What is a Rumble Strip?

Rumble strips are a device used on many roadways since the early 1990s for safety purposes. According to the Washington State Department of Transportation, "Rumble strips are grooves or rows of raised pavement markers placed perpendicular to the direction of travel to alert inattentive drivers. As a vehicle passes over the rumble strips, noise and vibration are produced, alerting the driver they are approaching a hazard." In other words, they are raised or corrugated sections of the roadway used for safety purposes. According to WiseGeek.com, rumble strips are most commonly "created by heavily grooving the pavement, creating a corrugated surface which will jar a car when its wheels pass over the rumble strip. The rumble strip is often embedded into the pavement, so that plows can remove snow and ice from the road. In other cases, a rumble strip is made with elevations in the roadway, such as Botts' dots."

Different Types

There are different types of rumble strips for different reasons. Roadway rumble strips (RRSs) are larger strips placed directly on the traveled area of the road where vehicles drive. This type of strip alerts drivers that there may be a change of condition or a hazard that may constitute lowering speed. For instance, when a highway ends and enters a more residential area, there may be roadway rumble strips to warn the driver to be more alert to the road and area ahead and often times used to signal drivers to slow down. These are also used sometimes during construction, near certain types of stations or districts (areas near schools and playgrounds, for instance), and places with a high volume of accidents due to drivers not being as alert as they ought to be.

The second type of rumble strip is a shoulder rumble strip (SRS). A shoulder rumble strip is defined by the Federal Highway Administration as "a longitudinal design feature installed on a paved roadway shoulder near the travel lane. It is made of a series of indented or raised elements intended to alert inattentive drivers through vibration and sound that their vehicles have left the travel lane. On divided highways, they are typically installed on the median side of the roadway as well as on the outside (right) shoulder." Shoulder rumble strips are placed just beyond the commonly traveled portion of the roadway (in the shoulder area of a paved road) to alert drivers that they are veering into an area not intended for vehicle use. These are often used on major highways to alert sleepy motorists and make them more vigilant when driving. Shoulder rumble strips are often placed on roads having certain higher speed limits and in areas where accidents occur from running off the road.

Lastly, the centerline rumble strips (CRSs) are placed on the center of an undivided highway (in between both lanes or in between the yellow divider lines) to warn drivers they are crossing over into oncoming traffic or leaving the proper driving area for their side of the road. This is also used as a device to wake driver's who might be sleepy or caught in highway hypnosis. These are often placed in areas that have a high incidence of accidents due to crossing over the yellow line, or center line, of a road.

How They are Made

There are also four different type of rumble strip designs: milled-in (made by grinding the surface and creating indentations), rolled-in (installed using a steel wheel roller metal pipe or steel bars are welded to and pressing the shape of the bar into the road surface), formed (added to freshly poured concrete with a form that is imbedded into the surface), and raised (which can be made from a variety of methods and materials).

The Good, the Bad, and the ... Loud?

Rumble strips are great for alerting motorists, but they also have some undesirable results as well. Some residents who live near busy roads that utilize rumble strips claim the noise level is unreasonable. Also, if there is a defect in the road near a rumble strip, they can have sharp edges and cause greater potential for a flat tire. There are also other trade offs associated with rumble strips, and they are not recommended to be used in areas with many bicyclists.

Much research has been done to validate the effectiveness of these safety features. As with almost everything, there is give and take. On the one hand, they are excellent safety devices to heighten awareness of drivers, but they can be loud for residents and create problems for those riding bikes. Perhaps a new, more effective version of these will be coming out soon. Happy driving -- be safe!

Sources:

http://www.wsdot.wa.gov/Design/Policy/RumbleStrips.htm
http://www.fhwa.dot.gov/legsregs/directives/techadvs/t504035.htm
http://www.wisegeek.com/what-is-a-rumble-strip.htm