................... 11-7

11-5 Example of positive offset left-turn lane............................................................................ 11-8

11-6 Guidelines for use of left-turn phasing............................................................................ 11-10

11-7 Guidelines for selection of type of left-turn phasing........................................................ 11-11

11-8 Minimum recommended sight distance for allowing permissive left turns...................... 11-12

11-9 Safety benefits associated with left-turn lane improvements for four approach, urban and

suburban intersection .................................................................................................. 11-12

11-10 Crash effects of modifying left-turn phases ................................................................... 11-13

11-11 Summary of issues for left-turn lanes ............................................................................ 11-14

11-12 Safety benefits associated with double left-turn lanes: selected findings...................... 11-17

11-13 Summary of issues for multiple left-turn lanes............................................................... 11-18

11-14 Channelized islands....................................................................................................... 11-19

11-15 Example illustration of a channelized right-turn lane..................................................... 11-21

11-16 Safety benefits associated with right-turn channelization: selected findings................. 11-22

11-17 Summary of issues for channelized right-turn lanes ...................................................... 11-23

11-18 Diagram of a typical right-turn lane ................................................................................ 11-24

11-19 Right-turn lane volume warrants .................................................................................... 11-25

11-20 Narrow (8 ft) right-turn lanes may be used effectively in retrofit situations .................... 11-26

11-21 Safety benefits associated with right-turn improvements .............................................. 11-27

11-22 Summary of issues for right-turn lanes .......................................................................... 11-28

11-23 Summary of issues for double right-turn lanes .............................................................. 11-30

11-24 Summary of issues for turn prohibitions......................................................................... 11-31

11-25 Diagram of an auxiliary through lane............................................................................. 11-32

11-26 Summary of issues for auxiliary through lanes .............................................................. 11-34

11-27 Example of delineated paths ......................................................................................... 11-35

11-28 Summary of issues for path delineation ........................................................................ 11-36

11-29 Summary of issues for reversible lanes......................................................................... 11-37

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Chapter 11. Individual Movement Treatments 

11-30 Example use of variable lane use sign to add a third left-turn lane during certain times

of day ........................................................................................................................... 11-38

11-31 Example use of variable lane use sign to add a second right-turn lane along a corridor

during certain times of day .......................................................................................... 11-39

11-32 Summary of issues for variable lane use ....................................................................... 11-39

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Chapter 11. Individual Movement Treatments 

11.0 INDIVIDUAL MOVEMENT TREATMENTS

This section identifies treatments for vehicle movements at signalized intersections. This

section will start with left- and right-turn lanes, including multiple turning lanes. Relocating or

prohibiting movements will be the next treatment discussed. Information related to through lane

treatments will follow. Finally, this chapter will cover treatments to be used sparingly, but are 

available in response to unusually heavy traffic conditions (e.g., variable and reversible lane

usage). The treatments in this section primarily address the following safety and operational

concerns facing practitioners: 

• Choosing appropriate treatment that addresses common crash types at signals.

• Impacts to all users are considered when choosing a treatment.

• An intersection that operates with nominal delay and queuing.

11.1 LEFT-TURN TREATMENTS

This section discusses the key safety, operational, and design characteristics associated with

left-turn treatments that range in scope from a single left-turn lane to multiple left-turn lanes.

Left-turning vehicles encounter conflicts from several sources: pedestrians; bicyclists;

opposing through traffic; through traffic in the same direction; and crossing traffic. These conflicts 

can cause angle-, sideswipe, left-turn, and rear-end crashes.

The demand for left-turn movements also affects the amount of green time that is allocated to

other traffic movements. Operational treatments may be justified to minimize the amount of green 

time that is allocated to left-turn movements. This will allow the practitioner to reallocate time to

other critical movements. 

11.1.1 Add Single Left-Turn Lane

Adding a single left-turn lane at an approach that currently has shared through and left-turn

movements is one the most common approaches to improve the safety and reduce delay. An

example of a typical left-turn lane is shown in Exhibit 11-1. Installing a left-turn lane on one 

approach does not necessarily mean that a left-turn lane for the opposing left is necessary. If

one left-turn lane is installed, the practitioner should ensure that the traveling path of through 

traffic transitions through the signal into the correct lane

Left-turning vehicles stopped in traffic while waiting for a gap in opposing traffic are prone to

rear-end crashes. Separate left-turn lanes provide a refuge while waiting for a gap. Reviewing

the crash history collision diagrams or the results of a traffic conflict study can provide the basis

for adding a left-turn lane or changing left-turn phasing. Practitioners should look for a history of 

rear ends or left-turn crashes on any given approach.

A left-turn lane provides left-turning vehicles space to safely decelerate away from through

traffic. Reducing this conflict directly impacts rear end collisions. If practicable, the left-turn lane 

should be long enough to accommodate most of the deceleration needed to stop at the 

intersection.

Left-turn lanes can help improve signals’ efficiency. Separating through movements from leftturning vehicles can decrease the headway between vehicles and improve the flow rate through 

the signal for both movements. Different phasing options can be utilized to accommodate 

fluctuating traffic flow occurring throughout the day. For example, a lagging left turn needed for

the morning commuters reverting back to simultaneous lefts for the rest of the day. The 

practitioner should always consider impacts to non-motorized travel. The typical impact is the 

additional pavement that pedestrians must cross and the walk time that must be added to signal’s

timing plan.

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Chapter 11. Individual Movement Treatments 

L = Storage length

R = Radius of reversing curve

S = Stopping sight distance for a speed of (0.7)(operating speed of highway)

T = Tangent distance required to accommodate reversing curve

W = Minimum distance of 12 m (40 ft)

Exhibit 11-1. Diagram of a single left-turn lane.(181)

Applicability

Review local agencies’ adopted guidelines and practices should be reviewed to determine 

whether left-turn lane warrants are in place for a particular roadway. Key elements to consider

when determining whether a left-turn lane is warranted include:

• Significant intersections. A left-turn lane should be considered at the intersections of

higher class facilities (i.e., arterials and principal arterials) and other public roads equal to

a collector or higher classification to accommodate both higher approach speeds and

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 can increase 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 2010 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.

Exhibit 11-2 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

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Chapter 11. Individual Movement Treatments 

than 20 percent of total approach volume or when a left-turn volume is greater than 100 vehicles

per hour in peak periods.(48)

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, 1 1,700 2,300 —

minor approach 2 2,400 3,000 — 

3 — — —

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, 1 1,600 2,100 2,300

minor approach 2 2,100 2,600 2,800

3 2,700 3,000 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, 1 1,500 1,800 2,000

minor approach 2 1,900 2,100 2,400

3 2,200 2,300 2,800

Notes: *Critical signal phases are non-concurrent 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(48)

Exhibit 11-2. Rule-of-thumb intersection capacities assuming various exclusive left-turn 

treatments.

