A lot riding on 'quiet pavement' in Bellevue as testing continues

From his large deck, Richard Kress has a beautiful view of the valley beneath his Bellevue home. But the 54-year-old international market developer doesn't use it because of noise from Highway 520.

Megan DeSantis, a 42-year-old Woodinville resident, turns a fan on to drown out the noise from nearby Avondale Road — the only way she can get to sleep at night.

They and countless others who live near Washington freeways and other busy roads have a lot riding on a 1.3-mile stretch of Interstate 405 in South Bellevue.

That segment, repaved in August, is the third and final site of a state Department of Transportation (DOT) experiment on the use of what is called "quiet pavement," a technology that has received increased attention since its successful use in Arizona.

Residents cheered when the DOT started the experiment here in 2006. But the first two test sections — on Interstate 5 and 520 — did not perform well in noise reduction or durability.

State officials tweaked the process for the I-405 test. Five months into the test, it's too soon to draw any conclusions, officials said. Even if the results are good, officials would not immediately repave any roads, but the technology may find its way into future projects.

In King County, an area divided by freeways, many residents could be affected. In addition to the annoyance factor, studies have shown that living near loud noise can lead to hearing loss or other health problems. It's a problem for motorists, too, who must crank up the radio or find other ways to deal with the din as they drive.

"This is not a socio-economic thing or divided along party lines," said Walter Scott, a 52-year-old Beaux Arts businessman who has long pushed for quiet pavement. It's "an important thing for everyone."

How it works

Still, few people know exactly why roads get so noisy.

DOT spokesman Travis Phelps explained that most of the noise comes not from cars themselves but from "tire slap" — the sound of tires striking pavement.

The most common way to mute it uses rubberized asphalt, a mixture of normal asphalt and tiny pieces of rubber — usually from recycled tires. That creates air pockets that absorb, redirect and change the frequency or pitch of tire slap. Another common method uses chemicals that also create air voids.

Both methods cost at least 50 percent more per lane-mile than standard asphalt, according to the DOT. But because less is needed to cover roads than normal asphalt, the cost is about the same. Quiet pavement may be even cheaper.

A Phoenix city engineer discovered the impact of rubberized asphalt in 1966 when filling potholes with pieces of recycled tire. Gradually, the Arizona Department of Transportation started using it for pavement overlays and today most Phoenix-area freeways and other state freeways are overlaid with it, said a spokesman for that department, Doug Nintzel.

"It's durable, it holds up well, it resists cracking," Nintzel said. "And we've had substantial noise reduction."

The experiment

After Arizona's success, Washington joined several other states in testing the technology.

To gauge whether it actually works here, DOT officials drive along the test sections each month in a "noise car," which has a microphone attached to a rear tire.

At first, the results were dramatic.

When the first test pavement was laid on two miles of southbound I-5 in Lynnwood in August 2006, noise levels measured about 95 decibels, while the traditional pavement next to it measured 99 decibels. That four-decibel difference is the equivalent of taking half the cars off the road.

But the difference was short-lived, cut in half within six months. The latest test on I-5, in December 2009, found that the quiet pavement was actually louder than the traditional, although by a very small amount.

The main reason? Soon after being paved, the test sections began to fall apart. While normal asphalt usually lasts for 16 years, the quiet-pavement stretch of I-5 will need to be replaced within three years, just seven years after being laid, Phelps said.

The second test section, laid in July 2007 on a mile of 520 between Hunts Point and Medina, yielded similar results.

States that have had good luck with quiet pavement mostly have been in the South, and Phelps said it's possible that the technology simply doesn't work in the Northwest climate. Other possible reasons for the problems are high traffic volumes and the presence of snow plows and trucks with chains.

But quiet-pavement advocates are convinced that the tests on I-5 and 520 were tainted by errors. Scott and others said the DOT used different materials and chemicals than Arizona used and did not apply the asphalt in the same way.

"It's like a paint job on your house," Scott said. "If you don't prepare the surface and you don't apply it correctly, your paint job is going to peel. There's a trick to this, and there's a learning curve."

Officials have acknowledged the possibility of problems in the earlier tests here and, for the 405 test, laid the asphalt on a hotter day and placed it over existing concrete instead of tearing up the road and starting from scratch.

Officials will not analyze the data until August, Phelps said, and no new tests are planned.

Rick Dunaway, 57, of Medina, urged state officials to continue experimenting until they get it right.

"They can't give up; they gotta keep at it," said Dunaway, sitting in his living room just off 520. "If they can crack the code, that'll be a very good thing."

Brian Rosenthal: 206-464-3195 or brosenthal@seattletimes.com