A New Concept Design of Directional Rumble Strips for Deterring Wrong-way Freeway Entries

Abstract

Wrong-way driving (WWD) on freeways has been identified as a serious traffic safety problem. Drivers who make wrong-way entries onto freeways pose a serious risk to the safety of other motorists and themselves. This study investigates the feasibility of a novel design of Directional Rumble Strips (DRS) to discourage wrong-way entries onto freeway exit ramps. In order to obtain the most optimal design of DRS, the study first evaluated the effectiveness of existing Transverse Rumble Strips (TRS) applications and set the driver’s perceptibility threshold of sound and vibration based on the field data. Particular attention was given to the TRS treatments on the approaches to the high speed intersections with typical installations in Alabama. The measurement of effectiveness was selected as attention-getting characteristics, speed changes, and driver braking behavior. The test results showed that implemented TRS can generate sound and vibration that have significant effects on vehicle speed and driver performance during both day and nighttime conditions. For sound levels at different speeds, the A-weighted volume in the area of the TRS was on average 14 dBA above the baseline noise level without TRS, and the vibration signal along the vertical axis resulted in an average difference of 0.68 m/s2 when compared with normal pavement. The average speed reductions ranged between 0.95 to 8.63 mph for time mean speed, and from 0.84 to 9.71 mph for the 85th percentile speed. The percentage of braking behavior accounted for 40% to 80% of recorded vehicles. All these findings support the possibility of using DRS to influence the wrong-way driver’s behavior and also provide references for the DRS design and effectiveness evaluations. Several conceptual designs of DRS were proposed based on the state DOT design guidelines, current practices, and feedback from a national survey. Each of the concept designs was expected to generate elevated noise and vibration for wrong-way driving, and normal noise and vibration for right-way traffic on exit ramps. A national survey collected the opinions on the conceptual designs from transportation practitioners and vendors who are knowledgeable about rumble strips design, manufacturing, or installation. Based on the survey and literature review results, a total of five patterns and eight configurations were developed for evaluation. The field tests were conducted to collect noise and vibrations generated by the proposed eight DRS configurations at the pavement test track of the National Center for Asphalt Technology (NCAT) of Auburn University. Six speed categories for the testing vehicles were set at 10 mph, 15 mph, 20 mph, 25 mph, 35 mph, and 45 mph. At least six field measurements were taken for each speed category in both directions. The generated sounds and vibrations for the WWD were compared with the ambient conditions and existing TRS stimuli levels. The results suggest that all the tested patterns generated adequate sound changes in the wrong-way direction to alert drivers to slow down (7.2 to 16.6 dBA increases). Pattern D Configuration 3 and Pattern E produced comparable vibration changes with previous studies (2.57 m/s2 and 2.30 m/s2, respectively). Statistical analyses were then conducted to examine if there was a significant difference in the sound and vibration between right and wrong directions. Pattern C generated significantly different sound and vibration signals when driving in the wrong-way direction and the right-way direction from 10 to 25 mph. The Pattern E generated significantly different vibration at speed of 45 mph. Finally, DRS Pattern C, Pattern D Configuration 3, and Pattern E were recommended for further optimization and implementation based on their attention-grabbing effects.