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64 Figure 8-2. Noise barrier height considerations. Deep-water marine ports have been actively developing Noise Barriers programs to reduce environmental impacts and improve air quality, and are another good source of information. Another set of mitigation tools that has been used to For example, the Port of Los Angeles developed a Com reduce noise and vibration effects are sound walls, beams, munity Advisory Committee with subcommittees on vari- and barriers. Sound walls have been used mostly around ous issues including air quality, noise, light, and traffic highways and transit facilities. (Port of Los Angeles 2010a). The Port Authority of New Noise barriers reduce sound generated by a transportation York and New Jersey developed a Clean Air Strategy to facility or corridor (e.g., highway) by absorbing the sound, reduce the port's polluting activity and its impact on the transmitting it, reflecting it, or forcing the sound to take a surrounding neighborhoods (Port Authority of New York longer path over and around the barrier. Noise barriers can and New Jersey 2010). Although described as a protection and be constructed from earth, masonry, wood, metal, or other preservation strategy in Chapter 5, the New York Shipping materials. Association Port Support Zone also can be thought of as an For noise barriers that are designed to alter the path of attempt to mitigate the negative effects of port operations. sound over and around the barrier, the barrier must be tall One of the expected benefits of relocating those activities enough to block the view of the transportation facility from that are able to be located away from the immediate port the area that is to be protected (see Figure 8-2), and should area was a reduction of negative impacts on surrounding be at least eight times as long as the distance from the noise residential areas. receiver (e.g., home) to the barrier (see Figure 8-3). Figure 8-3. Noise barrier length considerations (U.S. Department of Transportation 2010).