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

Details

• Creators:
  Saleem, Taha ; Srinivasan, Raghavan ; Levitt, Daniel ; Vann, Mike ; Worzella, Amy ; Storm, Richard
• Corporate Creators:
  University of North Carolina at Chapel Hill. Highway Safety Research Center ; Lakeside Engineers
• Corporate Contributors:
  Minnesota. Department of Transportation ; HDR, Inc.
• Subject/TRT Terms:
  Bayes' Theorem Crash Modification Factors Crash Rates Crash Severity Highway Safety Impacts Intersections Operating Speed Speed Limits Traffic Speed Two Lane Highways

  More +
• Publication/ Report Number:
  MN 2020-06
• Resource Type:
  Tech Report
• Geographical Coverage:
  Minnesota ; United States
• Edition:
  Final Report 2020-06
• Corporate Publisher:
  Minnesota. Department of Transportation
• Abstract:
  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.
• Format:
  PDF
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:fd5fdac50623db5d6dc4b2490dc2d87ed7a4afacba0c061e040c41358f145c04
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/54222/dot_54222_DS1.pdf
• File Type:
  [PDF - 2.10 MB ]