Economic Analysis of 65 mph Speed Limits on Rural Highways

Abstract

Speed management has been a long-standing concern of transportation agencies. Recently, nationwide speed limit policy modifications have resulted in a general upward trend in many states. In Michigan, legislation was proposed to raise the maximum speed limits on state-owned, rural, nonfreeway highways from 55 to 65 mph. In response to this proposed speed limit policy change, research was performed to assess the associated economic impacts through the use of benefit–cost analysis. Several potential implementation scenarios of the proposed speed limit policy were investigated; these included a limited subset of roadways with favorable geometry and full statewide implementation. A primary research task was to estimate the costs for infrastructure upgrades necessary to achieve compliance with state and federal design speed requirements for the cohort of roadways included within each 65 mph implementation scenario. User benefits and disbenefits associated with the proposed speed limit increase also were estimated, which included reduced travel times, increased fuel consumption, and increased traffic crashes. Although the travel time savings were estimated to exceed the fuel consumption costs, the resulting benefit was far outweighed by crash-related disbenefits and agency infrastructure costs for roadways that required major geometric modifications (e.g., vertical or horizontal realignment). Consequently, an increase in the speed limit to 65 mph on rural, nonfreeway highways should be considered only if the critical geometric elements can maintain design speed compliance without major modification. However, even for roadways on which design speed compliance is maintained, careful, site-specific consideration must be given to the potential safety impacts, particularly with respect to fatal and injury crashes, which may result after the speed limit is increased.