Development and Application of Crash Severity Models for Highway Safety: User Guidelines (2023)

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2023 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 1047 Development and Application of Crash Severity Models for Highway Safety USER GUIDELINES John N. Ivan Shanshan Zhao Kai Wang Julker Hossain University of Connecticut, Storrs Mansfield, CT Naveen Eluru Mohamed Abdel-Aty Tanmoy Bhowmik Dewanashraful Parvez Lauren Hoover University of Central Florida Orlando, FL Subscriber Categories Operations and Trafc Management • Safety and Human Factors Research sponsored by the American Association of State Highway and Transportation Ofcials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way 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 techniques—the 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 (FHWA), United States Department of Transportation, under Agree- ment No. 693JJ31950003. 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 TRB’s 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; TRB’s 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 iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. 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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 https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 1047 Project 17-85 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-69858-0 Library of Congress Control Number 2023936164 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trade- marks of the 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, APTA, FAA, FHWA, FTA, GHSA, or NHTSA 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; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or spec- ifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. 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. 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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 1047 Christopher J. Hedges, Director, Cooperative Research Programs Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program David M. Jared, Senior Program Officer Mazen Alsharif, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Doug English, Senior Editor NCHRP PROJECT 17-85 PANEL Field of Traffic—Area of Safety John C. Milton, Washington State Department of Transportation, Olympia, WA (Chair) Eric J. Fitzsimmons, Kansas State University, Manhattan, KS Mohammad Jalayer, Rowan University, Glassboro, NJ Pooya Najaf, Mitchell International, San Diego, CA Pradeep Tiwari, City of Phoenix, Phoenix, AZ Joyce Yassin, WSP, Detroit, MI Fan Ye, Ohio Northern University, Ada, OH Jerry Roche, FHWA Liaison Kelly K. Hardy, AASHTO Liaison Bernardo B. Kleiner, TRB Liaison

NCHRP Research Report 1047: Development and Application of Crash Severity Models for Highway Safety: User Guidelines presents guidelines on evaluating crash severity estima- tion models for use in different site conditions. The guidelines will be of interest to state departments of transportation (DOTs) seeking more informed model application, broader acceptance of model results, and, ultimately, improved safety decision making. The guide- lines could also be applied to existing crash prediction models and serve to improve pertinent models and model elements in the Highway Safety Manual (HSM) and its associated tools. As the HSM continues to evolve, determining the potential crash severity in different site conditions is an increasingly vital component to determining safety performance. Con- sistency in how states determine potential severity, for example with frequency-based tools and estimates, is a fundamental requirement for the adoption and use of the HSM and its associated tools. This consistency is a function of several factors: (1) results that are in general agreement from a multitude of analytical techniques available to practitioners; (2) availability of data sources that allow for broad state and interstate analysis; and (3) interpretability of results for policy application by national, state, and local agencies. Severity analysis tools currently available in the HSM do not fully meet this definition of consistency for various reasons, primarily due to the various analytical techniques not agreeing in consistency of estimating crash severity probabilities and frequencies. Under NCHRP Project 17-85, “Development and Application of Crash Severity Models for the Highway Safety Manual,” the University of Connecticut was asked to (1) identify gaps and opportunities in current severity prediction/estimation procedures within the HSM, (2) develop and validate new severity models to address the gaps and opportunities, and (3) develop guidelines that include protocols for use and application of severity-based models for possible incorporation into the HSM. Existing HSM models, as well as new alternatives proposed by the researchers, were evaluated, and this led to formal guidelines on when each method should be selected and implemented. Guidelines on how each of the alternative severity models can be integrated into the HSM were also developed. In addition to NCHRP Research Report 1047, three deliverables are not included in the published report but are available on the National Academies Press website (nap.national academies.org) by searching for NCHRP Research Report 1047: Development and Application of Crash Severity Models for Highway Safety. The deliverables are as follows: • A conduct of research report summarizing the entire effort, available as NCHRP Web-Only Document 351: Development and Application of Crash Severity Models for Highway Safety; • An offline interactive tool for predicting crashes by injury severity level; and • A PowerPoint presentation introducing NCHRP Research Report 1047. F O R E W O R D By David M. Jared Staff Officer Transportation Research Board

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 nap.nationalacademies.org) retains the color versions. 1 Chapter 1 Introduction 4 Chapter 2 Data Requirements 4 2.1 General Data Requirements 4 2.2 Data Requirements for Generating the Demographic and Vehicle Composition Variables 9 2.3 Data Requirements for Predicting the Crash Counts by Severity 17 Chapter 3 Introduction to the Tool 17 3.1 Access the Tool 17 3.2 Introduction of the QIE Step 22 3.3 Introduction of the Crash Prediction Step 32 Chapter 4 Summary 33 References 34 Appendix C O N T E N T S