[Code of Federal Regulations]
[Title 24, Volume 1]
[Revised as of April 1, 2006]
From the U.S. Government Printing Office via GPO Access
[CITE: 24CFR51.106]
[Page 384-386]
TITLE 24--HOUSING AND URBAN DEVELOPMENT
PART 51_ENVIRONMENTAL CRITERIA AND STANDARDS--Table of Contents
Subpart B_Noise Abatement and Control
Sec. 51.106 Implementation.
(a) Use of available data. HUD field staff shall make maximum use of
noise data prepared by others when such data are determined to be
current and adequately projected into the future and are in terms of the
following:
(1) Sites in the vicinity of airports. The noise environment around
airports is described sometimes in terms of Noise Exposure Forecasts,
abbreviated as NEF or, in the State of California, as Community Noise
Equivalent Level, abbreviated as CNEL. The noise environment for sites
in the vicinity of airports for which day-night average sound level data
are not available may be evaluated from NEF or CNEL analyses using the
following conversions to DNL:
DNL[ap]NEF+35
DNL[ap]CNEL
(2) Sites in the vicinity of highways. Highway projects receiving
Federal aid are subject to noise analyses under the procedures of the
Federal Highway Administration. Where such analyses are available they
may be used to assess sites subject to the requirements of this
standard. The Federal Highway Administration employs two alternate sound
level descriptors: (i) The A-weighted sound level not exceeded more than
10 percent of the time for the highway design hour traffic flow,
symbolized as L10; or (ii) the equivalent sound level for the
design hour, symbolized as Leq. The day-night average sound
level may be estimated from the design hour L10 or
Leq values by the following relationships, provided heavy
trucks do not exceed 10 percent of the total traffic flow in vehicles
per 24 hours and the traffic flow between 10 p.m. and 7 a.m. does not
exceed 15 percent of the average daily traffic flow in vehicles per 24
hours:
DNL[ap]L10 (design hour)--3 decibels
DNL[ap]Leq (design hour) decibels
Where the auto/truck mix and time of day relationships as stated in this
section do not exist, the HUD Noise Assessment Guidelines or other noise
analysis shall be used.
(3) Sites in the vicinity of installations producing loud impulsive
sounds. Certain Department of Defense installations produce loud
impulsive sounds from artillery firing and bombing practice ranges.
Noise analyses for these facilities sometimes encompass sites that may
be subject to the requirements of this standard. Where such analyses are
available they may be used on an interim basis to establish the
acceptability of sites under this standard. The Department of Defense
uses day-night average sound level based on C-weighted sound level,
symbolized LCdn,
[[Page 385]]
for the analysis of loud impulsive sounds. Where such analyses are
provided, the 8 decibel addition specified in Sec. 51.103(b), is not
required, and the same numerical values of day-night average sound level
used on an interim basis to determine site suitability for non-impulsive
sounds apply to the LCdn.
(4) Use of areawide acoustical data. HUD encourages the preparation
and use of areawide acoustical information, such as noise contours for
airports. Where such new or revised contours become available for
airports (civil or military) and military installations they shall first
be referred to the HUD State Office (Environmental Officer) for review,
evaluation and decision on appropriateness for use by HUD. The HUD State
Office shall submit revised contours to the Assistant Secretary for
Community Planning and Development for review, evaluation and decision
whenever the area affected is changed by 20 percent or more, or whenever
it is determined that the new contours will have a significant effect on
HUD programs, or whenever the contours are not provided in a methodology
acceptable under Sec. 51.106(a)(1) or in other cases where the HUD
State Office determines that Headquarters review is warranted. For other
areawide acoustical data, review is required only where existing
areawide data are being utilized and where such data have been changed
to reflect changes in the measurement methodology or underlying noise
source assumptions. Requests for determination on usage of new or
revised areawide data shall include the following:
(i) Maps showing old, if applicable, and new noise contours, along
with brief description of data source and methodology.
(ii) Impact on existing and prospective urbanized areas and on
development activity.
(iii) Impact on HUD-assisted projects currently in processing.
(iv) Impact on future HUD program activity. Where a field office has
determined that immediate approval of new areawide data is necessary and
warranted in limited geographic areas, the request for approval should
state the circumstances warranting such approval. Actions on proposed
projects shall not be undertaken while new areawide noise data are being
considered for HUD use except where the proposed location is affected in
the same manner under both the old and new noise data.
