In March 2016 the state of Oregon raised the speed limit by 10 mph for passenger vehicles and 5 mph for trucks on multiple two-lane, two-way rural highways in Eastern Oregon. Twelve highway segments were analyzed to study the before and after effects of raising the speed limit. Both the before and after study periods consisted of 34 months beginning in 2013 and ending in 2018. The crash data were obtained from ODOTs crash data reporting system and then analyzed using an observational before/after Empirical Bayes method selected from the Highway Safety Manual after researching various analysis methods through a literature review. The Empirical Bayes method was selected based on is ability to eliminate issues with regression to the mean and the inclusion of local calibration factors. The safety effectiveness of the highways decreased by 27% following the speed limit increase. This confirms that there is a correlation between speed and crash frequency.
