Application of Crash Modification Factors for Access Management, Volume 1: Practitioner's Guide (2021)

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2021 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 974 Application of Crash Modification Factors for Access Management Volume 1: Practitioner’s Guide Frank Gross Thanh Le Kristin Kersavage Catherine Chestnutt VHB Raleigh, NC Bhagwant Persaud Craig Lyon Persaud and Lyon, Inc. Toronto, ON Ottawa, ON Jerome Gluck AECOM Cedarhurst, NY Subscriber Categories Highways • Design • Transportation, General 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, 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. 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 https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 974, VOLUME 1 Project 17-74 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-67429-4 Library of Congress Control Number 2021945818 © 2021 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, FTA, GHSA, NHTSA, 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; the FHWA; 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 manufacturers’ names or logos 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. John L. Anderson 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.nationalacademies.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 provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. The Board’s varied activities annually engage about 8,000 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 974, VOLUME 1 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Associate Program Manager, National Cooperative Highway Research Program Camille Crichton-Sumners, Senior Program Officer Tyler Smith, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Ellen M. Chafee, Senior Editor NCHRP PROJECT 17-74 PANEL Field of Traffic—Area of Safety Bonnie S. Polin, Massachusetts Department of Transportation, Boston, MA (Chair) Osama A. Abaza, University of Alaska Anchorage, Anchorage, AK Gina Bonyani, Florida Department of Transportation, Tallahassee, FL Kelly E. Farlow, Professional Engineering Consultants, Lawrence, KS Reza Ray Jafari, Road Safety and Transportation Solutions, Inc., Raleigh, NC Daniel F. Mlacnik, Illinois Department of Transportation, Springfield, IL David Sheen, Hennepin County Public Works, Medina, MN Zahidul Q. Siddique, infraTECH Engineers & Innovators, LLC, Houston, TX Roya Amjadi, FHWA Liaison Bernardo B. Kleiner, TRB Liaison

NCHRP Research Report 974: Application of Crash Modification Factors for Access Manage- ment, Volume 1: Practitioner’s Guide and Volume 2: Research Overview, should be of interest to traffic management, access management, and other transportation safety practitioners inter- ested in corridor-level access management. Volume 1: Practitioner’s Guide offers methods to quantify the safety impacts of access management strategies and help make more informed access-related decisions on urban and suburban arterials. Volume 2: Research Overview pro- vides an analysis of crash modification factors and safety performance functions for access management features. Access management is the practice of providing safe access to land development while maintaining the flow of traffic on the adjacent roadway. Research has shown positive safety and operational benefits associated with good access management practices; however, addi- tional methods and tools are needed to help to quantify the safety performance of access management alternatives. The first edition of the Highway Safety Manual notes that access management is an effective element in the safety and operation of roadways but does not adequately address the quantitative safety benefits of related strategies and corridor-level access management (AASHTO 2010). There is some concern about whether its predictive method adequately captures the differences in access management features and the cumula- tive effects of multiple access management strategies. Beyond the Highway Safety Manual (1st Edition), there are numerous values in the FHWA’s Crash Modification Factors (CMF) Clearinghouse to quantify the expected safety impacts of access management strategies. Under NCHRP Project 17-74, “Application of Crash Modification Factors for Access Management,” VHB was asked to assess the performance of current access management methods in the Highway Safety Manual (1st Edition) and verify the reliability of existing safety performance functions (SPFs) to quantify the safety performance of urban and sub- urban arterials. The team was also tasked with quantifying the safety performance of access management features by developing and refining CMFs and SPFs for site, segment, inter- section, and corridor levels of analysis—advancing the current practice. To complete the project objectives, the research team conducted a literature review, collected traffic and crash data, conducted analyses, and developed updated instructions for estimating the safety effects of access management strategies. NCHRP Research Report 974: Application of Crash Modification Factors for Access Man- agement, Volume 1: Practitioner’s Guide and Volume 2: Research Overview, will aid practi- tioners in their use of access-management-related CMFs from the Highway Safety Manual (1st Edition) and the CMF Clearinghouse. The results of this research will help practi- tioners quantify the safety performance of access-related decisions at the site, segment, intersection, and corridor analysis levels. A PowerPoint presentation can also be accessed on www.trb.org by searching on “NCHRP Research Report 974”. F O R E W O R D By Camille Crichton-Sumners Staff Officer Transportation Research Board

