Reduction of speed limit from 110 km/h to 100 km/h on certain roads in South Australia: a preliminary evaluation

Abstract

In July 2003, the speed limit on approximately 1,100 km of rural arterial roads in South Australia was reduced from 110 km/h to 100 km/h. The crash experience on these roads in the two years before and the two years following the change has been compared with that on other roads where the 100 km/h limit was not changed. It appears that the speed limit reduction has had the effect of reducing casualty crashes by 20 per cent. However, the number of crashes on these roads is small and the time since the change is so short that this estimate is uncertain. It is reasonable to think that in the longer term the change might be anywhere between an increase of 4 per cent and a decrease of 44 per cent. There was a decrease in crashes and casualties on the 100 km/h roads where the speed limit did not change and that has been allowed for in the calculations. At six sites, speed measurements before and after the speed limit reduction were available: an average speed reduction of 2 km/h was found