Speed is a main risk factor in traffic safety, which increases both the chance and the severity of the crash. In order to work to a better traffic safety through influencing the travel speeds, road authorities may decide to lower the legally imposed speed limits. In 2001 the Flemish government decided to lower speed limits from 90 to 70 km/h at a considerable number of highways. Current study examines the effectiveness of this measure, through the application of a comparison group before-after study to account for general trend effects in road safety. Sixty-one road sections with a total length of 116 km were included. Those locations knew a restriction of the speed limit in 2001/2002. The comparison group consisted of 19 road sections with a total length of 53 km and an unchanged speed limit of 90 km/h during the total research period. Taking trend into a account, the analyses showed a 5% decrease [0.88; 1.03] in the crash rates after the speed limit restriction. A stronger effect was found for the crashes with serious injuries and fatalities, which showed a decrease of 33% [0.57; 0.79]. Separate analyses between crashes at intersections and at road sections showed a higher effectiveness at road sections. From this study can be concluded speed limit restrictions do have a favourable effect on traffic safety, especially on the severe crashes. Future research should examine the cause for the difference that was found in the effect between road sections and intersections, taking vehicle speeds into account. This publication may be accessed by Internet users at: http://www.ictct.org/workshop.php?workshop_nr=35
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