Development and testing of methodologies to estimate benefits associated with seat belt usage in Kansas

Abstract

Seat belt usage is considered to be one of the most effective ways of improving safety of motor vehicle occupants. Thus, increasing seat belt usage among motorists has become one of the top prioritized goals of many highway safety improvement programs. The main objective of this study was to develop a methodology to estimate potential economic benefits associated with increased seat belt usage by Kansas motorists based on conditions prevailing in the State of Kansas. Seat belt effectiveness in reducing injuries was estimated and those values were then used to estimate economic benefits due to injury reductions. Five methodologies were used to estimate seat belt effectiveness which included multiple logistic regression, double pair comparison method, Cox proportional hazards regression, conditional logistic regression, and risk ratio model using estimating equation approach. Crash data from Kansas Accident Reporting System (KARS) database was used. A procedure was developed to estimate economic benefits due to increased seat belt usage based on State conditions. The highest variation in estimated seat belt effectiveness values using different methods were observed for incapacitating injuries while the lowest variation was observed for possible injuries. For fatal injuries, the estimated seat belt effectiveness values ranged from 50-69% for passenger cars and 57-70% for other passenger vehicles. The range of seat belt effectiveness values for incapacitating injuries was 47-65% for passenger cars and 44-69% for other passenger vehicles. It was also found that the multiple logistic regression method provide relatively narrower confidence intervals for almost all the nonfatal injury categories in both vehicle groups. Based on estimations using logistic regression method, seat belts are 56% effective in preventing fatal injuries in passenger cars and 61% effective in other passenger vehicles. The seat belt effectiveness in reducing incapacitating injuries was found to be 53% in passenger cars and 52% in other passenger vehicles. It was found that if seat belt usage rate in Kansas reaches the national average rate of 81% (2006), the resulted annual economic benefits to the State is estimated to be about $ 191 millions in 2006 dollars or in other words, due to lower seat belt usage currently observed in Kansas compared to national usage level, the annual estimated economic loss is about $ 191 millions. Seat belt effectiveness values are currently not available based on KABCO (K-Fatal, A-Incapacitating, B-Non-incapacitating, C-Possible, and O-No injuries) injury scale. Therefore, this study could serve as an initiative towards establishing a procedure to estimate benefits of seat belt usage based on State highway crash data.