Safety impacts of differential speed limits on rural interstate highways

4419525752005Nedzesky, A. J.PDFTech ReportFHWA-HRT-05-042VRC-000S(007)Speed limitsSpeed measurementRural highwaysTraffic safetyTurner-Fairbank Highway Research CenterGarber, Nicholas J.Miller, John S.Yuan, BoSun, XinVirginia Transportation Research CouncilUnited States. Federal Highway Administration. Office of SafetyNTL-SAFETY AND SECURITY-Speed LimitsNTL-OPERATIONS AND TRAFFIC CONTROLS-Traffic FlowNTL-SAFETY AND SECURITY-Highway SafetyFederal Highway AdministrationTo compare the safety effects of a uniform speed limit (USL) for all vehicles as opposed to a differential speed limit (DSL) for cars and heavy trucks, detailed crash data, speed monitoring data, and traffic volumes were sought for rural interstate highways in 17 States for the period 1991 to 2000. Conventional statistical tests (analysis of variance, Tukey's test, and Dunnett's test) were used to study speed and crash rate changes in the four policy groups. A modified empirical Bayes formation was used to evaluate crash frequency changes without presuming a constant relationship between crashes and traffic volume