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2024 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 1100 MASH TL-3 De ection Reduction for 31-Inch Guardrail A GUIDE James Kovar Roger Bligh Sofokli Cakalli William Schroeder Daniel Curran Alondra Loza Maysam Kiani Sana Moran Heath Buttery Sumedh Khair Texas A&M Transportation Institute The Texas A&M University System College Station, TX Subscriber Categories Design ⢠Operations and Traf c Management ⢠Safety and Human Factors Research sponsored by the American Association of State Highway and Transportation Of cials 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 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 1100 Project 22-38 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-70953-8 Library of Congress Control Number 2024932852 © 2024 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. Cover photo credit: Courtesy of Texas A&M Transportation Institute 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. 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 program divisions of the National Academies of Sciences, Engineering, and Medicine. e mission of the Transportation Research Board is to mobilize expertise, experience, and knowledge to anticipate and solve complex transportation-related challenges. e Boardâs varied activities annually engage about 8,500 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 AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 22-38 by the Texas A&M Trans- portation Institute, a member of The Texas A&M University System. The authors acknowledge and appre- ciate the computational support provided by the Texas A&M High Performance Research Computing (HPRC) (http://hprc.tamu.edu/). CRP STAFF FOR NCHRP RESEARCH REPORT 1100 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 NCHRP PROJECT 22-38 PANEL Field of DesignâArea of Vehicle Barrier Systems Kenneth Mora, Texas Department of Transportation, Austin, TX (Chair) Robert W. Bielenberg, University of NebraskaâLincoln, Lincoln, NE Tracy Borchardt, AECOM, Spotsylvania, VA Lyman L. Hale, New York State Department of Transportation, Gansevoort, NY Randy Hiatt, California Department of Transportation, Sacramento, CA Eric C. Lohrey, ECL Engineering, PLLC, Warrensburg, NY Charles F. McDevitt, McDevitt Consulting, Matthews, NC Alex Hamel Price, Virginia Department of Transportation, Salem, VA Tom Rhoads, Iowa Department of Transportation, Decorah, IA Aimee H. Zhang, FHWA Liaison Kelly K. Hardy, AASHTO Liaison
NCHRP Research Report 1100: MASH TL-3 Deflection Reduction for 31-Inch Guardrail: A Guide presents the use of stiffening mechanisms to reduce the deflection for 31-inch guardrail installations while maintaining system integrity and safety performance. The Guide reflects test conditions specified in the Manual for Assessing Safety Hardware (MASH) and is based on computer simulations and full-scale crash testing. The Guide should be of interest to state departments of transportation and other agencies considering the imple- mentation of the stiffening mechanisms evaluated in this research. Roadside obstacles are often too close to the roadway to permit the installation of common guardrail designs. When this occurs, the protective capability of a guardrail system is desired but without large deflections from vehicle impacts. To achieve this, guardrail systems are often modified with a combination of tighter post spacing, nesting of rails, and other guard- rail stiffening mechanisms to reduce deflections. Considerable research has been completed on these topics, and the AASHTO Roadside Design Guide (RDG) provides guidelines on this topic. However, much of the available research is based on test conditions specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of High- way Features. Hence, a guide was needed on the use of stiffening mechanisms to locally reduce the deflection for 31-inch guardrail installations while maintaining system integrity and safety performance. This guide would reflect test conditions specified in MASH rather than NCHRP Report 350. Under NCHRP Project 22-38, âDevelopment of MASH TL-3 Deflection Reduction Guid- ance for 31-Inch Guardrail,â the Texas A&M University Transportation Institute was asked to develop a guide for the practical and cost-effective use of stiffening mechanisms to locally reduce the deflection for MASH TL-3-compliant 31-inch Midwest Guardrail System (MGS) installations or equivalent guardrail, including any needed transition from the standard system to the stiffened system while maintaining integrity and safety performance. The research team developed recommendations for selecting stiffening mechanisms to further investigate with computer simulation. This simulation effort estimated dynamic deflections and crash- worthiness for 26 stiffening mechanisms with a variety of evaluation conditions. From this effort, the research team provided recommendations for selecting stiffening mechanisms to further evaluate through full-scale crash testing, which involved four MASH crash tests: 3-10, 3-11, 3-20, and 3-21. All four crash tests showed the stiffening mechanism and appro- priate transition successfully met MASH evaluation criteria. The research team also provided guidelines for implementing this stiffening mechanism on the roadside. Finally, an updated table summarizing guardrail deflections from recent crash tests and computer simulations F O R E W O R D By David M. Jared Staff Officer Transportation Research Board
from this project was developed. This table is presented for consideration as a possible addition to future editions of the RDG. Two deliverables associated with the Guide are not included herein, but are available on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Research Report 1100: MASH TL-3 Deflection Reduction for 31-Inch Guardrail: A Guide. The deliverables are as follows: ⢠Slide presentation summarizing the project and including videos of crash testing. ⢠Slide presentation without the crash testing videos.
