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NAT IONAL COOPERAT IVE H IGHWAY RESEARCH PROGRAM NCHRP SYNTHESIS 488 TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2016 www.TRB.org Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SubScriber categorieS Highways â¢ Operations and Traffic Management Roundabout Practices A Synthesis of Highway Practice conSultantS Alek Pochowski, Andy Paul, and Lee A. Rodegerdts Kittelson & Associates, Inc.
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research is the most effective way to solve many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be stud- ied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Associa- tion of State Highway and Transportation Officials (AASHTO) in 1962 initiated an objective national highway research program using modern scientific techniquesâthe National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board (TRB) of the National Acad- emies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRBâs recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many rea- sons: TRB maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, universities, and industry; TRBâs relationship to the Academies is an insurance of objectivity; and TRB maintains a full-time staff of specialists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs identi- fied by chief administrators and other staff of the highway and trans- portation departments and by committees of AASHTO. Topics of the highest merit are selected by the AASHTO Standing Committee on Research (SCOR), and each year SCORâs recommendations are proposed to the AASHTO Board of Directors and the Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted propos- als. Administration and surveillance of research contracts are the responsibilities of the Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation prob- lems 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 by going to http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP SYNTHESIS 488 Project 20-05, Topic 46-02 ISSN 0547-5570 ISBN 978-0-309-27208-7 Library of Congress Control No. 2016959599 Â© 2016 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, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC 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 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 National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessari- ly those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; or the program sponsors. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are con- sidered essential to the object of the report.
The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Ralph J. Cicerone is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. C. D. Mote, Jr., is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.national-academies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to increase the benefits that transportation contributes to society by providing leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Boardâs varied committees, task forces, and panels annually engage about 7,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.
TOPIC PANEL 46-02 ANDREA R. BILL, University of WisconsinâMadison WILLIAM BRITNELL, Connecticut Department of Transportation, Newington JERRY CHAMPA, California Department of Transportation, Sacramento BERNARDO KLEINER, Transportation Research Board CHRISTOPHER T. ROY, Minnesota Department of Transportation, St. Paul BRIAN J. WALSH, Washington State Department of Transportation, Olympia SCOTT ZEHNGRAFF, Georgia Department of Transportation, Atlanta HILLARY ISEBRANDS, Federal Highway Administration (Liaison) WEI ZHANG, Federal Highway Administration (Liaison) SYNTHESIS STUDIES STAFF STEPHEN R. GODWIN, Director for Studies and Special Programs JON M. WILLIAMS, Program Director, IDEA and Synthesis Studies JO ALLEN GAUSE, Senior Program Officer GAIL R. STABA, Senior Program Officer DONNA L. VLASAK, Senior Program Officer TANYA M. ZWAHLEN, Consultant DON TIPPMAN, Senior Editor CHERYL KEITH, Senior Program Assistant DEMISHA WILLIAMS, Senior Program Assistant DEBBIE IRVIN, Program Associate COOPERATIVE RESEARCH PROGRAMS STAFF CHRISTOPHER W. JENKS, Director, Cooperative Research Programs CHRISTOPHER HEDGES, Manager, National Cooperative Highway Research Program EILEEN P. DELANEY, Director of Publications NCHRP COMMITTEE FOR PROJECT 20-05 CHAIR BRIAN A. BLANCHARD, Florida Department of Transportation MEMBERS STUART D. ANDERSON, Texas A&M University SOCORRO âCOCOâ BRISENO, California Department of Transportation DAVID M. JARED, Georgia Department of Transportation CYNTHIA L. JONES, Ohio Department of Transportation MALCOLM T. KERLEY, NXL, Richmond, Virginia JOHN M. MASON, JR., Auburn University CATHERINE NELSON, Salem, Oregon ROGER C. OLSON, Bloomington, Minnesota BENJAMIN T. ORSBON, South Dakota Department of Transportation RANDALL R. âRANDYâ PARK, Utah Department of Transportation ROBERT L. SACK, New York State Department of Transportation FRANCINE SHAW WHITSON, Federal Highway Administration JOYCE N. TAYLOR, Maine Department of Transportation FHWA LIAISON JACK JERNIGAN TRB LIAISON STEPHEN F. MAHER Cover figure: Roundabout. Courtesy: Town of Nantucket, Massachusetts via GreenmanâPedersen, Inc.
FOREWORD In mid-1997, NCHRP Synthesis of Highway Practice 264: Modern Roundabout Practice in the United States identified 50 roundabouts known to have been constructed since the beginning of the decade. As of 2013, there were an estimated 3,200 roundabouts in use throughout the country. This synthesis documents and summarizes roundabout policies, guidance, and practices in place within state departments of transportation (DOTs) as of 2015. The primary focus of the synthesis is on roundabout selection and design with a secondary focus on performance analysis. Information used in this study was gathered through a literature review and a survey of state DOTs. Personnel from seven states were interviewed to create case examples and more specific information. Alek Pochowski, Andy Paul, and Lee A. Rodegerdts, Kittelson & Associates, Inc., collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately use- ful document that records the practices that were acceptable with the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand. Highway administrators, engineers, and researchers often face problems for which infor- mation already exists, either in documented form or as undocumented experience and prac- tice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviat- ing the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evaluating such useful information and to make it available to the entire highway commu- nity, the American Association of State Highway and Transportation Officialsâthrough the mechanism of the National Cooperative Highway Research Programâauthorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Proj- ect 20-5, âSynthesis of Information Related to Highway Problems,â searches out and syn- thesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. PREFACE By Jo Allen Gause Senior Program Officer Transportation Research Board
CONTENTS 1 SUMMARY 3 CHAPTER ONE INTRODUCTION Objectives of Study, 3 Study Approach, 3 Synthesis Organization, 3 4 CHAPTER TWO LITERATURE REVIEW Roundabouts in the United States, 4 Roundabout Policies, 4 State Statutes, Codes, and Laws, 10 Public Outreach Efforts, 10 Roundabout Performance, 10 Roundabout Design, 13 16 CHAPTER THREE SURVEY RESULTS Roundabout Selection, 17 Roundabout Costs, 20 Public Outreach, 20 Roundabout Performance Analysis, 21 Roundabout Design, 22 26 CHAPTER FOUR CASE EXAMPLES OF ROUNDABOUT PRACTICES Roundabout Selection, 26 Modifications to Existing Roundabouts, 26 Phased Roundabout Implementation, 27 Design Vehicle Accommodation, 28 Accelerated, Low-Cost Roundabouts, 29 Effective Practices, 30 32 CHAPTER FIVE CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH 34 REFERENCES
38 APPENDIX A SUMMARY OF STATEWIDE ROUNDABOUT POLICIES 43 APPENDIX B STATE AGENCY QUESTIONNAIRE 59 APPENDIX C QUESTIONNAIRE RESPONSES 76 APPENDIX D CASE EXAMPLES Note: Photographs, figures, and tables in this report may have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org) retains the color versions.