Correlation of NCAP Performance with Fatality Risk in Actual Head-On Collisions

% U.S. Department of Transportation National Highway Traffic Safety Administration DOT HS 808 061 January 1994 NHTSA Technical Report Correlation of NCAP Performance with Fatality Risk in Actual Head-On Collisions Thi6 document is available to the public from the National Technical Information Service, Springfield, Virginia 22161. The United States Government does not endorse pnxlucts 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 808 061 4. Title end Subtitle S. Report Date January 1994 CORRELATION OF NCAP PERFORMANCE WITH 6. Performing Orgonixotion Cod* FATALITY RISK IN ACTUAL HEAD-ON COLLISIONS 8. Performing Orgonixotion Report No. 77, Author's) Charles J. Kahane, Ph.D. 9. Performing Orgonixotion Nome ond Address 10. Work Unit No. (TRAIS) Evaluation Division, Office of Strategic Planning and Evaluation ]. Contract or Gronf No. National Highway Traffic Safety Administration Washington, D.C. 20590 13. Type of Report ond Period Covered 12. Sponsoring Agency Name ond Address Department of Transportation NHTSA Technical Report National Highway Traffic Safety Administration Sponsoring Agency Code Washington, D.C. 20590 15. Supplemented Notes 16. Abstroct The New Car Assessment Program (NCAP) hits gauged the performance of vehicles in frontal impact tests since model year 1979. In response to Congressional direction, the National Highway Traffic Safety Administration studied the relationship between vehicle test scores in NCAP and the fatality risk in crashes of vehicles on the road. This study is based on head-on collisions, where the effect of crashworthiness can be separated from the effects of extraneous factors that influence fatality rates (drivers, roadways, mileage). Collisions between two 1979-91 passenger cars in which both drivers were wearing safety belts were selected from the Fatal Accident Reporting System. There were 396 collisions (792 cars) in which both cars were identical with or very similar to vehicles which had been tested in NCAP. In the analyses, adjustments were made for the relative weights of the cars, and for the age and sex of the drivers - factors which substantially affect fatality risk. There are statistically significant correlations between NCAP scores for head injury, chest acceleration and femur loading and the actual fatality risk of belted drivers. A composite NCAP score, based on the test results for all three body regions, has excellent correlation with fatality risk: in a head-on collision between a car with good composite score and a car of equal weight with poor score, the driver of the car with the better NCAP score has, on average, a 20 to 25 percent lower risk of fatal injury. Slightly smaller, but still significant fatality reductions are obtained even when the NCAP scores for just one body region (just HIC, or chest g's, or femur load) are used to partition the fleet into "good" and "poor" performance groups. The borderline between good and poor NCAP scores that optimizes the differences in actual fatality risk is close to the criteria specified in Federal Motor Vehicle Safety Standard (FMVSS) 208 for each of the three body regions. Cars built from 1979 through 1982 had, on the average, the poorest NCAP scores. Test performance unproved substantially in 1983 through 1986 models, and continued to improve in 1987 through 1991 cars. In parallel, fatality risk for belted drivers in actual head-on collisions decreased by 20 to 25 percent in model years 1979-91, with the largest decreases just after 1982. The 35 mph test speed for NCAP is 5 mph higher than the test speed for FMVSS 208. By now, most passenger cars meet the FMVSS 208 criteria at the NCAP test speed. The study shows that achievement of this enhanced level of test performance has been accompanied by a significant reduction in actual fatality risk. However, being a statistical study, it does not address what portion of the fatality reduction was directly "caused" by NCAP. Also, these results do not guarantee that any individual make-model with low NCAP scores will necessarily have lower fatality risk than another make-model with higher NCAP scores. 