U.S. Department of Transportation National Highway Traffic Safety Administration DOT HS 807 067 February 1987 NHTSA Technical Report A Preliminary Evaluation of Seat Back Locks for Two-Door Passenger Cars with Folding Front Seatbacks 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 807 067 4'. Title and Subtitle 5, Report Date A PRELIMINARY EVALUATION OF SEAT BACK LOCKS February 1987 for Two-Door Passenger Cars with 6. Performing Organization Code Folding Front Seatbacks 8. Performing Organization Report No. 7. Author's) Charles J. Kahane, Ph.D. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Office of Standards Evaluation National Highway Traffic Safety Administration 11. Contract or Grant No. Washington, D.C. 20590 13. Type of Report and Period Covered 12. Sponsoring Agency Name and Address Department of Transportation NHTSA Technical Report National Highway Traffic Safety Administration Washington, D.C. 20590 14. Sponsoring Agency Code 15. Supplementary Notes An agency staff review of an existing Federal regulation performed in response to Executive Order 12291. 16. Abstract Federal Motor Vehicle Safety Standard 207 specifies strength requirements for automotive seats and their attachment assemblies, so as to minimize the possibility of their failure by forces acting on them as a result of vehicle impact. The standard includes a requirement that front seats with folding seatbacks be equipped with a locking device, designed to limit the forward motion of the seatback in a collision and to keep the seatback away from front seat occupants. These seat back locks were installed in domestic two-door passenger cars during 1967-68. The objectives of this preliminary evaluation are to determine if seat back locks are effective in reducing deaths or injuries and to measure the actual cost of the locks. The evaluation is based on statistical analyses of Washington, Texas, New York, Fatal Accident Reporting System and Multidisciplinary Accident Investigation data (with special emphasis on back seat occupants, frontal crashes, and crashes involving occupant ejection or vehicle fire), sled test analyses and a cost study of production lock assemblies. It was found that the locks hold seatbacks in place in crashes when the back seat is unoccupied, but locks or other seat components often separate at moderate crash speeds when there are unrestrained back seat occupants. No statistically significant injury or fatality reductions were found for seat back locks in any of the accident data files or in the sled tests. The locks add about $14 (in 1985 dollars) to the lifetime cost of owning and operating a car. 17. Key Words IS. Distribution Statement seat back lock; seating system; Document is available to the public back seat; sled test; ejection; through the National Technical crashworthiness; evaluation; fire; Information Service, biomechanics; accident analysis; Springfield, Virginia 22161 statistical analysis; 19. Security Clossif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 253 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized TABLE OF CONTENTS Acknowl edgments xi i i Executive Summary xv 1. INTRODUCTION AND BACKGROUND 1 1.1 Evaluation of NHTSA regulations and programs 1 1.2 Evaluation of Standard 207 2 1.3 Why evaluate seat back locks? 3 1.4 SBL implementation dates 4 1.5 Costs of SBL 6 1.6 Potential benefits of SBL 8 1.7 Evaluation methods and their limitations 12 1.8 Review of Ball's study of SBL 17 2. STATISTICAL ANALYSES OF SLED TEST DATA 21 2.1 Planning and running the sled tests 21 2.1.1 Sled buck, test setup and crash modes 22 2.1.2 Dummies and injury parameters 24 2.1.3 Sled test matrix 25 2.1.4 Running the sled tests 28 2.2 Discussion of sled test results .32 2.3 Statistical analysis of sled test results 41 2.3.1 Average values of the injury criteria - wi th and wi thout SBL 41 2.3.2 Significance of the results: t tests of matched pairs 45 2.3.3 Nonparametric significance tests 50 3. ANALYSES OF NASHINGTON, TEXAS AND NEW YORK STATE ACCIDENT DATA 55 3.1 Analysis method .55 3.1.1 The control group: 4 door cars 56 3.1.2 Limiting the data set to reduce bias ...59 3.1.3 Statistical significance testing 62 3.2 Washington State data ...,..,.. 64 3.2.1 Analysis of injuries - full data set 65 3.2.2 Analysis of ejections - full data set 68 3.2.3 Analysis of injuries - matching makes and models ...73 3.2.4 Analysis of ejections - matching makes and models 76 3.2.5 Effect of SBL on injuries by seat position - full data set 77 3.2.6 Effect on injuries of restrained occupants - full data set 81 3.2.7 When children ride in the back seat 82 3.3 Texas data on drivers' injury risk 85 3.3.1 All crashes 87 3.3.2 Frontal crashes 89 3.4 New York State data - effect of SBL by injury type ...89 4. ANALYSES OF THE FATAL ACCIDENT REPORTING SYSTEM 97 4.1 Analysis method ,. .97 4.1.1 Fatal i ty data 98 4.1.2 Exposure data 99 4.1.3 Statistical significance testing ..105 4.2 Effect on fatalities 105 4.3 Effect on ejections 110 IV 4.4 Fatalities and ejections, by seat position 114 4.5 Effect for restrained occupants 119 4.6 Effectiveness in frontal crashes 121 4.7 Effect on fatal accidents involving fire 125 4.8 Effectiveness, by car size and manufacturer 128 4.8.1 Effect on fatalities. 