Speed distribution and traffic safety measures

A main traffic safety priority in many countries is implementing measures that reduce road user speed and increase speed limit compliance. This study compares changes in the speed distribution and estimated accident risk brought about by three measures: speed limit change from 110 to 100 km/h on roads without speed cameras speed limit change from 90 to 80 km/h on roads with speed cameras introducing new speed cameras on roads with a speed limit of 90 km/h The accident risk is estimated from mean speed since the impacts of a change in mean speed on the number of accidents and of injured and killed people are well known. The results indicate that installing speed cameras can reduce average speed more than can reducing the speed limit by 10 km/h, at least at the camera locations. Moreover, speed cameras reduce the standard deviation of speed and the percentage of drivers exceeding the speed limit by far more than does lowering the mean speed. This implies that the relationship between change in speed distribution, not only mean speed, and traffic safety merits further investigation.