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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2010. Roundabouts: An Informational Guide – Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22914.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2010. Roundabouts: An Informational Guide – Second Edition. Washington, DC: The National Academies Press. doi: 10.17226/22914.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2010 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 672 Subscriber Categories Highways • Design Roundabouts: An Informational Guide Second Edition Lee Rodegerdts, Justin Bansen, Christopher Tiesler, Julia Knudsen, and Edward Myers KITTELSON & ASSOCIATES, INC. Portland, OR Mark Johnson MTJ ENGINEERING, INC. Madison, WI Michael Moule LIVABLE STREETS INC. Tampa, FL Bhagwant Persaud and Craig Lyon PERSAUD AND LYON Toronto, ON, Canada Shauna Hallmark and Hillary Isebrands CENTER FOR TRANSPORTATION RESEARCH AND EDUCATION IOWA STATE UNIVERSITY Ames, IA R. Barry Crown RODEL SOFTWARE LTD United Kingdom Bernard Guichet CETE L’OUEST France Andrew O’Brien O’BRIEN TRAFFIC Australia Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board’s recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 672 Project 3-65A ISSN 0077-5614 ISBN 978-0-309-15511-3 Library of Congress Control Number 2010937912 © 2010 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The project that is the subject of this report was a part of the National Cooperative Highway Research Program, conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. The members of the technical panel selected to monitor this project and to review this report were chosen for their special competencies and with regard for appropriate balance. The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the Governing Board of the National Research Council. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The Transportation Research Board of the National Academies, the National Research Council, and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of the report.

CRP STAFF FOR NCHRP REPORT 672 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs B. Ray Derr, Senior Program Officer Eileen P. Delaney, Director of Publications Doug English, Editor NCHRP PROJECT 3-65A PANEL Field of Traffic—Area of Operations and Control Beatriz Caicedo-Maddison, Florida DOT, Ft. Lauderdale, FL (Chair) Robert R. Limoges, New York State DOT, Albany, NY Maria G. Burke, Texas DOT, Austin, TX Jerry Champa, California DOT, Sacramento, CA Leonard Evans, Science Serving Society, Bloomfield Hills, MI Steve King, Kansas DOT, Topeka, KS Richard Long, Western Michigan University, Kalamazoo, MI Richard Retting, Sam Schwartz Engineering, Arlington, VA Edward R. Stollof, Institute of Transportation Engineers, Washington, DC Brian J. Walsh, Washington State DOT, Olympia, WA Mohsin A. Zaidi, Virginia DOT, Chantilly, VA Joe Bared, FHWA Liaison Richard A. Cunard, TRB Liaison C O O P E R A T I V E R E S E A R C H P R O G R A M S

This report updates the FHWA’s Roundabouts: An Informational Guide based on experi- ence gained in the United States since that guide was published in 2000. The report addresses the planning, design, construction, maintenance, and operation of roundabouts. It also includes information that will be useful in explaining to the public the trade-offs asso- ciated with roundabouts. In 2000, the FHWA published Roundabouts: An Informational Guide. NCHRP Synthesis 264: Modern Roundabout Practice in the United States estimated that there were 38 modern roundabouts (i.e., those consistent with current international practice) as of October 1997. Since U.S. experience was limited, the FHWA Roundabout Guide was based largely on European and Australian guidelines. Publication of the FHWA Roundabout Guide has fostered acceptance of the roundabout as a viable alternative for intersection design, leading to more than 2,000 roundabouts across the United States. Extensive use of the Roundabout Guide and completion of national and state research efforts identified many possible improvements. Recognizing this, the NCHRP and the FHWA jointly funded an NCHRP project to update the Roundabout Guide. In NCHRP Project 3-65A, Kittelson & Associates, Inc., reviewed the literature and research conducted since the publication of the FHWA Roundabout Guide. They then con- ducted focus groups of practitioners to identify concerns with the original guide and ideas for improvements. After achieving consensus with the project oversight panel on an out- line, they developed the new guide and refined it through an extensive review process. The Second Edition of Roundabouts: An Informational Guide will be useful to anyone interested in evaluating or building a roundabout. The experience of the research team, cou- pled with the extensive review, has led to an authoritative, but not prescriptive, guide on roundabouts. F O R E W O R D By B. Ray Derr Staff Officer Transportation Research Board