17. K.y Words 18. Distribution Statement NCAP; New Car Assessment Program; Document is available to the public through crashworthiness; FARS; head-on collision; the National Technical Information Service, accident analysis; statistical analysis; Springfield, Virginia 22161 frontal crash; fatality risk index; HIC; chest g's; femur load; safety belts; Polk; 19. Security Clossif. (of this report) 30. Security Clessif. (of this page) 21. No. of Poges 22. Price Unclassified Unclassified 164 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized TMJLE OF OCNIENIS Surmary v Analysis overview vi Correlation of NCAP scores and fatality risk ix Improvements in actual crashworthiness and NCAP performance during 1979-91 xiv Principal findings, conclusions and caveats xvii 1. Introduction and analysis overview 1 1.1 NCAP performance vs. crashworthiness en the highway 2 1.2 The difficulty of isolating crashworthiness effects 3 1.3 Analysis overview 7 1.4 Sane preliminary caveats 12 2. An accident data file with NCAP information 15 2.1 Initial EARS data reduction 16 2.2 Curb weight data from Polk files 19 2.3 Adjusting Polk weights based on actual weight measurements 21 2.4 A file of NCAP test results 27 2.5 etching NCAP tests with FARS cases 29 2.6 Creation of the analysis file 32 3. Correlation of fatality risk with individual NCAP parameters . 35 3.1 Analysis objective 35 3.2 Regression analysis procedure 36 3.3 The initial regression - including all NCAP matches .... 39 3.4 Regressions on data sets with closer FARS-NCAP matches . 42 3.5 Surmary 50 4. A composite NCAP scare: oarrelatiai with fatality risk 53 4.1 A composite measure of NCAP performance 53 4.2 RELEXP: actual safety performance relative to expectations 60 4.3 Correlation of DELNCAP and RELEXP 63 4.4 Fatality reduction for the car with lower NCAPINJ 64 4.5 NCAP performance of cars that did better than expected in crashes 70 4.6 Fatality reduction for the car with lower head or chest injury risk 74 4.7 Sensitivity test: NCAPINJ on a different calibration data set 76 5. Collisions between a "good" and a "poor" NCAP performer 79 5.1 Cars with low NCAPINJ hit cars with high NCAPINJ 79 5.2 Cars with low NCAP chest g's hit cars with high chest g's . 86 5.3 Cars with low NCAP HIC hit cars with high HEC 89 5.4 Cars with low NCAP fenur loads hit cars with high fenur loads 93 5.5 Partitions of the fleet based an two NCAP parameters ... 98 5.6 Partitions of the fleet based an all three NCAP parameters 103 5.7 Sensitivity test: collisions of two cars with similar mass 106 5.8 Sensitivity test: weighted vs. unweighted canposite score . 108 5.9 Sensitivity test: analyses on a different calibration data set 110 5.10 Summary 115 6. Fatality risk indices for "good" and "poor" NCAP performers . 119 6.1 Procedure for catputing fatality risk indices 119 6.2 Risk indices for good and poor NCAP performers 123 7. Actual crashworthiness and NCAP performance during 1979-91 . 129 7.1 Cars with late model years hit cars with early model years 131 7.2 Fatality risk index and average NCAPINJ by model year . 135 7.3 Comparison of the NCAPINJ and mode]-year effects 142 References 149 IV SIMYBRY The Appropriations Act for Fiscal Year 1992 directs "NHISA to provide a study to the House and Senate Qcnttdttees on Appropriations comparing the results of NCAP data fran previous model years to determine the validity of these tests in predicting actual on-the-road injuries and fatalities over the lifetime of the models." In Decentoer 1993, the agency responded with a Report to the Congress that ccnpared NCAP results and real-world crash experience, based an various analyses of accident data files. One set of analyses demonstrated a statistically significant correlation between NCAP performance and the fatality risk of belted drivers in actual Vwiri-nn collisions. This technical report provides a more detailed exposition of the data sources, analytic approach and statistical findings in the analysis of head-on collisions. NHISA's goal was to see if cars witn poor NCAP scores had more belted- driver fatalities than would be expected, given the weights of the cars, and the age and sex of the drivers involved in the crashes. Without adjustment for vehicle weight, driver age and sex, the large diversity of fatality rates in accident data mainly reflects the types of people who drive the cars, not the actual crashworthiness of the cars. For example, "high-performance11 cars popular with young male drivers have an exceptionally high frequency of fatal crashes - because they are driven in an unsafe manner - even though they nay be just as crashworthy as other models. NHISA's analysis objective was to isolate the actual crashworthiness differences between cars, removing differences attributable to the way the cars are driven, the ages of the occupants, etc., and then to correlate NCAP performance with crashworthiness an the highway. Arra"lysis overview Since NCAP is a frontal irtpact test involving dummies protected by safety belts, the agency limited the accident data to frontal crashes involving belted occupants. However, NHISA did not consider all types of frontal crashes, but further limited the data to head-on collisions between two passenger cars, each with a belted driver, which resulted in a fatality to one or to both of the drivers.

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