Speed Distribution and Traffic Safety Measures

The main traffic safety priority in many countries is the implementation of measures that reduce road user speed and increase speed limit compliance. This chapter 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 and introducing new speed cameras on roads with a speed limit of 90 km/h. It also demonstrates that speed cameras reduce the standard deviation of speed and the percentage of drivers exceeding the speed limit by far more than those that reduce the mean speed. The Power model is applied to aggregate data from a road site, but other models estimate how speed affects accident risk at the individual level.