16.6 Rumble Strips

Rumble strips are raised or grooved indentations on the shoulder or median. When a vehicle departs its lane and travels over rumble strips, motorists hear an audible alert and experience a vibrating sensation that warns their vehicle has departed the travel lane. A 6 – 15 dBA increase in sound above ambient sound levels can be detected by motorists who are awake.
Rumble strip designs need to balance the provision of alerts with maintaining an acceptable travel surface for bicyclists and other users. Table 16.3 summarizes information on rumble strip dimensions and placement.

Table 16.3 Design Guidelines for Rumble Strips
Design Element	Suitable Values	Effect on Driver	Effectiveness
Lateral Placement / Offset	Typically, 6+ in. from the lane edge	When groves are closer to the lane edge, motorists experience them sooner.	Motorists have more space to recover the sooner the warning occurs.
Groove Width	16 in. (12 in. widths may be used value for narrow shoulders)	Wider rumble strips produce longer-duration sounds and vibrations when vehicles travel over them laterally.	Longer-duration sounds are easier to detect.
Groove Depth	7/16 in.	Deeper grooves increase sound and vibration.	Louder sounds and more pronounced vibrations can be detected easier against background noise.
Groove Separation	11 – 12 in.	Narrower separations increase the frequency of alerts.	Higher tones convey a greater sense of urgency.
Longitudinal Gaps	None, if bikes do not share the shoulder 12 ft. if bikes share the shoulder	Gaps ≤ 12 ft. reduce the likelihood of vehicles missing rumble strips.	Gaps are more effective because alerts are shorter over gap sections.

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Chris VanDyke

Research Scientist | Program Manager

chrisvandyke@uky.edu