RISK COMPENSATION AND THE ILLINOIS SEAT-BELT USE LAW

The question of whether drivers alter their behavior due to vehicle sa fety improvements or public policy changes (laws, enforcement) has bee n debated for some years. The possibility of risk compensation (offset ting behavior) has been offered: drivers may go faster or operate in a less safe manner in response to such a change. Three 1991 publication s purportedly find risk compensation due to mandatory seat belt use la ws. However, these conclusions are questionable due to the weaknesses in statistical methods that were used (before/after comparisons, regre ssion). This paper examines whether risk compensation occurred due to the 1985 use law in Illinois. It also compares the results of the befo re/after method to a preferred technique (ARIMA, developed by Box and others). These approaches are applied to monthly totals and rates of f atalities, injuries classified by level of severity, and total acciden ts from 1980-1991. Three types of accident are analyzed: vehicle/pedes trian, vehicle/bicycle, and all others. If nonoccupants have suffered adverse consequences, risk compensation could provide the explanation. Much less evidence of offsetting behavior was found. No statistically significant increase in accidents occurred. While other types of safe ty changes may alter driver behavior, this did not seem to occur in Il linois due to the belt use law.