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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Suggested Citation:"Front Matter." National Research Council. 2022. Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers. Washington, DC: The National Academies Press. doi: 10.17226/26679.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

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 996 Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers Christine E. Carrigan Malcolm H. Ray Roadsafe, LLC Canton, ME Subscriber Categories Highways • Design • 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, 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 996 Project 22-31 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-68705-8 Library of Congress Control Number 2022938470 © 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, 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 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 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 AUTHOR ACKNOWLEDGMENTS The crash data and inventory data used in this research report were graciously shared by the Tennessee DOT, Pennsylvania DOT, and Ohio DOT. The simulated vehicle trajectories used were conducted under ongoing NCHRP research at the Texas Transportation Institute and shared with this research effort. The authors thank the Tennessee, Pennsylvania, and Ohio DOTs and the Texas Transportation Institute for providing the data used in this research. The authors also thank Archie Ray and Ethan Ray, who made contributions to the completion of this research project. CRP STAFF FOR NCHRP RESEARCH REPORT 996 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Associate Program Manager, Project Delivery, National Cooperative Highway Research Program Sid Mohan, Associate Program Manager, Implementation and Technology Transfer, National Cooperative Highway Research Program Christopher T. McKenney, Senior Program Officer Robert Turner, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 22-31 PANEL Field of Design—Area of Vehicle Barrier Systems Aurora Meza, VRX, Inc., Austin, TX (Chair) Mark Randall Burkhead, Harrisburg, PA Ronald K. Faller, University of Nebraska, Lincoln, Lincoln, NE Joe H. Hall, West Virginia Department of Transportation, Charleston, WV Charles F. McDevitt, McDevitt Consulting, Matthews, NC Jeffrey K. Petterson, Washington State Department of Transportation, Olympia, WA Timothy J. Sheehan, Springfield, IL Victoria Brinkly, FHWA Liaison Kelly K. Hardy, AASHTO Liaison Stephen F. Maher, TRB Liaison

NCHRP Research Report 996: Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers presents comprehensive guidelines for the selection and place- ment of Test Level 2 through Test Level 5 median barriers. These guidelines were developed using cost-benefit and risk analysis approaches and based on traffic volume and mix, road- way and median geometry, median barrier placement, in-service performance, and barrier type (e.g., shape, material, and rigidity). In addition to the guidelines, charts were included with associated site-specific adjustment factors for selecting the appropriate median barrier test level and median barrier type and placement within the median. This report will be of immediate interest to roadway design engineers. Median barriers can be classified into six test levels as defined by the 2009 AASHTO Manual for Assessing Safety Hardware (MASH) and NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. Each test level is defined by impact conditions (speed and angle of approach) and the type of test vehicle the barrier is designed to redirect (ranging in size from a small car to a fully loaded tractor- trailer truck). The longitudinal barrier is the only classification for which all six test levels are defined at this time. Longitudinal median barriers are also grouped into three general categories: flexible, semi-rigid, and rigid. Although rigid barriers and flexible barriers can be designed to satisfy a given test level, they will have different applications. The rigid barrier will produce higher vehicle decelerations and prevent any lateral deflection, while the flexible barrier will produce lower accelerations. Less rigid barriers result in less energy dissipated by the vehicle; hence, accelerations imparted to the occupants inside the vehicle during an impact are lower as compared with vehicle impacts with rigid barriers. On the other hand, flexible barriers have been shown to have larger lateral deflections, thus limiting their use in narrow medians. Currently, the AASHTO Roadside Design Guide (RDG) is the primary national guide- line available to states in preparing their own policies for roadside design. The RDG offers guidance for selecting median barriers and cites a higher percentage of heavy trucks in the traffic flow, adverse geometries, and higher accident rates as conditions that may warrant barriers with a performance level higher than Test Level 3. However, thresholds for these values were not provided. Under NCHRP Project 22-31, “Recommended Guidelines for the Selection and Place- ment of Test Levels 2 through 5 Median Barriers,” Roadsafe, LLC, developed proposed guidelines for selecting and placing Test Levels 2 through 5 median barriers suitable for use by all government transportation agencies at state and local levels. F O R E W O R D By Christopher T. McKenney 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 2 Chapter 2 Definitions 3 Chapter 3 Literature Review 3 3.1 Interest in Developing Median Barrier Guidance 9 3.2 Evolution of Median Barrier Guidance 24 3.3 Crash Testing Specifications for Median Barriers 24 3.4 Median Barrier Placement 27 3.5 Run-off-road Crash Modeling 32 3.6 Summary 33 Chapter 4 Methodology 36 4.1 Probability of Reaching the Lateral Offset of Feature j—PY(Yj) 36 4.2 Probability of Crash Severity (PSEVj) 38 4.3 Probability of Passing Through a Feature (THRj) 41 Chapter 5 Guidelines 41 5.1 Median Barrier Guidelines 44 5.2 Roadside Barrier Guidelines 51 5.3 Cost–Benefit Guidelines 57 Chapter 6 Conclusions 59 References 62 Abbreviations A-1 Appendix A Survey of States B-1 Appendix B Probability of Reaching the Lateral Offset of Feature j—PY(Yj) C-1 Appendix C Probability of Crash Severity (PSEVj) D-1 Appendix D Probability of Passing Through, Over, or Under a Barrier (THRBAR) E-1 Appendix E Probability of Passing Across the Opposing Lanes (THREOL) C O N T E N T S

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The variety of median widths and terrains combined with evolving testing specifications and lack of conclusive data on median crossover crashes have been obstacles to developing median barrier guidance.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 996: Selection and Placement Guidelines for Test Level 2 Through Test Level 5 Median Barriers develops, in a format suitable for consideration and possible adoption by AASHTO, proposed guidelines for the selection and placement of Manual for Assessing Safety Hardware (MASH) Test Levels 2 through 5 (TL2-TL5) median barriers.

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