Less rumble, more mumble.
Tucked inside the Washington State Department of Transportation’s annual noise quality report is an update on the agency’s rumble strip research.
The carved grooves along the sides or down the center lines of many roadways serve as a wake-up call for drivers who stray over the solid painted lines.
The state has installed them since 1999 in problem areas. In 2008, the state spent $4 million to install center line rumble strips on U.S. 2 to combat deadly crossover crashes.
They’ve worked. Statewide, crossover crashes went down 65 percent in places where rumble strips were placed along both shoulder and center lines.
But apparently the grooves can be kinda noisy to the neighbors.
WSDOT ran some figures in recent years in an attempt to find the most effective noise-reducing dimensions. Test sites ran the decibel range, from garbage disposal to power mower. The answer they came up with: Divots 6 inches wide, 8 inches long, and a half-inch deep could produce at least a one-quarter reduction (5 decibels) in sound level to nearby homes.
The state’s now testing the new design on Highway 24 near Othello.
In the future, the agency might also try out “mumble strips.” These have a shallow wave design in long, parallel grooves. California, Pennsylvania and Minnesota have found them effective. These serve the same purpose as rumble strips but are quieter.
Then, too, there is the “virtual” rumble strip, as more cars take on the safety role. An increasing number of manufacturers offer systems that detect when a car veers from a lane and warn the driver with an audible or visual warning, or even a shake of the steering wheel.
Have a question? Email us at streetsmarts@heraldnet.com. Please include your first and last name and city of residence. Look for updates on the Street Smarts blog.
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