How, when and why does WSDOT build noise walls?
Noise walls are free-standing barriers built parallel to a highway. They are usually made of concrete and are found near public areas (such as parks) and residential homes. The walls range in height from 6 to 20 feet, but normally they are 12 to 15 feet tall. Around the Seattle area, examples of noise walls can be seen on:
- Interstate 5 just north of the Ship Canal bridge
- Interstate 90 just west of the Mount Baker Ridge tunnel
- Interstate 405 between Totem Lake and Bellevue.
Most noise walls are included as part of large construction projects that add new lanes (thus adding vehicle capacity) to highways. Long before construction begins, acoustical engineers evaluate sources and patterns of noise in neighborhoods near the project limits. The findings are used to determine if noise walls would be appropriate and cost-effective.
Noise evaluations take into account many factors, only one of which is actual highway noise. Among other things, acoustical engineers look at:
- Area topography
- Population density
- Expected levels of noise reduction a wall would provide.
If, for example, homes near a project are widely-spaced or built high on a hill, often we do not build noise walls because the:
- Cost to reduce noise for each resident is usually quite high
- Noise does not noticeably decrease.
Sometimes, we build noise walls in high-noise neighborhoods that were built before the freeway. These walls, known as "retrofit" walls, are rare because funds for these walls compete with other important programs like safety improvements and pedestrian accommodations. To be fair to everyone, retrofit noise walls are ranked and built according to a neighborhood priority list. We build on average one retrofit wall every two years. Even if your neighborhood qualifies for one, it may be several years before it is actually built.
Our agency gets many requests from citizens to build noise walls. But not everyone wants them. Sometimes finished walls obscure scenic views from residents' homes. And, in almost every case, we must remove trees and shrubs within our right-of-way to make room for a wall.
During the design phase of a project, we hold open houses to solicit public comments. We invite you to get involved by watching for notices of these open houses in your local newspaper. We want to hear your ideas and suggestions, especially if a project is planned near your neighborhood.
Sometimes proposed noise walls block scenic views or shade yards. Prior to construction, WSDOT may solicit community input to determine whether a noise wall is desired by the community. The community polling process used by WSDOT is outlined in Public Input Process when Planning Approved Noise Barriers (136k).
Sometimes, noise walls aren't found to be appropriate and cost-effective according to state and federal traffic noise policy. In this case, there may be other options for Improving the Noise Environment When Standard Options Aren't Available (545k). These options focus on installing some visual screening that also improves the noise environment for neighborhoods near highways.
Tips to Lower Noise around Your Home
- To reduce noise levels inside your home, consider reinsulating walls and ceilings, and replacing single-pane windows with insulated double-pane windows. Less expensive changes like sealing door and window cracks can also noticeably reduce noise levels. Use indoor fans, rather than open windows, to provide ventilation around the home and to reduce unwanted noise.
- Outside, use interesting landscaping to obscure the roadway. Even though plants do not effectively reduce noise levels, they give a sense of privacy and serenity. Some plants help mask traffic noise by rustling in the wind. Talk to a landscape architect for ideas.
- Enclose a favorite garden spot, deck or patio with transparent plastic or other barrier. Or, create a quiet spot in an area facing away from traffic.
- Consider building a "do-it-yourself" noise barrier. If it is properly built with appropriate materials, you can get significant noise reductions around your home. Talk to an acoustical consultant first.