Safety Effectiveness of Centerline Plus Shoulder Rumble Strips on Two-Lane Rural Roads

The combined application of centerline and shoulder rumble strips is intended to reduce the frequency of crashes by alerting drivers that they are about to leave the traveled lane. To date, this combination treatment has not been rigorously evaluated with a multistate database. To fill this void, this study evaluated treated two-lane rural road locations in three states. To account for potential site selection bias, an empirical Bayes (EB) before-after analysis was conducted. The combined results for all states indicate statistically significant crash reductions for all crash types analyzed. The crash type with the smallest crash modification factor (CMF) (i.e., the greatest crash reduction) is head-on with a CMF of 0.632 (i.e., a crash reduction of 36.8%). For run-off-road, head-on, and sideswipe-opposite direction crashes combined (i.e., lane departure crashes), the estimated CMF is 0.733. Benefit:cost (B:C) ratios were estimated to range from 28.2 to 67.7, depending on the treatment cost and service life assumption.