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2022 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 1006 Guide to Understanding Effects of Raising Speed Limits Karen Dixon Kay Fitzpatrick Dominique Lord Chiara Silvestri Dobrovolny Raul Avelar Bahar Dadashova Texas A&M Transportation Institute (TTI) College Station, TX Fred Mannering Nawaf Alnawmasi University of Southern Florida Tampa, FL Jennifer Atkinson Joseph Jones Adil Cheema K.C. Matthews Leidos Reston, VA Subscriber Categories Safety and Human Factors ⢠Operations and Trafc Management 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 universi- ties and others. However, the accelerating growth of highway trans- portation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coor- dinated 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 (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 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 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&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 https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 1006 Project 17-79 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-68737-9 Library of Congress Control Number 2022945873 © 2022 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 speci- fications. 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. Trade or manufacturersâ names or logos appear herein solely because they are considered essential to the object of the report.
e 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. e 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. e 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. e 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. e 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. e Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. e 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. e Boardâs 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. e 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 1006 Christopher J. Hedges, Director, Cooperative Research Programs Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Sid Mohan, Associate Program Manager, Implementation and Technology Transfer, National Cooperative Highway Research Program David M. Jared, Senior Program Officer Traci Caldwell, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Kami Cabral, Editor NCHRP PROJECT 17-79 PANEL Field of TrafficâArea of Safety Steven Buckley, JEO Consulting Group, Topeka, KS (Chair) Kelly L. Becker, North Carolina Department of Transportation, Garner, NC Christina Bennett, South Dakota Department of Transportation, Pierre, SD Joseph V. Gorman, Michigan Department of Transportation, Lansing, MI Beth Ann Larson, Maryland State Highway Administration, Baltimore, MD Chris Lindsey, Texas Department of Transportation, Austin, TX Jonathan Michael Lloyd, Illinois Department of Transportation, Schaumburg, IL Xiaoduan Sun, University of Louisiana, Lafayette, Lafayette, LA Jonathan Upchurch, Ivins, UT Guan Xu, FHWA Liaison Kelly K. Hardy, AASHTO Liaison Bernardo B. Kleiner, TRB Liaison
NCHRP Research Report 1006: Guide to Understanding Effects of Raising Speed Limits provides a better understanding of the expected safety implications of increasing speed limits to 75 mph or higher. The Guide will be of interest to state departments of transportation for integrating the findings into speed management and safety programs. This information will help practitioners determine whether the raised speed limits influence the number and type of crashes along the candidate corridor. Over the past decade, there has been a trend toward higher speed limits, especially on rural interstates and freeways. Eleven states have increased speed limits to 75 mph, with some of them raising the limit as high as 85 mph on freeways and 75 mph on other roads. Several states have increased speed limits up to 65 mph to 70 mph on two-lane rural roads. In some cases, these higher posted speed limits exceed design speeds. The impacts of these recent speed limit increases on safety have not been thoroughly studied. There are concerns about increased crash severity resulting from higher speeds. For example, roadside hard- ware is tested at lower speeds under AASHTOâs Manual for Assessing Safety Hardware (MASH) standards, and it is not well understood how various devices may perform on roadways with higher speed limits. Impact performance of a highway feature cannot be measured by a series of crash tests only; even the most carefully researched device has per- formance limits dictated by physical laws, vehicle stability, and crashworthiness. Under NCHRP Project 17-79, âSafety Effects of Raising Speed Limits to 75 mph and Higher,â Texas A&M Transportation Institute (TTI) was asked to develop a guide to assist highway agencies in estimating the safety impacts of increasing speed limits to 75 mph and higher. The Guide includes information to support where, when, and by how much speed limits may or may not be increased on existing facilities and newly constructed roads. It also identifies mitigation strategies that may be implemented to offset potential impacts. In addition to NCHRP Research Report 1006, the following deliverables are available on the National Academies Press website (www.nap.edu) by searching for NCHRP Research Report 1006: ⢠The research agencyâs report documenting the research methodology development and the research effort, published as NCHRP Web-Only Document 328: Safety Effects of Raising Speed Limits to 75 mph and Higher; and ⢠A presentation introducing NCHRP Research Report 1006. 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 www.nap.edu) retains the color versions. 1 Chapter 1 Introduction 1 Purpose and Scope of This Guide 2 Developing the Guide 3 Implementation Recommendations 4 Chapter 2 Safety and Operational Considerations 4 Assess the Potential Effects on System Safety 10 Consider the Effect on the Entire Roadway Network 16 Chapter 3 Collaboration and Communication 16 Collaborate with the State Legislature 17 Confer with Neighboring States 17 Use a Variety of Media Tools and Strategies 19 Chapter 4 Economic Considerations 19 Identify and Mitigate the Issues and Costs Associated with the Conversion 19 Analyze the Economic Impact 24 Chapter 5 Presentation of Evaluation Findings and Recommendations 25 Acronyms and Abbreviations 26 References C O N T E N T S