Speed Limit Change (55 mph to 60 mph) Safety Re-Evaluation Status: CompleteReport Date: 12/20/2023 Summary: 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 8 percent reduction in total crashes that was statistically significant, alongside a significant 15 percent increase in KAB injury crashes. The range of most of the segment CMFs hovered close to 1. 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 show on average between 10% to 20% statistically significant reduction in total and injury crashes. 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 estimated crash safety effects (for total and injury crashes) for combined segments and intersection sites show a reduction in total crashes but an increase in the KAB injury crashes. Final Deliverables: Speed Limit Change (55 mph to 60 mph) Safety Re-Evaluation (Report #2023-41) Related Materials: Related Research:
