As Figure 7-1 shows, advances in technology and airport management have resulted in significant reductions in airport noise contours (e.g., the perimeter around airports where DNLs exceed 65 dB). In fact, a 2007 study showed that the number of people exposed to high levels of air transport noise in the United States had decreased to approximately 500,000 (Waitz et al., 2007).Īs the numbers above reflect, reducing air transportation noise has been the focus of intense efforts by the public and by policy makers since the advent of the jet age. However, in the past 30 years, air transportation has led the way in technological developments and operational improvements to reduce noise and more recently to reduce environmental impacts in addition, economic analysis tools have been developed for determining the costs and benefits of these improvements to the environment. Although no studies have been conducted to determine surface transportation exposures since then, it is likely that population growth, increased residential development near highways, and increased traffic volume have also increased exposures to highway traffic noise.
Environmental Protection Agency (EPA) estimated that 24 million people were exposed to high day-night average sound levels (DNLs greater than 65 dB) of surface transportation noise (19.3 million for highway noise and 4.7 million for rail noise) in the same report the number of people exposed to air transportation noise was estimated at 2.5 million people. The committee decided to focus on surface transportation noise for several reasons. What is needed is a cost-benefit analysis of highway noise reduction to ensure that the best mitigation methods are being applied. A great deal of research has been done on the characteristics of pavements that result in lower noise levels. A layman’s discussion of the various sources can be found in The Little Book of Quieter Pavements, published by the Federal Highway Administration (FHWA Rasmussen et al., 2007). The generation of sound by this interaction is complicated and involves “air pumping” as the tread alternately engages and releases from the road surface, vibration of the sidewalls, and other mechanisms. At highway speeds most of the noise is generated by the interaction between vehicle tires and the road surface. Highway noise barriers are an effective means of noise reduction because they interrupt the propagation path between the noise sources and nearby homes. The costs and benefits of reducing highway noise have received less attention in the United States and have been emphasized in this chapter. The Federal Aviation Administration (FAA) is developing methods of using cost-benefit analyses to assess noise around airports.
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