Noise walls & barriers | WSDOT

2022-04-02 04:15:59 By : Mr. Lucas Ji

Find information about noise barriers, our process for determining where to build them and other options to reduce noise at your home.

If you live near a roadway, you may be concerned about traffic noise. We recognize this impact from our highways and work to reduce it where we can.

We provide noise barriers to reduce traffic noise through two types of projects.

When we build new improvement projects, we include noise barriers if noise standards are exceeded and other criteria are met. This type is triggered when we do at least one of the following:

We build “retrofit” barriers along highways in neighborhoods that existed before noise abatement regulations were established.

The effectiveness of a noise barrier depends on the distance between the listener and the barrier. For residences located directly behind a barrier, the noise level will often be cut in half. This benefit decreases as a listener moves farther away and is negligible at distances greater than 500 feet.

WSDOT uses earth, concrete, wood, and masonry block to build noise barriers. Earthen berms work the best and are the least expensive, but a lack of available right-of-way usually makes concrete walls the most practical solution. Most often we build noise walls – free-standing walls usually made of concrete. The walls range in height from 6 to 20 feet, but normally are 12 to 15 feet tall.

Trees and shrubs can decrease highway-traffic noise levels if high enough, wide enough, and dense enough (cannot be seen through), but are often impractical. It would take at least 100 feet of dense vegetation to provide the same benefit as our smallest feasible noise wall. Trees do provide a visual shield and some psychological benefit. The Federal Highway Administration (FHWA) has not approved using vegetation for noise abatement.

We follow the following standard practice to determine where to build noise barriers and decide how they are configured.

Long before construction begins, acoustical specialists evaluate sources and patterns of noise in neighborhoods near the project. Noise evaluations take into account many factors, including:

Computerized noise models are developed to predict future traffic-noise levels. To be conservative in our estimates, WSDOT typically models with rush hour traffic volumes, traveling at the posted speed limit.

Any applicable area predicted to have a future traffic-noise level of 66 decibels (dBA) or greater, qualifies as an impacted area. Research shows that above 66 dBA, a conversation between two people standing three feet apart and speaking in a normal voice is impaired.

All impacted areas are considered for noise abatement. Analysts make every attempt to qualify these impacted locations for noise barriers based on the reasonable and feasible criteria. A noise wall must provide at least a seven-dBA noise reduction, but we try to design walls that provide a ten-decibel reduction.

A barrier must meet both reasonable and feasible criteria to be constructed:

Barriers do have limitations. For a noise barrier to work, it must be high enough and long enough to block the view of the road. Noise barriers do very little good for homes on a hillside or for buildings that rise above the barrier. Openings in noise walls for driveway connections or intersecting streets destroy their effectiveness. In some areas, homes are scattered too far apart for noise barriers to be built at a reasonable cost.

Current construction costs average $51.61 per square foot. This translates into a fourteen-foot high wall (typical) costing about 3.9 million dollars per mile. Construction costs for rural barriers may be lower and urban barriers may be much higher. The higher urban costs are associated with other infrastructure (like retaining walls, water pipes, etc.) that may need to be changed or moved to allow the placement of the barrier.

Many noise walls built alongside interstate highways receive partial federal government funds, and WSDOT pays the remainder. On other state routes, WSDOT or local jurisdictions, depending on who is sponsoring the project, pays for an entire wall. In special cases, if a local community would like to enhance the barrier with aesthetic treatments or to make the barrier longer or taller than recommended, the community may provide additional funding. The proposed improvements must meet WSDOT safety, maintenance, and right-of-way needs.

WSDOT project design offices works closely with the impacted communities for a proposed noise wall to make sure all reasonable design requests get included in the project plans.

WSDOT has some of the most comprehensive data in the world on quieter pavement performance.

Because the noise reductions from quieter pavements decline long before the pavement typically needs to be replaced for other reasons, FHWA does not allow quieter pavement for noise abatement.

WSDOT does not have funds available to make modifications to residences to reduce traffic noise in the home. We only consider interior noise reductions for certain types of public structures defined as Category D in the 2020 WSDOT noise policy.

Residents can make changes at their home to reduce traffic noise impacts.

Replace single pane windows with insulated double pane windows.

Seal door, window and other cracks.

Use indoor fans or install air conditioning instead of opening windows.

Use noise-absorbing material in the walls of new buildings during construction, although this acoustic insulation is very expensive.

Noise masking – Many people have reported some success with white noise, such as a fan or waterfall, to drown out the traffic noise and make it less noticeable.

Use visually interesting landscaping to obscure the roadway. Some plants help mask traffic noise by rustling in the wind. Even though plants do not effectively reduce noise levels, they give a sense of privacy and serenity. Talk to a landscape architect for ideas.

Enclose a favorite garden spot, deck, or patio with transparent plastic or other barrier.

Build a "do-it-yourself" noise barrier. If properly built with appropriate materials, you can get significant noise reductions around your home. Talk to an acoustical consultant to make sure the barrier you plan to build will provide the noise reduction you expect. To prevent a substantial amount of noise, consider the following:

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