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The sound of traffic

The sound of traffic

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    Above: A device monitors noise levels in a residential neighborhood adjacent to a Quiet Pavement Pilot Program freeway segment. Photo: Arizona DOT. Below: This trailer—built by the National Center for Asphalt Technology—is used to directly measure tire/pavement noise levels using the close-proximity method. Photo: NCAT

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    The NCAT trailer uses microphones inside a sound-baffled chamber in the trailer to measure noise levels without outside interference. Photo: NCAT

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    Asphalt pavements constructed with an open-graded friction course have been proven to generate less traffic-related noise than traditional hot-mix asphalt pavements. Photo: NCAT

To be approved by the FHWA, a QPPP must account for documented noise reduction benefits of pavement types; include post-construction monitoring of projects including acoustic, texture, and friction measurements over a 5- to 10-year period; document the public's reaction to the project; and include commitments to provide the required noise reduction into perpetuity.

The QPPP must also be state-specific, although a group of state DOTs can submit a joint plan. Each QPPP must have a Program Plan and a Data Acquisition Plan, which are reviewed and approved by the FHWA.

Under this program, quiet pavement research also can be conducted. This research can be used to help substantiate possible future policy changes allowing the use of a pavement adjustment factor in traffic noise predictions. Additionally, the work may lead to the use of pavement types or surface textures as noise-abatement measures. To begin research under the program, an applicant must submit a Quiet Pavement Research Plan with an outline of the intended purpose, a detail of data acquisition, and periodic reporting requirements.

Those considering implementation of either a QPPP or the Quiet Pavement Research Plan must understand the differences between the two programs. A state may establish a QPPP only after submitting acceptable documentation on a specific pavement type along with predicted noise reductions and safety capabilities over time. Only then can the state adjust for pavement type in the noise level predictions and use specific pavement types as a noise reduction strategy. States conducting research cannot make any such adjustments until the required documentation is acquired through completion of the research plan.

A QPPP also must commit to the monitoring of noise levels over time and take appropriate actions, such as construction of an overlay, if noise reduction benefits do not last into perpetuity. Repaving also may be required if the pavement constructed through implementation of a QPPP or research plan fails structurally to the point that driver safety is compromised. Those conducting a research plan are not required to make such commitments.

Arizona's Quiet Pavements

Arizona, in cooperation with the Maricopa Association of Governments, was the first state to implement a QPPP. This three-year, $34 million program involves resurfacing 115 miles of freeways in the Phoenix area with rubberized asphalt. The plan was announced in December 2002 and work began on the first 21 miles in September 2003. The state expects to finish the project by December 2005.

The use of rubberized asphalt pavement in Arizona began more than 20 years ago. At the time, one of the primary purposes had been to recycle used tires. Arizona reports the use of more than 4.2 million tons of rubberized asphalt since 1988, resulting in the recycling of 15 million old tires. Studies and public perception have indicated that asphalt-rubber pavement also provided noise reduction benefits, providing an average decrease in traffic noise levels of 4 dB(A).

The city of Phoenix also has been active in placement of rubber-asphalt overlays, with more than 200 miles surfaced with 450,000 tons—an effort resulting in the use of 1.1 million old tires. The city has found that this pavement does not reflect cracks in existing pavement, the surface is more durable and skid-resistant than conventional asphalt, and the traffic noise is reduced providing a smoother and quieter ride. Noise studies have shown a reduction of 10 dB(A) in noise levels.

Rubberized pavement may not be the answer for every state. To achieve successful placement, the material must be placed when the pavement surface temperature is between 85° and 145° F.

More information about quiet pavements can be found at www.quietpavements.com, a site developed to provide information about traffic noise and the use of quiet pavements as a noise abatement strategy. The site provides reports, PowerPoint presentations, videos, and even an interactive tool—Sound Town USA. In Sound Town USA, users can try their hand at abating noise along a roadway using different noise abatement strategies.

As information about quiet pavements increases and states implement quiet pavement research, using quiet pavement as a noise abatement strategy may one day find acceptance within the FHWA regulations. For more information about Arizona's QPPP program, visit www.quietroads.com.

Broviak is a freelance writer in LaSalle, III.