Analysis of crash data from safety camera intersections in South Australia

Abstract

There are now many signalised intersections in South Australia that are equipped with safety cameras which photograph vehicles that either travel though a red signal or exceed the posted speed limit. The detection of infringing drivers is intended to reduce speeding and red light running and ultimately reduce the number and severity of crashes at the signalised intersections being monitored. This study analysed the injury crash data for 35 safety camera intersections in South Australia that have been in place for at least five years. By comparing the injury crash numbers for five years before and five years after site commissioning, an attempt was made to determine if the safety cameras are having a beneficial effect on injury crash numbers and to estimate the size of this effect. In an attempt to control for long term trends in injury crash numbers, changes in relevant injury crashes (those involving a vehicle passing a safety camera) were compared with changes in non-relevant injury crashes (those involving only vehicles not passing a safety camera) at the intersections. The analyses carried out suggest that safety cameras, as implemented in South Australia, are reducing injury crashes on the monitored legs of the treated intersections. Estimates of the size of the reduction range up to 21%. This is in general agreement with the literature suggesting a modest but real effect of fixed cameras. As more safety cameras are installed in South Australia, and more time passes to allow crash data to accumulate for newer sites, the current analysis can be extended to provide more precise estimates of the effect of the cameras (although there are limitations with the methods available).