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2018 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 RESEARCH REPORT 888 Development of Roundabout Crash Prediction Models and Methods Erin Ferguson James Bonneson Lee Rodegerdts Nick Foster Kittelson & AssociAtes, inc. Oakland, CA Bhagwant Persaud Craig Lyon PersAud And lyon, inc. Toronto, ON, Canada Danica Rhoades Write Rhetoric, Boise, ID Subscriber Categories Design â¢ Safety and Human Factors 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 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 studied 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 inter- est to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated 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 Academies 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 reasons: TRB maintains an extensive com- mittee 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, univer- sities, and industry; TRBâs relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists 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 identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the Federal Highway Administration. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&Iâs recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving 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 research 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 RESEARCH REPORT 888 Project 17-70 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-48004-8 Library of Congress Control Number 2018965100 Â© 2018 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 research 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 necessarily 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 considered 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. Marcia McNutt 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 National 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.
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 RESEARCH REPORT 888 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Ann M. Hartell, Senior Program Officer Jarrel McAfee, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Hilary Freer, Senior Editor NCHRP PROJECT 17-70 PANEL Field of TrafficâArea of Safety John P. Miller, Federal Highway Administration (FHWA), Jefferson City, MO (Chair) Seth Adu Asante, Boston Region Metropolitan Planning Organization, Boston, MA Timothy E. Barnett, Troy, AL W. Martin Bretherton, Jr., WMB Engineering, Atlanta, GA Craig A. Copelan, Winters, CA Matthew T. Enders, Washington State DOT, Olympia, WA Howard M. McCulloch, New York State DOT, Albany, NY Seri Park, Villanova University, Villanova, PA Hadi Shirazi, Louisiana DOTD, Baton Rouge, LA Jeffrey B. Shaw, FHWA Liaison Kelly K. Hardy, AASHTO Liaison Bernardo Kleiner, TRB Liaison
F O R E W O R D NCHRP Research Report 888 provides crash prediction models that quantify the expected safety performance of roundabouts for motorized and non-motorized road users. The report will be of interest to highway design engineers, highway safety analysts and researchers, and transportation planners, as well as those responsible for maintaining highway safety guidance, including the Highway Safety Manual (HSM). Safety performance factors (SPFs) and crash modification factors (CMFs) are predictive models that estimate expected crash frequencies. Transportation professionals use these models to identify locations where crash rates are higher than expected, to estimate safety benefits of a proposed project, and to compare the safety benefits of design alternatives. The models help identify and prioritize locations for safety improvements, compare project alternatives by their expected safety benefits, and guide detailed design decisions to opti- mize safety. Research indicates that roundabouts provide substantial reductions in crashes, especially crashes that result in serious injuries or fatalities. However, the 1st edition of the HSM did not include a crash prediction method for roundabouts; therefore, practitioners were not able to quantitatively assess the crash reduction benefits of providing a roundabout at a specific intersection or to investigate the safety effects of complex design decisions at single- lane and multilane roundabouts. NCHRP Report 888 provides practitioners with SPFs and CMFs for roundabouts. The models include variables for geometric features and operational characteristics, as well as their expected effects on crash rates for motorized and nonmotorized users. The models can be used for planning-level analysis, and, as a project develops and more detailed informa- tion is available, for analysis at the intersection level and leg level of an intersection. The research was conducted by Kittelson and Associates, with support from Persaud and Lyon, Inc., and Write Rhetoric. NCHRP Report 888 is accompanied by online resources, including recommended revisions for the 2nd edition of the HSM, detailed information on the data sources and data pre-processing, and a downloadable slide presentation summarizing the results of the research. These materials are available on the TRB website (trb.org) by search- ing for âNCHRP Research Report 888â. By Ann M. Hartell Staff Officer Transportation Research Board
C O N T E N T S 1 Summary 2 Chapter 1 Background 2 1.1 Overview 2 1.2 Research Problem Statement 3 1.3 Objectives 3 1.4 Summary of Research Approach 5 Chapter 2 Literature Review Approach and Findings 5 2.1 Critical Review of Literature 17 2.2 Outreach to Public Agencies with Roundabouts 19 2.3 Candidate Roundabout Configurations 19 2.4 Alternative Statistical Modeling Approaches 27 2.5 Roundabout-Related Crash Definitions 29 2.6 Model Development Literature Review 32 2.7 References and Bibliography 35 Chapter 3 Framework for Safety Prediction and Data Needs 35 3.1 Candidate Safety Performance Functions for Design Applications 39 3.2 Candidate Safety Performance Functions for Planning and Network Screening 39 3.3 Assessing Driver Learning Curve 39 3.4 Predicting Pedestrian and Bicycle Crashes 40 3.5 Study Designs for CMFs 40 3.6 Database Requirements for Developing SPFs and CMFs 41 3.7 Sample Size Requirements 41 3.8 References and Bibliography 42 Chapter 4 Data Collection Approach and Findings 42 4.1 Data Collection Approach 43 4.2 Desired Data Attributes based on Candidate SPFs and CMFs 44 4.3 Data Sources 47 4.4 Database Development 49 4.5 Final Database Attributes and Characteristics 52 4.6 References and Bibliography
53 Chapter 5 Crash Prediction Model Development Approach 53 5.1 Planning-Level Crash Prediction Models 66 5.2 Intersection-Level Crash Prediction Models for Design 126 5.3 Leg-Level Crash Prediction Models for Design 138 5.4 Practitioner Validation 138 5.5 Effect of Driver Learning Curve on Roundabout Safety Performance 142 5.6 References and Bibliography 143 Chapter 6 Research Findings 143 6.1 Crash Prediction Models 168 6.2 Calibration of Crash Prediction Models 169 6.3 Effect of Driver Learning Curve on Roundabout Safety Performance 170 6.4 Pedestrian and Bicycle Safety at Roundabouts 171 6.5 Speed and Roundabouts 171 6.6 Contributions to the Highway Safety Manual 172 6.7 Summary 173 6.8 References and Bibliography 174 Chapter 7 Conclusions and Suggested Research 174 7.1 Conclusions 174 7.2 Recommendations for Practitioners 175 7.3 Suggested Research 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.