Everyone has, at some point in time, heard highway noise and seen a freeway noise. We may live close to or far away from highways, use the freeway infrequently, or have it as a normal part of our lives.
Therefore, the noise and the barriers are a fact of life. But how many of us actually know how such things work?
Noise Barriers: What Are They & How Do They Work
A noise barrier wall, is simply a large wall made out of brick, concrete, or some other durable and strong material designed to block unwanted noise.
The noise of the highway is either absorbed into the wall, passes through the wall, or reflects back off the wall. In general, if the height of the wall is increased, the surface area will be more able to absorb, transmit or reflect the sound, thereby better neutralizing it.
But basic physics of sound dictates that some of the sound will always diffract over the wall and dissipate over suburbia.
Certain types of barriers will actually diffuse unwanted noise by absorbing it, in contrast to reflecting it with unpredictable consequences.
Studies have shown that from an acoustics perspective, the use of absorptive noise barriers is better than reflective materials when practical.
The Department of Transportation (DOT) has issued metrics encourage all barriers be designed to reduce the noise level by 5 decibels. Each added meter of height above the line-of-sight between the receiver and the source will typically add a reduction of noise by 1.5 decibels.
This is because the diffraction of the noise (meaning the scattering of it in acoustical terms) reduces the amount of sound that is able to hop the wall.
The Good, The Bad and The Ugly
It is easy to think that highway noise isn’t that big of a deal. Sure, it’s a bit of a nuisance, but nothing that is really irritating. Or, maybe it is irritating, but not so bad as to stress one out unduly.
That would be wrong.
The Environmental Protection Agency, a federal organization, has found that 20 percent of people become very annoyed if the level of sound gets up to 55 decibels.
Unfortunately, this amount of noise is common in areas that are some distance away from freeways, and an amount that many transportation departments would like to have in suburbs and neighborhoods near expressways.
Noise absorbing panels take care of the higher pitched noises, but even after that, the trucks rumbling past can still be heard.
Some communities, California among them, simply build the walls higher. If people cannot see the trucks, they might not pick up on the noise.
Another problem with the common highway noise barriers is that they are simply ugly! Very often, vandals spray-paint them and the builders do not always take into account of how the walls appear.
However, it is a recognized problem; various communities are fighting back. Texturing and visual patterns on a barrier can be pleasing to the eyes. Some advocate for planting ivy along the way, and others vote for artwork to cover the walls.
But there simply isn’t always the money to sponsor beautifying programs. In some places, such as tourist stops, it may be worth it, but that is a relatively small problem.
Overall, the benefit of highway noise abatement typically makes the barriers and walls along the way worth building and maintaining.