HomeMy WebLinkAboutCT 79-04; RANCHO LA QUESTA; NOISE EVALUATION; 1981-04-24-• HILLIARD & BRICKEN-----81
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John HIiiiard • Consulting Acoustl~al & Energy Engineers • Gordon Brlcken
April 24, l98l
Mr. Bob. McClaire
Ayres Construction Company
Drawer A
Huntington Beach, California 92648
Subject: Noise Evaluation, Tract 7~-4, in the City
of Carlsbad~
Dear Mr. McClaire:
At your request we have evaluated the noise conditions
in Tract 79.--4 .. The s·ite is· located along El Camino Real.
Lots 38 and 39 are ·adjacent to El Camino Real as noted
in Exhibit l.
Design Nois·e Cotid:itions·
The design noise conditions· is based on a ten (10) year
design year. There are no forecasts available so it is
necessary to construct one Based on an evaluation of
historic growth trends. The basic data is listed in
table l.
Table l
Traffic Volume on El Camino Real
1976
1978
1980
8300
9188
l4,650
The average four year growth is 20% per year. It is
unlikely this will be sustained. A reasonable average
growth rate is l0-l2% a year. On this basis in the ten
(.10). year range would be 38,943 to 49,730 ADT. A Design
value of 40,000 ADT was selected for the study.
/
1538 East Fourth Street D Franklin Square D Santa Ana, California 92701 D (714) 835-3728
Bob McClaire A
Ayres Construc~n
April., 1981
Page~
This is also the capacity of the street at "C" level
service. With a 40,000 ADT, 45 mph average speed
and estimate 4% trucks, the reference noise level is
73.5 CNEL 50' for CNEL.
Applicable Noise Criteria
The City of Carlsbad adheres to the requirements of Table 2.
Table 2 (.J. l
Applicable Noise Criteria
Exterior
Interior
65 CNEL
45 CNEL
Cl}_ See Noise Rating Methods, Application Note #6 for
explanation of acoustical terminology.
Mitigation
Exterior
The s.i.te i.s approximately 30.1• below street grade
as. noted on· Exhibi.t 1. There is shelding from the
slope "i.n the order of J.O -. 12 dB. The schedule
noi~e le~el at· 6• along the site grade will be
55 CNEL. This· is below-the 65 CNEL limit. No
furture mitigation i's requi'red.
'Interior
Buildings of standard construction yield 20 dBA noise
reduction with closed windows and 10 dBA with open
windows. Design interior values will be 35 CNEL with
closed windows and 45 CNEL with open windows. Even
the open case conforms to the crite • ~-......_ ditional
mitigation is required.
Prepared by:
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Gordo~~ --..--. C:,;-::
Yi.ce President , r
/kmt
Enclosures: Exhibit l
Application Note #6
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Exhibit J.·. -
TRACT 79-4 Carlsbad
Newport Shores Builders
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-APieCATION NOTE .. #6
HILLIARD & BRICKEN----------
John HIiiiard • Consulting Acoustical Engineers • Gordon Brlcken
NOISE RATING METHODS
The A-weighted decibel of "A" scale on the sound level
meter is most often used in .the measurement of noise
because the weighting characteristics of this scale
approximates the subjective response of the human ear
to a broad frequency band noise source by discriminating
against the very low and the very high frequencies of
the audible spectrum.
Since community noise is seldom constant,.varying from
moment to moment and throughout the day, the "A" weighted
noise level needs to be further described to provide
meaningful data. The Environmental Protection Agency,
Federal Department of Transportation, foreign countries
and private consultants are now using three time-exceeded
percentile figures to describe noise:
1. L90 is the noise level which is exceeded 90% of any
sample time period (such as 24 hours) and is used
to describe the background or ambient noise level.
2. Lso is the noise level which is exceeded 50% of the
time. It is the median level.
3. LlO is the noise level which is exceeded 10% of the
time and is a good descriptor of fluctuating noise
sources such as vehicular traffic. It indicates
the near-maximum levels which occur from grouped
single events. Being related to the subjective
annoyance to community noise, it is a good design
tool in the planning of acoustical barriers.
More recent noise assessment methods are ·based on the
equivalent energy concept where Leq !x) represents the
average energy content of a fluctuating noise source
over a sample period.
The subscript (x) represents the period in which the
energy is computed and measured. Current practice
references the quantity to either one hour, 8 hours or
24 hours. When referenced to ·one hour, Leg is also
sometimes called HNL (Hourly Noise Level).
1538 East Fourth Street □ Franklin Square □ Santa Ana, California 92701 □ (714) 835-3728 1
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NOISE RATING METHODS PAGE 2 -
Since Le is the summation of the functional products of
noise leiel and duration, many combinations of noise
level,. duration time and time history. can make up the same
L value. Thus, an L (24) equals 50 means only that
tff~ aver~ge noise levelqis 50 dB.· During the 24 hour
period there can be times when the noise level is higher
than 50 dB and many times when it is lower.
If the period of the raeasurement is only a single event,
the energy content is not averaged. The energy expression
for a single event is simply the sum of the functional
product of the noise level and duration. time of the event ..
This term ~s called Le or SENEL {Single Event Noise
Exposure Level). The sum.~ation of L values averaged over
one hour is Leg(l) -Leg(B) and Leq -~24 ), etc.).
Leq is further refined into Ldn (Level Day-Night) and
CNEL (Community Noise Equivalent Level) where noises that
occur during certain hours of the day are weighted
(or penalized) because they-are considered subjectively
more annoying during these time ~eriods:
1. Ldn is the sound level in dBA which corresponds to
the average eriergy content of the noise being •
measured over a 24-hour period including a 10 dBA
weighting penalty for sound levels which occur during
the nighttime hours of 10PM to 7AM. This is a
rating method recommended by the Environmental
Protection Agency because it takes into account those
subjectively more annoying noise events which occur
during the sleeping hours.
2. CNEL is the sound level in dBA.which corresponds to
the average energy content of the noise being measured
over a 24-hour period including a 3 dBA weighting
penalty for noises that occur during the evening hours
of 7PM to l0Pm, plus a 10 dBA penalty for noise
events that occur during the nighttime hours of 10PM
to 7AM. For typical highway vehicular traffic
situations, computer analysis has shown that CNEL
and Ldn co~relate within 0.5 dBA.
The percentile figures L10 , L50 and L90 can be·directly
scaled from a graphical recoraing of the Measured noise
over a particular time period. They are also convenient_
to implement in automatic measurement equipment .. Energy
parameters Le, Leq, La and CNEL require expensive and
complicated equipment ~hat has only recently become
available on the commercial market. As a result, engineers
have devised ways of estimating Leq (and hence Lan) using
standard instrumentation and methods.