An investigation of the relationship between speed enforcement, vehicle speeds and injury crashes in New Zealand

There exists in the literature material dealing with dose-response relationships between enforcement effort and vehicle speeds and also vehicle speeds and crash risk. This literature pertains to various road networks and jurisdictions around the world. New Zealand?s mix of road network and enforcement has some unique features which merit further investigation.

This paper examines the relationship between enforcement activity, vehicle speeds and injury crashes in New Zealand. Enforcement activity taken into account includes speeding infringements (camera and non-camera), hidden and visible speed camera activity and the advent of marked State Highway Patrol cars.

Estimated reductions in open road mean speeds of 0.7% and 0.8% were found, associated with each increase of 10000 speed camera infringements and 10000 other speed infringements respectively. Higher reductions of 1.1% and 1.6% were found in the 85th percentile speeds. An estimated injury crash reduction of 12% was found to be associated with a 1km/h reduction in mean open road speed during low alcohol hours. The relationships between enforcement, speeds and crashes apply to the systems in place in New Zealand over the study period of 1996-2002 and should not be applied beyond the range of the enforcement practices studied.