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)

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. In practice, some deceleration (10 mph) is considered acceptable in the 

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Chapter 11. Individual Movement Treatments 

through lane prior to entering the turn lane. 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 for 30 mph to 15:1 for 50 mph or greater 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 too long of a taper 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 100 ft for a single turn lane and 150 ft for a dual turn lane.

(3)

Storage length. The length of the left-turn bay should be sufficient 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 HCM can also be used to 

estimate queues, as noted in Chapter 7.(2) Traffic models used to develop signal timing can 

provide an accurate estimate on queue length.

Lane width. Lane width requirements for left-turn lanes are largely based on operational

considerations. Generally, lane widths of 12 ft are desirable to maximize traffic flow; however,

right-of-way or non-motorized needs may dictate the 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-thanideal lane is likely an improvement over providing no left-turn lane. Lane widths less than 9 ft are 

not recommended for new design. However, in some very constrained retrofit situations on lower

speed roadways, lane widths as low as 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 12-ft lanes to narrower lanes should be considered where 

appropriate.(57),(182)

Exhibit 11-3 shows an example from Montgomery County, Maryland, where a 

narrow left-turn lane has been used effectively.

Exhibit 11-3. Narrow 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 signal phase, this

can lead to collisions between vehicles turning left and through vehicles on the opposing

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Chapter 11. Individual Movement Treatments 

approach. In a situation with a negative offset or no offset, left-turning motorists can be blocked 

by opposing left turners (see Exhibit 11-4(a)). This should be avoided when possible.

The practitioner should consider left-turn lanes with a positive offset that allow drivers to see 

oncoming traffic without obstruction (see Exhibit 11-4(c)).

This practice 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 18 ft should have

positive offset left-turn lanes. However, providing any amount of offset that moves obstructing

vehicles out of the way should be pursued. One method for laterally shifting left-turning vehicles

is to narrow the turn-lane width using pavement markings.

Positive offsetting has other benefits. Positive offsetting of left-turn lanes ensures that the 

turning radii for opposing left-turning vehicles do not overlap each other. This allows these

movements to be concurrent phases. Also, positive offsetting of the left-turn lanes can be useful

for staged improvements. For example, dual lefts can be built on the major street approach, but

cannot be utilized until the minor streets are widened. The outside turn lane is striped out to

provide positive offset.

Offset left-turn lanes should remain parallel to the through travel route if practical. Exhibit 11-

4 illustrates a positive offset at an intersection.(1)

Exhibit 11-4. Illustration of negative, no, and positive offset left-turn lanes. Positive offset is

preferred.(183)

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Chapter 11. Individual Movement Treatments 

Exhibit 11-5. Example of positive offset left-turn lane.

Dropped Lane. In constrained areas, through lanes are sometimes converted to left-turn

lanes. This type of lane is sometimes referred to as a “dropped” lane. The traffic control used to

alert or raise awareness by the driver in this situation is critical especially at locations with higher

speeds or congested areas. For this reason, the MUTCD requires the use of a wide dotted white

lane line to distinguish the drop lane from the adjacent through lane (refer to MUTCD Section 

3B.04).

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 channelize 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, 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 or where the design vehicle can be better accommodated. However, paint is more 

difficult to see at night, especially at intersections that are not lighted.

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Chapter 11. Individual Movement Treatments 

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-turn to through lanes or vice

versa are prevented.

• Median refuge for pedestrians providing a two stage crossing.

• Median islands can used to control speed across crosswalks.

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 the safety and

operational performance of the turn. The practitioner should always strive to utilize the smallest

number of phases. To accomplish this, less-restrictive phasing schemes are preferable where

appropriate because these phases result in lower delay to all users of the intersection. However,

the responsible agency for the signal’s performance should review the operation and safety of the 

intersection on an annual basis to ensure the intersection is operating within expectations.

Exhibit 11-6 presents suggested guidelines for determining whether left-turn phasing is

appropriate, and Exhibit 11-7 presents suggested guidelines for determining the type of left-turn

phasing. Current signal equipment allows practitioners the flexibility to alter timing and phasing

throughout the day as conditions warrant. Exhibit 11-8 presents the minimum recommended

sight distance for permissive left turns. Note that many agencies have adopted similar guidelines

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 leftturn 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.

• Some municipalities (Tucson, AZ; Denver, CO) allow the use of protected-permissive

phasing at double left turns, while most States use protected-only phasing for those

locations.

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Chapter 11. Individual Movement Treatments 

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 0.5 mi):

One opposing lane: 45,000 Two opposing lanes: 90,000

b. Platoon arrivals (other traffic signals within 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 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

Exhibit 11-7.

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.

Exhibit 11-6. Guidelines for use of left-turn phasing.(184),(185)

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Chapter 11. Individual Movement Treatments 

The type of phasing to use can be based on the following criteria:

1. Insignificant number of adequate gaps in opposing traffic to complete a left

turn.

2. Permissive left-turn phasing may be considered at sites that do not satisfy any

of the left-turn phasing criteria listed in Exhibit 11-6.

3. Protected-permissive left-turn phasing may be considered at sites that satisfy

one or more of the left-turn phasing criteria listed in Exhibit 11-6 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.

4. 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,

a flashing yellow arrow, or other such devices.

5. 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 exceed 130,000-150,000 for one opposing

lane or 300,000 for two opposing lanes.

b. The posted speed of opposing traffic exceeds 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

Exhibit 11-8.

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, number of older drivers,

and operational requirements unique to preemption systems.

Exhibit 11-7. Guidelines for selection of type of left-turn phasing.(184,185)

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Chapter 11. Individual Movement Treatments 

Design Intersection

Design Speed Sight Distance for

(mph) Passenger Cars* (ft)

20 165

25 205

30 245

35 285

40 325

45 365

50 405

55 445

60 490

65 530 * 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

Exhibit 11-8. Minimum recommended sight distance for allowing permissive left turns.

Safety Performance

The HSM contains information that allows practitioners to quantify the safety impacts of leftturning phasing and/or left-turn lanes. Exhibits 11-9 and 11-10 identify CMFs used to calculate

the number of crashes per year. The exhibits show favorable impacts towards safety through the

addition of a lane and exclusive left-turn movements.

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 particularity if short

tapers are used to shift through traffic. Off-tracking increases the likelihood of sideswipe and head 

on crashes between left-turning and adjacent through vehicles and between opposing left-turning

vehicles. These impacts to large vehicles can be reduced with proper lengths of tapers and 

appropriate pavement markings.

