Evaluating the Impacts of Speed Limit Increases on Identified Case Studies

Since 2000, the Michigan Department of Transportation (MDOT) with the Michigan State Police have raised the posted speed limit of several rural and urban freeways. Research done in 2000, The Impacts of Raising the Speed Limit on Freeways, Michigan, evaluated the change of posted speeds along 1,500 miles of freeways. The results showed a slight increase in fatal crashes but a decrease in incapacitating injury crashes. Total crashes did increase. The research also showed a decrease in severe truck crashes but an increase in crashes involving trucks. Overall, there was a small increase in the speed of traffic. However, this increase was not experienced at all locations and the change was not greater than 2 mph at any location. The purpose of this research is to evaluate if these conclusions regarding crashes and an increase in operating speed in response to an increase in posted speed limits are still valid today on freeways.