WSDOT began installing rumble strips on undivided highways in 1999 as a countermeasure for roadway departure crashes. Installations on the shoulders were intended to reduce run-off-the-road crashes, while centerline rumble strips targeted reductions in cross-centerline crashes. A March 2011 report detailed the performance of centerline rumble strips on Washington State highways. This study:
• Examines the combined effects of centerline and shoulder rumble strips.
• Details the performance of rumble strips on undivided highways in Washington State under a variety of conditions.
• Explores various traffic volumes, geometric conditions, lane and shoulder widths, and driver contributing circumstances.
• Compares various installation scenarios with shoulder and centerline rumble strip installation at different times, as well as simultaneous installation.