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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
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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.
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