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.

Exhibit 11-9 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.

Crash Modification Factor (CMF1i) for Installation of Left-Turn Lanes on Intersection Approaches 

Intersection 

Type 

Intersection traffic 

control 

Number of approaches with left-turn lanes a 

One approach Two 

approaches 

Three 

approaches 

Four 

approaches 

3 Approaches Traffic signal 0.93 0.86 0.80 0.80

4 Approaches Traffic signal 0.90 0.81 0.73 0.66

Exhibit 11-9. Safety benefits associated with left-turn lane improvements for four approach, urban 

and suburban intersection.

Source: Highway Safety Manual.(11)

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Chapter 11. Individual Movement Treatments 

Exhibit 11-10. Crash effects of modifying left-turn phases

Source: Highway Safety Manual (11)

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.

Practitioners considering adding protected left turn phasing should evaluate the impacts to 

other movements at the intersection. Other movements may experience increases in queue

lengths, and stopped approach delay for all users. Impacts to coordination also should be

evaluated prior to implementation of additional left turn phasing.

Multimodal Impacts

For cases where widening is required to add a left-turn lane, the pedestrians will need to walk

further to cross the street increasing the conflict between vehicles and pedestrians. Consider

pedestrian refuges (along with push buttons) for wide roadway sections (approximately 75 ft).

(186)

Practitioners should consider the volumes of truck and bus traffic using the lane in the design 

of a left-turn lane.

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Chapter 11. Individual Movement Treatments 

Physical Impacts

Adding 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, striping, and additional signal

equipment 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

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 and phasing will be the same as for other areas of the

intersection. Pavement markings, signs, and indications should be kept visible and legible.

Pavement skid resistance should be maintained. Detection systems should be checked for any

call failures. In addition, ongoing reviews through intersection counts, observations, and periodic

checks of performance goals related to crashes, delay, and network compatibility are needed.

Summary

Exhibit 11-11 provides a summary of the issues associated with left-turn lanes.

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Chapter 11. Individual Movement Treatments 

Characteristic Potential Benefits Potential Concerns

Safety Separation of left-turn vehicles from

though movements.

Increased pedestrian exposure.

Operations Additional capacity. Potential for

shorter cycle lengths and/or allocation 

Spillback; inadequacy of design.

of green to other movements.

Multimodal Left-turn lane may result in shorter Depending on design, may result in longer

pedestrian delays due to shorter cycle 

length.

crossing time and exposure for pedestrians.

Physical None identified. Increased intersection size. *

Socioeconomic Travel time reduced. Right-of-way and construction costs. *

Vehicle emissions reduced.

Enforcement, None identified. None identified.

Education, and

Maintenance

Adding signals without funding adjustment

reduces ability to properly maintain all

intersections.

* Applies to situations where the left-turn lane is added by physical widening rather than restriping.

Exhibit 11-11. Summary of issues for left-turn lanes.

11.1.2 Multiple Left-Turn Lanes

Multiple left-turn lanes are widely used at signalized intersections where traffic volumes have

increased to the point that signal timing cannot alleviate excessive queues and delay with the 

current number of lanes. 

Multiple left-turn lanes allow for the allocation of green time to other critical movements or

utilize a shorter cycle length. Using multiple left-turn lanes helps reduce the queue waiting to turn

left; the practitioner will need to estimate how many vehicles may be in each lane. Rarely will

there be an even distribution among the turn lanes, which can dramatically impact the signal

timing.

Applicability

Double and triple left-turn lanes are appropriate at intersections with high left-turn volumes

that cannot be adequately served in a single lane. As a rule-of-thumb, consider dual left-turn 

lanes 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. Lane distribution for triple lefts is critical to

operational success.

(187)

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.

• Other alternative intersections may be a more appropriate option.

• An insufficient number of departure lanes exist.

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Chapter 11. Individual Movement Treatments 

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 the width of the receiving lanes should be

considered. The following are design considerations for triple left-turn lanes provided by

Ackeret.(188) 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 and signing visibility.

• Placement of stop lines 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.

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, located over each lane if feasible, should be used

with triple left-turn movements, especially in advance of the intersection. The signing will

help maximize the benefits of triple lefts. Lane distribution for triple left-turn lanes should

be estimated as close as possible. Practitioners should reevaluate marking and signing

immediately after the triple lefts are constructed for any necessary adjustments.

• 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.

• Triple left turns should not include a permissive phase; they should be protected only at

all times of day.

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.(189) These 

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Chapter 11. Individual Movement Treatments 

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.(190) 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 change and clearance intervals and 

limited sight distance, not operation of the triple left.

Exhibit 11-12 presents selected findings of the safety benefits of multiple left-turn lanes.

Treatment

Double left-turn lane.

(163)

Finding

29 percent estimated reduction in all fatal/injury collisions.

26 percent estimated reduction in all PDO collisions.

29 percent estimated reduction in fatal/injury rear-end collisions.

47 percent estimated reduction in fatal/injury left-turn collisions.

20 percent estimated reduction in angle fatal/injury collisions.

Triple left –turn lanes. Texas study found triple lefts did not raise any major safety issues.

Exhibit 11-12. Safety benefits associated with double left-turn lanes: selected findings.

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.

To achieve this level of performance, these turning movements should still be serviced

through normal phasing sequences. If these turns require split-phasing and/or independent

phasing, the advantages mentioned in the previous paragraph will not be long term. Evaluation

of the signal timing necessary for the triple left-using traffic software and simulation is key to a 

successful implementation of multiple left-turn lanes. The practitioner may need to compare triple

lefts with other alternative intersection designs.

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

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.

Multimodal Impacts

Adding turn lanes increases the crossing distance for pedestrians, as well as their exposure

to potential conflicts if roadway widening is required. One method to mitigate this exposure is the 

use of median refuge islands for pedestrians. The islands reduce the walking distance and 

provide safe areas for pedestrians and bicyclists to wait. These refuge islands also allow for a 

two stage crossing.

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,

practitioners should consider right-of-way costs and access to adjacent properties. 

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Chapter 11. Individual Movement Treatments 

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

Exhibit 11-13 summarizes the issues associated with multiple left-turn lanes.

Characteristic Potential Benefits Potential Concerns

Safety Potential reduction in collisions. Permissive phasing can increase

the opportunity for left turn 

crashes.

Operations Potential improvement in capacity. Unbalanced lane utilization.

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. Maintaining more equipment,

pavement, marking, signing.

Enforcement of triple lefts may be 

an issue.

Exhibit 11-13. Summary of issues for multiple left-turn lanes.

