A Comprehensive Evaluation of Operational and Safety Performance of Directional Rumble Strips on Freeway Off-Ramps

Abstract

A freeway off-ramp is a short section of roadway that allows vehicles to exit the freeway. Wrong-way driving (WWD) and failure in speed management were found to be the major issues on these off-ramps. Countermeasures have been implemented at off-ramp terminals to prevent wrong-way (WW) entries and control vehicle speeds, including signs and pavement markings. Intelligent transportation system (ITS) technologies were also implemented at limited sites due to the higher cost and lack of quick emergency responses in rural areas. Studies found that these signs or pavement markings might not be effective. Moreover, the costly ITS technologies, with inherent false alarm rate, request a quick emergency response. To overcome the issues of WWD and speed control on freeway off-ramps, this study presents the field evaluation results of a low-cost countermeasure – directional rumble strips (DRS), which are expected to deter WWD and slow down right-way (RW) vehicles. Initially, five DRS patterns (named A to E) with various configurations were developed and tested. Three patterns (D3, C, and E.1) of DRS were recommended for field implementation based on the closed-course test results. 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 E.1 was placed on the tangent part before the ramp curve. Southbound off-ramps at Exits 208 and 284 on I-65 in Alabama were selected for implementation as they were ranked as high-risk locations by a network screening tool developed by Auburn University. A total of 1, 296 hours of video data was recorded to monitor WW incidents using portable cameras. Another 1, 344 hours of traffic speed data were collected using magnetic sensors. Field driving tests were conducted to collect sound and vibration data at various speed categories for both RW and WW directions. Before-and-after studies evaluated the effectiveness of the DRS patterns in reducing WW incidents and traffic speeds on off-ramps. Sound and vibration analysis quantified the differences between RW and WW drivers’ perceptions. Results showed that the number of WWD incidents and average driving distances were significantly reduced after implementing all the DRS. The results confirmed that WW drivers can perceive elevated sound and vibrations when passing the DRS. The DRS can also reduce the mean, 85th percentile, and standard deviations of RW traffic speeds. Transportation agencies can utilize these findings as well as the general guidelines developed from this study to implement DRS for the purpose of deterring WWD and controlling traffic speeds on the freeway off-ramps.