Approximately 40% of all 2004 fatal crashes were single-vehicle, run-off-the-road (SVROR) crashes. The problem was even more significant on two-lane rural roads, where shoulder rumble strips were an important treatment in the prevention of these crashes and have proved effective on freeways. However, no studies have evaluated the effectiveness of shoulder rumble strips in reducing SVROR crashes on two-lane rural highways. An empirical Bayes before-and-after study was performed to evaluate the safety-effectiveness of milled-in continuous shoulder rumble strips on two-lane rural highways in Minnesota. The treatment was installed at 23 treatment sites (183 mi). This study reports a 13% reduction in all SVROR crashes and an 18% reduction in injury-producing SVROR crashes after installation of this treatment.