An Evaluation of Head Restraints Usdepor,Ment Federal Motor Vehicle Safety of Transportation R>J
Total Page:16
File Type:pdf, Size:1020Kb
February 1982 DOT HS-806-108 NHTSA Technical Report An Evaluation of Head Restraints usDepor,ment Federal Motor Vehicle Safety of Transportation r>j. *j *j r\r\r\ Nj3p» standard 202 Administration Plans and Programs Office of Program Evaluation This document is available to the U.S. public through the National Technical Information Service, Springfield, Virginia 22161 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catolog No. DOT HS-806 108 A. Title and Subtitle 5. Report Dote AN EVALUATION OF HEAD RESTRAINTS February 1982 Federal Motor Vehicle Safety Standard 202 6. Performing Organization Code NPP-10 8. Performing Orgonizatjon Report No. 7. Author's) Charles Jesse Kahane, Ph.D. 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Office of Program Evaluation National Highway Traffic Safety Administration 11. Contract or Grant No. 400 Seventh Street, S.W. 13. Type of Report and Period Covered 12. WashingtonSponsoring Agenc, y D.CNam.e and2059 Addres0s U.S. Department of Transportation NHTSA Technical Report National Highway Traffic Safety Administration 14. Sponsoring Agency Code Washington, D.C. 20590 15. Supplementary Notes An Agency staff review of an existing Federal regulation performed in response to Executive Order 12291. 16. Abstract Head restraints were installed in passenger cars largely in response to Federal Motor Vehicle Safety Standard 202. The purpose of a head restraint is to prevent whiplash injury of the neck in rear impact crashes. The objectives of this Agency staff evaluation are to determine how many injuries integral and adjustable head restraints have eliminated in highway accidents, to measure the actual cost of the restraints, to assess cost effectiveness and to describe the operational performance and problems of integral and adjustable restraints. The evaluation is based on statistical analyses of three years of Texas accident data and the National Crash Severity Study, National Accident Sampling System and Fatal Accident Reporting System files; cost analyses of actual head restraint assemblies; a review of laboratory and crash tests and in-depth accident investigations; and head restraint sales data. It was found that: o 75 percent of adjustable restraints are left in the down position. o Integral head restraints reduce the overall injury risk in rear impacts by 17 percent; adjustable restraints, by 10 percent, o Integral restraints add $12 to the lifetime cost of owning and operating a car; adjustable restraints, $40. o 72 percent of the cars sold during 1969-81 had adjustable restraints; 28 percent had integral, o The existing mix of adjustable and integral restraints prevents 64,000 injuries per year. 17. Key Words 18. Distribution Statement head restraint; rear impact; rear-end Document is available to the public collisions; Federal Motor Vehicle Safety through the National Technical Information Standard; Standard 202; accident analysi; ; Service, Springfield, Virginia 22161. evaluation; statistical analysis; cost effectiveness 19. Security Cloisif. (of this report) 20, Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 308 Form DOT F 1700.7 (8-72) Reproduction of completed poge outhorized METRIC CONVERSION FACTORS Aapiaiiauta Caavarsiens ta Mttrie Maasurat Atartiiouu Caavaniaat fraai Matric Maataras Wkn In hi* M«lti»rr ir Te FM Whcs YM Kane Udtialy »Y T« FM LENGTH LENGTH m a •nllinatars 0.04 mct.es B centtmetera 0.4 inches la inch** "2.5 centimeters cm meters 3.3 feet « leet 30 centimeters cm meters 1.1 Yards yd »Md* 0.9 motets m kilometers 0.6 •Mlee mi miles Ijl kilometers km AREA AREA 2 square centimeters 0.11 Kjoare taches i. squan indM* 6.S square centimeter! en2 square miters 1.2 squam yards tqun tMt 0.09 square meiars •>> 2 km square kilometers 0.4 squan «• hn square yarde O.» square maters m* 2 ha hectares (10.000 m ) 2.5 acres square mitts z.« square kilometers km1 •ens 0.4 hectares ha MASS (weight) MASS (weight) grams 0.035 a* ounc«s 28 grams 9 ounces kg 2.2 Ib pounds 0.45 kilograms kg kilograms pounds short tons 0.9 tonnes t t tonnes 11000 kg] 1.1 short Ions (2800 Ib) VOLUME * VOLUME up teaspoons s milliliters ml milliliters 0.03 fluid ounces flat Tbsp tablespoons 15 millilitert ml I liters 2.1 puns pt II M fluid ounces 30 millititers ml then 1.0* quarts «t c cups 0.24 liters 1 I liters 0.2C gallons pt pints 0.47 liters 1 cubic meters 35 cubic feat q« quarts 0.9S liters 1 cubic meter* 1.3 cubic yards gallons 3.8 liters 1 3 ft cubic feM 0.03 cubic meters m3 yd' cubic yards 0.76 cubic meters m3 TEMPERATURE (txact) TEMPERATURE (auct) Celsius 9/5 (then temperature add 32) Fahrenheit 5/9 (after Celsius *C tamparature subtracting temperature 321 •F -40 140 M I 110 140 too- 1 '1 in « 2.54 {exactly). Fur other exact conversions and more detailed tables. se« NSS Mi&c. Pufai. 