HomeMy WebLinkAboutAppendix I-Acoustics AssessmentAPPENDIX I
Acoustics Assessment for the Froom Ranch Project
Froom Ranch Specific Plan Project
Draft EIR
This Page Intentionally Left Blank.
45dB
Acoustics
David Lord, PhD dl@45dB.com
Sarah Taubitz, MSME st@45dB.com
P.O. Box 1406
San Luis Obispo
California 93406
tel. 805.704.8046
www.45dB.com
June 7, 2017
Project 1721-1
RE:
Acoustics Assessment
Froom Ranch Project
San Luis Obispo, CA 93401
Client:
John Madonna
P.O. Box 5310
San Luis Obispo, CA 93403
1 Summary
This is a report on the existing and future noise impacts on the proposed Froom Ranch Project
located on the southwest side of Los Osos Valley Road (LOVR), between Froom Ranch Road
and Calle Joaquin. All noise sources are considered, including occasional air traffic from San
Luis Obispo County Regional Airport, and vehicular traffic noise from adjacent Los Osos Valley
Road and Calle Joaquin, as well as U.S. Highway 101 to the southeast of the project. The intent
of this assessment is to determine noise levels that may potentially impact the proposed
residential units at the eastern edge and elsewhere throughout the site.
Several sound level measurement data sets were collected at different locations on site. Existing
sound levels were correlated for each of the measurement locations, for use in “calibrating” noise
modeling software. The objective is to generate existing sound level contours, which may be
compared with generalized sound level contours published by the City of San Luis Obispo in the
1996 Noise Element (Figures 5 and 6).
This report shows the results of an initial sound level survey to establish existing and future
sound level contours resulting from transportation noise.
Two sound level ‘portraits’ for the overall site are shown in addition:
1. Existing sound levels with no development on the site, i.e., no project.
2. Potential future sound levels once the proposed project is built.
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Contents
1 Summary ..........................................................................................................................1
2 Location ...........................................................................................................................3
2.1 Sound Level Measurements .................................................................................5
2.2 Sound Level Contours ..........................................................................................5
2.3 Contour Disparities ..............................................................................................8
2.4 Graphic Results ....................................................................................................9
2.5 Future Sound Level ..............................................................................................10
3 Regulatory Setting ...........................................................................................................12
3.1 State Regulation ...................................................................................................13
3.2 Local Regulation ..................................................................................................13
4 Traffic Characteristics ......................................................................................................14
4.1 Traffic Growth .....................................................................................................14
4.2 Traffic Flow and Sound Level .............................................................................15
5 Meteorological Conditions...............................................................................................16
6 Sound Level Data .............................................................................................................17
7 Conclusion .......................................................................................................................19
8 Glossary of Acoustical Terms ..........................................................................................20
9 Sound Level Modeling and Measurement .......................................................................22
9.1 Sound level modeling ..........................................................................................22
9.2 Sound Level Measurement ..................................................................................22
10 References ........................................................................................................................22
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2 Location
The project is located west of the intersection of Los Osos Valley Road and Calle Joaquin, near
the U.S. Highway 101 interchange. The project site is shown in Figure 1. Vicinity of Site,
currently open land separated from Los Osos Valley Road by shrubbery and trees and a barbed
wire fence.
The measurement stations on the site were chosen to be near potential future residential building
elevations exposed to Los Osos Valley Road, Calle Joaquin, and U.S. Highway 101 in the
distance.
During the sound level survey, occasional overflight of small aircraft was observed, departing
from San Luis Obispo County Regional Airport and over 1,000 feet above the project area.
Figure 1. Vicinity of Site,
southwest of Los Osos Valley Road and west of Calle Joaquin.
U.S. Highway 101 is further in the distance toward the southeast of the site.
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Figure 2. Sources of traffic noise: Los Osos Valley Road,
Calle Joaquin and U.S. Highway 101, two lanes.
Location of the three transportation noise sources is shown in Figure 2.
Toward the southeast of the site, U.S. Highway 101 is a significant transportation noise source
with an Average Annual Daily Traffic Flow between 62,000 to 69,000.
