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. For general information about noise walls and barriers, refer to our Frequently Asked Questions (PDF 395KB) document.
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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 WSDOT noise policy.
Residents can make changes at their home to reduce traffic noise impacts.
Replace single pane windows with insulated double pane windows.
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Reinsulate walls and ceilings.
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:
The effects of frequent loud noise can be extensive; increasing stress, interfering with sleep and much more. The World Health Organisation (WHO) recommends outdoor sound levels of 50 dBA to prevent people becoming ‘moderately annoyed’, but many of the noises we encounter on a daily basis exceed this recommendation.
Incorporating acoustic barriers can reduce the amount of noise pollution in an area, either through reflecting or absorbing sound from the source. To help you understand what to expect from acoustic fencing, we’ve answered the most common questions about it here:
First of all we would strongly recommend contacting a qualified sound engineer who will specify the type, length and most critically, the correct height of the barrier to ensure optimum performance is achieved. There are a variety of factors which should be taken into consideration before purchasing your acoustic barrier, which include the surrounding environment, the proximity of the noise source to the barrier and the receiver. A realistic dB reduction could be between 9-15 decibels – this reduction to the human ear represents a halving of sound. If you consider road traffic rates as 70dB and conversational speech at 60dB, that’s a dramatic drop in volume! Be aware that although the term 'sound proof fencing' is often used, a fence cannot completely sound proof an outdoor space, but it will make a considerable difference.
There are a host of factors that differentiates a certified acoustic fence from a normal domestic fence but the key differences are the following
An acoustic barrier requires a minimum surface mass density of at least 10kg per M2. This is because a mass of this weight will start to reflect noise back, rather than allowing it to simply travel straight through– a domestic fence produces circa 4kg per M2 whereas the Jakoustic barrier produces 25kg!
An acoustic barrier needs to be completely imperforate so sound cannot travel through – a domestic fence by nature will generally have some gaps throughout it’s design, after all, it’s designed for screening only and not to reduce noise.
An acoustic barrier should have a life of at least 20 years. Be sure to check that the fence actually comes with a guarantee and not just an expected lifespan. Fortunately for our customers' peace of mind, all of Jacksons products, regardless whether it’s an acoustic fence or not, are guaranteed for 25 years against rot, insect attack, and manufacturing defects.
As long as acoustic fencing meets certain requirements, it will provide sound reduction. The effectiveness of an acoustic fence is determined by five main factors:
Material density: greater mass provides greater sound reduction.
Barrier construction: good structural integrity is critical to performance. Gap-free construction eliminates direct paths for sound through the barrier.
Barrier height: Sound barriers create an acoustic shadow in which the free flow of sound waves is blocked. Higher fences change the direction of sound by the greatest angle and increase the size of the ‘shadow zone’.
Distance between noise source and receiver: A certain amount of noise is diffracted by acoustic barriers, most audible to anyone standing in such a way that the barrier is an equal distance between them and the noise source. To avoid the effects of this diffraction, acoustic barriers should be built as close as possible to either the noise source or those being protected from the noise.
Relative height of source and receiver with respect to barrier: Ultimately, taller walls reflect and absorb sound better. It’s also important to consider the height of the noise source; the lower a source sits, the greater the angle of reflection will be, increasing the shadow zone.
Acoustic fencing doesn’t have any special planning permission requirements except those that apply to regular fences. For example, if a fence will be over one metre high and next to a highway or footpath next to a highway, or if it will be over two metres high, regardless of location, you need to apply for planning permission. No matter the height of your fence, it is always best to consult the local authority before installation.
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