Changes in police-reported injuries associated with Michigan's safety belt law: 1988 update. Final report

The objectives of this study were to evaluate the intermediate-term effects of Michigan's safety belt law on police-reported injuries and to monitor trends in motor vehicle crash injury frequencies and rates. In addition, the aggregate economic savings to the people of the State of Michigan produced by decreased fatalities and injuries following implementation of the law were estimated. Monthly frequencies of crash-induced injuries and fatalities from January 1978 through December 1987 were analyzed using time-series methods. Exposure to injury risk was controlled by including aggregate frequency of crashes as a covariate in time-series models. Effects of economic conditions on traffic crashes were controlled by including an index of unemployment as a covariate in the models. The following statistically significant effects were associated with the safety belt law: (a) in crashes of minor severity, 14.6% reduction in B-level injuries and 11.0% reduction in C-level injuries; (b) in crashes of moderate severity, 16.8% reduction in A-level injuries, 11.6% reduction in B-level injuries, and 10.7% reduction in C-level injuries; (c) in severe crashes, 6.3% reduction in fatalities, 11.8% reduction in B-level injuries, and 4.7% reduction in C-level injuries; and (d) in all crashes, 14.0% reduction in B-level injuries, 8.3% reduction in C-level injuries, and 6.4% reduction in injuries to front-seat occupants. Based on these results, Michigan's adult safety belt law from July 1985 through December 1988 has prevented 31,710 injuries, a cost savings of $734.72 million.