Policy considerations for evaluating the safety effectiveness of passing lanes on rural two-lane highways with lower traffic volumes: Wyoming 59 case study

Transportation agencies across the nation are continuously evaluating the safety and operation of their rural two-lane highways. The three most common countermeasures are to do nothing, add passing lanes to target sections, or to upgrade to four-lane. The goal of this article is to update the current body of knowledge available to agencies on the process of implementing countermeasures and realistically evaluating their safety effectiveness. The Wyoming Department of Transportation (WYDOT) constructed nine passing-lane segments on a 26-mile stretch of rural two-lane highway. Preliminary analysis using 7-year crash data showed that the safety benefit was negligible at best. However, utilizing Empirical Bayes and Wyoming-specific safety performance functions, it was shown that the basic approach of comparing crash rates underestimated fatal and injury (F+I), and lane-departure crashes and that the passing lanes had a significant safety benefit. Furthermore, the authors looked at what would have happened from a safety and cost perspective had no countermeasure been implemented and then also if the road had been upgraded to four-lane undivided instead of just adding passing lanes. It was shown that passing lanes are the best option from a safety and cost perspective especially when agencies have constrained budgets.