SPECIAL REPORT 265

The National Highway Traffic Safety Administration’s Rating System for Rollover Resistance

An Assessment

TRANSPORTATION RESEARCH BOARD

THE NATIONAL ACADEMIES



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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 SPECIAL REPORT 265 The National Highway Traffic Safety Administration’s Rating System for Rollover Resistance An Assessment TRANSPORTATION RESEARCH BOARD THE NATIONAL ACADEMIES

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 Transportation Research Board Special Report 265 Subscriber Category IVB safety and human performance Transportation Research Board publications are available by ordering individual publications directly from the TRB Business Office, through the Internet at national academies.org/trb, or by annual subscription through organizational or individual affiliation with TRB. Affiliates and library subscribers are eligible for substantial discounts. For further information, contact the Transportation Research Board Business Office, National Research Council, 2101 Constitution Avenue, NW, Washington, DC 20418 (telephone 202-334-3214; fax 202-334-2519; or e-mail TRBsales@nas.edu). Copyright 2002 by the National Academy of Sciences. All rights reserved. Printed in the United States of America. NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to the procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. This report was sponsored by the National Highway Traffic Safety Administration. Library of Congress Cataloging-in-Publication Data National Research Council (U.S.). Committee for the Study of a Motor Vehicle Rollover Rating System. The National Highway Traffic Safety Administration’s rating system for rollover resistance : an assessment / Committee for the Study of a Motor Vehicle Rollover Rating System. p. cm. — (Special report ; 265) “Transportation Research Board, National Research Council.” Includes bibliographical references. ISBN 0-309-07249-2 1. Motor vehicles—United States—Evaluation. 2. Motor vehicles—Stability. 3. United States. National Highway Traffic Safety Administration—Research. 4. Motor vehicles—Rollover protective structures. I. Title. II. Special report (National Research Council (U.S.). Transportation Research Board) ; 265. TL245.8 .N38 2002 629.2′31—dc21 2002067171

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council. The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board’s mission is to promote innovation and progress in transportation by stimulating and conducting research, facilitating the dissemination of information, and encouraging the implementation of research results. The Board’s varied activities annually engage more than 4,000 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.

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 Committee for the Study of a Motor Vehicle Rollover Rating System Committee David N. Wormley, The Pennsylvania State University, Chair Karin M. Bauer, Midwest Research Institute, Kansas City, Missouri James E. Bernard, Iowa State University, Ames Ann Bostrom, Georgia Institute of Technology, Atlanta Susan A. Ferguson, Insurance Institute for Highway Safety, Arlington, Virginia B. John Garrick, NAE, Independent Consultant, Laguna Beach, California Paul A. Green, University of Michigan Transportation Research Institute, Ann Arbor David L. Harkey, University of North Carolina Highway Safety Research Center, Chapel Hill J. Karl Hedrick, University of California at Berkeley David C. Holloway, University of Maryland, College Park L. Daniel Metz, Metz Engineering and Racing, Champaign, Illinois N. Eugene Savin, University of Iowa, Iowa City Kimberly M. Thompson, Harvard School of Public Health, Boston, Massachusetts Transportation Research Board Staff Jill Wilson, Study Director

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 Preface This study was conducted in response to a congressional mandate, contained in the Department of Transportation and Related Agencies Appropriations Act, 2001 (Public Law 106–346), which required the U.S. Department of Transportation to fund a study by the National Academy of Sciences on whether the static stability factor is a scientifically valid measurement that presents practical, useful information to the public, including a comparison of the static stability factor test versus a test with rollover metrics based on dynamic driving conditions that may induce rollover events.1 In response to a request from the National Highway Traffic Safety Administration (NHTSA), the Transportation Research Board (TRB) of the National Research Council (NRC) formed a committee of 13 members under the leadership of David Wormley, Dean of the College of Engineering at the Pennsylvania State University. Panel members have expertise in the following areas: mechanical engineering and vehicle dynamics; vehicle safety and testing; vehicle control systems; roadway and roadside design; statistics, econometrics, and data analysis; risk assessment and communication; public policy; consumer information; and human factors and driver behavior. The committee met four times between April and October 2001. The first two meetings were devoted primarily to information gathering; details of invited presentations and participation in the open discussions are given in Appendix B. Additional information-gathering activities undertaken by committee members included visits to the Consumers Union Vehicle Test Facility in East Haddam, Connecticut, and site visits to Ford, General Motors, and DaimlerChrysler facilities in the Detroit area (see Appendix B). The third and fourth committee meetings were devoted to deliberative discussions and preparation of the committee’s final report. An interim report, issued in July 2001, presented the committee’s preliminary findings and identified outstanding issues to be addressed during the remainder of the study. To expedite the study process, the committee divided into three groups, each of which assumed primary responsibility for information gathering and 1 The full text of the congressional mandate is provided in Appendix A.

