Evaluation of the crash and casualty effects of average speed enforcement, carried out at 14 sites in Norway, found a 12-22% reduction of the number of injury crashes – and a “statistically significant” KSI reduction of between 49-54% (ITS International).
The study was carried out by the Institute of Transport Economics (TOI) at the Norwegian Center for Transport Research and funded by the Norwegian Public Roads Administration.
The study takes account of trend, volumes, speed limit changes at some of the sites, speed cameras at some of the sites in the before period, and regression to the mean (RTM). Regression to the mean is controlled for by using the empirical Bayes method which takes into account that exceptionally high crash numbers in the before period usually are associated with a reduction of the number of crashes in the after period, even without any effective safety measure. Most of the sites have an 80km/h speed limit.
Eight of the sites are in tunnels and the results indicate that the crash reduction in tunnels is at least of the same magnitude as on open roads.
The effects of average speed enforcement on stretches of road three kilometres downstream of the section control sites were evaluated using the same methods as at the section control sites, and injury crashes were found to be reduced by 46%.