(b) Site assessments. Compliance with the standards contained in
Sec. 51.103(c) shall, where necessary, be determined using noise
assessment guidelines, handbooks, technical documents and procedures
issued by the Department.
(c) Variations in site noise levels. In many instances the noise
environment will vary across a site, with portions of the site being in
an Acceptable noise environment and other portions in a Normally
Unacceptable noise environment. The standards in Sec. 51.103(c) shall
apply to the portions of a building or buildings used for residential
purposes and for ancillary noise sensitive open spaces.
(d) Noise measurements. Where noise assessments result in a finding
that the site is borderline or questionable, or is controversial, noise
measurements may be performed. Where it is determined that noise
measurements are required, such measurements will be conducted in
accordance with methods and measurement criteria established by the
Department. Locations for noise measurements will depend on the location
of noise sensitive uses that are nearest to the predominant noise source
(see Sec. 51.103(c)).
(e) Projections of noise exposure. In addition to assessing existing
exposure, future conditions should be projected. To the extent possible,
noise exposure shall be projected to be representative of conditions
that are expected to exist at a time at least 10 years beyond the date
of the project or action under review.
(f) Reduction of site noise by use of berms and/or barriers. If it
is determined by adequate analysis that a berm and/or barrier will
reduce noise at a housing site, and if the barrier is existing or there
are assurances that it will be in place prior to occupancy, the
environmental noise analysis for the site may reflect the benefits
afforded by the berm and/or barrier. In the environmental review process
under Sec. 51.104(b), the location height and design of the berm and/or
barrier shall be evaluated
[[Page 386]]
to determine its effectiveness, and impact on design and aesthetic
quality, circulation and other environmental factors.
[44 FR 40861, July 12, 1979, as amended at 61 FR 13334, Mar. 26, 1996]
Appendix I to Subpart B of Part 51--Definition of Acoustical Quantities
1. Sound Level. The quantity in decibels measured with an instrument
satisfying requirements of American National Standard Specification for
Type 1 Sound Level Meters S1.4-1971. Fast time-averaging and A-frequency
weighting are to be used, unless others are specified. The sound level
meter with the A-weighting is progressively less sensitive to sounds of
frequency below 1,000 hertz (cycles per second), somewhat as is the ear.
With fast time averaging the sound level meter responds particularly to
recent sounds almost as quickly as does the ear in judging the loudness
of a sound.
2. Average Sound Level. Average sound level, in decibels, is the
level of the mean-square A-weighted sound pressure during the stated
time period, with reference to the square of the standard reference
sound pressure of 20 micropascals.
Day-night average sound level, abbreviated as DNL, and symbolized
mathematically as Ldn is defined as:
[GRAPHIC] [TIFF OMITTED] TC12OC91.000
Time t is in seconds, so the limits shown in hours and minutes are
actually interpreted in seconds. LA(t) is the time varying
value of A-weighted sound level, the quantity in decibels measured by an
instrument satisfying requirements of American National Standard
Specification for Type 1 Sound Level Meters S1.4-1971.
3. Loud Impulsive Sounds. When loud impulsive sounds such as sonic
booms or explosions are anticipated contributors to the noise
environment at a site, the contribution to day-night average sound level
produced by the loud impulsive sounds shall have 8 decibels added to it
in assessing the acceptability of a site.
A loud impulsive sound is defined for the purpose of this regulation
as one for which:
(i) The sound is definable as a discrete event wherein the sound
level increases to a maximum and then decreases in a total time interval
of approximately one second or less to the ambient background level that
exists without the sound; and
(ii) The maximum sound level (obtained with slow averaging time and
A-weighting of a Type 1 sound level meter whose characteristics comply
with ANSI S1.4-1971) exceeds the sound level prior to the onset of the
event by at least 6 decibels; and
(iii) The maximum sound level obtained with fast averaging time of a
sound level meter exceeds the maximum value obtained with slow averaging
time by at least 4 decibels.
[44 FR 40861, July 12, 1979; 49 FR 10253, Mar. 20, 1984; 49 FR 12214,
Mar. 29, 1984]