On most interstate highways worldwide that bisect suburbs and bustling cities you will see giant walls separating any existing buildings, homes or communities. These are highway sound barriers.
They started popping up around the 1970s in order to protect high populated areas from the noise pollution that comes from the busy highways. The sound walls go on for miles and miles all over, for example there are around 252 miles of these barriers in Florida and 760 miles in California.
They are built on average of 14 feet tall and are made primarily from concrete which some people may say make an area feel a bit prison-yard-like, however most of the public are in favor of these sound walls. There has been some speculation and homeowner testimonies that sound barriers may actually make the noise worse rather than block it.
Highway sound barriers are not only made from concrete alone but have included materials such as steel, wood, plastic, masonry and insulating wool, just to name a few. The reason for these different types of materials used is because the highway noise is absorbed differently depending on which materials have been used in the production of the barrier.
With the world becoming more and more green, there is now the possibility of using specialized materials like solar panels so that clean energy can be produced at the same time as cutting down on noise pollution.
The Science of How Noise Barriers Work
The science behind how a highway sound barrier works is down to how the sound waves travel. The barrier is built in such a way and for many miles so as to block the sound waves as they travel and bend around with the barrier. This is called diffraction, the bending of sound waves as it goes around the corners of an obstacle. As you can see, in order for a highway noise barrier to work effectively, it must stretch for hundreds of miles to block out as much as the sound waves as possible.
However, as there are so many sounds reflected off a busy highway such as tire noise, engine noise and aerodynamic noise – refractions can happen – where sound waves change in direction due to crossing over with others, and this can complicate things. Therefore, this could be a factor in why many residents and homeowners have experienced amplified noise rather than less with sound barriers.
Noise barriers force sound waves coming from highway noises around or over the top of the barrier therefore must be high enough to decrease the sound as much as possible. Some people may think that the highway noise walls are designed to eliminate the noise pollution, however, they are actually built to decrease the noise. The barriers are perfect for first, second or third rows of buildings and houses, but for any residents up on hilltops or overlooking the highways the barriers don’t actually do much good.
Whether highway noise barriers actually work in helping with noise pollution in many areas is still under discussion, as some people have said that walls being placed on both sides of a highway can actually cause the sound to reverberate; ultimately increase the noise when these clashing sound waves become higher in frequency.
The construction and development of these sound barriers is always changing in order to effectively help communities and areas experiencing highway noise. Sound dampening materials and understanding the science behind using sound walls is constantly advancing in order to tackle the problem of noise pollution around the globe.