AUTHOR ACKNOWLEDGMENTS This guide was developed through the National Cooperative Highway Research Program Project 03- 65A, Update of FHWA’s Roundabouts: An Informational Guide. The international project team consisted of Lee Rodegerdts (principal investigator), Justin Bansen, Julia Knudsen, Christopher Tiesler, and Edward Myers, Kittelson & Associates, Inc. (prime contractor); Mark Johnson, MTJ Engineering; Michael Moule, Livable Streets Inc.; Bhagwant Persaud and Craig Lyon, Persaud and Lyon; and Shauna Hallmark and Hillary Isebrands, Center for Transportation Research and Education, Iowa State University. In addition, the team had three international advisors: R. Barry Crown (United Kingdom), Bernard Guichet (France), and Andrew O’Brien (Australia). Ralph Bentley, John Henriksen, Jon Sommerville, and Bonnie Middle- ton of Kittelson & Associates, Inc., assisted with exhibits and production. The authors thank each of the panel members for their diligence in providing quality direction and review throughout the project. Additional review was provided by Carl Andersen, FHWA; Mark Lenters, Ourston Roundabout Engineering; Howard McCulloch, New York State Department of Transportation; Patrick McGrady, Reid Middleton; and Eugene Russell, Kansas State University. The authors also profoundly thank the authors and reviewers of the first edition, which formed the foundation for this document. The first edition of this guide was groundbreaking in many ways, partic- ularly in combining many of the best roundabout practices from around the world with principles, tech- niques, and policies in place in the United States. Without the collaborative work of this group, this sec- ond edition would not be possible. The acknowledgments that were intended to be published with the first edition are included below. ACKNOWLEDGMENTS FROM FIRST EDITION This guide was developed as part of the Federal Highway Administration project DTFH61-97-R-0038. The international project team consisted of Kittelson & Associates, Inc. (prime contractor) in association with Rod Troutbeck of the Queensland University of Technology (Australia); Werner Brilon and Lothar Bondzio of Ruhr-University Bochum (Germany); Ken Courage of the University of Florida; Michael Kyte of the University of Idaho; John Mason and Aimee Flannery of Pennsylvania State University; Edward Myers of Hurst-Rosche Engineers; Jonathan Bunker of Eppell Olsen & Partners (Australia); and Georges Jacquemart of Buckhurst Fish and Jacquemart. Michael Ronkin and Thomas Ronkin provided transla- tion of the French guides for urban roundabouts, rural roundabouts, and roundabout lighting. Bruce Robinson was the principal investigator for Kittelson & Associates, Inc. Co-investigators were Lee Rodegerdts and Wade Scarbrough. Wayne Kittelson was the project principal. Paul Ryus and Christoff Krogscheepers assisted with review, editing, and production. Ralph Bentley and John Henrik- sen assisted with exhibits and production. Joe G. Bared was the technical representative for the Federal Highway Administration at the Turner- Fairbank Highway Research Center. The project advisory panel consisted of John Sacksteder of the Kentucky Department of Transporta- tion and AASHTO (Geometric Design Committee); Larry Sutherland of the Ohio Department of Trans- portation and AASHTO (Geometric Design Committee); Mike Neiderhauser of the Maryland State High- way Administration; Michael Thomas of the California Department of Transportation; and Leif Ourston of Ourston & Doctors, Inc. Several FHWA advisors as well as many other reviewers represented various departments, including Raymond Krammes, Davey Warren, Bill Prosser, Carol Tan-Esse, Rudolph Umbs, Janet Coleman, Ernest Huckaby, and John Fegan. In addition, we are indebted to many individuals, organizations, and committees, too numerous to name, who provided voluminous comments on draft versions of the guide. In particular, the extraordi- nary efforts of the following contributors are acknowledged: Barry Crown (United Kingdom); Owen Arndt of the Main Roads Department of Queensland (Australia); Bernard Guichet (France); Michael Moule, formerly of the City of Asheville, North Carolina; and Lois Thibault of the U.S. Access Board.

