Evaluating the impacts of speed limit policy alternatives.

PDFTech ReportRC-16092013-0070Speed limitsRural highwaysHighway safetyTraffic accidentsFatalitiesAccident ratesBenefit cost analysisAccident risk forecastingRecommendationsSurveysMichiganMichigan. Dept. of Transportation. Office of Research AdministrationSavolainen, PeterGates, TimothyHacker, ElizabethDavis, AmeliaFrazier, SterlingRusso, BrendanRista, EmiraParker, MartinMannering, FredSchneider, WilliamWayne State UniversityUS Transportation CollectionAs of June 2014, Michigan is one of eight states with a differential speed limit in place on its ruralfreeways, which sets a maximum speed of 70 mph for passenger vehicles and 60 mph for trucks andbuses. In select urban environments, these speed limits are both reduced to a uniform 55 mph limit.Legislation was introduced in early 2014 that proposed increases to these speed limits. In order toascertain the potential impacts of these proposed speed limit increases, this research examined a broadrange of traffic safety, operational, environmental, and economic data. This study involved acomprehensive state-of-the-art review of prior research on the relationships between traffic speed, safety,and crash risk. A survey was conducted of state agency practices with respect to speed limitestablishment and another survey was conducted to obtain feedback on proposed changes from thetrucking industry. National fatality data were collected and analyzed to ascertain the effects of speedlimit policies on traffic fatalities, with specific emphasis on maximum speed limits and the effects ofuniform vs. differential limits on urban and rural interstates. Further analyses were conducted at thedisaggregate level to examine crash trends on Michigan freeways. These results were supplemented bythe analysis of field speed data that were collected on freeways in Michigan, Indiana, and Ohio.Differences in mean speeds, 85th percentile speeds, and the standard deviation in speeds among passengercars, trucks, and buses were examined with respect to the speed limit policies in place at each of 160roadway locations. Based upon the results of the fatality and speed data analyses, a benefit-cost analysisof the proposed speed limit change was conducted in consideration of both road user and agency costs.Recommendations were presented to aid in decision-making related to speed limit policies