July 13, 2011 By Sarah Rich
Freeway noise is one of the biggest public nuisances of modern society, and billions of dollars have been spent erecting sound barriers to muffle the din of constant traffic on America’s freeways and thoroughfares.
Virginia is joining a growing number of state transportation departments that are experimenting with the roads themselves in order to dampen the noise. This month the Virginia Department of Transportation (VDOT) will lead the installation of “quiet pavement” technologies in three demonstration project locations.
According to VDOT, the testing will take place on four-lane, divided high-speed roads in Leesburg, Williamsburg and an area near Chester. Each location will test a variation of traditional hot-mix asphalt called “porous friction course.” The technologies will be monitored over the next two years to see how they perform.
Virginia Gov. Bob McDonnell signed legislation in late May to direct VDOT to construct the projects. “These demonstration projects will take results from one recent study and put them to work to make our roads safer and last longer, and to improve the quality of life for those living near the roadways,” McDonnell said in a statement.
This won’t be the first time quiet pavement has been tested in Virginia. In 2008, the Virginia Center for Transportation Innovation and Research — a research branch of VDOT — piloted the porous friction course for a year in Manassas, which is about 90 miles north of Richmond.
The porous friction course was cost-competitive with traditional hot-mix asphalts while reducing tire noise, according to the research center.
“This ‘open-graded mix’ allows air and water to seep down from the road surface away from tires,” according to VDOT. “It reduces hydroplaning, tire noise, and splash and spray. The improved drainage also cuts wet-night glare and improves the visibility of road markings.”
For at least the past decade, several states including California, Arizona, Colorado and Kansas have tried different asphalt types in an effort to reduce noise on roadways. For example, the Arizona Department of Transportation has in the past resurfaced hundreds of miles of highways with rubberized asphalt composed partly of old tires.
But a study from the Washington State Department of Transportation found that some quiet pavements can degrade relatively quickly in harsher climates. Others lose their noise-reducing benefit as the pavement ages.
Back in Williamsburg, Va., early phases of the state’s quiet pavement project began July 5. Tom Druhot, the Williamsburg project-area construction engineer, said quiet pavement technology involves changing the gradation of stone in the asphalt and the binder that holds the stone together.
“You leave out some small-sized aggregates so you have more porous asphalt,” Druhot said. “And what happens there is as the tires are going over the roadway the noise — the sound waves — when they go down and hit the pavement, they don’t get bounced back up.”
Druhot said after Nov. 1, VDOT plans to put cameras at “wheel level” in the three project areas to capture acoustic readings of the passing vehicles. By capturing this information, VDOT will be able to measure the sound levels and compare them against adjacent sections that don’t have the porous friction course asphalt. The noise levels will be measured periodically over the next two years.
“After two years, we no longer gather the data and we [will] keep an eye on the asphalt and see what its useful life is,” Druhot said. “When it needs repairing, we will document it, and we’re hoping it will be a standard, useful life of 10-plus years before it has to be repaired or replaced again.”
The total contract for the quiet pavement project is about $7.5 million, which will come out of VDOT’s maintenance fund, Durhot said. In addition to the three asphalt projects, concrete demonstration projects will be installed on a section of interstate in two other locations.
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