Safety of U-Turns at Unsignalized Median Openings (2004)

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T R A N S P O R T A T I O N R E S E A R C H B O A R D WASHINGTON, D.C. 2004 www.TRB.org NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 524 Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration SUBJECT AREAS Highway and Facility Design Safety of U-Turns at Unsignalized Median Openings INGRID B. POTTS DOUGLAS W. HARWOOD DARREN J. TORBIC KAREN R. RICHARD Midwest Research Institute Kansas City, MO JEROME S. GLUCK Urbitran Associates New York, NY HERBERT S. LEVINSON New Haven, CT AND PHILIP M. GARVEY RAMY S. GHEBRIAL Pennsylvania State University State College, PA

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. 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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. Note: The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual states participating in 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 this report. 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 524 Project G17-21 FY’00 ISSN 0077-5614 ISBN 0-309-08805-4 Library of Congress Control Number 2004111239 © 2004 Transportation Research Board Price $24.00 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. Such approval reflects the Governing Board’s judgment that the program concerned is of national importance and appropriate with respect to both the purposes and resources of the National Research Council. The members of the technical committee selected to monitor this project and to review this report were chosen for recognized scholarly competence and with due consideration for the balance of disciplines appropriate to the project. The opinions and conclusions expressed or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of the Transportation Research Board, the National Research Council, the American Association of State Highway and Transportation Officials, or the Federal Highway Administration, U.S. Department of Transportation. Each report is reviewed and accepted for publication by the technical committee according to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council.

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol- ars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and techni- cal matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Acad- emy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achieve- ments of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board’s mission is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, the Board facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provides expert advice on transportation policy and programs; and disseminates research results broadly and encourages their implementation. The Board’s varied activities annually engage more than 5,000 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. www.TRB.org www.national-academies.org

COOPERATIVE RESEARCH PROGRAMS STAFF FOR NCHRP REPORT 524 ROBERT J. REILLY, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Manager, NCHRP B. RAY DERR, Senior Program Officer EILEEN P. DELANEY, Director of Publications HILARY FREER, Editor NCHRP PROJECT G17-21 PANEL Field of Traffic—Area of Safety PATRICK T. MCCOY, University of Nebraska—Lincoln (Chair) (Deceased) W. MARTIN BRETHERTON, JR., P.E., Gwinnett County (GA) DOT PHILIP B. DEMOSTHENES, Parametrix, Denver, CO MARYAM GHYABI, P.E., Ghyabi, Lassiter & Associates, Deland, FL KURT KUNDE, P.E., Grand Ledge, MI DAVID NOYCE, P.E., University of Wisconsin–Madison RICHARD F. TWARDOKUS, P.E., Bloomfield, NY JOE BARED, P.E., FHWA Liaison Representative RICHARD A. CUNARD, P.E., TRB Liaison Representative

This report presents guidelines for locating and designing unsignalized median openings. A methodology is included for comparing the relative safety performance of different designs. Primarily, geometric designers for both state and local agencies will benefit from the report, but it will also be useful to those discussing the impacts of installing medians with business and property owners. Designs for nontraversable medians vary widely and the safety and operational effects of the different designs have not been well documented. A thorough review of the safety and operational effects of the various designs was needed, both for setting design policy and in project-level design. Transportation agencies often face resistance to installing nontraversable medians on multilane highways. One of the arguments made is that the number of U-turning vehicles will increase. However, the effect of an increase in U-turns on the safety of the road is not clear. Studies attributing safety gains to a nontraversable median have not focused on the specific situation at the median opening, either isolated or at an inter- section, where U-turns occur. After a nontraversable median has been installed, agencies are often approached by abutting property owners who want a new median opening. Additional information would be helpful in reviewing these requests, determining if an opening should be allowed, and developing a design that does not unduly affect the safety or operation of the road. In NCHRP Project 17-21, Midwest Research Institute and their subcontractors determined state and local agency design practices and policies related to unsignalized median openings for U-turns. After promising designs were identified, their effects on safety were assessed through field observation and crash data analysis. The knowledge gained was distilled into design guidelines and a methodology for comparing the expected safety performance of different designs. FOREWORD By B. Ray Derr Staff Officer Transportation Research Board

1 SUMMARY 3 CHAPTER 1 Introduction Background, 3 Research Objectives and Scope, 3 Organization of This Report, 3 5 CHAPTER 2 Literature Review Location of Median Openings, 5 Spacing of Median Openings, 6 Safety of Median Openings, 7 Median Width, 8 Median Opening Length, 10 Safety Effects of Median Treatments (Raised/Depressed/Flush/TWLTL), 10 Safety Effects of Increasing U-Turn Maneuvers Through Use of Nontraversable Medians, 15 Left-Turn Lanes, 16 Median Acceleration Lanes, 18 Loons to Assist Larger Vehicles in Completing U-Turn Maneuvers, 20 Sight Distance at Median Openings, 20 Indirect Left-Turn Maneuvers, 21 Access Management, 24 Spacing Between Access Points, 25 Effects of Adjacent Traffic Signals, 26 27 CHAPTER 3 Current Design Policies and Practices of Highway Agencies Survey Recipients, 27 Response Rate, 27 Location and Design of Median Openings, 27 Treatment of U-Turns at Median Openings, 28 Median and Roadway Widths to Accommodate U-Turn Maneuvers, 31 Traffic Operational and Safety Problems at Median Openings, 32 Mitigation Measures for Safety Problems, 32 33 CHAPTER 4 Classification and Assessment of Typical Median Opening Designs Factors Used in Classification of Median Opening Designs, 33 Overview of Typical Median Opening Designs, 34 Factors That Influence the Safety and Operational Performance of Median Openings, 42 Relative Safety of Median Opening Designs Based on Traffic Conflict Points, 52 Combinations of Median Openings Along Arterial Streets, 53 59 CHAPTER 5 Data Collection and Analysis Catalog of Existing Median Openings, 59 Data Collection and Analysis for Selected Median Openings, 62 68 CHAPTER 6 Findings Accident and Field Data, 68 Median Opening Accident Frequencies, 68 Median Opening Accident Rates, 69 Median Opening Conflict Rates, 71 Comparison of Median Opening Accident and Conflict Rates, 72 Combinations of Median Openings, 74 79 CHAPTER 7 Conclusions and Recommendations Conclusions, 79 Recommendations, 80 81 REFERENCES A-1 APPENDIX A Highway Agency Survey Questionnaire B-1 APPENDIX B Summary of Survey Responses From State and Local Highway Agencies C-1 APPENDIX C Guidelines for the Use, Location, and Design of Unsignalized Median Openings CONTENTS