11.2 RIGHT-TURN TREATMENTS

The purpose of this section is to highlight what strategies are available to practitioners for

right-turning movements. Significant volumes of right-turning vehicles can adversely impact the 

operations and safety of a signalized intersection. Typical improvements used to offset these 

adverse impacts range from channelizing islands to right-turn lanes. This section will move from

lower to higher impact improvements related to additional property.

Practitioners should consider phasing overlaps for right-turning movements. The ability to

share green time with compatible movements at the intersection can reduce the need for some of

the following treatments.(187) 

11.2.1 Channelizing Islands

Channelizing islands that physically separate through and right-turning movements are 

constructed to improve the operations and/or safety of an intersection. These islands can be 

constructed as standalone improvements or built in combination with a right-turn lane.

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Chapter 11. Individual Movement Treatments 

Applicability

Channelization of the right turn with a raised or painted island can provide larger turning radii

to accommodate large design vehicles. A larger turning radius also allows higher turning speeds.

These higher speeds help increase the efficiency of the right-turning vehicles. The island allows

some queuing of through traffic and provides access for right-turning vehicles to travel through 

the intersection.

Agencies increasingly install raised channelized islands to provide an area for pedestrian 

refuge. Crosswalks with long crossing distances can be reduced somewhat by providing these 

islands.

(11-14a) (a. City of Columbia, MO)

Exhibit 11-14. Channelized islands.

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Chapter 11. Individual Movement Treatments 

(11-14b) (200)

Exhibit 11-14. Channelized islands (cont’d).

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.(191) 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.

Raised channelized islands using simple curves find high incidences of rear-end and 

pedestrian crashes. As driver’s focus to their left anticipating on-coming traffic, they lose sight of

the vehicle they were following who chooses to yield. To aid driver’s line of sight while turning 

right, an “Australian” right is used. A large radius allows a right turn vehicle to maneuver by the 

island, but allows viewing all of the details in front of them.

Exhibit 11-15 illustrates a channelized right-turn lane.

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Chapter 11. Individual Movement Treatments 

Exhibit 11-15. Example illustration of a channelized right-turn lane.

Channelized right-turn lanes apply for intersections with a high volume of right-turning 

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, especially if

the speed varies greatly from the road the vehicle is turning from. Additionally, larger turn radii

and higher speeds can pose a pedestrian safety issue.

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. 

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.

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Chapter 11. Individual Movement Treatments 

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 Exhibit 11-16.

Exhibit 11-16. Safety benefits associated with right-turn channelization: selected findings.(200)

Treatment Finding

Channelization 25 percent decrease in all collisions

50 percent 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.

Multimodal Impacts

Curbed islands offer a pedestrian refuge. 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. Right-turn roadways increase crossing distances and 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 will turn 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

Exhibit 11-17 summarizes the issues associated with channelized right-turn lanes.

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Chapter 11. Individual Movement Treatments 

Characteristics Potential Benefits Potential Liabilities

Safety Separation of decelerating right-turn

vehicles.

Potential for sideswipes and rear-end 

collisions on departure leg. 

Pedestrian crosswalk design compatibility.

Operations Higher right-turn capacity.

Shorter green time.

Less delay for following through 

vehicles.

None identified. “Australian Right” may

not accommodate large vehicles

Multimodal Pedestrian refuge area. Longer pedestrian crossing distance and 

exposure.

Higher vehicle speeds.

Physical

Socioeconomic

Smaller impact than a lane along the 

right-of-way

Support a mixed use, walkable 

community

Larger intersection footprint.

Right-of-way costs.

Access restrictions to property.

Enforcement,

Education, and

Maintenance

None identified. Higher maintenance of islands, marking,

signing

Exhibit 11-17. Summary of issues for channelized right-turn lanes.

11.2.2 Right-Turn Lanes

Turning vehicles’ deceleration 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 reduce vehicular delay and increase intersection capacity.

Exhibit 11-18 illustrates the operational impacts of a right-turn lane.

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Chapter 11. Individual Movement Treatments 

Exhibit 11-18. Diagram of a typical right-turn lane.(adapted from 192)

Right-Turn Lane Warrants 

Similar to left-turn lane warrants, review the adopted guidelines and practices from local

agencies when determining if a right-turn lane is warranted. Factors to consider 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 Exhibit 11-19.

(48) These warrants are based on the percentage of vehicles turning right (as a

percentage of through vehicles) during the peak period.

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Chapter 11. Individual Movement Treatments 

State

Alaska

Conditions Warranting Right-Turn Lane off Major (Through Highway)

Through Volume Right-Turn Volume Highway Conditions

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

Exhibit 11-19. Right-turn lane volume warrants.(48)

Design features

The key design criteria for right-turn lanes are: entering taper; deceleration length; storage

length; lane width; corner radius; and sight distance. A Policy on Geometric Design for Highways

and Streets and agencies’ policies describe the design criteria for selecting an appropriate rightturn lane length.

(3)

Entering taper and deceleration length. Determine the entering taper and deceleration

length based on vehicle speed. Design the storage length 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 in the through

travel lane.

Storage length. Make right-turn lanes 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, design the auxiliary lane to 

accommodate 1.5 to 2 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 exist, but increased 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, right-turning

vehicles will spill back into the through traffic stream, thus increasing the potential for rear-end 

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 12 ft maximize traffic flow; however, right-of-way or

pedestrian needs may dictate use of a narrower lane width. Consider restriping from 12 ft-lanes

to narrower lanes in order to create more travel lanes where appropriate.

(57) Exhibit 11-20 shows

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Chapter 11. Individual Movement Treatments 

an example from Montgomery County, MD, where a narrow right-turn lane has been used 

effectively.

Exhibit 11-20. Narrow (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 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.(89) Right-turn channelization demonstrably reduces 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.

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

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Chapter 11. Individual Movement Treatments 

be appropriate in situations with 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.(190)

Selected findings of safety benefits associated with various right-turn lane improvements are

given in Exhibit 11-21.

Crash Modification Factor (CMF3i) for Installation of Right-Turn Lanes on Intersection Approaches

Intersection Intersection traffic 

Number of approaches with right-turn lanes a

Type control One

approach

Two

approaches

Three

approaches

Four

approaches

3 Approaches Traffic signal 0.96 0.92 -- --

4 Approaches Traffic signal 0.96 0.92 0.88 0.85

Exhibit 11-21. Safety benefits associated with right-turn improvements.

