Speed Limit Change (55 mph to 60 mph) Safety Evaluation

The objective of this study was to evaluate the safety impacts of increasing the speed limit from 55 mph to 60 mph on two-lane, two-way state highway road segments in Minnesota. An empirical Bayes (EB) before-after analysis was used to estimate crash modification factors (CMFs) for both segments and intersections. The segment analysis showed a 7 percent increase in total crashes that was statistically significant, alongside insignificant increases/decreases in injury and run-off-road and head-on crashes. The range of most of the segment CMFs hovered close to 1 (essentially meaning that the crashes either remained unchanged or the change was minor). The intersection analysis was split into two groups (all traffic control types and thru-stop control only). The aggregate CMFs for all intersections within these two groups showed that most of the CMFs hovered close to 1. Analysis was also performed on four subgroups (3- and 4-leg, lighting/no lighting) within the two main intersection groups. Disaggregating the intersections into further groups led to smaller sample sizes that led to higher standard errors, showing a widespread range of CMFs around 1 for the individual crash types and severities. The aggregate analysis conducted using all the segment and intersection data showed a minor increase/decrease in the total and injury crashes. This aggregate result along with before-and-after operating speed data from another Minnesota Department of Transportation (2019) study showing that the 85th percentile operating speed remained the same and that mean operating speeds increased by 1 mph following the speed limit increase can lead to a conclusion that the speed limit increase from 55 mph to 60 mph had a very minor to no effect on total and injury crashes or operating speeds.

  • Record URL:
  • Record URL:
  • Corporate Authors:

    University of North Carolina, Chapel Hill

    Highway Safety Research Center
    Chapel Hill, NC  United States  27599

    Lakeside Engineers

    Wauwatosa, WI  United States 

    Minnesota Department of Transportation

    Office of Traffic Engineering
    Roseville, MN  United States 
  • Authors:
    • Saleem, Taha
    • Srinivasan, Raghavan
    • Levitt, Daniel
    • Vann, Mike
    • Worzella, Amy
  • Publication Date: 2020-2


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 53p

Subject/Index Terms

Filing Info

  • Accession Number: 01751660
  • Record Type: Publication
  • Report/Paper Numbers: MN 2020-06
  • Created Date: Aug 27 2020 11:05AM