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 analyses in one of the major subject areas of the study—vehicle dynamics, statistics and data analysis, and consumer information. Contributions from each of the working groups were used by the committee as a whole to develop this consensus report. This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the NRC’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the authors and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The content of the review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: James W. Dally, University of Maryland, College Park; Thomas D. Gillespie, University of Michigan Transportation Research Institute, Ann Arbor; Robert L. Mason, Southwest Research Institute, San Antonio, Texas; M. Granger Morgan, Carnegie Mellon University, Pittsburgh, Pennsylvania; Paul A. Ruud, University of California, Berkeley; John M. Starkey, Purdue University, West Lafayette, Indiana; and Michael S. Wogalter, North Carolina State University, Raleigh. Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the committee’s conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Morris Tanenbaum, AT&T Corporation (retired), Short Hills, New Jersey, appointed by the Report Review Committee, and Lester A. Hoel, University of Virginia, Charlottesville; they were responsible for making certain that an independent examination of the report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution. The committee wishes to thank the many individuals who contributed to this study through presentations at meetings, correspondence, and telephone calls. The assistance of Pat Boyd of NHTSA and Scott Schmidt of the Alliance of Automobile Manufacturers in arranging briefings and responding to committee requests for information is gratefully acknowledged. The committee also wishes to thank the representatives of Consumers Union, Ford Motor Company, General Motors, and DaimlerChrysler for hosting the visits to their facilities. Special appreciation is expressed to Sue Partyka at NHTSA for her timely responses to the committee’s requests for further statistical analyses of crash data, and to Simon Lee of the Department of Economics, University of Iowa, for statistical analyses in support of the study.

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 Jill Wilson managed the study under the supervision of Stephen R. Godwin, Director of Studies and Information Services. Suzanne Schneider, Associate Executive Director of TRB, managed the report review process. The report was edited by Rona Briere and prepared for publication under the supervision of Nancy A. Ackerman, Director of Reports and Editorial Services. Frances E. Holland assisted in logistics and communications with the committee, and Alisa Decatur provided assistance with word processing and production of the final manuscript.

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265 Contents     Executive Summary   1 1   Introduction   9      National Highway Traffic Safety Administration’s Initiatives on Rollover   10      NHTSA’s Star Ratings for Rollover Resistance   13      Consumer Information on Motor Vehicle Safety   15      Study Approach and Organization of Report   17 2   Vehicle Dynamics   21      Background   22      Static Measures of Rollover Propensity   24      Need for Dynamic Testing   31      Dynamic Testing: Features and Challenges   34      Findings and Recommendation   36 3   Statistics and Data Analysis   38      Rollover Crash Data   39      Background and Notation   43      Statistical Models   47      Scenario Effects   54      Nonparametric Model   59      Rollover Curve and Star Rating System   59      Findings and Recommendations   62 4   Consumer Information   64      Practicality and Utility of NHTSA’s Rollover Resistance Ratings   64      Availability and Use of NHTSA’s Rollover Resistance Ratings   74      Future Approaches   76      Findings and Recommendations   80

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265            5   Summary, Major Findings, and Recommendations for a Future Approach   84      Context   84      Static Stability Factor   85      NHTSA’s Star Ratings for Rollover Resistance   89      Recommendations for a Future Approach   93     Appendixes     A   Congressional Request for Study   96 B   Committee Meetings and Other Activities   97 C   Supplementary Statistical Results   100 D   Rollover Information from NHTSA’s Website   104     Study Committee Biographical Information   131

