Vehicle Weight, Fatality Risk and Crash Compatibility of Model Year 1991-99 Passenger Cars and Light Trucks
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U.S. Department http://www.nhtsa.dot.gov of Transportation National Highway Traffic Safety Administration ____________________________________________________________________________________________ DOT HS 809 662 October 2003 NHTSA Technical Report Vehicle Weight, Fatality Risk and Crash Compatibility of Model Year 1991-99 Passenger Cars and Light Trucks _____________________________________________________________________ This document is available to the public from the National Technical Information Service, Springfield, Virginia 22161. The United States Government does not endorse products or manufacturers. Trade or manufacturers’ names appear only because they are considered essential to the object of this report. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No. DOT HS 809 662 4. Title and Subtitle 5. Report Date Vehicle Weight, Fatality Risk and Crash Compatibility October 2003 of Model Year 1991-99 Passenger Cars and Light Trucks 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Charles J. Kahane, Ph.D. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Evaluation Division; Office of Planning, Evaluation and Budget National Highway Traffic Safety Administration 11. Contract or Grant No. Washington, DC 20590 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Department of Transportation NHTSA Technical Report National Highway Traffic Safety Administration 14. Sponsoring Agency Code Washington, DC 20590 15. Supplementary Notes 16. Abstract Logistic regressions calibrate crash fatality rates per billion miles for model year 1991-99 passenger cars, pickup trucks, SUVs and vans during calendar years 1995-2000 – by vehicle weight, vehicle type, driver age and gender, urban/rural, and other vehicle, driver and environmental factors – a cross-sectional analysis of the fatality rates of existing vehicles. These analyses suggest that, after controlling for driver age/gender, urban/rural, annual mileage, and other factors: • The association between vehicle weight and overall crash fatality rates in the heavier MY 1991-99 LTVs (light trucks and vans) was not significant. • In three other groups of MY 1991-99 vehicles – the lighter LTVs, the heavier cars, and especially the lighter cars – fatality rates increased as weights decreased. • MY 1996-99 pickup trucks and SUVs had, on the average, higher fatality rates than MY 1996-99 passenger cars or minivans of comparable weight. Logistic regression analyses of fatalities per billion miles in two-vehicle collisions show that MY 1991-99 LTVs were more aggressive than MY 1991-99 cars when they struck other vehicles. The analyses show correlations between occupants’ fatality risk in the struck car and the frontal height-of-force and rigidity of the striking LTV. 17. Key Words 18. Distribution Statement mass; safety; car weight; car size; logistic Document is available to the public through the regression; weight reduction; FARS; statistical National Technical Information Service, Springfield, Virginia 22161 analysis; evaluation; aggressiveness 19. Security Classif. (Of this report) 20. Security Classif. (Of this page) 21. No. of Pages 22. Price Unclassified Unclassified 325 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized TABLE OF CONTENTS Acknowledgements....................................................................................................................... v Executive summary.....................................................................................................................vii Effects of 100-pound weight reductions on fatality rates ..................................................vii Fatal-crash and fatality rates by vehicle type, model years 1996-99................................xiii Car-light truck compatibility...........................................................................................xviii Limitations of the analyses ...............................................................................................xxi 1. A new study of vehicle weight and fatality risk and car-light truck compatibility.............. 1 1.1 The need for a new NHTSA study.............................................................................. 1 1.2 Why heavier vehicles have usually had lower fatality rates....................................... 2 1.3 NHTSA's earlier reports on vehicle weight and fatality risk...................................... 6 1.4 NHTSA’s car-light truck compatibility research...................................................... 11 1.5 Scope and limitations of this study ........................................................................... 12 2. Database to study fatalities per million years or billion miles........................................... 15 2.0 Summary................................................................................................................... 15 2.1 Vehicle classification and curb weight ..................................................................... 15 2.2 Fatal crash involvements: FARS data reduction....................................................... 19 2.3 Vehicle registration years: Polk data reduction ........................................................ 26 2.4 Annual mileage and vehicle occupancy: NASS data reduction................................ 26 2.5 Induced-exposure crashes: State data reduction ....................................................... 31 2.6 Assembling the analysis data files ............................................................................ 36 3. Vehicle weight and fatality risk in passenger cars............................................................. 41 3.0 Summary................................................................................................................... 41 3.1 The calibration data set: 4-door cars, excluding police cars..................................... 41 3.2 Visible trends in the data........................................................................................... 43 3.3 Screening the control variables; defining the age/gender variables.......................... 63 3.4 Regression analyses of fatality risk by car weight.................................................... 75 3.5 Summary and discussion of basic regressions.......................................................... 89 3.6 “Driver quality” issues and pedestrian fatality rates................................................. 94 3.7 Best estimates of the effect of a 100-pound weight reduction.................................. 99 3.8 Effect of weight reductions on the number of fatalities.......................................... 104 iii 4. Vehicle weight and fatality risk in light trucks................................................................ 111 4.0 Summary................................................................................................................. 111 4.1 Visible trends in the data......................................................................................... 111 4.2 Screening the control variables............................................................................... 125 4.3 Regression analyses of fatality risk by light truck weight ...................................... 128 4.4 Sensitivity tests and discussion............................................................................... 145 4.5 Best estimates of the effect of a 100-pound weight reduction................................ 153 4.6 Effect of weight reductions on the number of fatalities.......................................... 158 4.7 The “crossover weight”: crash fatality rates increase for heavier LTVs ................ 163 4.8 Comparison with NHTSA’s 1997 report ................................................................ 167 5. Fatality rates per billion miles in 4-door cars vs. SUVs, pickup trucks and minivans .... 175 5.0 Summary................................................................................................................. 175 5.1 The calibration data set: MY 1996-99 personal-transportation vehicles................ 175 5.2 Unadjusted fatality rates ......................................................................................... 179 5.3 Regressions of fatality risk by vehicle type/size group, by crash mode ................. 182 5.4 Regressions of overall fatality risk by vehicle type/size group .............................. 194 5.5 Fatality rate differences between vehicle types: point estimates............................ 205 5.6 Sources of uncertainty, interval estimates .............................................................. 208 5.7 Effect of a different mix of vehicle types on the number of fatalities .................... 220 6. Car-light truck compatibility: analyses of crash data ...................................................... 225 6.0 Summary................................................................................................................. 225 6.1 MY 1991-99 LTV aggressiveness in head-on collisions........................................ 225 6.2 Frontal rigidity and height-of-force in head-on collisions...................................... 237 6.3 Exposure database to study fatality rates in 2-vehicle crashes ............................... 245 6.4 MY 1991-99 LTV aggressiveness in 2-vehicle collisions...................................... 249 6.5 Frontal rigidity and height-of-force in 2-vehicle