Access management is the process that provides (or manages) access to land develop- ment while preserving the flow of traffic on the surrounding road network in terms of safety, capacity, and speed. While research and empirical evidence have shown positive safety and operational benefits associated with good access management practices, it can be challenging for transportation agencies to implement access management strategies on the basis of safety performance without methods and tools to quantify the safety performance of alternatives. The Highway Safety Manual (1st Edition) (AASHTO 2010), provides a framework and method (i.e., Part C Predictive Method) to predict the safety performance of sites, segments, intersections, or corridors based on the geometric design and traffic operations charac- teristics. This has revolutionized highway engineering practice by providing a method for assessing and quantifying the safety consequences of planning, design, and operational decisions. While the Highway Safety Manual (1st Edition) recognizes that access manage- ment is considered an effective component in the safety and operation of roadways, it pro- vides limited coverage of the quantitative safety benefits of related strategies. Further, it is not well-suited to account for corridor-level access management strategies such as intersection density and median opening spacing. For these reasons, some have questioned the perfor- mance and reliability of the Part C Predictive Method across sites with different combina- tions of access management characteristics. For example, the Part C Predictive Method would produce the same predicted number of crashes for two intersections that are 0.1 miles apart and two identical intersections that are 0.5 miles apart. The question remains as to whether or not the Part C Predictive Method adequately captures the differences in access management features as well as the cumulative effects and potential interactions among multiple access management strategies. Beyond the Highway Safety Manual (1st Edition), there are numerous values in FHWA’s Crash Modification Factors Clearinghouse to quantify the expected safety impacts of access management strategies. The Clearinghouse contains more than 1,000 crash modification factors for access management strategies, but less than 60 percent are rated three stars or higher on a scale of one to five stars where a five-star rating represents the highest quality. Given the range in quality of the underlying research and applicability of results, there is a need to better understand if and how this information can be used to inform decisions. NCHRP Project 17-74, “Application of Crash Modification Factors for Access Manage- ment,” helped to answer the questions introduced in the previous paragraphs. Specifically, the project assessed the performance of current methods in the Highway Safety Manual (1st Edition); developed new crash modification factors; and developed guidance for the use of the Highway Safety Manual (1st Edition), Crash Modification Factors Clearinghouse, and other research in quantifying the safety impacts of decisions related to access management. P R E F A C E

Employing more consistent and reliable methods to quantify the safety performance of access-related decisions will support agencies as they develop and implement access man- agement policies and strategies. This guide focuses on the application of the Highway Safety Manual (1st Edition), considering the results of NCHRP Project 17-74 and other existing research, to quantify the safety performance of access-related decisions at the site, segment, intersection, and corridor level. While the second edition of the Highway Safety Manual is expected to be generally consistent with the first edition with respect to the predictive method, this guide identifies potential changes to the methods that could be incorporated in use of the second edition of the Highway Safety Manual.

1 Summary 4 Chapter 1 Introduction 5 Objective and Scope 6 Target Audience 6 Guide Organization 7 Chapter 2 Definitions for Quantitative Safety Analysis 7 Introduction to Quantitative Safety Analysis 8 Definitions 10 Chapter 3 Safety Effects of Access Management 10 Overview of Strategies 12 Access Spacing 20 Roadway Cross Section 29 Intersection Treatments 38 Property Access 45 Counterintuitive Results (Do Not Use) 50 Chapter 4 Predictive Method for Segment- and Intersection-Level Analysis 53 Select and Apply an Applicable SPF 58 Select and Apply Applicable CMFs 62 Sample Problem 1 69 Sample Problem 2 76 Sample Problem 3 77 Chapter 5 Predictive Method for Corridor-Level Analysis 77 Predictive Method Options 78 Corridor-Level Prediction Models 87 Sample Problems to Illustrate Corridor-Level Prediction Models 108 Chapter 6 Communicating Results 108 Audiences 109 Methods 110 Measures 113 Format 118 Summary 120 Appendix A Resources 123 Appendix B Overview of Quantitative Safety Analysis 138 Appendix C Calibration C O N T E N T S

140 Appendix D Summary Statistics by Land Use and Region 156 Appendix E Summary of Models by Land Use and Crash Type 171 Appendix F Correlation Coefficients by Land Use 178 References 180 Abbreviations 181 Variables 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.