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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 790 Factors Contributing to Median Encroachments and Cross-Median Crashes Douglas W. Harwood, David K. Gilmore, Jerry L. Graham, and Mitchell K. OâLaughlin MRIGlobal Kansas City, MO Alison M. Smiley and Thomas P. Smahel HuMan FactoRs noRtH Toronto, ON, Canada Subscriber Categories Design â¢ Safety and Human Factors TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2014 www.TRB.org 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 Boardâs 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 790 Project 17-44 ISSN 0077-5614 ISBN 978-0-309-28426-4 Library of Congress Control Number 2014944697 Â© 2014 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 manufacturersâ names appear herein solely because they are considered essential to the object of the report.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon 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 technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy 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 achievements of engineers. Dr. C. D. Mote, Jr., 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, upon its own initiative, to identify issues of medical care, research, and education. Dr. Victor J. Dzau 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 Academyâs purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, 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 Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. C. D. Mote, Jr., are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transporta- tion Research Board is to provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Boardâs varied activities 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 individu- als interested in the development of transportation. www.TRB.org www.national-academies.org
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 CRP STAFF FOR NCHRP REPORT 790 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program B. Ray Derr, Senior Program Officer Andrea Parker, Senior Program Assistant Eileen P. Delaney, Director of Publications Hilary Freer, Senior Editor NCHRP PROJECT 17-44 PANEL Field of TrafficâArea of Safety Howard R. Ressel, New York State DOT, Rochester, NY (Chair) David K. Olson, Rochester, WA James A. Barna, Ohio DOT, Columbus, OH Rick O. Drumm, Federal Highway Administration, Indianapolis, IN Erik O. Emerson, Wisconsin DOT, Madison, WI Young-Jun Kweon, Virginia DOT, Charlottesville, VA Xiaokun âCaraâ Wang, Rensselaer Polytechnic Institute, Troy, NY J. Richard Young, Jr., Atkins North America, Inc., Jackson, MS Nicholas A. Artimovich, II, FHWA Liaison Stephen F. Maher, TRB Liaison
F O R E W O R D By B. Ray Derr Staff Officer Transportation Research Board This report identifies design and operational factors that contribute to the frequency and severity of median encroachments and cross-median crashes. It also identifies counter- measures for addressing those contributory factors. The report will be useful to designers and safety professionals in reducing these highly visible crashes. Cross-median crashes frequently result in high-severity injuries and fatalities. Previous studies of contributory factors associated with cross-median crashes have typically focused on median width and average daily traffic (ADT). A few studies have looked at the influence of geometry and cross-sectional elements. Although these studies have been helpful, they did not explore many other design and operational factors that may contribute to cross- median crash frequency or severity (e.g., interchange ramps, interchange spacing, mix- ture of vehicle types, peak-period volumes, peak-period duration, land use, access control, driver workload, posted speed, or presence of speed transition zones). All median-related incidents begin with a median encroachment. Reducing median encroachments will reduce both cross-median crashes and fixed-object crashes in the median. Consequently, analyzing median encroachments should provide additional insight into the causes of cross-median crashes. There is also a knowledge gap regarding countermeasures appropriate for the various fac- tors contributing to median encroachments and cross-median crashes. Although installing a barrier will greatly reduce cross-median crashes, it will also increase fixed-object crashes and the crash risk of maintenance personnel. Other countermeasures besides barriers exist, and knowing which ones effectively address the contributory factors on a highway will allow an engineer to develop a more effective design. In NCHRP Project 17-44, MRIGlobal reviewed the literature on median encroachments and cross-median crashes. Based on a survey of states, Canadian provinces, and turnpike/toll road authorities, the team compiled a list of design and operational factors likely to contribute to median encroachments and cross-median crashes. The research team then collected data to determine the relative contribution of each of the factors to median encroachments and cross-median crashes. Appendix D of the report provides recommended guidelines for reducing the frequency and severity of median-related crashes. This material is designed to be easily incorporated into a transportation agencyâs design manual.
C O N T E N T S 1 Summary 4 Section 1 Introduction 4 1.1 Background 4 1.2 Research Objectives and Scope 5 1.3 Research Approach 5 1.4 Organization of This Report 6 Section 2 Review of Median Safety Studies 6 2.1 Median Encroachments 9 2.2 Median-Related Crashes 18 2.3 Crash Countermeasures for Improving Median Safety 20 2.4 Road Safety Audits 21 2.5 Median Design Practice 23 Section 3 Survey Results 23 3.1 Survey Method 23 3.2 Response Rate 23 3.3 Survey Summary 37 Section 4 Interdisciplinary Field Reviews 37 4.1 Overview of Interdisciplinary Field Review Approach 37 4.2 Site Selection for Interdisciplinary Field Reviews 38 4.3 Interdisciplinary Field Review Procedure 40 4.4 Site Characteristics for Interdisciplinary Field Review Sites 40 4.5 Interdisciplinary Field Review Results 40 4.6 Interdisciplinary Crash Review Results 55 4.7 Summary of Contributing Factors 56 Section 5 Crash Data Analyses to Investigate Contributing Factors 56 5.1 Crash Analysis Approach 57 5.2 Analysis Results for Median-Related Crashes on Rural Freeways 60 5.3 Comparison of Results for Median-Related Crashes to Other Crash Types 62 5.4 Involvement of Road Surface Condition in Median-Related Crashes and Other Crash Types 62 5.5 Discussion of Contributing Factors 63 Section 6 Guidelines for Geometric Design and Countermeasure Implementation to Reduce Median-Related Crashes 65 Section 7 Conclusions and Recommendations
67 References 70 Abbreviations 71 Appendixes A through C 72 Appendix D Guidelines for Reducing the Frequency and Severity of Median-Related Crashes on Divided Highways Note: Many of the photographs, figures, and tables in this report 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.