Source: Highway Safety Manual, Chapter 12.(11)

Operational Performance

Right-turn lanes remove decelerating and slower-moving vehicles from the through traffic

stream, which reduces 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.(193)

Installation of a right-turn lane can 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; 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. Carefully consider delineation of the turn lane 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 pedestrian change (upraised hand) interval phase. Other issues to

consider when designing a right-turn lane include potential conflicts between turning vehicles and 

bicyclists proceeding through the intersection. Also, right-turning drivers from the inside right-turn

lane might not see pedestrians in a parallel crosswalk that has a concurrent WALK signal.

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.

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.

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Chapter 11. Individual Movement Treatments 

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

Exhibit 11-22 summarizes the issues associated with right-turn lanes.

Characteristic Potential Benefits Potential Liabilities

Safety Separation of right-turn vehicles. Higher speed of right-turning vehicles

increases risk to pedestrians.

Operations Higher right-turn capacity. Potential for off-tracking of large vehicles.

Shorter green time.

Less delay for following through vehicles.

Additional storage for approach queues.

Multimodal None identified. Longer pedestrian crossing distance, time,

and exposure.

May require transit stop relocation.

Physical None identified. Larger intersection footprint.

Socioeconomic None identified. Right-of-way/construction costs.

Access restrictions to property.

Enforcement, None identified. Periodic enforcement may be needed to 

Education, and prevent red light violations, especially if

Maintenance right turns on red are prohibited.

Exhibit 11-22. Summary of issues for right-turn lanes.

11.2.3 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.

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Chapter 11. Individual Movement Treatments 

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.

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. In some cases the outside lane will be handled

with yield control while the inside right-turn lane is under signal control. Periodic enforcement

may be needed to ensure drivers obey any right turn on red prohibitions.

Summary

Exhibit 11-23 summarizes the issues associated with double right-turn lanes.

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Chapter 11. Individual Movement Treatments 

Characteristics Potential Benefits Potential Liabilities

Safety Separation of right-turn vehicles. Potential for sideswipes.

Operations Higher right-turn capacity. Off-tracking of large vehicles.

Shorter green time.

Less delay for following through 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, None identified. None identified.

Education, and

Maintenance

Exhibit 11-23. Summary of issues for double right-turn lanes.

11.2.4 Restricting Turns, U-Turns

One of the easiest methods to improve the operation of signals is reducing the number of

phases or movements. Typically, these restrictions relate to a turning movement; however, any

movement like through movements from the minor street could be restricted. 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. Analyze alternative routes to ensure 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).

Restricting right turns on red is a commonly done due to the number of pedestrians crossing 

at the intersection. Certain vehicles, such as school buses, have policies in place to prohibit

drivers from turning right on red. The HSM equation 12-35 calculates a CMF using this formula:

CMF = 0.98n

, in which n is the number of approaches that have the prohibition.

The key to success is how well the prohibition is communicated through signing, marking,

and may require public outreach to inform drivers.

Managing access near signals is often problematic. Adding medians and restricting existing

entrances to right in, right out can improve operational efficiency. Providing a U-turn at the signal

for access can help offset these restrictions. Note that U-turning vehicles proceed through an

intersection at a slower speed than left-turning vehicles and can adversely affect both operations

and safety at the intersection. Consider prohibition of U-turns at intersections with high volumes

of 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 with opposing through traffic. Rear-end crashes involving U-turning vehicles

followed by left-turning or through vehicles may be a sign of operational problems with the U-turn 

maneuver.

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Chapter 11. Individual Movement Treatments 

Consider sight distance limitations. 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.

Accommodate the turning radius of the design vehicle by a combination of 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.

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.(194)

Summary

Exhibit 11-24 summarizes the issues associated with 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.

Could adversely affect adjacent

intersections.

Multimodal Fewer conflicts with turning vehicles.

Lower delay to all users.

None identified.

Physical Could reduce the footprint of

intersection.

Upkeep of delineators, marking, and islands

to restrict movements.

Socioeconomic Part of a traffic calming measure 

while enhancing main street

efficiency.

Reduce emissions.

Impacts from adverse travel.

Enforcement,

Education, and

Maintenance

None identified. Enforcement of turn restrictions may be 

needed.

Exhibit 11-24. Summary of issues for turn prohibitions.

11.2.5 Provide Auxiliary Through Lanes

Adding auxiliary through lanes (i.e., additional through lanes with limited length) at signalized

intersections can 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, reduced downstream of the intersection, or dropped at a subsequent

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 may also serve as an

acceleration lane for vehicles turning right from the adjacent approach. Exhibit 11-25 illustrates an 

auxiliary through lane.

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Chapter 11. Individual Movement Treatments 

Exhibit 11-25. Diagram of an auxiliary through lane. (195) Source: NCHRP Report 707.

Applicability

Auxiliary through 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 through 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 through lane on both sides of an intersection helps determine 

whether the lane will be used; longer lanes get more use by through vehicles than do shorter

ones. Ideally, the lane should be of sufficient length to allow a smooth merge once the lane is

reduced. 

Clearly communicating when the lane will end also determines how well the auxiliary lane will

be used.(196) The reduction of the auxiliary lane downstream should be signed and marked 

according to the MUTCD.(1) If not properly signed and marked, motorists can become trapped 

near the end of the reduced lane, without advance notice of the reduction. Therefore, pay

particular attention should be made to discontinuing the lane line at the 3⁄4d distance from the end 

of the full width lane (see MUTCD Figure 3B-14). Note that "d", placement of the warning sign, is 

found in MUTCD Table 2C-4.

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 through 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 through lane due to compressed gaps in the through movement. 

Safety Performance

Based on the subjective assessment of the authors, the safety experience of an intersection 

with auxiliary through lanes should not significantly differ from conventional intersections without

the additional lane. The downstream merge maneuver this design requires may lead to an

increase in merge-related collisions (sideswipes), but studies have not evaluated this.

Again, the length of the auxiliary through lane impacts the safety of the intersection. Drivers

not comfortable with an auxiliary lane will stay in the through lane. No reduction in rear end

crashes at the signal should be expected. Right-turning vehicles off the minor street may conflict

with the vehicles on the main street using the auxiliary lane. The right-turning vehicles may use 

the auxiliary lane as an acceleration lane and not properly yield to the major street. This could 

lead to right turn, right angle crashes or right turn rear end crashes.

NCHRP 707 lists the following elements as critical to its safe operation:

(195)

• Downstream length should be sufficient to allow enough acceleration to merge back into

through movement easily.

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Chapter 11. Individual Movement Treatments 

• Access control is necessary to reduce the number of conflicting movements along the

lane.

• Sight distance should be adequate to view all signing, marking, merge area, and judge

traffic flow.

• Queuing downstream of the auxiliary through lane merge should be prevented if possible

from bottlenecks.

• Taper design should match AASHTO Green Book standards.

