OTREC-RR-11-18

This research sought to evaluate the safety implications of advisory speeds at horizontal curves on Oregon rural two-lane highways. The goal of this research is to characterize driving at such curves with advisory speed signs, and to determine what role the signs play in enhancing safety. Speed and signage compliance data was collected at 16 sites. Site crash data and an examination of how advisory speed relates to historic crash information are included with a statistical model that identifies critical variables associated with the posted speed and how they relate to the expected crash frequency. An advisory speed model was developed to assess predicted crash outcomes based on geometric design, operations, and signage. The resulting model was compared to advisory speeds based on Oregon policy and 2009 MUTCD thresholds. The safety-based model predicted advisory speeds that are less conservative than those recommended by the ball-bank thresholds in the 2009 MUTCD or the thresholds Oregon has been using.