Fatality Reduction by Seat Belts in the Center Rear Seat and Comparison of Occupants’ Relative Fatality Risk at Various Seating Positions
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DOT HS 812 369 February 2017 Fatality Reduction by Seat Belts in The Center Rear Seat and Comparison of Occupants’ Relative Fatality Risk at Various Seating Positions Disclaimer This publication is distributed by the U.S. Department of Transportation, National Highway Traffic Safety Administration, in the interest of information exchange. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Department of Transportation or the National Highway Traffic Safety Administration. The United States Government assumes no liability for its content or use thereof. If trade or manufacturers’ names or products are mentioned, it is because they are considered essential to the object of the publication and should not be construed as an endorsement. The United States Government does not endorse products or manufacturers. Suggested APA Format Reference: Kahane, C. J. (2017, February). Fatality reduction by seat belts in the center rear seat and comparison of occupants’ relative fatality risk at various seating positions (Report No. DOT HS 812 369). Washington, DC: National Highway Traffic Safety Administration. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. DOT HS 812 369 4. Title and Subtitle 5. Report Date Fatality Reduction by Seat Belts in the Center Rear Seat and February 2017 Comparison of Occupants’ Relative Fatality Risk at Various Seating 6. Performing Organization Code Positions 7. Author(s) 8. Performing Organization Report No. Charles J. Kahane, Ph.D. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Bowhead Logistics Solutions, LLC 4900 Seminary Road, Suite 1200 11. Contract or Grant No. Alexandria, Virginia 22311-1858 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered National Highway Traffic Safety Administration NHTSA Technical Report 1200 New Jersey Avenue SE. 14. Sponsoring Agency Code Washington, DC 20590 15. Supplementary Notes 16. Abstract In 2002, Anton’s Law (Public Law 107-318) directed NHTSA to require 3-point belts for each rear seating position – including center rear seats – in new passenger motor vehicles by September 1, 2007. Manufacturers had begun installing 3-point belts at the center rear seats in some makes and models as early as 1994 and completed the transition from lap belts to 3-point belts on time. Double-pair comparison and logistic regression analyses of FARS data for 1990 to 2014 show that 3-point belts are highly effective in the center rear seats: Buckling up reduces passengers’ fatality risk by an estimated 58 percent in passenger cars (95% confidence bounds: 41% to 69%) and by 75 percent in LTVs (confidence bounds: 63% to 84%). In cars of the 1960s and 70s, when few people buckled up, the rear seats were substantially safer than the front seats for unrestrained occupants, and the center rear seat even safer than the outboard rear seats. These differences between seats have substantially diminished over the past 30 years. Statistical analyses of FARS do not show statistically significant mitigation of fatality risk for outboard rear or center rear seats of passenger cars relative to the driver’s or right front seats, for belted occupants of the same age and gender. Corresponding analyses of LTVs show reduced fatality risk for the right front and right rear seats relative to the driver’s seat; however, they do not show significant advantages for the outboard rear or center rear seats relative to the right front seats. 17. Key Words 18. Distribution Statement FARS, occupant protection, fatality reduction, outcome Document is available to the public from the National Technical Information Service www.ntis.gov. evaluation, effectiveness, crashworthiness, seat belt 19. Security Classif. (Of this report) 20. Security Classif. (Of this page) 21. No. of Pages 22. Price Unclassified Unclassified 77 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized i TABLE OF CONTENTS List of Abbreviations ................................................................................................................... iii Executive Summary .......................................................................................................................v 1. Fatality reduction by seat belts in the center and outboard rear seats ..................................1 1.1 Anton’s Law and the transition to 3-point belts in center rear seats ...........................1 1.2 Analysis method and database .....................................................................................5 1.3 Basic double-pair comparison for center rear seats .....................................................7 1.4 Significance testing and adjustment for age and gender with LOGISTIC ................11 1.5 Are 3-point belts more effective than lap belts? ........................................................18 1.6 Updated effectiveness estimates for 3-point belts in the outboard rear seats ............20 1.7 Summary ....................................................................................................................25 2. Comparison of occupants’ relative fatality risk at the various seating positions in a vehicle ................................................................................................................................26 2.1 Relative risk – 30 years ago – and more recently ......................................................26 2.2 Analysis goal and database ........................................................................................29 2.3 Basic fatality risk ratios .............................................................................................31 2.4 Adjustment for age and gender with logistic regression ...........................................36 2.5 Results .......................................................................................................................43 2.6 A closer look at the right versus the left seats ...........................................................48 2.7 Trends of the ObdR:driver risk ratio in the latest vehicles ........................................54 2.8 ObdR:RF risk ratios by passenger age group ............................................................56 2.9 Summary ....................................................................................................................59 Appendix: Initial model year for 3-point belts in the center rear seat, MY 1994-2007 ..............61 ii LIST OF ABBREVIATIONS AIS Abbreviated Injury Scale CAC certified-advanced compliant frontal air bag CDS Crashworthiness Data System of NASS CR3PT center rear 3-point belt CFR Code of Federal Regulations CR center rear [seating position] CUV crossover utility vehicle CY calendar year df degrees of freedom FARS Fatality Analysis Reporting System, a census of fatal crashes in the United States since 1975 FMVSS Federal Motor Vehicle Safety Standard GES General Estimates System of NASS GVWR gross vehicle weight rating (specified by the manufacturer, equals the vehicle’s curb weight plus maximum recommended loading) IIHS Insurance Institute for Highway Safety LTV light trucks and vans, includes pickup trucks, SUVs, CUVs, minivans, and full-size vans MY model year NASS National Automotive Sampling System, a probability sample of police- reported crashes in the United States since 1979, investigated in detail NCAP New Car Assessment Program: safety ratings of new vehicles issued by NHTSA since 1979 NOPUS National Occupant Protection Use Survey NTSB National Transportation Safety Board ObdR outboard rear [seating positions] RF right front [seating position] SAS statistical and database management software produced by SAS Institute, Inc. UEF universal exaggeration factor for belt effectiveness estimates after seat belt laws VIN Vehicle Identification Number iii EXECUTIVE SUMMARY Three-point seat belts are a safety technology whose high fatality-reducing effectiveness has repeatedly been demonstrated by statistical analyses of crash data for outboard front- and rear- seat occupants. Before 2005, the 3-point belts were only required at all outboard seats of passenger cars and LTVs (light trucks and vans, including SUVs) in the United States, while lap belts, an ostensibly less effective device, were allowed for center rear seats. Anton’s Law, Public Law 107-318 (December 4, 2002) directed NHTSA to require 3-point belts for each rear seating position – i.e., including center rear seats – in passenger motor vehicles with a GVWR of 10,000 pounds or less. NHTSA amended FMVSS No. 208, “Occupant crash protection,” to require the phase-in of 3-point belts in center rear seats in nearly all new passenger vehicles to start on September 1, 2005, and to be completed by September 1, 2007. In fact, manufacturers had already developed and begun installing 3-point belts at center rear seats of many vehicles well in advance of the new requirement. NHTSA’s Fatality Analysis Reporting System for 1990 through 2014 now has enough crash data to estimate the fatality-reducing effectiveness of 3-point belts for center rear seat passengers.1 This report presents double-pair comparison analyses and logistic regression analyses estimating belt effectiveness, based on 1,512 FARS cases of center rear seat passengers riding in vehicles equipped with a 3-point belt at that seating position. The report also presents effectiveness analyses of the lap belt alone for center rear seat passengers