Figure 3. 2015 Traffic Volumes, U.S. Highway 101, from Caltrans data
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Figure 4. Los Osos Valley Road, Calle Joaquin Average Daily Traffic
2.1 Sound Level Measurements
Six sound level measurement sites are shown in Figure 6. Plan showing measurement stations
and sound levels, Leq = dBA, at each station. Two measurement sites are stationary; four sites
are spot check locations. In addition to the six sites, synchronized duplicate measurements were
made at the two stationary sites for a total of eight data sets. The sound level data was compared
with nearby data. The fixed measurement stations were then used to calibrate the noise modeling
software, in order to generate sound level contours based on precision measurements of existing
sound. Future sound level is projected using future growth assumptions for average daily traffic
flow.
2.2 Sound Level Contours
A Sound Level Contour is a line on a map that represents equal levels of noise exposure.
SoundPlan is an acoustics modeling software program used to calculate noise contours, based on
topographic relationships of noise sources and noise receivers. The standard calculation software
for modeling traffic noise is the Federal Highway Administration program, Transportation Noise
Model, TNM. SoundPlan, used for this report, implements TNM in its calculation.
On-site measured sound level values are used to calibrate and to validate the SoundPlan -
generated sound level contours. The graphic sound level contours depict sound level on the site
from a composite of three transportation noise sources: Los Osos Valley Road, Calle Joaquin
and U.S. Highway 101.
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Figure 5. Site Plan, proposed project
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Figure 6. Plan showing measurement stations and sound levels, Leq = dBA, at each station.
There were two stationary measurement stations, one next to LOVR and the other next to Calle Joaquin.
There were four ‘spot-check’ stations near future potential building elevations.
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Figure 7. City of San Luis Obispo Sound Level Contours, based on a study by Brown Buntin, 1991.
Results appear in City of San Luis Obispo Noise Element, last revised 1996.
2.3 Contour Disparities
The difference between the sound level contours shown by the City in its 1996 Noise Element
exhibit and the measured and modeled contemporaneous sound level contours presented in this
report can be attributed to the difference in technology utilized in the 1990s and that used today.
In 1990, when the City’s commissioned noise study was completed by Brown-Buntin Associates,
the method for drawing sound level contours was based on a mathematical calculation of sound
level at fixed and specific distances from the centerline of the roadway. The calculations ignored
the effects of topography, shielding by buildings, ground surface variations, absorption and
reflection. In 1990, sound level contours were drawn at a constant distance along major roads in
the city and ended at the city limits. The calculations accommodated three vehicle types, autos,
heavy trucks and medium trucks at constant speeds. Described at the time, “the noise contour
information prepared by the consultants and staff generally reflects conservative (worst case)
assumptions, so significant noise exposure concerns are not likely to be omitted or understated.”
(See Reference 9.)
Today, using contemporary sound level mapping, there are noticeable effects and multiple
variations due to terrain, ground absorption, reflection and blocking of sound by the built
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environment. Noise contours change as urban density and traffic patterns change. Today’s
sound level contours are a more realistic representation of actual conditions.
2.4 Graphic Results
Figure 8. This is the measured, existing 60 dBA Sound Level Contour,
based on measured values from the six stations shown previously.
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2.5 Future Sound Level
The calculated future Ldn/CNEL (year 2037) along the east and south side of the site will depend
on growth of traffic, generally accepted to be about one percent per year growth rate.
Figure 9. Future, calculated, 60 dBA Sound Level Contour at Buildout or year 2037
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Figure 10. No Project, Sound Level Contours Across the Site
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Figure 11. Future Sound Level Contours with Proposed Project (year 2037)
3 Regulatory Setting
Noise is regulated at the federal, state and local levels through regulations, policies and/or
local ordinances. Local policies are generally adaptations of federal and state guidelines, adjusted
to prevailing local condition.
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3.1 State Regulation
The State of California’s Guidelines for the Preparation and Content of Noise Element
of the General Plan (1987) make reference to land use compatibility standards for community
noise environments as developed by the California Department of Health Services,
Office of Noise Control. Sound levels up to 65 Ldn or CNEL are determined to be normally
acceptable for multi-family residential land uses. Sound levels up to 70 CNEL are normally
acceptable for buildings containing professional offices or defined as business commercial.
All new Multi-Family housing must comply with California Code of Regulations (CCR)
Title 24. This is included in the California Building Code (CBC), Section 1207, “Sound
Transmission” – which specifies the maximum level of interior noise due to exterior sources
allowable for new residential developments.
