Evaluation of Michigan 70-mph Speed Limit

Abstract

On August 1, 1996, the speed limit on certain sections of Michigan freeways increased from 104.6 to 112.6 km/h (65 to 70 mph). This was due to the Michigan Legislature passing a bill that permitted the governor of Michigan to increase the speed limit given that a study be conducted to determine the effects on safety and capacity. Michigan State University conducted the study that determined the effects of increasing the speed limit on certain sections of highway. This study examined not only freeways that were increased to 112.6 km/h (70 mph), but also the speeds and capacities of freeway sections where the speed limit was not increased. Different types of speed analyses were done in comparing the test sections where the speed limits were raised with the control sections where the speed limits were not raised. The analysis also included categorizing the roadway into intercity and recreational routes to determine the effect on speeds for different uses in road use. The speed data also were broken down into different vehicle types. A preliminary accident analysis was performed on the control and test sections to determine the effect of increasing the speed limit on accidents. It was proved that increasing the speed limit on certain sections of freeway in Michigan had little effect on the change in speed and capacity on both test and control sections.