Rumble strips have become a popular treatment in North Carolina for reducing run-off-road collisions. Though the safety benefit is a compelling argument for further implementation, installations on two-lane roads have occasionally resulted in complaints from residents. A new rumble strip design, developed in Minnesota, has the potential to provide similar collision reduction benefits, with lower noise levels. This effort will evaluate the noise effects of the standard rumble strip design and a new design.
Residents living near or along roadways with shoulder rumble strips have complained about the excessive noise caused when a vehicle leaves the travel lane and strikes a rumble strip. In an effort to reduce this noise, a new, sinusoidal rumble strip, has been designed and installed in some locations. Sinusoidal rumble strips are designed to reduce noise along the roadside while also delivering the necessary auditory and vibratory cue to alert the driver of the vehicle that the vehicle has left the travel lane. An evaluation of two rumble strip designs - sinusoidal and rounded - was conducted at a test site along NC-71 in the study area near Shannon, North Carolina. The research team tested the rumble strips using three sound meters, a dump truck, a passenger vehicle, and an oscilloscope. This evaluation found that the standard rumble strip was generally louder than the sinusoidal rumble strip and that the distance away from the roadway impacted the difference. At a distance of 50 feet from the edge of the roadway, the loudness of the designs was similar, however at further distances of 100 feet and 200 feet, the sinusoidal design was 3 dBA and 9 dBA quieter, respectively. These results are expected given the results of the frequency analysis because sounds with higher frequency (as generated by striking the sinusoidal rumble strip) do not carry as far as the lower frequency standard rumble strip strike. However, both the standard and sinusoidal rumble strips produce a noise level that is substantially higher (more than double) than the ambient noise level - suggesting that both designs should provide a sufficient warning to drivers of errant vehicles.
