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(ARA) - Motorized cars have only been around since the early 1900s, but people have been dealing with road noise for centuries. In ancient Rome, they were bothered by the clickety-clank of iron wheels on cobblestone pavement; in 17th century England, people complained about the rumble made by wagons with iron-tyred wheels as they drove over granite block streets. Today, the complaints about road noise come from people who live close to the busy highways that take us, and cargo, from place to place.
Communities have tried everything from planting trees and shrubs along highways to adding barrier walls to keep noise levels down and improve the quality of life for people who live near busy roads. The latter solution can be expensive.
According to a study done by the Federal Highway Administration (FHWA) in 2001, the average cost of putting up a noise wall is $1.2 million per mile. "Cost isn't the only problem with these walls. They have limited success because of the laws of physics," says Wayne Jones, a field engineer at the Asphalt Institute. "Noise walls only protect those within the sound shadow. If you live in a building next to the freeway that's taller than the wall, or a house a block away, you will still hear the road noise. The best solution is to go with a road surface that absorbs sound."
Jones has been studying road noise for four years and points out that the best solutions he has found so far are the variety of quiet pavement technologies offered by asphalt. "By its nature, asphalt is more flexible than the rigid concrete pavements," he says. "As a result, less noise is generated over all and there's even evidence that as the sound resonates from the tire, less is reflected off the surface."
To demonstrate how effective asphalt is at noise reduction, the Asphalt Pavement Alliance -- a coalition made up of the Asphalt Institute, the National Asphalt Pavement Association, and the State Asphalt Pavement Associations -- recently launched a new interactive Web site. Jones played a key role in its development.
"The site is intended to be a resource for people who want to learn more about the issue of road noise and how to deal with it," he says. When you log on to www.quietpavement.com, you will learn about different noise mitigation strategies such as planting shrubs and trees, putting in noise walls, and changing the pavement surface.
"The site demonstrates what people who live near highways paved with concrete know all too well," says Jones. "You can put up a barrier wall, and even plant a row of trees behind it, and it won't stop the sound from disrupting your life. But switch the road surface to asphalt, and the noise is significantly reduced."
In 2002, the Arizona Department of Transportation (ADOT) widened 12 miles of U.S. 60 in Phoenix and topped the concrete with a 1-inch-thick layer of open-graded asphalt rubber. The public's response was unexpected, says Paul Burch, ADOT's chief pavement-design engineer. "People called in saying, 'This is incredibly quiet. Why don't you pave the whole freeway this way?'"
The effort is under way. In 2003, ADOT initiated the Quiet Pavements Program, a $34 million overlay of 115 miles of highway in Phoenix with rubber-modified asphalt. The project should be complete by 2007. "Several other states across the country are conducting studies to see if quiet pavement technology can work for them too," says Jones.
Cutting down on road noise is important because over time, exposure to loud noises can lead to hearing loss and permanent damage. Sound is measured in decibels (dB). Conversations take place in the 50 dB range, normal highway traffic sounds rank about 75 dB, and jet airliners around 90 dB. For most people, discomfort starts in the 70 to 80 dB range, with the threshold of pain around 140 dB. The FHWA has chosen 67 decibels as the point where state and federal agencies must consider reducing the noise level.
"Using quiet pavement technology, asphalt pavements often measure 7 to 9 dB lower than concrete," says Jones.
You can learn more about road noise by logging on to www.quietpavement.com. The site also features links to information about the history of road noise, case studies, and a tool that lets you compare the decibel levels of such common neighborhood noises as people carrying on a conversation, a dog barking, a blender mixing a drink and a jackhammer tearing up the road. Courtesy of ARA Content