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Although roundab outs ha ve been in widespread use in other coun-

tries for a number of years, it is only during the past few years

that their application in the United States has received increased at-

tention by both the public and transportation professionals. A lack of

sufficient information on roundabout operation and design under local

U.S . co nditions is one o f the rea sons why thes e rounda bout intersec tions

ha ve s een only spo radic implementa tion. This na tiona l guide bridg es this

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

freew a y intercha nge rounda bouts.

To ma ke the information widely acc es sible,

the guide ha s been s tructured a nd w ritten

to address the needs of a wide range of

readers, including the general public,

policy-makers, transportation planners,

operations a nd sa fety ana lysts, a nd con-

ceptual and detailed designers. Not only

does the guide provide general informa-

tion and planning-level analysis tech-

niques, but it also includes evaluation

procedures for assessing operational and

safety performance, as well as design

guidelines. Input from transportation prac-

titioners and researchers from around the

world was used in developing the guide.

This b ook co vers the need s of a ll travel

modes and provides des ign g uida nce for in-

corporating thes e need s into final pla ns.

SAFETY AND OPERATIONAL

BENEFITS

Many international studies have found that one of

the most significant benefits of a roundabout instal-

lation is the improvement in overall safety perform-

ance. Specifically, in the United States, it has been found

that single-lane roundabouts operate more safely than two-

THE DEFINITIVE SOURCE OF

INFORMATION RELATED TO THE PLANNING,

OPERATION, DESIGN, AND CONFIGURATION OF

MODERN ROUNDABOUTS IN THE UNITED STATES.

COMP REHENSIVE COVERAGE IS PROVIDED FOR ALL TRAV-

EL MODES THAT NEED TO BE CONSIDERED IN ROADWAY DE -

SIGN. THE INFORMATION CONTAINED IN THIS GUIDE IS THE

CULMINATIO N OF EXTENSIVE RESEARCH I NTO B EST PR AC-

TICES FROM AROUND THE WORLD , INTERPRETED IN

THE LIGHT OF ACCEPTED U.S. DESIGN STAN-

DARDS SUCH AS AASHTOS GREEN

BOOK AND THEMUTCD.

ROUNDABOUTS:

AN INFORMATIONALGUIDE

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w a y s top-controlled intersec tions . The freq uency

of crashes might not always be lower at round-

abouts, but the injury rates are reduced.

Pedestrians and bicyclists require specific de-

sign treatments to improve their safety.

On a planning level, it can be assumed thatroundabouts will provide higher capacity and

lower delays than all-way stop control, but less

than two-way stop control if the minor move-

ments a re not experiencing opera tiona l problems.

A single-la ne rounda bout ma y be a ss umed to op-

erate within its capacity at any intersection that

does not exceed the peak-hour volume warrant-

ed for signals. A roundabout that operates within

its capacity will generally produce lower delays

than a signalized intersection operating with the

sa me tra ffic volumes a nd right-of-w a y limita tions.

Chapter 1, Introduction.

Defines the key features and dimen-sions of a roundabout and describesthe various types of roundabouts. Itclearly highlights the differences be-tween roundabouts and other forms of

traffic circles with the generous use ofphotographs to depict a variety of sit-uations.

Chapter 2, Policy Considerations.

Provides a broad overview of round-about performance characteristics, in-cluding safety, delay, environmentalfactors, traffic calming, aesthetics,

and multimodal considerations, aswell as the policy considerations thatpertain to their use. Costs associatedwith roundabouts relative to other in-tersection forms, legal issues, and ed-ucation and public involvement tech-niques are also discussed.

Source: J acquemart, G.Synthesis of Highway Practice264: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%

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apter 3, Planning.esents planning-level guidelines forentifying appropriate intersectionntrol options. This chapter presentsily traffic volume-based proceduresr evaluating roundabout feasibility at

given location.

apter 4, Operational Analysis.etails methods for analyzing the op-ational performance (capacity, delay,d queuing) of each type of round-out. This chapter describes trafficerations at roundabouts, lists theta required for evaluating round-

outs, shows how to estimate capac-, describes measures of effective-ss, and provides a brief overview ofailable software tools.

Chapter 5, Safety.Discusses the improvements in safetyperformance that roundabouts typical-ly provide at intersections. Round-about safety related to vehicles, bicy-cles, and pedestrians is discussed,

and international roundabout safetyexperience is presented for compari-son. In addition, crash predictionmodels are given for evaluating crash-es at roundabouts.

Chapter 6, Geometric Design.The chapter presents the basic designphilosophy of speed reduction andspeed consistency to maximize thesafety of a roundabout. This chapterpresents specific roundabout geomet-ric design principles, and then dis-cusses each design element in detail,along with appropriate parameters touse for each type of roundabout.

WHEN TO RECOMMEND ROUND-ABOUTS: PLANNING ANALYSIS

Roundabouts can be considered for a variety

of rea so ns. The rounda bo ut guide d es cribes

ca tegories for selection that range from c om-

munity enhancement and traffic calming, tosa fety improvements a nd o perational be nefits.