• Signing, marking, and lighting of the auxiliary through lane should be in accordance with

MUTCD guidelines, should be clear and concise, and should accommodate nighttime

operations.

Operational Performance

NCHRP 707 contains a step by step procedure to estimate the usage of a proposed auxiliary

lane. This example is for the additional of a single auxiliary lane adjacent to a single, continuous

through lane.(195)

where: V T = 15 - minute through - movement demand flow rate on the approach,

expressed in vehicles per hour;

S T = A adjusted through saturation flow rate per lane on the approach, in 

vehicles per hour;

g = Effective green time for the approach, in seconds; and

C = Intersection cycle length, in seconds.

where: V ATL = The predicted through movement flow rate in the auxiliary through lane (in

vehicles per hour), and all other variables are as previously defined.

Remaining volume traveling in the continuous through lanes is VCTL = VT - VATL.

Multimodal Impacts

Wider intersections result in longer crossing times for pedestrians and bicyclists, as well as

increased exposure to vehicle conflicts.

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.

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Chapter 11. Individual Movement Treatments 

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 should 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. Only critical, location-specific signs should be located within the downstream

auxiliary through lane area due to the merge and reduction demand on the driver. Markings and 

signing for lane use and arrangement are generally sufficient upstream, and lane reduction

signing and markings are sufficient downstream.

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

Exhibit 11-26 summarizes the issues associated with auxiliary through lanes.

Characteristic

Safety

Potential Benefits

May reduce rear-end crashes due 

to improved signal operation.

Potential Liabilities

Potential for sideswipes downstream of

merge. Right-turn crashes with minor street.

Operations Decreased delay for through 

vehicles.

Improper use of auxiliary lane downstream;

under use of auxiliary lane upstream.

Multimodal Reduces queues may decrease

overall cycle length

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 Enforcement responding to crashes from rear 

ends and side swipes. Right-turning drivers

not yielding to through movement.

Exhibit 11-26. Summary of issues for auxiliary through lanes.

11.2.6 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 Exhibit 11-27.

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Chapter 11. Individual Movement Treatments 

Exhibit 11-27. Example of delineated paths.

Source: MUTCD 2009 Fig 3B-13.

(1)

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 multi-leg intersections

may all present situations where additional guidance can improve safety and operations.

Delineating 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

Exhibit 11-28 summarizes the issues associated with path delineation.

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Chapter 11. Individual Movement Treatments 

Characteristic

Safety

Potential Benefits

Fewer erratic maneuvers.

Potential Liabilities

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.

Exhibit 11-28. Summary of issues for path delineation.

11.3 VARIABLE LANE USE TREATMENTS

11.3.1 Provide Reversible Lanes

Reversible lanes 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.

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.(68) 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.(10)

Safety Performance

Reversible lanes help reduce congestion and likely 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.” (10, p. 130)

Reversible lanes may preclude the use of median treatments as an access- management

technique along an arterial street.

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Chapter 11. Individual Movement Treatments 

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. This type of facility may not be viewed as conducive to the type of

development along the route.

Summary

Exhibit 11-29 summarizes of the issues associated with reversible lanes.

Characteristics Potential Benefits Potential Concerns

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.

Potential confusion by drivers during off

peak times.

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

Enforcement,

Education, and

Maintenance

Relatively low cost.

None identified.

May not be compatible with adjacent

property uses.

New treatment to the area would require 

some communication.

Exhibit 11-29. Summary of issues for reversible lanes.

11.3.2 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 assignments include: (57)

• 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.

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Chapter 11. Individual Movement Treatments 

• The use of similar variable advance lane use signs to provide adequate notice to drivers

of the lane use in effect.

Impacts to signal timing and phasing require special attention when implementing variable

lane use assignments. Variable lane assignments should be evaluated using traffic software and 

simulations. 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). Today’s traffic software and simulation programs allow the practitioner to evaluate

different scenarios prior to implementing this strategy on the street.

Exhibits 11-30 and 11-31 provide examples from Montgomery County, Maryland, 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.(57)

(a) Double left turn during morning peak and off-peak periods.

(b) Triple left turn during evening peak period.

Exhibit 11-30. Example use of variable lane use sign to add a third left-turn lane during certain 

times of day.

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Chapter 11. Individual Movement Treatments 

Exhibit 11-31. Example use of variable lane use sign to add a second right-turn lane along a 

corridor during certain times of day.

Summary

Exhibit 11-32 summarizes the issues associated with variable lane use.

Characteristics Potential Benefits Potential Concerns

Safety None identified. None identified.

Operations Improved peak-period utilization of

existing right-of-way.

None identified.

Reduced queuing during peak periods.

Multimodal None identified. Barrier to adding bike lanes.

Physical Reduces or eliminates need for additional

right-of-way.

None identified.

Socioeconomic Lower cost than adding lanes. None identified.

Enforcement, None identified. Communicate any changes to the 

Education, and public.

Maintenance Maintain additional equipment

Exhibit 11-32. Summary of issues for variable lane use.

Signalized Intersections: Informational Guide 11-39 
 

 

List of Acronyms 

List of Acronyms

AADT Average Annual Daily Traffic

AASHTO American Association of State Highway and Transportation Officials

ADA Americans with Disabilities Act

ADAAG Americans with Disabilities Act Accessibility Guidelines

ADT Average Daily Traffic

ATC Advanced Transportation Controller

BCR Benefit-Cost Ratio

BIU Bus Interface Unit

CLA Critical Lane Analysis

CMF Crash Modification Factor

CW Continuous Wave

EB Empirical Bayes

EPDO Equivalent Property Damage Only

FARS Fatality Analysis Reporting System

FHWA Federal Highway Administration

GPS Global Positioning System

HCM Highway Capacity Manual

HSIS Highway Safety and Information System

HSM Highway Safety Manual

IESNA Illuminating Engineering Society of North America

ITE Institute for Transportation Engineers

ITS Intelligent Transportation Systems

LED Light Emitting Diode

LOS Level of Service

MMU Malfunction Management Unit

MMUCC Model Minimum Uniform Crash Criteria

mph mile(s) per hour

MUTCD Manual on Uniform Traffic Control Devices

NCHRP National Cooperative Highway Research Program

NEMA National Electrical Manufacturers Association

NHTSA National Highway Traffic Safety Administration

NTCIP National Transportation Communication for ITS Protocol

PDO Property Damage Only

PHB Pedestrian Hybrid Beacons

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v/c Volume-to-Capacity

List of Acronyms 

PPLT Protected-Permissive Left-Turn

PROWAG Public Rights of Way Accessibility Guidelines

PSI Potential for Safety Improvement

QEM Quick Estimation Method

RF Radio Frequency

RSA Road Safety Audit

RSI Relative Severity Index

SCP Signal Control and Prioritization

SDLC Synchronous Data Link Control

SPF Safety Performance Function

SPUI Single Point Urban Intersection

SSAM Surrogate Safety Analysis Model

STV Small Target Visibility

SUV Sport Utility Vehicle

TCQSM Transit Capacity and Quality of Service Manual

TRB Transportation Research Board

UPS Uninterrupted Power Supply

USDOT United States Department of Transportation

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Glossary of Terms 

Glossary of Terms

Actuated Signals: Vary the amount of green time allocated to each phase based on traffic demand. Can 

operate either in a fully actuated mode, semi-actuated mode, or coordinated mode.

