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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2011 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 705 Subscriber Categories Design â¢ Safety and Human Factors Evaluation of Safety Strategies at Signalized Intersections Raghavan Srinivasan Jongdae Baek Sarah Smith Carl Sundstrom Daniel Carter UNIVERSITY OF NORTH CAROLINA HIGHWAY SAFETY RESEARCH CENTER Chapel Hill, North Carolina Craig Lyon Bhagwant Persaud PERSAUD AND LYON, INC. Ontario, Canada Frank Gross Kim Eccles Ajmal Hamidi Nancy Lefler VANASSE HANGEN BRUSTLIN, INC. Raleigh, North Carolina 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 705 Project 17-35 ISSN 0077-5614 ISBN 978-0-309-21345-5 Library of Congress Control Number 2011935404 Â© 2011 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. 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 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. Charles M. Vest 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 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. Charles M. Vest 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
CRP STAFF FOR NCHRP REPORT 705 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Charles W. Niessner, Senior Program Officer Andrea Harrell, Senior Program Assistant Eileen P. Delaney, Director of Publications Maria Sabin Crawford, Assistant Editor NCHRP PROJECT 17-35 PANEL Field of TrafficâArea of Safety Troy A. Jerman, Iowa DOT, Fairfield, IA (Chair) Gerry J. Forbes, Intus Road Safety Engineering, Inc., Milton, ON Jeryl D. Hart, Jr., X8Environmental, Inc., Lubbock, TX Kohinoor Kar, Arizona DOT, Phoenix, AZ Brian Mayhew, North Carolina DOT, Garner, NC John McFadden, Federal Highway Administration, Baltimore, MD Anna R. Okola, World Bank, Washington, DC Thomas C. Werner, Bergmann Associates, Albany, NY R. Scott Zeller, Washington State DOT, Olympia, WA Roya Amjadi, FHWA Liaison Richard Pain, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 17-35. The University of North Carolina Highway Safety Research Center (HSRC) was the contractor for this study. Vanasse Hangen Brustlin, Inc. (VHB), Persaud and Lyon, Inc., and Iowa State University were subcontractors. The authors of the report are Raghavan Srinivasan (HSRC), Frank Gross (VHB), Craig Lyon (Persaud and Lyon), Bhagwant Persaud (Persaud and Lyon), Kim Eccles (VHB), Ajmal Hamidi (VHB), Jongdae Baek (HSRC), Sarah Smith (HSRC), Nancy Lefler (VHB), Carl Sundstrom (HSRC), and Daniel Carter (HSRC). Raghavan Srinivasan was the Principal Investigator. Finally, this project would not have been possible without the help and support of members of many state and city DOTs who provided valuable data for this project. 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 presents crash modification factors (CMFs) for safety strategies at signalized intersections. CMFs are a tool for quickly estimating the impact of safety improvements. The report will be of particular interest to safety practitioners responsible for programming and implementing highway safety improvements at intersections. Crash modification factors (CMFs), also known as Accident modification factors, provide a computationally simple and quick way of estimating crash reductions. Many states and local agencies have a set of CMFs that are used for estimating the safety impacts of various types of engineering improvements. Typically, these factors are computed using before- after comparisons, although recent research also has suggested the use of cross-sectional comparisons. Currently, CMFs are often used in program planning to make decisions concerning whether to implement a specific treatment and/or to quickly determine the costs and ben- efits of selected alternatives. CMFs are also used in project development for nonsafety as well as safety-specific projects and could be used by agencies in deciding on policies affecting general project design (e.g., context-sensitive design solutions and traffic calming). CMFs are also key components of the latest safety-estimation tools and procedures, including the Interactive Highway Safety Design Model, SafetyAnalyst, and the procedures in the AASHTO Highway Safety Manual. NCHRP Project 17-18(3) developed a series of guides to assist state and local agencies in reducing injuries and fatalities in targeted emphasis areas. Each guide includes a brief intro- duction, a general description of the problem, strategies to address the problem, and a model implementation process. NCHRP Report 500, Volume 12: Guidance for Implementation of the AASHTO Strategic Highway Safety Plan, A Guide for Reducing Collisions at Signalized Inter- sections includes strategies for improving the safety of signalized intersections. However, the safety effectiveness of many of the strategies in the guide have not been rigorously evaluated. Under NCHRP Project 17-35, âEvaluation of Safety Strategies at Signalized Intersec- tions,â researchers at the University of North Carolina Highway Safety Research Center developed reliable CMFs for a number of safety strategies outlined in NCHRP Report 500, Volume 12. The research team reviewed the literature and ongoing research related to CMF development, surveyed the state DOTs, and developed a priority list of treatments deemed to be important in safety decisions. The final list was determined based on the availability of data needed in CMF development. CMFs were developed for the installing dynamic advanced warning flashers, converting signalized intersections to roundabouts, increasing clearance intervals, changing left-turn phasing, and introducing flashing yellow arrow. F O R E W O R D By Charles W. Niessner Staff Officer Transportation Research Board
Users are encouraged to consider the quality and applicability of CMFs when selecting a CMF for use in the decision-making process. Users are also encouraged to consider the mea- sures of uncertainty (standard error or standard deviation) associated with a given CMF. The details of each evaluation are included in the appendices. The appendices are posted on the TRB project website at http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp? ProjectID=461.
C O N T E N T S 1 Summary 5 Chapter 1 Introduction 5 Background 5 Study Objectives and Overview 7 Chapter 2 Literature Review 13 Chapter 3 Survey of Agencies 13 Web-Based Surveys 13 Assessment of User Priorities and Development of Short List 14 Phone Calls to Selected Agencies 16 Chapter 4 Prioritization of Strategies 17 Interim Meeting with NCHRP Panel 18 Chapter 5 Safety Evaluation 18 Overview of Methods 19 Evaluation Summaries 29 Chapter 6 Compilation of CMFs 35 Chapter 7 Conclusions 37 References 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.