The ma ximum da ily service volume of a s in-

gle-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 do uble-la ne roundab out ma y s ervice 40,000

to 50,000 vehicles per da y.

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Chapter 1Introduction1.1 Scope of Guide1.2 Organization of Guide1.3 Defining Physical Features1.4 Key Dimensions

1.5 Distinguishing RoundaboutsFrom Other CircularIntersections

1.6 Roundabout Categories

Chapter 2Policy Considerations2.1 Characteristics2.2 Multimodal Considerations2.3 Costs Associated With

Roundabouts2.4 Legal Considerations2.5 Public Involvement

2.6 Education

Chapter 3Planning3.1 Planning Steps3.2 Considerations of Context3.3 Number of Entry Lanes3.4 Selection Categories

3.5 Comparing OperationalPerformance of AlternativeIntersection Types

3.6 Space Requirements3.7 Economic Evaluation

Chapter 4Operation4.1 Traffic Operation at

Roundabouts4.2 Data Requirements4.3 Capacity4.4 Performance Analysis

4.5 Computer Software forRoundabouts

Chapter 5Safety5.1 Introduction5.2 Conflicts5.3 Crash Statistics5.4 Crash Prediction Models

Chapter 6Geometric Design6.1 Introduction

6.2 General Design Principles6.3 Geometric Elements6.4 Double-Lane Roundabouts6.5 Rural Roundabouts6.6 Mini-Roundabouts

Chapter 7Traffic Design andLandscaping7.1 Signing7.2 Pavement Markings7.3 Illumination7.4 Work-Zone Traffic Control7.5 Landscaping

Chapter 8System Considerations8.1 Traffic Signals at Roundabouts8.2 At-Grade Rail Crossings8.3 Closely Spaced Roundabouts8.4 Roundabout Interchanges8.5 Roundabouts in an Arterial

Network8.6 Microscopic Simulation

Chapter 7, Traffic Design and Land-

scaping. Discusses a number of traf-fic design aspects that should be con-sidered once the basic geometric de-sign has been established. These de-tails include signs, pavement mark-ings, illumination, and landscaping.Chapter 7 also discusses issues re-garding work-zone traffic control atroundabouts.

Chapter 8, System Considerations.Identifies specific issues and treat-ments that may arise within a systems

context. The chapter discusses signalcontrol at roundabouts and the issueof rail crossings through or near aroundabout. Roundabouts in serieswith other roundabouts are also dis-cussed, including those at freeway in-terchanges and those in signalized ar-terial networks. Finally, Chapter 8presents simulation models as supple-mentary operational tools capable ofevaluating roundabout performancewithin an overall roadway system.

ROUNDABOUTS:AN INFORMATIONALGUIDE

Table of Conten ts

Additionally, the guide contains over 150 charts,diagrams, plans and photographs which illus-trate the various features of roundabouts.

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Roundabout or Traffic Circle?S ince the distinctions betw een mod ern roundab outs a nd other kinds of circula r intersec tions may not a lwa ys be

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

Therefore, the a bility to c a refully dis tinguish round a bo uts from tra ffic c ircles is impo rtant in terms o f public un-

derstanding.

TrafficControl

Priority toCirculatingVehicles

PedestrianAccess

Direction ofCirculation

Yield c ontrol is use d on a ll entries. The

circulato ry road wa y ha s no c ontrol.

Circulating vehicles have the right of

way.

Pedestrian access is allowed only

ac ross the legs of the roundab out, be-

hind the yield line.

All vehicles circulate counter-clock-

wise and pass to the right of the cen-

tral island .

Some traffic circles use stop control,

or no c ontrol, on o ne 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 al-

low left-turning vehicles to pa ss to the

left of the c entral island .

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The importa nt difference betw een roundab outs a nd

other forms of traffic circles is the reduction of ab-

solute a nd rela tive speed s b etween users.

Roundabouts require conformance to common

practices to ensure sa fe, optimal operation. A sc a t-

tered approach to design can lead to inconsisten-cies at a national level that are consequential in

terms of driver expectation and sa fety.

Contributors to the book include:

Kittelson &Associates, Inc.

Ruhr-University Bochum (Germany)

University of Idaho

Hurst-Ros che Engineers

Buckhurst Fish &Jacquemart

Queens la nd U niversity o f Tec hnolog y (Aust ralia )

University o f Florida P ennsylvania S tate University

Eppell Olsen &Partners (Australia)

In addition the document benefited

from exte nsive review by representa -

tives o f Frenc h and B ritish prac tice s a s

w ell a s AAS HTO, MUTC D, a nd repre-

sentatives of the Americans With Disa-

bilities Act.

FHWA project manager:

J oe B a red, (202) 493-3314,

Joe.Bared@fhwa.dot.gov.

Roundabouts: An Informational Guide(FHWA-

RD-00-067) will be available on the internet at

the Turner-Fa irba nk Highw a y R es ea rch Ce nter

w eb s ite: http: //w w w.tfhrc. g ov.

Turner-Fa irba nk Highw a y Res ea rch Ce nter

6300 Georgetown Pike

McLea n, 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 pub-

lished. The Report Center may be reached byphone at (301) 577-0818.