Evaluation of Safety Strategies at Signalized Intersections (2011)

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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 • 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

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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 Traffic—Area 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, “Evaluation of Safety Strategies at Signalized Intersec- tions,” 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.