This paper aims to provide a link between simulated measures of safety performance and observed crash occurrence. Safety performance is expressed in terms of a crash potential index (CPI), established as a function of individual vehicle deceleration rates required to avoid a crash and braking capabilities. Safety performance is compared to a sample of crashes observed on an instrumented segment of freeway. Three test results are reported: (1) comparing safety performance in 1 minute increments for a period five minutes prior to the precise crash time, (2) comparing safety performance in 1 minute increments over five minutes for matching crash and non-crash cases and (3) comparing average safety performance to observed crash ratesfor a one hour period at the same site. The results of this study confirmthat crashes tend to occur when measures of safety performance at a givensite are higher than normal, and that this measure increases with the approaching time to crash. The results provide basic evidence that the CPI measure of safety performance tends to reflect or explain increased crash risk subject to real-time changes in traffic conditions.
Samenvatting