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Table 10-3. Land use categories and metrics for transit noise impact criteria Land use Noise metric category (dBA) Description of land use category Tracts of land where quiet is an essential element of their intended purpose. Leq(h)* This category includes lands set aside for serenity and quiet and for such land 1 (outdoor) uses as outdoor amphitheaters and concert pavilions, as well as for National Historic Landmarks with significant outdoor use. Ldn(h) Residences and buildings where people normally sleep. This category includes 2 homes, hospitals, and hotels where a nighttime sensitivity to noise is assumed (outdoor) to be of utmost importance. Institutional land uses with primarily daytime and evening use. This category includes schools, libraries, and churches where it is important to avoid interference with such activities as speech, meditation, and concentration on Leq(h)* reading material. Buildings with interior spaces where quiet is important, such 3 (outdoor) as medical offices, conference rooms, recording studios, and concert halls fall into this category, as do places for meditation or study associated with cemeteries, monuments, museums. Certain historical sites, parks, and recreational facilities are also included. * Leq for the noisiest hour of transit-related activity during hours of noise sensitivity. Mitigation. Noise mitigation is often considered as a part of a transportation project study if a noise impact is expected. Results of noise analyses may include the mitigated noise levels, and could still result in project noise impacts even though all reasonable and feasible measures were included. Noise mitigation measures include barriers such as noise walls or earthen berms; other measures include reducing speeds, limiting truck usage, or moving roadway alignments further from a receptor. Consideration also should be given to possible side effects of noise mitigation, such as aesthetics, safety, and visibility. These effects can be evaluated using techniques provided in other chapters of this guidebook. Examples of impacts include blocked views of features considered valuable by property owners, such as sunlight, wetlands, parks, and other aesthetic views. Communication with residents is an important element in determining whether any planned mitigation is desirable. SELECTING AN APPROPRIATE METHOD OF ANALYSIS Table 10-4 provides a summary of the methods presented in this chapter. Because noise is one of the most common community concerns with transportation projects, noise evaluation methods for highway, transit, and rail projects are well developed and commonly used. Both the FHWA and the FTA have developed standards and guidance for evaluating noise impacts. Integrating standard noise-effect information with demographic information therefore is the best way to perform an environmental justice assessment of noise effects. The demographic information must adequately characterize the activity spaces within which protected populations 236
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may be subject to increased noise levels. Because noise impacts are highly localized, detailed information that identifies demographic characteristics of persons associated with specific properties (i.e., living, working, or otherwise spending significant amounts of time at a site) is preferred over census data. Census data can be used to evaluate distributive effects in cases where the affected area is relatively large or where only screening-level results are needed. Table 10-4. Summary of methods for analyzing noise effects Assessment Appropriate Use Data Expertise Method level uses when needs required 1. Initial Screening Project, In early planning Low Spreadsheet, evaluation corridor and stages and for initial knowledge of system initial environmental review census data, GIS review to or for evaluating helpful identify projects with limited potential for noise effects or with noise effects few nearby noise receptors 2. Highway Detailed Assess noise Highway construction High FHWA project exposure and operation noise Transportation noise levels from effects must be noise model, analysis transportation evaluated in detail and knowledge of projects there is potential for demographic effects to protected data, GIS helpful populations 3. Transit Screening/ Assess noise Transit construction Medium/ FTA project detailed exposure and operation noise high noise/vibration noise levels from effects must be evaluation analysis transit projects evaluated in detail and methods, know- there is potential for ledge of demo- effects to protected graphic data, populations spreadsheet, GIS helpful Three general methods are described in the next section of this chapter. The first method, initial evaluation, can be used in most situations (highway, transit, rail, and multiple modes) to determine if there is potential for noise effects and if protected population groups could experience those effects. It does not, however, provide information on the level of noise effects or if protected populations would be disproportionately affected. The method is best suited for identifying projects that require more thorough evaluation and for targeting specific sites within an affected area that may require environmental justice outreach and detailed assessment. The second and third methods are based on FHWA and FTA noise assessment standards and can be used to perform detailed environmental justice assessment relative to noise effects of highway projects and transit projects, respectively. 237