129 4.8.2 Ejections 131 4.9 When children ride in the back seat 134 5. ANALYSES OF THE PERFORMANCE OF CAR DOORS AND SEATS IN NHTSA ACCIDENT FILES 137 5.1 Description of the data files 137 5.2 Analysis of ejections 139 5.3 Analysis of door integrity in crashes 141 5.4 Seat performance in crashes of 2 door cars with SBL 146 6. SUMMARY AND COMPARISON OF FINDINGS 153 6.1 Do SBL hold seatbacks in place during crashes? 153 6.2 Do SBL reduce fatalities and injuries in crashes? 156 6.2.1 All occupants - all crashes 156 6.2.2 Frontal crashes 159 6.2.3 By injury type 162 6.2.4 By seat position 164 6.2.5 Restrained occupants. 169 6.2.6 Summary 171 6.3 Do SBL affect the risk of occupant ejection? 172 6.4 Do SBL affect fatality risk in car fires? 176 APPENDIX A: Sled test results 179 APPENDIX B: Detailed State data tabulations .185 APPENDIX C: Detailed FARS data tabulations 213 References 235 LIST OF TABLES Table 2-1 Sled test matrix (in chronological order) 29 2-2 Sled test matrix (in schematic order) ....30 2-3 Performance of unrestrained dummies relative to Standard 208 criteria 38 2-4 Performance of unrestrained dummies relative to the head and chest criteria of Standard 208 40 2-5 Sled test results - all dummies 42 2-6 Sled test results - dummies in the front seat with no dummy positioned behind them 44 2-7 Sled test results - dummies in the front seat with a dummy positioned behind them 46 2-8 Sled test results - dummies; in the back seat.... 47 2-9 Nonparametric analysis of sled test results - all dummies...52 2-10 Nonparametric analysis of sled test results - by seat position 53 3-1 Washington State 1973-77: K + A (fatal or serious) injury rates - all occupants 57 3-2 Washington State 1973-77: K + A + B (moderate/serious) injury rates - all occupants 67 3-3 Washington State 1973-77: overall injury rates - all occupants 69 3-4 Washington State 1973-77: ejectees per 1000 occupants, all seating positions 70 3-5 Washington State 1973-77: net effect of SBL on injury risk (by severity level) and ejection risk 72 3-6 Washington State 1973-77: net effect of SBL on injury risk (by severity level) and ejection risk: 2 door vs. 4 door sedans and hardtops of the same makes and models 74 3-7 Washington State 1973-77: net effect of SBL on injury risk (by severity level) - by seat position , 78 vri 3-8 Washington State 1973-77: net effect of SDL on injury risk (by severity level) - belted occupants 83 3-9 Washington State 1973-77: net effect of SBL on nonejected occupants' injury risk (by severity level) when unrestrained children are in the back seat -...84 3-10 Texas 1972-74: net effect of SBL on drivers' injury risk (by severity level) 88 3-11 New York State 1974: net effect of SBL on injury risk - by injury type ..92 3-12 New York State 1974: net effect of SBL on injury risk, nonejected occupants in frontal impacts - by injury type 94 4-1 FARS 1975-85: fatality rates per million vehicle years, all occupants 106 4-2 FARS 1975-85: fatality rates per million vehicle years, all occupants - 2 door vs. 4 door sedans and hardtops of the same makes and models 109 4-3 FARS 1975-85: ejectees per million vehicle years, all seating positions .111 4-4 FARS 1975-85: ejectees per million vehicle years, all seating positions - 2 door vs. 4 door sedans and hardtops of the same makes and model s 113 4-5 FARS 1975-85: net effect of SBL on fatality risk - by seat position 116 4-6 FARS 1975-85: net effect of SBL on occupant ejection rates - by seat position 118 4-7 FARS 1975-85: fatality rates per million vehicle years, all restrained occupants 120 4-8 FARS 1975-85: fatality rates in frontal crashes, per million vehicle years, all occupants 122 4-9 FARS 1975-85: ejectees per million vehicle years, in frontal crashes, all seating positions 123 4-10 FARS 1975-85: nonejection fatality rates in frontal crashes, per million vehicle years, all occupants 124 4-11 FARS 1975-85: net effect of SBL on fatality risk in crashes involving fires 127 4-12 FARS 1975-85: net effect of SBL on fatality risk - by car size and manufacturer 130 4-13 FARS 1975-85: net effect of SBL on occupant ejection rates - by car size and manufacturer 132 4-14 FARS 1975-85: net effect of SBL on fatality risk when children are in the back seat 135 5-1 NCSS and MDAI files: ejectees per 1000 occupants, all seating positions 140 5-2 NCSS and MDAI files: incidence of doors opening during Impacts ;.