Effects on Accidents of Automatic Speed Enforcement in Norway

Automatic speed enforcement by means of photo radar was introduced in Norway in 1988. The results of a before-and-after study of the effects of automatic speed enforcement on accidents are reported in this paper. The study controlled for general trends in the number of accidents and regression to the mean. A statistically significant reduction of 20 percent in the number of injury accidents was found. The number of property-damage-only accidents was reduced by 12 percent. This change was not statistically significant at the 5 percent level. The effect of automatic speed enforcement on the number of injury accidents varied according to the level of conformance with official warrants for its use. The warrants refer to accident rate (accidents per vehicle kilometer) and accident density (accidents per kilometer of road). A decline of 26 percent in injury accidents was found on road sections conforming with both warrants. On road sections not conforming with any of the warrants, injury accidents declined by 5 percent. The results of this study confirm the results of previous studies of the effects of automatic speed enforcement on accidents.