Evaluating the Impacts of Speed Limit Increases on Rural Two-Lane Highways using Quantile Regression

Understanding speed selection behavior of drivers following speed limits increases is critically important. To date, the literature has largely focused on freeways and the effects of speed limit changes on two-lane highways remains under researched. Prior research has also generally focused on changes to mean speeds, though the speeds of both the highest and lowest drivers are also of great interest. This study investigates trends in free-flow travel speeds following 2017 legislation that increased the posted speed limit from 55 to 65 mph on 943 miles of rural highways in Michigan. Speed data were collected for over 46,000 drivers at 67 increase segments and 28 control segments, where the speed limits remained unchanged, before and during each of the two successive years following the speed limit increases. Site-specific traffic, geometric, and cross-sectional information was also collected. The impacts of the speed limit increases on the 15th, 50th, and 85th percentile speeds were evaluated using quantile regression. Separate analyses were conducted for passenger cars and heavy vehicles. Locations where the speed limits were raised experienced increases in travel speeds ranging from 3.8 to 5.1 mph. The control sites experienced marginal changes in speeds, which suggests any spillover effects of the higher speed limits have been limited. Significant differences were observed across the quantiles with respect to the effects of the speed limit increases, as well as numerous site-specific variables of interest. The results provide important insights as to the nature of driver speed selection and the impacts of speed limit increases.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Maps; References; Tables;
  • Pagination: 18p

Subject/Index Terms

Filing Info

  • Accession Number: 01763754
  • Record Type: Publication
  • Report/Paper Numbers: TRBAM-21-02356
  • Files: TRIS, TRB, ATRI
  • Created Date: Dec 23 2020 11:10AM