DOT HS 811 206 December 2009 Lives Saved Calculations for Seat Belts and Frontal Air Bags 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 author(s) 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. Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. DOT HS 811 206 4. Title and Subtitle 5. Report Date Lives Saved Calculations for Seat Belts and Frontal Air Bags December 2009 6. Performing Organization Code NVS-421 7. Author(s) 8. Performing Organization Report No. Glassbrenner, Donna, Ph.D., and Starnes, Marc 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Mathematical Analysis Division, National Center for Statistics and Analysis National Highway Traffic Safety Administration 11. Contract or Grant No. NVS-421, 1200 New Jersey Avenue SE. Washington, DC 20590 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Mathematical Analysis Division, National Center for Statistics and Analysis NHTSA Technical Report National Highway Traffic Safety Administration NVS-421, 1200 New Jersey Avenue SE. 14. Sponsoring Agency Code Washington, DC 20590 15. Supplementary Notes Abstract One of the ways the National Highway Traffic Safety Administration quantifies the benefits of seat belts and frontal air bags is to estimate the number of passenger vehicle occupants whose lives were saved by these protective devices, and the lives sav- able if more passenger vehicle occupants had buckled up. Passenger vehicles include passenger cars, sport utility vehicles, pickup trucks, and vans. This report details how NHTSA produces these lives saved estimates for seat belts and frontal air bags. The methodology is described in detail, including the use of effectiveness ratings for seat belts and frontal air bags. Seat belt effectiveness ratings vary according to the seat belt type (i.e., 3-point belt versus 2-point lap belt), vehicle type, occupant seating position, and occu- pant age. Frontal air bag effectiveness ratings are consistent for all passenger vehicles. The interactions of the effectiveness of seat belts and the effectiveness of frontal air bags are discussed in this report. The effectiveness of side air bags, child safety seats, motorcycle helmets, and other safety devices are discussed in other NHTSA reports, and are not quantified within this report. When calculating lives saved by seat belts and air bags, it is important to remember that these calculations are estimates based on a methodology that uses the tremendous amount of knowledge that National Highway Traffic Safety Administration has gained. This knowledge has been expanded through the analysis of decades of data on the roles played by seat belts and air bags in fatal crashes. 17. Key Words 18. Distribution Statement lives saved, effectiveness, seat belts, Document is available to the public from the National Technical Information Service air bags, potential lives saved www.ntis.gov 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 68 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized i ii Table of Contents 1. Summary................................................................................................................................... 1 2. Introduction............................................................................................................................... 2 2.1 Terminology.................................................................................................................. 4 3. Fatalities Used in the Calculations............................................................................................ 5 3.1 Data Source................................................................................................................... 5 3.2 Inclusion Criteria .......................................................................................................... 5 3.3 Restraint Configurations ............................................................................................... 6 4. Effectiveness Ratings and Potential Fatalities .......................................................................... 9 4.1 For a Sole Safety Device............................................................................................... 9 4.1.1 Devices and Settings...................................................................................... 9 4.1.2 Potential Fatalities........................................................................................ 10 4.1.3 Effectiveness Ratings................................................................................... 11 4.1.4 Estimated Effectiveness............................................................................... 11 4.1.5 Devices That Can Be Used Improperly ....................................................... 12 4.1.6 Passive Devices............................................................................................ 12 4.1.7 Estimating the Potential Fatalities ............................................................... 12 4.2 For Multiple Devices .................................................................................................. 13 4.2.1 Devices and Settings.................................................................................... 14 4.2.2 Potential Fatalities........................................................................................ 15 4.2.3 Effectiveness Ratings................................................................................... 15 4.2.4 Estimating the Potential Fatalities ............................................................... 17 4.3 For Seat Belts and Frontal Air Bags ........................................................................... 17 4.3.1 A Two-Device Scenario............................................................................... 17 4.3.2 Potential Fatalities........................................................................................ 17 4.3.3 Effectiveness Ratings................................................................................... 18 5. Example 1 and Notation.......................................................................................................... 23 5.1 Example 1 ................................................................................................................... 23 5.2 Notation....................................................................................................................... 24 5.2.1 Estimating the Potential Fatalities for Seat Belts and Frontal Air Bags...... 26 6. Lives Saved............................................................................................................................. 27 6.1 For a Sole Device........................................................................................................ 27 6.2 For Multiple Devices .................................................................................................. 28 6.2.1 The Total Lives Saved ................................................................................. 28 iii 6.3 For Seat Belts and Frontal Air Bags ........................................................................... 29 6.3.1 The Total Lives Saved ................................................................................. 29 6.3.2 Attribution.................................................................................................... 31 7. Potential Lives Saved.............................................................................................................. 35 7.1 For a Sole Device........................................................................................................ 35 7.2 For Multiple Devices .................................................................................................. 35 7.2.1 Potential Lives Saved................................................................................... 36 7.3 For Seat Belts and Frontal Air Bags ........................................................................... 38 7.3.1 Determining the Hypothetical Use Among Potential Fatalities................... 39 7.3.2 Potential Lives Saved................................................................................... 42 8. Summary of Formulas............................................................................................................. 48 Appendix: The Treatment of Factors Affecting Survival as Devices or Part of the Setting ........ 50 A1.1 A Virtually Unlimited Number of Factors Could Be Argued to Affect Survival....... 50 A1.2 Devices Must Be Rated for Effectiveness. ................................................................. 51 A1.2.1 Ratings Needed to Compute the Combined Lives Saved by All Devices ... 52 A1.3 The Effect of Considering an Air Bag as a Device Versus