Although roundabouts have been in widespread use in other countries for a number of years, it is only during the past few years

that their application in the United States has received increased attention by both the public and transportation professionals. A lack of

sufficient information on roundabout operation and design under local

U.S. conditions is one of the reasons why these roundabout intersections

have seen only sporadic implementation. This national guide bridges this

gap by providing a comprehensive source of information on modern roundabouts, from small mini-roundabouts to large 

freeway interchange roundabouts.

To make the information widely accessible,

the guide has been structured and written

to address the needs of a wide range of

readers, including the general public,

policy-makers, transportation planners,

operations and safety analysts, and conceptual and detailed designers. Not only

does the guide provide general information and planning-level analysis techniques, but it also includes evaluation

procedures for assessing operational and

safety performance, as well as design

guidelines. Input from transportation practitioners and researchers from around the

world was used in developing the guide.

This book covers the needs of all travel

modes and provides design guidance for incorporating these needs into final plans.

SAFETY AND OPERATIONAL

BENEFITS

Many international studies have found that one of

the most significant benefits of a roundabout installation is the improvement in overall safety performance. Specifically, in the United States, it has been found

that single-lane roundabouts operate more safely than twoTHE DEFINITIVE SOURCE OF

INFORMATION RELATED TO THE PLANNING,

OPERATION, DESIGN, AND CONFIGURATION OF

MODERN ROUNDABOUTS IN THE UNITED STATES.

COMPREHENSIVE COVERAGE IS PROVIDED FOR ALL TRAVEL MODES THAT NEED TO BE CONSIDERED IN ROADWAY DESIGN. THE INFORMATION CONTAINED IN THIS GUIDE IS THE

CULMINATION OF EXTENSIVE RESEARCH INTO BEST PRACTICES FROM AROUND THE WORLD, INTERPRETED IN

THE LIGHT OF ACCEPTED U.S. DESIGN STANDARDS SUCH AS AASHTO’S GREEN

BOOK AND THE MUTCD.

ROUNDABOUTS:

AN INFORMATIONAL

GUIDE
way stop-controlled intersections. The frequency

of crashes might not always be lower at roundabouts, but the injury rates are reduced.

Pedestrians and bicyclists require specific design treatments to improve their safety.

On a planning level, it can be assumed that

roundabouts will provide higher capacity and

lower delays than all-way stop control, but less

than two-way stop control if the minor movements are not experiencing operational problems.

A single-lane roundabout may be assumed to operate within its capacity at any intersection that

does not exceed the peak-hour volume warranted for signals. A roundabout that operates within

its capacity will generally produce lower delays

than a signalized intersection operating with the

same traffic volumes and right-of-way limitations.

Chapter 1, Introduction.

Defines the key features and dimensions of a roundabout and describes

the various types of roundabouts. It

clearly highlights the differences between roundabouts and other forms of

traffic circles with the generous use of

photographs to depict a variety of situations. 

Chapter 2, Policy Considerations.

Provides a broad overview of roundabout performance characteristics, including safety, delay, environmental

factors, traffic calming, aesthetics,

and multimodal considerations, as

well as the policy considerations that

pertain to their use. Costs associated

with roundabouts relative to other intersection forms, legal issues, and education and public involvement techniques are also discussed. 

Source: Jacquemart, G. Synthesis of Highway Practice

264: Modern Roundabout Practice in the United States.

National Cooperative Highway Research Program.

Washington, D.C.: National Academy Press, 1998.

Average annual crash frequencies at 11 U.S. 

intersections converted to roundabouts.

Type of Percent Change

Roundabout Sites Total Injury PDO

Single-Lane 8 -51% -73% -32%

Multi-Lane 3 -29% -31% -10%

Total 11 -37% -51 -29%
Chapter 3, Planning.

Presents planning-level guidelines for

identifying appropriate intersection

control options. This chapter presents

daily traffic volume-based procedures

for evaluating roundabout feasibility at

a given location. 

Chapter 4, Operational Analysis.

Details methods for analyzing the operational performance (capacity, delay,

and queuing) of each type of roundabout. This chapter describes traffic

operations at roundabouts, lists the

data required for evaluating roundabouts, shows how to estimate capacity, describes measures of effectiveness, and provides a brief overview of

available software tools. 

Chapter 5, Safety.

Discusses the improvements in safety

performance that roundabouts typically provide at intersections. Roundabout safety related to vehicles, bicycles, and pedestrians is discussed,

and international roundabout safety

experience is presented for comparison. In addition, crash prediction

models are given for evaluating crashes at roundabouts. 

Chapter 6, Geometric Design.

The chapter presents the basic design

philosophy of speed reduction and

speed consistency to maximize the

safety of a roundabout. This chapter

presents specific roundabout geometric design principles, and then discusses each design element in detail,

along with appropriate parameters to

use for each type of roundabout.

WHEN TO RECOMMEND ROUNDABOUTS: PLANNING ANALYSIS

Roundabouts can be considered for a variety

of reasons. The roundabout guide describes

categories for selection that range from community enhancement and traffic calming, to

safety improvements and operational benefits.

The maximum daily service volume of a single-lane roundabout varies between 20,000

and 26,000 vehicles per day, depending on

the left-turn percentages and the distribution

of traffic between the major and minor roads.

