Sound Barriers
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alt="" Noise Barrier Walls Virginia Department of Transportation (VDOT)Sound barriers are constructed to protect noise sensitive areas from noise pollution. The most common application of sound barrier walls is to insulate residential communities from highway noise, although they are also installed along railways and around industrial work areas for similar reasons. They can also be used outside specific building locations to dampen the sounds of pad-mounted mechanical equipment, such as air conditioners. Sound barrier walls and noise pollution regulations came with increased vehicle traffic and greater public awareness in the 1970’s. Today, for example, the National Environmental Policy Act of 1970 still requires a noise analysis and barrier wall construction effort, if necessary, as part of federally funded highway projects. A more recent concern of sound barrier walls is that they be aesthetically pleasing and blend well within existing landscapes and communities.
Most sound barrier walls are specified in accordance with, or largely based on, the American Association of State Highway and Transportation Officials (AASHTO) Guide specifications for Structural Design of Sound Barriers. This is a common guide specification that addresses sound barrier walls manufactured of concrete, wood, steel, masonry, and others. Among the topics discussed are: dimensional requirements for height, length and sight clearance; design requirements for wall loading including wind, seismic and snow loads; access for emergency vehicles; general maintenance; and even wall installations on bridges. Earth berms are another category of noise barrier that can be considered during site development, if excess soils are suitable and available.
Sound barriers are typically designed with the assistance of computer programs that can model proposed wall effectiveness using known entering parameters such as vehicle volumes and speeds, type of road surface, proposed wall location, and topography. During design and installation it is very important to ensure that there are no gaps in wall panel placement. Sound waves will transmit through any void spaces in the wall, and can bend over the top or flank around wall edges. Proper dimensions and placement are therefore very important. Any shortcomings in these design parameters could cause the wall to be ineffective.
Manufacturers provide a variety of materials for sound barrier walls. An important consideration is the cost of maintenance through a wall’s multi-decade life-span, as well as its initial installation costs. Common wall construction materials include pre-cast concrete panels, vertical steel H-section “soldier piles” with wood or composite plank lagging, and concrete masonry units. Various wall designs can be assigned a Sound Transmission Class (STC) rating, largely based on their material type, weight, finish, and thickness. Most applications will call for a minimum STC rating in the low 30s with ratings in the 40-60 range typically being most desirable and effective.
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