Two-lane rural highways in Washington State represent approximately 4,900 miles. From 1999 to 2005 , 42.8% of the fatal collisions reported on state highways occurred on two-lane rural highways. WSDOT determined that the traditional high collision frequency location approach does not necessarily reflect the safety needs of two-lane rural highways. The research team first conducted a systematic review of the network and then developed a proposed decision-matrix for the selection of countermeasures on two-lane rural highways. A rate-based approach was used to show various trends across different user groups, geometric features, and contexts.
It is generally accepted that the context of the two-lane rural highway would influence countermeasure choice. The project tested two contextual surrogates for the identification of particular two-lane rural highways that may exhibit safety characteristics that are different from the rest of the network. First, proximity to K12 schools (in half mile increments up to 2 miles) was tested to determine whether it could assist in identifying more developed areas, such as rural town centers. It showed promise and identified areas with lower collision severity but higher collision frequency along with a higher incidence of pedestrian related collisions. Second, proximity to urban boundaries (increments up to 2 miles) as a means to identify transition areas showed less promise.
The decision-matrix summarizes countermeasure effectiveness by collision group and also make reference to the findings from the systematic assessment. The project also included a limited before-after study of centerline rumble strip installations (CLRS). Caution is needed in terms of application of these findings because of small sample sizes in the analysis and the fact that roadside characteristics could not be incorporated in the evaluation process. The report recommends the development of safety performance functions that would incorporate these features. These multivariate approaches could further assist the department in the development of system-wide and corridor level approaches for two-lane rural highways.