United States Department of Transportation
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Edition:Final report
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Abstract:In July and August 2014, the Pennsylvania Department of Transportation (PennDOT) and Pennsylvania Turnpike Commission
(PTC) raised the posted speed limit on rural sections of Interstates 80, 380, and 76 from 65 to 70 mph. The purpose of this study
was to assess the speed and safety performance of these “pilot” sections. This was done by comparing the operating speeds and
crash frequencies before and after the posted speed limit increase. Additionally, operating speed data in several work zones were
collected to assess how drivers comply with posted speed limits in work zones on the pilot sections. An inferred design speed
method and pavement friction degradation method are proposed as methodologies to assess site conditions on rural Interstate
roadways with 65 mph posted speed limits. Collectively, the operating speed, safety, inferred design speed, and friction information
can be used by PennDOT and the PTC to identify candidate locations for 70 mph posted speed limits. The findings suggest that
mean and 85th-percentile operating speeds increased after increasing the posted speed limit from 65 to 70 mph; however, the
increases were less than 5 mph. A framework was developed to estimate the safety effects of the posted speed limit increase,
because only 12 to 16 months of after period crash data were available for the analyses included in this study.
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