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

Abstract

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.