Safety effects of reducing the speed limit from 90 km/h to 70 km/h

Abstract

Speed is one of the main risk factors in traffic safety, as it increases both the chances and the severity of acrash. In order to achieve improved traffic safety by influencing the speed of travel, road authorities maydecide to lower the legally imposed speed limits. In 2001 the Flemish government decided to lower speedlimits from 90 km/h to 70 km/h on a considerable number of highways. The present study examines theeffectiveness of this measure using a comparison group before- and after study to account for generaltrend effects in road safety. Sixty-one road sections with a total length of 116 km were included. The speedlimits for those locations were restricted in 2001 and 2002. The comparison group consisted of 19 roadsections with a total length of 53 km and an unchanged speed limit of 90 km/h throughout the researchperiod. Taking trend into account, the analyses showed a 5% decrease [0.88; 1.03] in the crash ratesafter the speed limit restriction. A greater effect was identified in the case of crashes involving seriousinjuries and fatalities, which showed a decrease of 33% [0.57; 0.79]. Separate analyses between crashesat intersections and at road sections showed a higher effectiveness at road sections. It can be concludedfrom this study that speed limit restrictions do have a favorable effect on traffic safety, especially onsevere crashes. Future research should examine the cause for the difference in the effect between roadsections and intersections that was identified, taking vehicle speeds into account.