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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 CMFshovered 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 aconclusion 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.

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 an 8 percent reduction in total crashes that was statistically significant, alongside a significant 15 percent increase in combined fatal, serious injury, and minor injury (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 showed, on average, between a 10% and 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 showed a reduction in total crashes but an increase in the KAB injury crashes.

The objective of this study was to evaluate the change in crash frequency or severity of varying lateral offset distances of high-tension cable median barriers in Minnesota. Crash and traffic data from 2016 to present were conjoined with roadway cross-sectional data and high-tension cable barrier locations to perform cross-sectional analyses for interstate segments equal to or greater than 0.05-miles long. Negative binomial regression models were estimated and used to develop crash modification factors (CMFs) for the following crash types: total crashes, target crashes, and barrier crashes. In addition to evaluating the impact of lateral offset, a naïve before-after evaluation was completed to quantify the impact of installing high-tension cable barrier.