Setting an appropriate speed limit is necessary to provide safe and efficient traffic flow. Lower than required speed limits may make the majority of drivers non-compliant, whereas higher speed limits may increase the number of crashes together with related injuries and fatalities. Speed limits on more than 800 miles of freeway sections were raised from 70 mph to 75 mph in Kansas in 2011. This study evaluated the safety impact of the speed limit increase by applying the empirical Bayes observational before-after studies approach. Details of crashes by severity level were obtained from the state crash database for 3 years before and 3 years after the speed limit change. The crash modification factor (CMF) was estimated and showed that the total crashes increased by 16% after the speed limit increase. The results from this study will help for the safety improvement of freeways in Kansas in the future.
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