Trying to make the roadways a bit quieter Arizona Republic Bill Taylor, who lives in the F.Q. Story historic district near 15th Avenue and McDowell Road, says traffic from the nearby Papago Freeway generates way too much noise. A sound wall added last year along Interstate 10 has helped, Taylor says, but not enough to truly enjoy his back yard. "The thing that really makes the racket on the road is the tire-to-concrete roar," said Taylor, 48, who's lived there since 1983, before the freeway was built. So why, Taylor asks, doesn't the Arizona Department of Transportation put a layer of asphalt on I-10, as it did last year when it rebuilt a seven-mile section of the Black Canyon Freeway (I-17)? The asphalt offers a quieter ride for drivers and the surrounding neighborhoods. "You hit that asphalt (on I-17), and it feels like you're driving on sponge rubber," says Taylor. ADOT spokesman Matt Burdick says a rubberized asphalt surface is up to 4 decibels quieter than concrete, because noise is trapped in the porous asphalt. But that quality deteriorates over time as the asphalt compacts under the weight of traffic. That has kept the Federal Highway Administration from approving rubberized pavement for noise reduction. Rubberized asphalt, though, is popular in Arizona. It covers about 2,500 of the state's 6,000 miles of highways. Cost is about $75,000 per lane, per mile. But on metro freeways, with traffic counts up to 250,000 cars per day, foot-thick concrete is used because it lasts 20 years or longer, about twice as long as rubberized asphalt. On freeways older than 20 years, such as the Black Canyon, ADOT uses rubberized asphalt to extend the life of existing concrete. When the Superstition Freeway is widened in Tempe and Mesa starting this summer, sections also will be surfaced with it. Since I-10 is only about 15 years old in the area near Taylor's neighborhood, it's too new to be considered for asphalt resurfacing. ADOT plans to test noise levels over the next 10 years on various road surfaces around the state to gather noise data. A vehicle will pull a trailer, with a microphone attached to one of its wheels, to measure noise levels coming from the surfaces. ADOT will then turn the data over to the feds. "We're trying to quantify if there's a consistent noise benefit to that," Burdick said. A six-year noise study was done on a Sacramento expressway that showed a reduction of 4 decibels when using rubberized asphalt. "I think it's pretty significant, especially on interstates made with Portland concrete," said Doug Carlson of the Rubber Pavement's Association, a Tempe firm that promotes the industry. ADOT's noise level goal is 64 decibels. The agency uses permanent walls and berms on freeways running next to established neighborhoods in many cases. When rubberized asphalt is
used, Burdick says it's considered a bonus noise benefit. "You can tune yourself out to it," Bill Taylor says, "but it gets to be kind of a pain when that's all you're doing." Copyright 2000, The Arizona Republic. All rights reserved.
Letter to the editor
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