Summary:
Sinusoidal rumble strips were designed to alleviate noise concerns by reducing roadside noise for residents, while maintaining adequate levels of in-vehicle noise and vibration. However, while research has shown that traditional rumble strip designs are effective towards reducing lane departure crashes, the safety performance of the sinusoidal rumble strip design remains unproven. Additionally, it is not well understood how the various corrugation designs impact bicyclist stability and comfort. Research was conducted to evaluate the effectiveness of sinusoidal shoulder corrugations as a traffic safety strategy, considering noise and vibration, stability and comfort for bicyclists, and traffic crashes. Five primary tasks were conducted, which included: (1) a field evaluation of roadside noise and in-vehicle noise and vibration produced by sinusoidal shoulder corrugations compared to traditional shoulder corrugations; (2) a field evaluation of bicyclist comfort, stability, and vibration when contacting sinusoidal vs. traditional corrugations; (3) an online nationwide survey of bicyclists’ perceptions and experiences with rumble strips; (4) a survey of motorcyclists traveling in Michigan to determine their perceptions and experiences with rumble strips; (5) a safety performance analysis to develop crash modification factors for sinusoidal shoulder rumble strips. Overall, it was concluded that sinusoidal shoulder corrugations effectively reduce roadside noise compared to traditional corrugations without compromising the level of in-vehicle noise or vibration necessary to alert drivers. At 55 mph, the sinusoidal corrugations generated roadside noise levels that were 2.4 decibels lower than the traditional corrugations, regardless of vehicle type. At 65 mph, the sinusoidal corrugations generated roadside noise levels that were 4.8 dBA and 8.8 dBA lower than the traditional corrugations when contacted by a minivan and snowplow truck, respectively. The results of the safety performance analysis show that installation of sinusoidal shoulder corrugations reduced total crashes by 8.3 percent and single vehicle lane departure crashes by 29.6 percent. In contrast, results from the bicycle field study indicated that riders preferred the traditional corrugation design over the sinusoidal design, due to the lower comfort and reduced controllability experienced when traversing sinusoidal corrugations. This finding was supported by the vibration measurements, as the sinusoidal corrugations produced greater vibration at the bicycle handlebar than the traditional design. However, both the bicyclist field study and the nationwide bicyclist survey found that bicyclists value a smooth and debris-free shoulder of at least 3-ft in width as the most important aspect towards ensuring comfort, stability, and overall safety. Motorcyclists were in general agreement with bicyclists in that debris on the pavement surface represents greater safety concern than rumble strips, as motorcyclists generally do not experience significant safety or control issues when encountering rumble strips. Collectively, the results suggest that continued use of sinusoidal shoulder corrugations in noise-sensitive environments is warranted, although additional design considerations, such as including regular gaps in the corrugations and/or placing the corrugations on the edge line, should be considered along highways utilized by bicyclists
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