A double-lane roundabout may service 40,000

to 50,000 vehicles per day.
Chapter 1—

Introduction

1.1 Scope of Guide

1.2 Organization of Guide

1.3 Defining Physical Features

1.4 Key Dimensions

1.5 Distinguishing Roundabouts 

From Other Circular 

Intersections

1.6 Roundabout Categories

Chapter 2—

Policy Considerations

2.1 Characteristics

2.2 Multimodal Considerations

2.3 Costs Associated With 

Roundabouts

2.4 Legal Considerations

2.5 Public Involvement

2.6 Education

Chapter 3—

Planning

3.1 Planning Steps

3.2 Considerations of Context

3.3 Number of Entry Lanes

3.4 Selection Categories

3.5 Comparing Operational 

Performance of Alternative 

Intersection Types

3.6 Space Requirements

3.7 Economic Evaluation

Chapter 4—

Operation

4.1 Traffic Operation at 

Roundabouts

4.2 Data Requirements

4.3 Capacity

4.4 Performance Analysis

4.5 Computer Software for 

Roundabouts

Chapter 5—

Safety

5.1 Introduction

5.2 Conflicts

5.3 Crash Statistics

5.4 Crash Prediction Models

Chapter 6—

Geometric Design

6.1 Introduction

6.2 General Design Principles

6.3 Geometric Elements

6.4 Double-Lane Roundabouts

6.5 Rural Roundabouts

6.6 Mini-Roundabouts

Chapter 7—

Traffic Design and

Landscaping

7.1 Signing

7.2 Pavement Markings

7.3 Illumination

7.4 Work-Zone Traffic Control

7.5 Landscaping

Chapter 8—

System Considerations

8.1 Traffic Signals at Roundabouts

8.2 At-Grade Rail Crossings

8.3 Closely Spaced Roundabouts

8.4 Roundabout Interchanges

8.5 Roundabouts in an Arterial 

Network

8.6 Microscopic Simulation

Chapter 7, Traffic Design and Landscaping. Discusses a number of traffic design aspects that should be considered once the basic geometric design has been established. These details include signs, pavement markings, illumination, and landscaping.

Chapter 7 also discusses issues regarding work-zone traffic control at

roundabouts.

Chapter 8, System Considerations.

Identifies specific issues and treatments that may arise within a systems

context. The chapter discusses signal

control at roundabouts and the issue

of rail crossings through or near a

roundabout. Roundabouts in series

with other roundabouts are also discussed, including those at freeway interchanges and those in signalized arterial networks. Finally, Chapter 8

presents simulation models as supplementary operational tools capable of

evaluating roundabout performance

within an overall roadway system. 

ROUNDABOUTS:

AN INFORMATIONAL

GUIDE

Table of Contents

Additionally, the guide contains over 150 charts,

diagrams, plans and photographs which illustrate the various features of roundabouts.
Roundabout or Traffic Circle?

Since the distinctions between modern roundabouts and other kinds of circular intersections may not always be

obvious, the negative aspects of older rotaries or traffic circles may be mistaken by the public with a roundabout.

Therefore, the ability to carefully distinguish roundabouts from traffic circles is important in terms of public understanding.

Traffic

Control

Priority to

Circulating

Vehicles

Pedestrian

Access

Direction of

Circulation

Yield control is used on all entries. The

circulatory roadway has no control.

Circulating vehicles have the right of

way.

Pedestrian access is allowed only

across the legs of the roundabout, behind the yield line.

All vehicles circulate counter-clockwise and pass to the right of the central island.

Some traffic circles use stop control,

or no control, on one or more entries.

Some traffic circles require circulating

traffic to yield to entering traffic.

Some traffic circles allow pedestrian

access to the central island.

Some neighborhood traffic circles allow left-turning vehicles to pass to the

left of the central island.
The important difference between roundabouts and

other forms of traffic circles is the reduction of absolute and relative speeds between users.

Roundabouts require conformance to common

practices to ensure safe, optimal operation. A scattered approach to design can lead to inconsistencies at a national level that are consequential in

terms of driver expectation and safety. 

Contributors to the book include:

• Kittelson & Associates, Inc.

• Ruhr-University Bochum (Germany)

• University of Idaho

• Hurst-Rosche Engineers

• Buckhurst Fish & Jacquemart

• Queensland University of Technology (Australia)

• University of Florida

• Pennsylvania State University

• Eppell Olsen & Partners (Australia)

In addition the document benefited

from extensive review by representatives of French and British practices as

well as AASHTO, MUTCD, and representatives of the Americans With Disabilities Act.

FHWA project manager:

Joe Bared, (202) 493-3314,

Joe.Bared@fhwa.dot.gov.

Roundabouts: An Informational Guide (FHWARD-00-067) will be available on the internet at

the Turner-Fairbank Highway Research Center

website: http://www.tfhrc.gov. 

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 

22101

FHWA-RD-00-068

A report may be obtained from the FHWA

Report Center. Fax requests to (301) 577-1421

or e-mail requests to report.center@fhwa.dot.gov.

Requests for the report will be logged and

copies mailed when the document is published. The Report Center may be reached by

phone at (301) 577-0818.