Road noise and noise walls

If you live near a roadway, you may be concerned about traffic noise. At the Washington State Department of Transportation (WSDOT), we recognize this impact from our highways and work to reduce it where we can.

Continue reading below to find out more about:

Noise barriers

WSDOT provides noise barriers to reduce traffic noise through two types of projects:

  • Type I barriers: Federal law requires projects to include noise abatement if they exceed noise standards, meets reasonable and feasible criteria, and do at least one of the following:
    • Construct a highway at a new location
    • Significantly change either the horizontal or the vertical alignment of a highway
    • Increase the number of traffic lanes
    • Altering roadside topography
  • Type 2 barriers: We build “retrofit” barriers in areas that existed before the highway was put in. Type II barriers are rare because funds for these barriers compete with other important programs, like safety improvements and pedestrian accommodations. To be fair to everyone, retrofit noise barriers get ranked and built according to a statewide priority list. We build, on average, one retrofit barrier every two years.

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.

Options to reduce noise at your home

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 2011 WSDOT noise policy.

Nonetheless, residents can make changes at their home to reduce traffic noise impacts. For noise reduction inside the home, consider:

  • Replacing single pane windows with insulated double pane windows
  • Reinsulating walls and ceilings
  • Sealing door, window, and other cracks
  • Using indoor fans or installing air conditioning instead of opening windows
  • Using 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.

To reduce noise levels outside:

  • 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.
  • Consider building 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:
    • The material used must weigh at least 4 pounds per square foot.
    • The wall or fence can't have gaps.
    • Blocking the line of sight to the noise source will usually result in a 5-decibel reduction.
    • Increasing the height of the barrier will provide additional noise reduction until the fence fully blocks the line of sight to the roadway. Beyond that, the noise reductions from additional height are minimal.
    • Either the fence must be long enough to prevent noise from coming around the ends, or it must continue around the property line to enclose the target area.

WSDOT Noise Barrier Process

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

Traffic noise analysis

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:

  • Highway noise
  • Area topography
  • Population density
  • Cost
  • Expected levels of noise reduction a wall would provide

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.

Reasonable and feasible criteria

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

  • Feasible refers to whether the barrier can provide at least a five-dBA reduction at the majority of first row receivers and meets other constructability requirements.
  • Reasonable refers to whether the barrier can provide minimum seven-dBA noise reduction requirements while meeting cost effectiveness requirements.

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.

Noise wall costs

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.

Public input on noise walls

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

Quieter pavement

WSDOT has some of the most comprehensive data in the world on quieter pavement performance. See our quieter pavement webpage for more information on our research.

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