Impact of Centerline Rumble Strips and Shoulder Rumble Strips

To prevent roadway departure crashes, rumble strips have been installed on Louisiana’s two-lane highways. This study investigated the impact of rumble strips on 1,593.09 miles of two-lane highways in Louisiana, on which centerline rumble strips (CLRS) and shoulder rumble strips (SRS) were installed between years 2010 and 2016. The comprehensive evaluation consists of observed crash analysis and state-of-the-art crash countermeasure evaluation methods. To capture all departure scenarios and take full advantage of crash data, the observed crash analysis includes not only conventional total crashes and targeted crashes, but also crashes with combined key crash attributes, as well as selected crash report reviews, which helps to the clarify the ambiguous or inconsistent information identified during the initial analysis. The biggest reductions come from fatal and severe injury crashes, which are 34% for rural two-lane and 45% for urban two-lane highways. The safety evaluations from multiple evaluation methods consistently demonstrate the success of rumble strips, particularly the centerline rumble strips installations. The before and after empirical Bayes (EB) analysis, comparison group EB analysis, with-and-without cross-sectional analysis, and ARIMA Intervention Model of trend analysis yield reliable CMF estimations for centerline rumble strips. The expected CMFs from before-after EB method are 0.845, 0.95, and 0.764for CLRS, SRS, and combination of CLRS and SRS on rural two-lane highways, respectively. They are 0.677, 0.655, and 0.839on urban two-lane highways, respectively. The huge economic benefits of rumble strips are manifest by the ratio of benefit to cost –12.98for combined all rumble strips cases on rural two-lane highways, and 14.64, 1.9, and 7.37 for the CLRS, SRS, and both (CLRS and SRS), respectively. The ratio is 37.2 for all rumble strips on urban two-lane highways, 38.27for CLRS, and 83.55 for CLRS and SRS combined. This study demonstrates rumble strips as a low cost, effective crash countermeasure on two-lane highways. To reach the state’s goal of Destination Zero Deaths, rumble strips should be considered for installation along two-lane highways everywhere, if financially feasible, or if not, by prioritizing the installation projects based on either the crash frequency or crash risk at the network level. The full report can be downloaded from the Louisiana Transportation Research Center at https://www.ltrc.lsu.edu/pdf/2021/FR_648.pdf