281 I- ' ' I 'I' V fl UmK of MeighM and Measures. Puce >2JS. SO Catalog No. C13.10:216. -40 -10 0 CO 140 (0 ao 100 —= §= S •C •c TABLE OF CONTENTS Acknowledgements xv Executive Summary xvii 1. INTRODUCTION 1 1.1 Federal Motor Vehicle Safety Standards - the program and its evaluation 1 1.2 What is Standard 202? 4 1.3 Why evaluate Standard 202? 5 1.4 Contents of the evaluation 5 2. FINDINGS AND CONCLUSIONS 7 2.1 Principal statistical findings 7 2.2 Discussion of findings 13 2.2.1 The problem: injuries in rear impact crashes 13 2.2.2 Integral and adjustable restraints 18 2.2.3 Effectiveness of head restraints 23 2.2.4 Benefits, costs and cost-effectiveness 36 2.2.5 Head restraint height and injury reduction 42 2.3 Summary: why are head restraints effective? 48 2.4 Strengths and weaknesses of the evaluation 50 2.5 Conclusions 54 3. THE PROBLEM: INJURIES IN REAR IMPACT CRASHES 57 3.1 The number of injuries in rear impacts 57 3.1.1 Estimates from earlier studies 58 3.1.2 The prime estimate: from the National Accident Sampling System 59 3.1.3 Three alternative estimates 67 3.2 The severity of rear impact injuries 71 m 3.3 Injury mechanisms 80 3.3.1 "The enigma of whiplash injuries" 80 3.3.? Other injury mechanisms 83 3.3.3 Statistical analysis of injury mechanisms 85 3.3.4 Analysis of rear' impact fatalities 91 3.4 Factors mfluencinq nuw impact injury risk 95 3.4.1 Occupant sex and neck injury risk 95 3.4.2 Crash severity and overall injury risk 97 3.5 Other standards that may protect occupants in rear impacts 97 4. THE DEVELOPMENT OF HEAD RESTRAINTS.... 103 4.1 Before Federal regulations 103 4.2 Regulatory history 104 4.3 Head restraint designs • 106 4.4 Problems with head restraints ....107 4.5 Sales trends of adjustable and integral restraints 113 5. THE OVERALL EFFECTIVENESS OF HEAD RESTRAINTS 125 5.1 Review of previous effectiveness studies 125 5.1.1 Studies based on insurance company data 125 5.1.2 Studies based on State data 127 5.1.3 Studies based on investigator-collected data 129 5.2 Analysis of National Crash Severity Study data 134 5.2.1 Overview and definitions ....134 5.2.2 Effectiveness based on multidimensional contingency table analysis 138 5.3 Analysis of 1972 Texas accident data 145 5.3.1 Overview and motivation 145 5.3.2 Effectiveness based on multidimensional contingency table analysis 149 5.3.3 Effectiveness based on comparison of rear and side impact injury rates 1 54 5.3.4 Summary 159 5.4 Analysis of Fatal Accident Reporting System data 161 5.4.1 Method 162 5.4.2 Results of the contingency table analyses 165 5.4.3 Results of the regression analyses '. 770 5.4.4 Analysis of rear impact fatalities per million vehicle years..175 IV 5.5 The long-term trend in fatal rear-end collisions 178 5.6 Analysis of 1972, 74 and 77 Texas accident data 181 5.6.1 Overv lew and rno1.1 va1.1on 181 5.6.2 Rear impact injury r<it,es in 1968 versus 1969 models 183 5.6.3 Regression of rear impact injury rates 187 5.6.4 Rear and side impact; injury rates in 1967-68 versus 1969-70 models 194 5.6.5 The overall effectiveness of head restraints 198 5.6.6 Summary of findings 201 6. EFFECTIVENESS COMPARISONS OF INTEGRAL AND ADJUSTABLE HEAD RESTRAINTS 203 6.1 Earlier comparative studies -....••• 203 6.2 Analysis of National Crash Severity Study data 206 6.3 Analysis of 1972, 74 and 77 Texas accident data 212 6.3.1 Met hod 212 6.3.2 Results - integral versus adjustable restraints 216 6.3.3 Results - integral versus no restraints 221 6.3.4 Summary 225 7. THE ACTUAL COSTS AND BENEFITS OF HEAD RESTRAINTS 227 7.1 Objectives 227 7.2 The cost of head restraints 228 7.2.1 Procedure for estimating costs 228 7.2.2 Average and total cost 233 7.3 The benefits of head restraints 237 7.4 Cost-effectiveness , 245 8. THE EFFECT OF HEAD RESTRAINT HEIGHT ON INJURY RISK 251 8.1 Anthropometric considerations 251 8.2 Sled and crash test results 254 8.3 Results from the National Crash Severity Study 257 8.3.1 Distribution of seatback heights 257 8.3.2 Seatback height and injury risk 264 8.4 Computations based on Texas effectiveness and NCSS seatback he ights 268 8.4.1 Head restraint height and injury risk 268 8.4.2 Effect of positioning adjustable restraints properly 277 8.4.3 The effects of raising or lowering height requirements 277 References 285 Appendix A: Programs and tables for Texas effectiveness analyses * Appendix B: Programs and tables for NCSS effectiveness analyses * Appendix C: Programs and tables for FARS effectiveness analyses * Appendix D: Programs and tables for NASS estimates of injuries * Appendix E: Programs and tables on head restraint height vs.