PHOENIX (Ivanhoe Newswire) -- We have 4 million miles of roads and streets in the U.S. highway network. With millions of cars and trucks travelling those roads every day, the federal government wants to find ways to reduce the noise impact on nearby neighborhoods. How? The answer might be right under your wheels.
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Betsy Gilpin moved away from the city so she'd have plenty of room to train her agility dogs … and plenty of peace and quiet. Eventually, the city caught up with her.
A new freeway down the street means no more quiet.
"It's just loud," Gilpin told Ivanhoe. "I think of it more. When I'm outdoors trying to do something, then I'm really aware of it because it's just this drone in the background all the time. It never really goes away."
Concrete road surfaces are durable, but noisy.
"What you hear here is really the sound of the tires rolling over the pavement," Doug Nintzel, of the Arizona Department of Transportation in Phoenix, Ariz., told Ivanhoe.
Engineers have discovered that covering concrete with a layer of rubber asphalt softens the pavement and reduces sound as tires roll over it.
"These actually pick up the vector of sound coming off the tire," Paul Donavan, an acoustical engineer at Illingworth & Rodkin, Inc., in Petaluma, Calif., told Ivanhoe.
Donovan developed specialized testing equipment with high-sensitivity microphones that measure road surface noise. He found that rubberized road surfaces cut noise by eight to 10 decibels.
"We're seeing levels that are somewhere in the upper 70s," Donavan said. "The original measurements with the concrete were in the upper 80s, so we're seeing about a nine dB reduction."
How much quieter is that? Think of the difference you hear between a passenger car and a tractor trailer.
"A car and a truck, a heavy truck, are basically 10 db different, so if you can imagine a car going by and then compare it to a truck, that would be about the difference we're looking at, which is pretty amazing for just changing the pavement," Donavan said.
The crumb rubber used to make rubberized asphalt is made from old tires. Ten-thousand to 12,000 tires go into each mile of roadway instead of landfills and junk piles.
City or country, it's turning highways into better neighbors … one mile at a time.
Virtually every highway mile in the Phoenix area has been resurfaced with the quieter rubberized material.
The Acoustical Society of America, the American Society of Civil Engineers, and the Materials Research Society contributed to the information contained in the TV portion of this report.