Impacts of Directional Rumble Strips on Vehicle Speeds and Driver Behavior at Freeway Off-Ramps

Drivers have an increased crash or incident risk when driving on freeway interchange ramps compared with the other interchange-related segments. Directional rumble strips (DRS), a pattern similar to the traditional traversable rumble strip, were developed as a low-cost traffic control device to deter wrong-way driving, meanwhile reducing right-way traffic speeds and changing driver behavior on off-ramps. This paper presents the impact of DRS on vehicle speed and driver behavior based on the two case studies at southbound off-ramps at Exits 208 and 284 on Interstate-65 (I-65) in Alabama. Three DRS patterns (D3, C, and E2) were implemented at different locations on off-ramps. Pattern D3 was installed at the off-ramp terminal near the stop bar or yield line. Pattern C was implemented at the segment between the terminal and ramp curve. Pattern E2 was placed on the tangent part before the ramp curve. A total of 1,344 h traffic speed data before and after the implementation were collected using magnetic sensors. Driver behavior was monitored for 576 h using video cameras. Before-and-after studies evaluated the impact of three DRS patterns on traffic speed on these two off-ramps. The results revealed that DRS can significantly reduce the mean, 85th percentile, and standard deviations (SDs) of off-ramp traffic speeds. In addition, DRS can help to mitigate aggressive driver behavior (e.g., exceeding the ramp speed limit) and guide turning traffics at ramp terminals. (C) 2020 American Society of Civil Engineers.