Quiet Pavement


	In the world today, noise has become one of the most pervasive forms of environmental pollution. Noise is everywhere. It affects our lives at home, at work and at play. Wherever people live there is noise. Noise, by definition, is any unwanted or excessive sound. It can be a nuisance, interfering with sleep, work or recreation, and in extreme situations, it can lead to anxiety, stress and other health problems. As we know from our high school science classes, sound waves are created when an object moves or vibrates. When these waves reach our ears, they cause our eardrums to vibrate, sending signals to the brain that we interpret as sound. A measurement of the wave traveling through the air is used as an indication of the intensity of sound or its volume, and is described in terms of a scale

called the decibel (dB). Noise measurements made by filtering high- and low-pitched sounds—approximating the way an average person hears sounds—is called the A-weighted level or dBA.

The dB(A) scale begins at zero, which represents the faintest sound that can be heard by humans with very good hearing. Conversations take place in the 50 dB(A) range and a chainsaw whines at about 100 dB(A). Normal highway traffic sounds rank about 75 dB(A) and jet airliners around 90 dB(A). For most people, discomfort starts in the 70 to 80 dB(A) range, with the threshold of pain around 140 dB(A). The Federal Highway Administration (FHWA) has chosen 67 decibels as the point where state and federal agencies must consider reducing the noise level.

Road Noise Abatement Options
If road noise abatement is needed, the construction of noise walls is the latest solution. Barrier wall construction currently costs between $1.3 and $3 million per mile, depending on how much other construction is going on at the same time.

When a noise barrier wall is constructed, there is a significant noise drop immediately behind the wall. The problem is that those buildings that are on hillsides, at intersections or driveways or anywhere there is an opening in the wall, will not benefit from noise reduction. In some cases where noise walls are built parallel to one another, noise reflections or echoes of the sound waves off the opposite wall can actually increase noise levels at a location near the highway.

Studies show that when all these inefficiencies are considered, the average noise reduction from noise barriers is approximately 7 dB(A). Other noise abatement options such as vegetation or green walls have the same limitations.

Quiet HMA
There is no better way to reduce road noise than to treat the problem at its source. By paving roads and highways with hot mix asphalt the noise inside homes and businesses can be significantly reduced.

Research in the U.S. and Europe shows that a Stone Matrix Asphalt (SMA) or Open-Graded FrictionCourse (OGFC) mix will reduce highway noise by 3 to 5 dB(A). To the average person, this reduction is the same as doubling the distance between the source of the noise and their location.

When comparing the noise reduction that is possible by choosing HMA pavement—up to 7 dB(A) —we see how much more practical pavement surface selection is than construction of noise barrier walls.