Potential Crash Reduction Benefits of Safety Improvement Projects. Part A: Shoulder Rumble Strips

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Potential Crash Reduction Benefits of Safety Improvement Projects. Part A: Shoulder Rumble Strips

A. Abdel-Rahim / M. Khan

This research provides a comprehensive evaluation of the safety benefits of shoulder rumble strips in rural highways in Idaho. The effectiveness of shoulder rumble strips in reducing the number and severity of run-off-the-road (ROR) crashes was examined based on Idaho's crash experience for 3 different roadway types: 2-lane rural highways, 4-lane rural highways and rural freeways. All ROR, severe ROR crashes, and truck ROR crashes were analyzed as part of this study. The evaluation was done using two different evaluation methods: Comparison Groups (CG) before-and-after analysis and Empirical Bayes (EB) before-and-after analysis. For cases where control section data was limited or not available, naive before-and-after analysis was used. Based on Idahos crash data, the installation of shoulder rumble strips on 2-lane rural highways resulted in a 15 percent reduction in all ROR crashes and a 74 percent reduction in severe ROR crashes. The benefits seem higher in roadway segments that have little to moderate roadway curvature. For rural freeways, the percent reduction in all ROR crashes and severe ROR crashes was 29 percent and 67 percent, respectively. The big difference between the two numbers is because there seems to be a higher percentage of minor (less severe) crashes on the freeway segments tested. The percent reduction in all ROR crashes and severe ROR crashes when shoulder rumple strips were installed in 4-lane rural highways were 60 percent and 45 percent, respectively, which is statistically significant. Truck crashes in all rural highways also decreased after shoulder rumble strips installation by a range of 42 to 62 percent.