Effectiveness of Lap/Shoulder Belts in the Back Outboard Seating Positions
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U.S. Department of Transportation http://www.nhtsa.dot.gov National Highway Traffic Safety Administration DOT HS 808 945 June 1999 NHTSA Technical Report Effectiveness of Lap/Shoulder Belts in the Back Outboard Seating Positions 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 808 945 4. Title and Subtitle 5. Report Date Effectiveness of Lap/Shoulder Belts in the Back June 1999 Outboard Seating Positions 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Christina Morgan 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Evaluation Division, Plans and Policy 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 Most of the analyses are based on Fatality Analysis Reporting System (FARS) data from 1988 through the first six months of 1997. The primary analysis compares the fatality risk for back seat outboard belted occupants (lap or lap/shoulder belted) to the corresponding risk for unbelted occupants, as well as the fatality risk for lap/shoulder belted occupants to the risk for lap belted occupants. Fatality risk is the ratio of fatalities in the back seat to fatalities in the front seat (a control group). This procedure of comparing a subject group to a control group is called “double pair comparison.” The principal conclusions are: back seat lap belts are 32 percent effective in reducing fatalities and lap/shoulder belts are 44 percent effective in reducing fatalities when compared to unrestrained back seat occupants in passenger cars. In passenger vans and Sport Utility Vehicles, lap belts are 63 percent effective and lap/shoulder belts are 73 percent effective. The change from lap to lap/shoulder belts has significantly enhanced occupant protection, especially in frontal crashes. In all crashes, lap/shoulder belts are 15 percent more effective than lap belts alone. In frontal crashes, lap/shoulder belts are 25 percent more effective than lap belts alone. Back seat lap belts reduce the risk of head injuries while increasing the risk of abdominal injuries in potentially fatal frontal crashes. Lap/shoulder belts reduce the risk of both head and abdominal injuries in potentially fatal frontal crashes relative to lap belts only: head injuries by 47 percent and abdominal injuries by 52 percent. 17. Key Words 18. Distribution Statement lap/shoulder belt; lap belt; occupant protection; fatal crash; fatality rates; FARS; fatality analysis; statistical analysis; evaluation; passenger cars; light trucks; frontal crash; abdominal injury 19. Security Classif. (Of this report) 20. Security Classif. (Of this page) 21. No. of Pages 22. Price Unclassified Unclassified 141 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized TABLE OF CONTENTS TABLE OF CONTENTS .................................................... iii LIST OF SELECTED TABLES ...............................................vii EXECUTIVE SUMMARY ................................................... ix CHAPTER 1 ...............................................................1 INTRODUCTION AND BACKGROUND ........................................1 1.1 RESULTS OF EARLIER EFFECTIVENESS STUDIES ..................2 1.2 BELT USE .....................................................5 1.2.1 Observed Belt Use .........................................6 CHAPTER 2 ..............................................................13 FATALITY REDUCTION BY BACK SEAT BELTS, WHEN USED, IN PASSENGER CARS ..................................................................13 2.1 DATA PREPARATION ..........................................13 2.1.1 Vehicle-level File .........................................13 2.1.2 Paired-occupant File .......................................14 2.1.3 Restraint Type and Restraint Use Categories .....................16 2.2 ANALYSIS USING THE ENTIRE DATA SET .......................17 2.3 OVERALL EFFECTIVENESS ....................................20 2.4 ANALYSIS LIMITED TO “MATCHING” MAKE-MODELS ............21 2.4.1 Confidence Bounds .......................................25 2.5 LAP/SHOULDER BELT EFFECTIVENESS VS. LAP BELT ONLY .......30 2.6 LIVES SAVED PER YEAR ......................................35 2.7 BELT EFFECTIVENESS BY TYPE OF CRASH ......................38 2.7.1 Lap/shoulder Belt Effectiveness Vs. Lap Belt in Frontal Crashes ......44 2.8 BELT EFFECTIVENESS BY OCCUPANT AGE AND SEX .............47 2.9 CAVEATS FOR EFFECTIVENESS ANALYSIS ......................51 2.10 LAP/SHOULDER BELT EFFECTIVENESS IN FRONTAL CRASHES, USING NON-FRONTALS AS A CONTROL GROUP .........................52 2.10.1 Lap/shoulder Belt Effectiveness in Frontal Crashes by Occupant Age and Sex ....................................................54 2.11 ANALYSES USING BACK CENTER SEAT OCCUPANTS AS THE CONTROL GROUP ............................................55 2.11.1 Fatality Reduction for Back Seat Outboard Lap/shoulder Belts Relative to Lap Belts ...............................................59 iii 2.11.2 Fatality Reduction for Back Seat Outboard Lap/shoulder Belts in Frontal Crashes .................................................60 CHAPTER 3 ..............................................................63 FATALITY AND INJURY REDUCTION BY BELTS, AS USED, IN PASSENGER CARS ..................................................................63 3.1 LAP/SHOULDER BELT FATALITY REDUCTION IN FRONTAL CRASHES, USING NON-FRONTAL CRASHES AS A CONTROL GROUP ..........63 3.2 FATALITY REDUCTION, USING FRONT SEAT OUTBOARD OCCUPANTS AS THE CONTROL GROUP .....................................65 3.3 FATALITY REDUCTION, USING BACK CENTER SEAT OCCUPANTS AS THE CONTROL GROUP ........................................67 3.4 “AS USED” FATALITY RATES PER 100,000 REGISTERED VEHICLE YEARS, BASED ON “MATCHING MAKE/MODEL” CARS ............69 3.5 INJURY REDUCTION BY BELTS IN STATE DATA ..................75 3.5.1 Analysis Using The Pennsylvania Data .........................76 3.5.2 Analysis Using The Florida Data ..............................80 CHAPTER 4 ..............................................................83 FATALITY REDUCTION BY BACK SEAT BELTS, WHEN USED, IN PASSENGER VANS AND SPORT UTILITY VEHICLES ..................83 4.1 DATA PREPARATION ..........................................83 4.1.1 Vehicle-level File .........................................84 4.1.2 Paired-occupant File .......................................84 4.2 “WHEN-USED” ANALYSIS .....................................86 4.2.1 Lap/shoulder Belt Effectiveness Vs. Lap Belt Only ................89 4.2.2 Belt Effectiveness in Frontal Crashes ...........................93 4.2.3 Lap/shoulder Belt Effectiveness Vs. Lap Belt in Frontal Crashes .......................................................95 CHAPTER 5 ..............................................................99 FATAL INJURY RATES BY BODY REGION AND RESTRAINT SYSTEM, IN PASSENGER CARS ............................99 5.1 THE MULTIPLE CAUSE OF DEATH FILE ........................100 5.2 DATA PREPARATION .........................................102 5.3 “WHEN USED” ANALYSIS BASED ON “ALL MAKE/MODEL” PASSENGER CARS ...........................................106 REFERENCES ...........................................................113 iv APPENDIX A ............................................................115 APPENDIX B ............................................................125 APPENDIX C ............................................................129 Proof 1 ...........................................................129 Proof 2 ...........................................................132 v vi LIST OF SELECTED TABLES TABLE 2-1 FARS 1988- FIRST 6 MONTHS OF 1997 EFFECTIVENESS OF ALL BACK SEAT OUTBOARD LAP AND LAP/SHOULDER BELTS RELATIVE TO BACK SEAT OUTBOARD OCCUPANTS * BY RESTRAINT USAGE AND RESTRAINT TYPE .................19 TABLE 2-7 FARS 1988- FIRST 6 MONTHS OF 1997 EFFECTIVENESS OF BACK SEAT OUTBOARD LAP/SHOULDER BELTS RELATIVE TO LAP BELTED BACK SEAT OUTBOARD OCCUPANTS * BY RESTRAINT USAGE AND RESTRAINT TYPE FOR “ALL MAKE/MODELS” ...........................34 TABLE 2-9 FRONTAL CRASHES: FARS 1988-FIRST 6 MONTHS OF 1997 EFFECTIVENESS OF BACK SEAT OUTBOARD LAP AND LAP/SHOULDER BELTS RELATIVE TO UNRESTRAINED BACK SEAT OUTBOARD OCCUPANTS * BY RESTRAINT USAGE AND RESTRAINT TYPE FOR ALL MAKE/MODELS ........40 TABLE 2-13 FARS 1988-FIRST 6 MONTHS OF 1997 EFFECTIVENESS, CONFIDENCE BOUNDS, AND T TEST VALUES OF BACK SEAT LAP/SHOULDER BELTS RELATIVE TO LAP BELTED BACK SEAT OUTBOARD OCCUPANTS * BY RESTRAINT USAGE, RESTRAINT TYPE, AND ANALYSIS TYPE IN FRONTAL CRASHES ...............45 TABLE 2-14 FARS 1988-FIRST 6 MONTHS OF 1997 EFFECTIVENESS OF BACK SEAT OUTBOARD LAP AND LAP/SHOULDER BELTS RELATIVE TO UNRESTRAINED AND LAP BELTED BACK SEAT OUTBOARD OCCUPANTS * BY RESTRAINT USAGE, RESTRAINT TYPE, AND CRASH TYPE ....46 TABLE 2-15 FARS 1988-FIRST 6 MONTHS OF 1997 EFFECTIVENESS OF BACK SEAT OUTBOARD