1 Summary 3 Chapter 1 Introduction 4 Chapter 2 Literature Review and State Survey 4 Overview 4 Midwest Guardrail System 4 Guardrail Deflections 5 Development and Implementation of the Simplified MGS Stiffness Transition 6 Post Spacing 11 Fill Condition 12 Post Length and Embedment Depth 15 Nested and 10-Gauge Rail 17 Blockout Depth 19 Backup Rails 19 AASHTO RDG Guardrail Stiffening Guidelines 19 State Survey 51 Literature Review and State Survey Conclusions 53 Chapter 3 Computer Simulation and Modeling 53 Baseline Model and Validation 60 Stiffening Mechanism Investigation 69 Rub Rail 90 Backup Rail 139 Combination Rails 171 Summary and Conclusions 177 Chapter 4 System Details 177 Test Article and Installation Details for Stiffened MGS 177 Test Article and Installation Details for Stiffened MGS Transition 177 Design Modifications During Tests 183 Material Specifications 183 Soil Conditions 185 Chapter 5 Test Requirements and Evaluation Criteria 185 Crash Test Performed/Matrix 185 Evaluation Criteria 187 Chapter 6 Test Conditions 187 Test Facility 187 Vehicle Tow and Guidance System 187 Data Acquisition Systems C O N T E N T S
190 Chapter 7 MASH Test 3-10 (Crash Test No. 612941-02-2) 190 Test Designation and Actual Impact Conditions 190 Weather Conditions 190 Test Vehicle 193 Test Description 193 Damage to Test Installation 194 Damage to Test Vehicle 194 Occupant Risk Factors 194 Test Summary 199 Chapter 8 MASH Test 3-11 (Crash Test No. 612941-02-1) 199 Test Designation and Actual Impact Conditions 199 Weather Conditions 199 Test Vehicle 202 Test Description 202 Damage to Test Installation 203 Damage to Test Vehicle 203 Occupant Risk Factors 203 Test Summary 208 Chapter 9 MASH Test 3-21 (Crash Test No. 612941-02-3) 208 Test Designation and Actual Impact Conditions 208 Weather Conditions 208 Test Vehicle 211 Test Description 211 Damage to Test Installation 212 Damage to Test Vehicle 212 Occupant Risk Factors 212 Test Summary 217 Chapter 10 MASH Test 3-20 (Crash Test 612941-02-4) 217 Test Designation and Actual Impact Conditions 217 Weather Conditions 217 Test Vehicle 220 Test Description 220 Damage to Test Installation 221 Damage to Test Vehicle 221 Occupant Risk Factors 221 Test Summary 226 Chapter 11 Conclusions, Findings, and Suggested Research 226 Assessment of Test Results 226 Summary of Research Effort 226 Findings and Implementation 234 References 237 Acronyms
238 Appendix A Details for the Stiffened MGS and Transition 269 Appendix B Supporting Certification Documents 273 Appendix C MASH Test 3-10 (Crash Test No. 612941-02-2) 283 Appendix D MASH Test 3-11 (Crash Test No. 612941-02-1) 293 Appendix E MASH Test 3-21 (Crash Test No. 612941-02-3) 303 Appendix F MASH Test 3-20 (Crash Test No. 612941-02-4) 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.