Advance Stop Lines: Vehicle stop lines 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 bicyclists and crossing 

pedestrians for motorists who are turning right.

All-way Stop control: Requires that vehicles approaching the intersection from all directions come to a 

stop prior to entering the intersection.

Americans with Disabilities Act (ADA): Law passed in 1990 that prohibits discrimination and ensures

equal opportunity and access for persons with disabilities (http://www.fta.dot.gov/civilrights/12325.html).

Auxiliary Lane: A lane added in advance of (and sometimes carried through) an intersection for a limited 

distance to facilitate speed change (acceleration or deceleration), added capacity (throughput), separate 

turning or weaving.

Back-of-Queue: The maximum backward extent of queued vehicles during a typical cycle.

Before and After Study: Crash frequencies at a site are compared before and after implementation of a 

treatment.

Benefit-Cost Ratio (BCR) Method: First the present worth of benefits and costs is calculated. Then the 

ratio of present worth of benefits over present worth of costs is calculated. If the ratio is greater than 1.0,

the project is economically justified.

Bicycle Box: Advance stop lines are placed on the approach to a signalized intersection, typically in the 

rightmost lane, at a location upstream from the normal stop line location. These create a dedicated space 

for bicyclists—a bicycle box—to occupy while waiting for a green indication.

Capacity: The maximum sustainable flow 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, and 

width of lanes, grades, and lane use allocations, as well as signalization conditions.

Change and Clearance Interval: The amount of time, in seconds, based on speed and corresponding to 

distance, provided for vehicles to either stop at or clear an intersection (refer to ITE Recommended 

Practice).

Crash Modification Factor (CMF): The ratio of expected crash frequency at a location with a 

countermeasure divided by the expected crash frequency at the location without the countermeasure.

Critical Phase: One phase of a set of phases that occur in sequence and whose combined flow ratio is

the largest for the signal cycle.

Cut-through Median: A median on which the pedestrian path is at the same grade as the adjacent

roadway.

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Glossary of Terms 

Curb Extensions (also known as “Bulbouts” or “Neckdowns”): Involve extending the sidewalk or

curb line into the street, reducing the effective street width.

Curb Ramp: A ramp leading from a sidewalk to a street to provide access for people who use 

wheelchairs and scooters.

Cycle Length: The time allotted or used for one complete sequence of signal indications.

Decision Sight Distance: 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.

Delay: The additional travel time experienced by a driver, passenger, bicyclist, or pedestrian beyond that

is required to travel at the desired speed, including stop and start-up time.

Detectable Warning: A surface of truncated domes built in or applied to walking surfaces to alert visually

impaired pedestrians of the presence of the vehicular travel way and to provide physical cues to assist

pedestrians in detecting the boundary from sidewalk to street.

Detectors (also called Sensors): Inform the signal controller that a motor vehicle, pedestrian, or bicycle

is present at a defined location on the approach to an intersection or within a signal system.

Dilemma Zone: Length of roadway in advance of an intersection wherein drivers may be indecisive and 

respond differently to the onset of a yellow signal.

Dilemma Zone Detection System: Uses detectors placed at one or more locations on an intersection 

approach to extend the green and prevent the onset of yellow while approaching vehicles are in the 

dilemma zone.

Disability Glare: The glare that results when stray light is superimposed in the eye on top of the retinal

image of the object of interest, altering the apparent brightness of that object and the background in which 

it is viewed.

Dropped Lane: A through lane that becomes a left- or right-turn lane at an intersection.

Effective Green Time: The amount of usable time available to serve vehicular movements during a 

phase of a cycle.

Empirical Bayes (EB) Method: Calculates expected crash frequencies through a combination of

observed and predicted crash frequencies. The predicted crash frequencies are derived through the 

development of a safety performance function (SPF).

Exclusive Pedestrian Signal Phase: Allows pedestrians to cross in all directions at an intersection at

the same time, including diagonally. Sometimes called a “Barnes dance” or “pedestrian scramble.”

Far-side Transit Stop: A transit stop located downstream of an intersection.

Forgiving Roadway: An information-driven concept 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.

Fully-actuated Signals: Traffic signals that recognize users on all approaches.

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Glossary of Terms 

Gap Reduction: A predetermined, constant time (often fraction of a second) which is subtracted from the 

maximum extension or passage time beginning at a point after the initial or minimum green has timed out.

Highway Safety Manual (HSM): An American Association of State Highway Transportation Officials

(AASHTO) document that provides tools to practitioners to conduct quantitative safety analyses.

Human Factors Research: Deals with human physical, perceptual, and cognitive abilities and 

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

Illuminance: The amount of light incident on the pavement surface from the lighting source.

Intersection Count: Number of vehicles entering a signalized intersection. This is often counted by

turning movement and direction of travel.

Intersection Sight Distance: The distance required for a driver without the right of way to perceive and 

react to the presence of traffic signal indications, conflicting vehicles, and pedestrians.

Lagging Pedestrian Interval: Retiming the signal splits so that the pedestrian WALK signal begins a few

seconds after the vehicular green for turning movement.

Leading Pedestrian Interval: Retiming the signal splits so that the pedestrian WALK signal begins a few

seconds before the vehicular green. While the vehicle signals are in “All Red,” this allows pedestrians to

establish their presence in the crosswalk before the turning vehicles, thereby enhancing the pedestrian 

right-of-way.

Light Level: Represents the intensity of light output on the pavement surface. Reported in units of lux

(metric) or footcandles (U.S. Customary).

Lost Time: The unused portion of a vehicle phase that occurs twice during a phase: at the beginning 

when vehicles are accelerating from a stopped position, and at the end when vehicles decelerate in 

anticipation of the red indication; often calculated as the sum of start-up loss and clearance interval.

Luminance: The amount of light reflected from the pavement toward the driver’s eyes.

Manual on Uniform Traffic Control Devices (MUTCD): A compilation of national standards for all traffic

control devices, including traffic signals.

