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Noise Contours: Lines drawn about a noise source indicating equal levels of noise exposure.
CNEL and Ldn are the metrics
utilized herein to describe annoyance due to noise and to establish land use planning criteria for noise.
Ambient Noise: The composite of noise from all sources near and far. In this context, the ambient noise level constitutes the
normal or existing level of environmental noise at a given location.
Intrusive Noise: That noise which intrudes over and above the existing ambient noise at a given location. The relative
intrusiveness of a sound depends upon its amplitude, duration, frequency, and time of occurrence, and tonal or informational
content as well as the prevailing noise level.
Noisiness Zones: Defined areas within a community wherein the ambient noise levels are generally similar (within a range
of 5 dB, for example).
Typically, all other things being equal, sites within any given noise zone will be of comparable proximity
to major noise sources. Noise contours define different noisiness zones.
Local airports are subject to the noise requirements of the Federal Aviation Administration and noise standards under the
California Code of Regulations,
Title 21, section 5000, et seq
. These standards are designed to encourage the airport proprietor,
aircraft operators, local governments, pilots, and Caltrans to work cooperatively to diminish excessive aircraft noise impacts.
However, the U.S. Secretary of Transportation must review and approve all local airport noise and access restrictions adopted
after 1990, and they must meet specified criteria (
49 U.S.C. § 47524)
.
Proposed school sites within two nautical miles of an airport runway or potential runway in an airport master plan are subject to
review by CalTrans Division of Aeronautics (
Cal. Code Regs., tit. 21, § 3570
, and
Ed. Code § 17215
).
The regulations authorize
CalTrans to object to the acquisition or lease of a school site within a 65 decibel annual CNEL aircraft noise contour. If Caltrans
recommends against it based on noise considerations, the board may not acquire or lease the site (
Ed. Code § 17215(d)
).
Specific considerations for noise generated by or related to military facilities can be found in the
California Advisory Handbook
for Community and Military Compatibility Planning
.
Noise Measurement and Modeling
The local planning agency should select the method of measurement or modeling that best suits its needs, either CNEL or Ldn.
See
Appendix D
for more information about these two types of noise measurements and noise descriptors.
Noise should be measured at multiple receptors. The volume of traffic noise, construction noise,
and the noise of an
environment (such as loud schools, playgrounds, or agricultural areas) depends on many factors, including the location of
dwellings and the location and types of trips made in neighborhoods en route to school, work, or shopping.
iv
Measuring noise
at multiple receptors throughout a community will ensure that the noise element is accurate. The noise element should address
the following:
• Major noise sources, both mobile and stationary
• Ground borne noise, ground borne
vibration from public transit, freight trains, or light rail transit lines
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• Existing and projected levels of noise and noise contours for major noise sources
• Existing and projected land uses in relation to existing and projected noise sources
• Existing and proposed sensitive receptors, including:
» Residential land uses
» Hospitals
» Convalescent homes
» Schools
» Churches
» Sensitive wildlife habitat, including the habitat of rare, threatened,
or endangered species
• Time-of-day, day-of-week, or seasonable variability of noise sources
Projections of future noise sources, noise levels, and anticipated impacts, including health impacts, upon existing and proposed
land uses should provide information useful for guiding decisions about land use, locations of noise generating sources, and
noise reduction mitigation measures. Mapping noise contours creates an opportunity to engage
the community in a practical
discussion about noise, and the tradeoffs between noise and other local priorities.
Mitigation Measures
Not all noise can be minimized, and there may even be areas where noise is desired. Some noise sources are inherent to a
region, such as noise generated from farming activities in agriculture intensive areas, wildlife noise from nearby habitat, and
noise associated with urban
infill
developments. Creating
healthy communities
includes minimizing
harmful exposure to
excessive noise. Local planning areas are encouraged to embrace the noise characteristics inherent to their region and “design
with noise in mind” to minimize harmful exposure to excessive noise.
There are many ways to minimize harmful exposure to excessive noise. Mitigation measures include soundproofing with
soundproof windows and insulation, landscaping and berms, building design and setbacks, buffer areas, operating hours of
major sources, roadway maintenance and traffic flow, quieter pavement strategies, and other techniques.
Noise mitigation measures are not one-size-fits-all solutions: some noise mitigation measures are better suited for some
communities than others. For example, while sound walls may be a fitting mitigation
measure for a rural area, they may not be
the best solution for urban infill areas, because they impair community connectivity. Increased building setback zones or buffer
zones are likely not appropriate in more urban areas where land is limited. In areas where available land is limited, alternative
mitigation measures should be employed. The noise element should be flexible and consider the different needs of various
communities to determine the best measures to minimize exposure to excessive noise.
Caltrans administers several freeway noise control programs. In general, these are applied to residential and school uses
that existed before a freeway was constructed. For instance, the
New Construction or Reconstruction
and Community Noise
Abatement programs
provide for installation of noise attenuating walls. In addition, the
School Noise Abatement Program
funds