Frequently Asked Questions
Q: What are rumble strips and how do they improve roadway safety?
A: Rumble strips are grooved patterns placed in the pavement perpendicular to the direction of travel. They can be installed either at the centerline of the roadway or on the roadway shoulder, as illustrated in the photo above.
When a vehicle passes over a rumble strip the driver receives an audible warning (rumbling sound) and feels a vibration warning him/her that they are encroaching on the centerline or roadway shoulder.
Inside a vehicle the sound volume from radio and conversation can diminish some of the audible benefits of rumble strips, but most drivers can't miss the physical effect of the vibrations they feel when their vehicle's tires hit the rumble strips. In fact, a study by the Virginia DOT showed that milled-in rumble strips produce a vibration level 12 times greater than rolled strips, which were previously used in Iowa.
These physical and audible warnings provide the drowsy, distracted or impaired driver with an opportunity to correct their behavior and return their vehicle to the travel lane, avoiding a crash similar to the one depicted in the photo above.
Note: Although not addressed on this site, Iowa is also one of handful of states in the U.S. that use transverse rumble strips. These strips increase safety by reducing the approach speed of a vehicle and provide an audible warning to the driver that they are approaching an intersection. Transverse rumble strips are most commonly used on rural, two-lane roadway intersections with two-way, three-way or four-way stops. These types of strips have also proven particularly effective during nighttime periods when drivers are unsuspecting of approaching conditions due to unfamiliarity with the roadway, may be drowsy or their vision is inhibited by the darkness.
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