Results are presented of an analysis of the effects that speed variance among vehicles, level of enforcement, and interchanges have on accidents and involvement rates. The data analysed were collected by twenty state highway departments. The results demonstrate that on the interstate system, as the speed of a vehicle varies from the mean speed of traffic, either above or below the mean speed, the chance of the vehicle being involved in an accident increases. The level of enforcement has little or no apparent effect on the mean speed or on the accident experience of a study section. Proximity to interchanges, especially in urban areas, appears to affect significantly the accident experience of the study section. These results present some insight into areas in which more intensive research should be conducted, such as interchange spacing and utilisation and more effective methods of speed control.
Abstract