Safety effects of fixed speed cameras - An empirical Bayes evaluation

Abstract

The safety effects of 223 fixed speed cameras that were installed between 2000 and 2010 in Norway were investigated in a before–after empirical Bayes study with control for regression to the mean (RTM). Effects of trend, volumes, and speed limit changes are controlled for as well. On road sections between 100 m upstream and 1 km downstream of the speed cameras a statistically significant reduction of the number of injury crashes by 22% was found. For killed and severely injured (KSI) and on longer road sections none of the results are statistically significant. However, speed cameras that were installed in 2004 or later were found to reduce injury crashes and the number of KSI on road sections from 100 m upstream to both 1 km and 3 km downstream of the speed cameras. Larger effects were found for KSI than for injury crashes and the effects decrease with increasing distance from the speed cameras. At the camera sites (100 m up- and down-stream) crash reductions are smaller and non-significant, but highly uncertain and possibly underestimated.