Roundabouts are a common form of intersection control used throughout the world and increasingly in the United States. The information supplied in this document builds exten- sively on the first edition published in 2000 by the Federal Highway Administration and is based on established and emerging U.S. practices and recent research. The guide continues to be comprehensive in recognition of the diverse needs of transportation professionals and the public for introductory material, planning and design guidance, operational and safety performance evaluation techniques, construction and maintenance information, and the wide range of potential applications of roundabouts. Selection and design of a roundabout, as with any intersection treatment, requires the balancing of competing objectives. These range from transportation-oriented objectives like safety, operational performance, and accessibility for all users to other factors such as eco- nomics, land use, aesthetics, and environmental aspects. Sufficient flexibility is provided to encourage independent designs and techniques tailored to particular situations while emphasizing performance-based evaluation of those designs. Since there is no absolutely optimum design, this guide is not intended as an inflexible rule book but rather attempts to explain some principles of good design and indicate poten- tial trade-offs that one may face in a variety of situations. In this respect, the principles and techniques in this document must be combined with the judgment and expertise of engi- neers, planners, and other professionals. Adherence to these principles still does not ensure good design, which remains the responsibility of the professionals in charge of the work. Much as one cannot become a master chef merely by reading cookbooks, one cannot become a master roundabout planner or engineer solely by reading this guide. However, professionals can combine the principles in this guide with their own experiences and judg- ment and with the continually growing wealth of experience in our respective professions to produce favorable outcomes that benefit the traveling public and our communities. Lee A. Rodegerdts, P.E. Principal Investigator P R E F A C E

C O N T E N T S 1-1 Chapter 1 Introduction 1-3 1.1 Introduction 1-3 1.2 Distinguishing Characteristics of a Roundabout 1-10 1.3 Categories of Roundabouts 1-17 1.4 Scope of the Guide 1-17 1.5 Organization of the Guide 1-19 1.6 References 2-1 Chapter 2 Roundabout Considerations 2-3 2.1 Introduction 2-3 2.2 General Characteristics 2-13 2.3 User Considerations 2-21 2.4 Policy and Legal Issues 2-22 2.5 References 3-1 Chapter 3 Planning 3-4 3.1 Introduction 3-5 3.2 Planning Steps 3-6 3.3 Considerations of Context 3-10 3.4 Potential Applications 3-20 3.5 Planning-Level Sizing and Space Requirements 3-30 3.6 Comparing Performance of Alternative Intersection Types 3-33 3.7 Economic Evaluation 3-38 3.8 Public Involvement 3-45 3.9 References 4-1 Chapter 4 Operational Analysis 4-3 4.1 Introduction 4-3 4.2 Principles 4-6 4.3 Data Collection and Analysis 4-10 4.4 Analysis Techniques 4-10 4.5 Highway Capacity Manual Method 4-18 4.6 Deterministic Software Methods 4-19 4.7 Simulation Methods 4-20 4.8 References 5-1 Chapter 5 Safety 5-4 5.1 Introduction 5-5 5.2 Principles 5-14 5.3 Observed Safety Performance 5-22 5.4 Intersection-Level Crash Prediction Methodology 5-28 5.5 Approach-Level Crash Prediction Methodology 5-34 5.6 References

