Noise walls & barriers | WSDOT - WA.gov

Learn more about noise barriers, the procedures for determining their placement, and various ways to decrease noise levels in your home.

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If you reside near a roadway, traffic noise can be a significant concern. We are aware of this issue caused by our highways and strive to minimize its impact whenever possible.

Understanding Noise Barriers

We implement noise barriers specifically designed to mitigate traffic-related noise through two primary project categories.

Category One Noise Barrier Projects

For new improvement projects, we incorporate noise barriers if noise level standards are breached, alongside fulfilling other essential criteria. This category is activated when we undertake any of the following actions:

• Develop a highway at a new site.
• Make substantial changes to the highway's horizontal or vertical alignment.
• Expand the number of traffic lanes.
• Modify the roadside landscape.

Category Two Noise Barrier Projects

We construct retrofit barriers along highways in areas that were established prior to the noise abatement regulations.

The effectiveness of a noise barrier is closely related to the distance from the listener to the barrier itself. For homes positioned directly behind a barrier, the noise level can often be reduced by as much as half. However, this benefit diminishes as the listener moves further away, becoming insignificant at distances exceeding 500 feet.

Materials such as earth, concrete, wood, and masonry block are utilized by WSDOT in the construction of noise barriers. Earth berms are typically the most effective and economical; however, due to space limitations, concrete walls frequently emerge as the most viable option. In most cases, we construct noise walls, which are freestanding concrete structures ranging from 6 to 20 feet in height, with a common height of 12 to 15 feet.

While trees and shrubs can help attenuate highway traffic noise if they possess sufficient height, width, and density, they are often impractical solutions. A dense vegetation buffer of at least 100 feet is necessary to achieve noise-reduction benefits comparable to those of our smallest feasible noise wall. Although trees can offer visual concealment and some psychological relief, the Federal Highway Administration (FHWA) does not endorse vegetation as a substitute for traditional noise abatement measures.

Process for Implementing Noise Barriers

We adhere to a standardized approach when deciding where to place noise barriers and how to configure them.

Acoustic Noise Analysis

Even before construction kicks off, acoustic professionals assess noise sources and patterns in neighborhoods surrounding the project area. This analysis encompasses various elements, including:

• Highway noise levels.
• Topological features of the area.
• Population density metrics.
• Associated costs.
• Projected noise reduction outcomes of proposed walls.

By employing computerized noise modeling, we can forecast potential traffic noise levels. To ensure conservative estimates, WSDOT usually models using peak traffic volumes during rush hours at the speed limit.

Any area projected to experience future traffic noise levels of 66 decibels (dBA) or higher is classified as impacted. Studies indicate that conversations between two people standing three feet apart become impaired at levels exceeding 66 dBA.

All identified impacted areas are evaluated for potential noise reduction measures. Analysts strive to classify these locations as suitable for noise barriers based on reasonable and feasible standards. Ideally, a noise wall should yield at least a 7-dBA reduction, but we aim for designs that can deliver a 10-dBA reduction.

Criteria for Reasonable and Feasible Barriers

For a barrier to be constructed, it must fulfill both reasonable and feasible criteria:

• Feasibility pertains to whether a barrier can achieve a minimum 5-dBA reduction at three primary receivers while adhering to other construction requirements.
• Reasonableness assesses whether a barrier can yield a minimum 7-dBA noise reduction while maintaining cost-effectiveness.

It is essential to understand that barriers have inherent limitations. For optimal effectiveness, a noise barrier must be sufficiently tall and long to obstruct the view of the road. Unfortunately, these walls offer little to no benefit for homes situated on hillsides or for buildings that surpass the height of the barrier. Openings for driveways or intersecting streets can compromise a barrier's effectiveness, and scattered housing layouts may hinder reasonably-priced barrier construction.

Construction Costs of Noise Walls

The current average construction cost is $51.61 per square foot. A typical 14-foot high wall can cost approximately $3.9 million per mile. Urban barriers often incur higher costs due to additional infrastructure needs like retaining walls or water pipes that may require modifications.

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A portion of funding for many noise walls constructed along interstate highways comes from the federal government, with WSDOT covering the residual expenses. For other state routes, the responsibility for funding falls on either WSDOT or local jurisdictions, depending on the project sponsor. In special instances, local communities wishing to enhance the barriers with aesthetic improvements or extend their length or height can contribute additional funding, provided that these enhancements align with WSDOT's safety, maintenance, and land use requirements.

Community Involvement in Noise Wall Projects

WSDOT's project design teams engage closely with affected communities concerning proposed noise walls to ensure that all reasonable design requests are incorporated into the project plans.

Exploring Quieter Pavement Options

WSDOT has comprehensive data regarding the performance of quieter pavements. However, because the noise reduction benefits from quieter pavements diminish before they require replacement for other reasons, the FHWA does not permit their use for noise abatement purposes.

Home Noise Reduction Strategies

WSDOT lacks the funds necessary for residence modifications aimed at reducing traffic noise. Our focus is primarily on interior noise reduction measures for specific public structures classified as Category D according to the WSDOT noise policy.

Homeowners can take steps to lessen noise impacts in their residences.

Enhancing Indoor Noise Levels

Consider replacing single-pane windows with insulated double-pane options.

Reinsulating walls and ceilings is highly effective.

Seal any cracks around doors, windows, and other openings.

Utilize indoor fans or install air conditioning in place of opening windows.

Incorporate noise-absorbing materials in new construction, although this insulation can be costly.

Noise masking can also make a difference—many individuals find success using white noise from fans or water features to drown out traffic noise.

Reducing Outdoor Noise Levels

Employ visually appealing landscaping that obscures roadside views. Certain plant types can muffle traffic noise through natural rustling. While landscaping won’t provide substantial noise reduction, it can enhance privacy and tranquility. Consulting with a landscape architect for ideas may prove beneficial.

Enclose your preferred garden area, deck, or patio using transparent plastic or constructing another type of barrier.

Consider building your own noise barrier. If designed properly with suitable materials, achieving significant noise reduction around your home is possible. Consulting with an acoustic expert can help ensure the barrier you construct will yield the expected noise reduction. Keep in mind the following:

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• Materials should weigh a minimum of 4 pounds per square foot.
• The wall or fence must have no openings.
• Obscuring the line of sight to the noise source can typically lead to a 5-decibel decrease in noise levels.
• Increasing barrier height will further diminish noise levels until the line of sight to the roadway is completely obstructed; thereafter, additional height offers marginal reductions.
• The barrier must extend sufficiently to prevent noise from circumventing its ends or enclose the target area along the property line.