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Â© 2021 National Academy of Sciences. All rights reserved. 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 transportation results in increasingly complex problems of wide interest 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 initiated an objective national highway research program using modern scientific techniquesâ 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 Agreement No. 693JJ31950003. 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 endorsement by TRB and any of its program sponsors 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. DISCLAIMER To facilitate more timely dissemination of research findings, this pre-publication document is taken directly from the submission of the research agency. The material has not been edited by TRB. The opinions and conclusions expressed or implied in this document are those of the researchers who performed the research. They 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, 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. This pre-publication document IS NOT an official publication of the Cooperative Research Programs; the Transportation Research Board; or the National Academies of Sciences, Engineering, and Medicine. Recommended citation: Gross, F., T. Le, K. Kersavage, C. Chestnutt, B. Persaud, and C. Lyon. 2021. Application of Crash Modification Factors for Access Management: Practitioner's Guide. Pre-publication draft of NCHRP Research Report 974, Volume 1. Transportation Research Board, Washington, D.C.
Preface v Preface Access management is the process that provides (or manages) access to land development 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) provides a framework and method (i.e., the Part C Predictive Method) to predict the safety performance of sites, segments, intersections, or corridors based on the geometric design and traffic operations characteristics. 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 management is considered an effective component in the safety and operation of roadways, it provides 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 performance and reliability of the Part C Predictive Method across sites with different combinations 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 Federal Highway Administrationâs Crash Modification Factor 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 3-star or above on a scale of 1 to 5 stars where 5-star represents the highest quality rating. 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 Management, helped to answer the above questions. 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 Factor Clearinghouse, and other research in quantifying the safety impacts of decisions related to access management. Employing more consistent and reliable methods to quantify the safety performance of access-related decisions will support agencies as they develop and implement access management 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 Highway Safety Manual (2nd Edition) 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 Highway Safety Manual (2nd Edition).