Noise barriers reduce the sound which enters a community from sources such as a busy roadway network or industrial type area.
This noise reduction is achieved by absorbing the sound, transmitting it, reflecting it, or forcing it to take a longer path over and around the barrier.
Along motorways a noise barrier must be tall enough and long enough to block the view of the roadway from the area that is to be protected, the “receiver”.
A noise barrier can achieve a 5 dB noise level reduction, when it is tall enough to break the line-of-sight from the roadway to the home or receiver. After it breaks the line-of-sight, it can achieve approximately 1.5dB of additional noise level reduction for each metre of barrier height.
To effectively reduce the noise coming around its ends, a noise barrier should be at least eight times as long as the distance from the home or receiver to the barrier.
Openings in noise barriers for entrances or intersecting streets destroy their effectiveness. In some areas, homes are scattered too far apart to permit noise barriers to be built at a reasonable cost. Noise barriers are normally most effective in reducing noise for areas that are within 60m of the noise source.