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An Assessment of the National Highway Traffic Safety Administration's Rating System for Rollover Resistance: Special Report 265           TRANSPORTATION RESEARCH BOARD 2002 EXECUTIVE COMMITTEE* Chairman: E. Dean Carlson, Secretary, Kansas Department of Transportation, Topeka Vice Chairman: Genevieve Giuliano, Professor, School of Policy, Planning, and Development, University of Southern California, Los Angeles Executive Director: Robert E. Skinner, Jr., Transportation Research Board William D. Ankner, Director, Rhode Island Department of Transportation, Providence Thomas F. Barry, Jr., Secretary of Transportation, Florida Department of Transportation, Tallahassee Michael W. Behrens, Executive Director, Texas Department of Transportation, Austin Jack E. Buffington, Associate Director and Research Professor, Mack-Blackwell National Rural Transportation Study Center, University of Arkansas, Fayetteville Sarah C. Campbell, President, TransManagement, Inc., Washington, D.C. Joanne F. Casey, President, Intermodal Association of North America, Greenbelt, Maryland James C. Codell III, Secretary, Kentucky Transportation Cabinet, Frankfort John L. Craig, Director, Nebraska Department of Roads, Lincoln Robert A. Frosch, Senior Research Fellow, Belfer Center for Science and International Affairs, John F. Kennedy School of Government, Harvard University, Cambridge, Massachusetts Susan Hanson, Landry University Professor of Geography, Graduate School of Geography, Clark University, Worcester, Massachusetts Lester A. Hoel, L.A. Lacy Distinguished Professor, Department of Civil Engineering, University of Virginia, Charlottesville (Past Chairman, 1986) Ronald F. Kirby, Director of Transportation Planning, Metropolitan Washington Council of Governments, Washington, D.C. H. Thomas Kornegay, Executive Director, Port of Houston Authority, Houston, Texas Bradley L. Mallory, Secretary of Transportation, Pennsylvania Department of Transportation, Harrisburg Michael D. Meyer, Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta Jeff P. Morales, Director of Transportation, California Department of Transportation, Sacramento David Plavin, President, Airports Council International, Washington, D.C. John Rebensdorf, Vice President, Network and Service Planning, Union Pacific Railroad Company, Omaha, Nebraska Catherine L. Ross, Executive Director, Georgia Regional Transportation Agency, Atlanta John M. Samuels, Senior Vice President, Operations Planning and Support, Norfolk Southern Corporation, Norfolk, Virginia (Past Chairman, 2001) Paul P. Skoutelas, CEO, Port Authority of Allegheny County, Pittsburgh, Pennsylvania Michael S. Townes, Executive Director, Transportation District Commission of Hampton Roads, Hampton, Virginia Martin Wachs, Director, Institute of Transportation Studies, University of California, Berkeley (Past Chairman, 2000) Michael W. Wickham, Chairman and CEO, Roadway Express, Inc., Akron, Ohio M. Gordon Wolman, Professor of Geography and Environmental Engineering, The Johns Hopkins University, Baltimore, Maryland Mike Acott, President, National Asphalt Pavement Association, Lanham, Maryland (ex officio) Joseph M. Clapp, Administrator, Federal Motor Carrier Safety Administration, U.S. Department of Transportation (ex officio) Susan M. Coughlin, Director and Chief Operating Officer, The American Trucking Associations Foundation, Inc., Alexandria, Virginia (ex officio) Jennifer L. Dorn, Administrator, Federal Transit Administration, U.S. Department of Transportation (ex officio) Ellen G. Engleman, Administrator, Research and Special Programs Administration, U.S. Department of Transportation (ex officio) Robert B. Flowers (Lt. Gen., U.S. Army), Chief of Engineers and Commander, U.S. Army Corps of Engineers, Washington, D.C. (ex officio) Harold K. Forsen, Foreign Secretary, National Academy of Engineering, Washington, D.C. (ex officio) Jane F. Garvey, Administrator, Federal Aviation Administration, U.S. Department of Transportation (ex officio) Thomas J. Gross, Deputy Assistant Secretary, Office of Transportation Technologies, U.S. Department of Energy (ex officio) Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, D.C. (ex officio) John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, D.C. (ex officio) Michael P. Jackson, Deputy Secretary, U.S. Department of Transportation (ex officio) James M. Loy (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington, D.C. (ex officio) William W. Millar, President, American Public Transportation Association, Washington, D.C. (ex officio) (Past Chairman, 1992) Margo T. Oge, Director, Office of Transportation and Air Quality, U.S. Environmental Protection Agency, Washington, D.C. (ex officio) Mary E. Peters, Administrator, Federal Highway Administration, U.S. Department of Transportation (ex officio) Valentin J. Riva, President and CEO, American Concrete Pavement Association, Skokie, Illinois (ex officio) Jeffrey W. Runge, Administrator, National Highway Traffic Safety Administration, U.S. Department of Transportation (ex officio) Jon Allan Rutter, Administrator, Federal Railroad Administration, U.S. Department of Transportation (ex officio) William G. Schubert, Administrator, Maritime Administration, U.S. Department of Transportation (ex officio) Ashish K. Sen, Director, Bureau of Transportation Statistics, U.S. Department of Transportation (ex officio) Robert A. Venezia, Earth Sciences Applications Specialist, National Aeronautics and Space Administration, Washington, D.C. (ex officio) * Membership as of April 2002