Maximum Green Time: The maximum limit to which the green time can be extended for a phase in the 

presence of a call from a conflicting phase.

Near-side Transit Stop: A transit stop located upstream of an intersection.

Pedestrian Hybrid Beacon (PHB): A special type of traffic control device used to warn and control traffic

at an unsignalized location to assist pedestrians in crossing a street or highway at a marked crosswalk.

Pedestrian Signal Detector: Devices to help pedestrians, including those with visual or mobility

impairments, activate the pedestrian phase, such as pushbuttons or other passive detection devices.

Permissive-only Left-Turn Phasing (also called “Permitted-Only” Phasing): Signal phasing that

allows two opposing approaches to time concurrently, with left turns allowed after motorists yield to 

conflicting traffic and pedestrians.

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Glossary of Terms 

Positive Guidance: Concept that focuses on understanding and making allowances for how road

users—primarily motorists—acquire, interpret, and apply information in the driving task.

Potential for Safety Improvement (PSI): The difference between expected crashes (obtained from the 

Empirical Bayes method) and predicted crashes (obtained from safety performance functions).

Preemption: 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 serve the special task.

Presence Detection: Alerts the controller to waiting vehicles during the red interval and calls for

additional green time (passage or extension) for moving vehicles during the green interval.

Pre-timed Signals: Traffic signals that are programmed to give green indications to movements based 

on a predetermined allocation of time. Operate with fixed cycle lengths and green splits, and in turn can 

operate either in an isolated or coordinated mode.

Priority: 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.

Progression: The movement of vehicle platoons from one signalized intersection to the next.

Prohibited Left-Turn Movements: A scenario under which left-turning drivers are required to divert to 

another facility or turn in advance of or beyond the intersection via a geometric treatment such as a 

jughandle or a downstream median U-turn.

Protected-only Left-Turn Phasing: Signal phasing that provides 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.

Protected-Permissive Left-Turn (PPLT) Phasing: A combination of protected and permissive left-turn 

phasing.

Public Rights of Way Accessibility Guidelines (PROWAG): Guidelines developed specifically for

pedestrian facilities in the public right-of-way that address conditions and constraints that exist in the 

public right-of-way.

Pulse Detection: A type of detection located well upstream of the intersection to provide inputs to the 

controller regarding approaching vehicles.

Queue Storage Ratio: The proportion of the available queue storage distance that is occupied at the 

point in the cycle when the back-of-queue position is reached.

Ramped Median: A median on which the pedestrian path is raised to the grade of the top of the curb.

Red Clearance Interval: Optional interval that follows the yellow change interval and precedes the next

conflicting green interval. Provides additional time following the yellow change interval before conflicting

traffic is released.

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Glossary of Terms 

Red Light Running: When a motorist enters an intersection when the red signal is displayed and as a 

consequence sometimes collides with another motorist, pedestrian, or bicyclist who is legally within the 

intersection.

Red-Red Flashing Operation: A mode of flashing operation in which all approaches receive a flashing 

red indication. Typically used where traffic volumes on all approaches are roughly the same.

Red-Yellow Flashing Operation: A mode of flashing operation in which the minor street receives a 

flashing red indication and the major street receives a flashing yellow indication. Used in situations where 

traffic is very light on the minor street.

Ring-and-Barrier Structure: Signal phasing that prohibits conflicting movements (e.g., eastbound and 

southbound through movements) from timing concurrently while allowing non-conflicting movements

(e.g., northbound and southbound through movements) to time together.

Road Safety Audit (RSA): A formal safety performance examination of an existing or future road or

intersection by an independent audit team that considers the safety of all road users and qualitatively

estimates and reports on road safety issues and opportunities for safety improvement.

Road Safety Management Process: Systematically identifying deficient locations from safety

perspectives and addressing safety problems of these locations.

Roundabout: A circular intersection with design features that promote safe and efficient traffic flow.

Safety Performance Function: An equation that presents the mathematical relationship between crash 

frequency and volume for a reference group.

Safety Effectiveness Evaluation: The process of developing quantitative estimates of how a 

countermeasure, project, or a group of projects has affected crash frequencies or severities.

Semi-actuated Signals: Traffic signals that use various detection methods to identify roadway users on

the minor approaches and/or major approach left-turn lanes.

Signal Interval: The part of the signal cycle during which signal indications do not change.

Signal Phase: 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.

Signal Phasing: 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 rightof-way.

Split Phasing: Signal phasing that 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).

Small Target Visibility (STV): The level of visibility of an array of targets on the roadway. Determined by

the average of three components: the luminance of the targets and background, the adaptation level of

adjacent surroundings, and the disability glare.

Stopping Sight Distance: 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.

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Glossary of Terms 

System Detection: A collection of vehicular data such as count, speed, occupancy, queue length used 

by the controller to order and recall special override timing plans, traffic responsive timing plans, and 

adaptive signal control.

Traffic Demand: For an intersection, traffic demand represents the arrival pattern of vehicles.

Traffic Signals: Electrically operated traffic control devices that provide indication for roadway users to 

advance their travels by assigning right-of-way to each approach and movement.

Traffic Signal Controller: Acts as the “brain” of a traffic signal, changing signal indications based on user

needs. The controller determines when the indication for the approach will change and how much time 

will be given to each movement. 

Traffic Signal Heads: Informs roadway users of when their movement can proceed through the 

intersection. Signal heads vary in configuration, shape, and size depending on the movement for which 

they are used.

Traffic Volume: For an intersection, traffic volume is generally measured as the number of vehicles that

pass through the intersection over a specific period of time.

Uniformity: Represents the ratio of either the average-to-minimum light level (Eavg/Emin) or the maximumto-minimum light level (Emax/Emin) on the pavement surface.

Variable Initial: A volume-density feature used to improve intersection efficiency by using each pulse 

detector actuation during the red interval, typically on the major through approach, to incrementally alter

the minimum green time in order to clear the accumulated queue for each cycle.

Variable Lane Use Treatments: Individual lane assignments at a signalized intersection are changed by

time of day.

Veiling Luminance: 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.

Volume-to-Capacity (v/c) Ratio (also called degree of saturation): Represents the sufficiency of an 

intersection to accommodate the vehicular demand.

Yield-to-Bus Law: A law requiring all motorists to yield to buses pulling away from a bus stop in order to 

reduce transit/vehicle conflicts.

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References 

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Signalized Intersections: Informational Guide R-13 
For More Information:

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

FHWA, Office of Safety

Jeffrey Shaw

jeffrey.shaw@dot.gov

202.738.7793

FHWA-SA-13-027

Updated July 2020