6-1 Chapter 6 Geometric Design 6-6 6.1 Introduction 6-8 6.2 Principles and Objectives 6-16 6.3 Size, Position, and Alignment of Approaches 6-22 6.4 Single-Lane Roundabouts 6-33 6.5 Multilane Roundabouts 6-45 6.6 Mini-Roundabouts 6-53 6.7 Performance Checks 6-67 6.8 Design Details 6-90 6.9 Closely Spaced Roundabouts 6-91 6.10 Interchanges 6-95 6.11 Access Management 6-98 6.12 Staging of Improvements 6-102 6.13 References 7-1 Chapter 7 Application of Traffic Control Devices 7-4 7.1 Introduction 7-4 7.2 Principles 7-5 7.3 Pavement Markings 7-17 7.4 Signing 7-31 7.5 Signalization 7-38 7.6 At-Grade Rail Crossings 7-42 7.7 References 8-1 Chapter 8 Illumination 8-3 8.1 Introduction 8-3 8.2 General Considerations 8-5 8.3 Lighting Levels 8-6 8.4 Equipment Type and Location 8-11 8.5 References 9-1 Chapter 9 Landscaping 9-3 9.1 Introduction 9-7 9.2 Principles 9-8 9.3 Central Island Landscaping 9-13 9.4 Splitter Island and Approach Landscaping 9-13 9.5 Maintenance 9-15 9.6 References 10-1 Chapter 10 Construction and Maintenance 10-3 10.1 Introduction 10-3 10.2 Public Education 10-4 10.3 Construction Staging 10-10 10.4 Work Zone Traffic Control 10-11 10.5 Construction Plans 10-11 10.6 Construction Coordination 10-13 10.7 Maintenance 10-16 10.8 References 1 Glossary 13 Bibliography

A-1 Appendix A Example Pavement Marking Designs for Roundabouts B-1 Appendix B User Education C-1 Appendix C Rules of the Road D-1 Appendix D Design Supplemental Materials

American Structurepoint Inc.: Exhibit 1-16(b), 6-87 Brian Walsh: Exhibit 3-10, 9-6(a), 10-7 Casey Bergh: Exhibit 1-16(a) City of Clearwater, Florida: Exhibit 2-3 City of Fort Worth, Texas: Exhibit 1-3 Clackamas County, Oregon: Exhibit 3-5 Connecticut Department of Transportation: Exhibit 6-23 Edward Myers: Exhibit 10-5 Erin Ferguson: Exhibit 3-22(b) Hillary Isebrands: Exhibit 6-19(a) Howard McCulloch: Exhibit 3-11, 6-91(b), 10-8 Joe Bared: Exhibit 6-83(a) Joe Sullivan: Exhibit 1-13(a) Kansas Department of Transportation: Exhibit 6-20, 6-90 Ken Courage: Exhibit 1-7(f) Lee Rodegerdts: Exhibits 1-4(all), 1-5(all), 1-7(b-e), 1-8(a-d,f-h), 1-11, 2-2, 2-4(all), 3-2, 3-6, 3-7, 3-8, 3-9, 6-3, 6-6, 6-19(b), 6-22(all), 6-41, 6-65, 6-71(all), 6-88, 6-90(a), 6-91(a), 6-92(all), 7-26, 7-27(all), 7-29(all), 7-31(all), 7-33(a), 8-3(all), 9-1(all), 9-5, 9-6(b-d), 9-9(all), 10-4(all), 10-6 Livingston County, Michigan: Exhibit 6-83(b) Mark Johnson: 6-86, 7-2 Mark Lenters: Exhibit 1-6(a), 1-7(a), 1-8(e), 9-8 Maryland State Highway Administration: Exhibit 3-3, 3-4, 6-45 Michael Moule: Exhibit 7-33(b) Missouri Department of Transportation: Exhibit 3-22(a) New York State Department of Transportation: Exhibit 1-6(b) Skagit County: Exhibit 1-13(b) Wisconsin Department of Transportation: Exhibit 1-16(c) I M A G E C R E D I T S

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 672: Roundabouts: An Informational Guide – Second Edition explores the planning, design, construction, maintenance, and operation of roundabouts. The report also addresses issues that may be useful in helping to explain the trade-offs associated with roundabouts.

This report updates the U.S. Federal Highway Administration’s Roundabouts: An Informational Guide, based on experience gained in the United States since that guide was published in 2000.

Errata

Equation 6-3 on page 6-58 incorrectly contains an addition sign (+) as an operator. The correct operator should be a subtraction sign (-).

Errata #2

Exhibit 5-23 on page 5-29 of NCHRP Report 672 contains an incorrect calculation of estimated injury crashes.

There is a summary document, Paths to Practice, available.

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