Human Factors Considerations in the Design of Rumble Strips

Although a number of technical reports have considered different aspects of construction on crash statistics, human factors considerations are less prevalent, and no study has examined the perceptual consequence of altering the frequency of the repetition pattern. In experiment 1, the effect of frequency on perceived urgency in an auditory-only simulation of rumble strips was considered using a magnitude-estimation task. Results indicated that the ideal frequency range (yielding the highest urgency) was between 12.5 to 25 Hertz (Hz), which is lower than the range produced by typical rumble strip spacing. A psycho-acoustic explanation of this result is that the frequency range between 12.5 to 25 Hz is within the range in which sequential noise bursts can be resolved but below the range in which noise bursts fuse and give rise to pitch perception. In experiment 2, participants estimated pitch strength and matched the pitch of simulated rumble sound to a pure tone. As expected, pitch strength estimates and the accuracy of pitch matches were consistently low between 17 to 50 Hz but increased linearly with frequency beyond 50 Hz. On the basis of this auditory-only simulation, it appears that rumble strip spacing leading to audible but infra-pitch sound is ideal.