3.2 Local Regulation
CCR Title 24 also defers to local requirements if applicable. The Noise Element of the City of
San Luis Obispo General Plan specifies a maximum allowable interior noise level of 45 dBA
Ldn for multi-family projects which is consistent with the above policies for interior noise and
also extends this requirement to new single-family dwellings. The City of San Luis Obispo Noise
Element also states that 60 dBA Ldn or less is the exterior noise goal for outdoor common areas,
defined as areas intended for the use and enjoyment of residents.
Guidelines for transportation noise exposure are contained in City of San Luis Obispo, General
Plan Noise Element and Noise Guidebook (1996). The maximum noise exposure standards for
noise-sensitive land uses are shown in Figure 12. The maximum noise exposure standards for
noise-sensitive land uses due to traffic are shown in Figure 13.
Figure 12. Community Noise Exposure Ldn / CNEL
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Figure 13. Maximum Exposure for Noise Sensitive Uses due to Traffic
4 Traffic Characteristics
This section examines the effects of traffic growth over time on the sound level contours of the
site, and the relationship of traffic flow to sound levels on site.
4.1 Traffic Growth
Federally funded projects and environmental reviews typically require the projection of traffic
volumes 10–30 years in the future, typically assuming a 1–2% annual growth in vehicle volume.
In this report, we have assumed a 20-year period of growth to year 2037, at an annual growth
rate of 1 percent (0.01). The calculation in Figure 14 shows the result for Los Osos Valley Road.
Figure 14. Growth of Noise from Average Daily Traffic
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4.2 Traffic Flow and Sound Level
Consulting the Highway Traffic Manual (reference 15) helps to understand the issues in
measuring sound level resulting from traffic flow. There are several descriptors of traffic flow
from Average Daily Traffic (ADT) to Design Hourly Volume (DHV) of traffic on a road or
highway. DHV is sometimes used as a benchmark for sound level measurements. However, the
DHV is defined as the 30th highest hourly volume in the “design” year, whereas the Peak Hour
Volume (PHV) is defined as the highest hourly volume during an average day.
Depending on the type of roadway, the PHV may be from 5 to 45 percent lower than the DHV.
The definition infers that if a highway or street is to adequately serve throughout its life, its
physical capacity will only be exceeded for about 30 hours out of the total 8,760 hours in the
“design” year. The choice of the 30th highest hourly volume is a long-held concept which stems
from research published in A Policy on Geometric Design of Rural Highways (Reference 1.)
Figure 15. Relationship Between Peak-Hour and Average Daily Traffic Volumes.
Visually comparing the traffic flow trend lines above indicates that significant traffic flow
changes occur at the inflection point of the 30th highest volume hour of the year. The difference
in volume of traffic between the 1st highest hourly volume and the 30th increases rapidly. For the
remainder of the hours between the 30th and the 170th, there is very little change in the slope of
the curves. This indicates that designing for that 30th hour would cover the expected traffic
volume at almost any given hour in a given day of a given week in a given month of a given
year.
Noise impacts are measured during the one-hour period when the worst-case noise levels are
expected to occur. This may or may not be the peak hour of traffic. That is, higher traffic
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volumes can lead to higher congestion and lower operating speeds. Since higher speeds lead to
higher noise emissions from motor vehicles, the worst-case noise levels may occur in hours with
lower volumes and higher speeds. In addition, vehicle mix may also change hourly. On many
highways, the percentage of heavy trucks is reduced during peak hour. Since heavy trucks have
greater sound emissions than passenger cars, vehicle mix is an important component in
determining the peak hour of noise impact.
During the sound level measurement for this project, Level of Service (LOS) was observable and
gives us confidence that we are measuring during a busy-but-not-congested time period.
The LOS during the measurements was generally Level B to Level C and at one time became
Level of Service D.
Figure 16. Level of Service vs General Operating Conditions
5 Meteorological Conditions
During the measurement period from 10 am to 12 noon on Saturday, April 22, 2017, the sky was
essentially clear and the wind speed was less than 10 mph from the west and north. Wind speed
and direction data was taken from San Luis Obispo County Regional Airport weather station.
Wind speed above 12 mph has an increasing adverse effect on the accuracy of sound level
measurements (reference: Federal Highway Administration, Noise Measurement).
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Figure 17. Weather conditions at SBP San Luis Obispo Airport, 3.2 km SE of the project site.
6 Sound Level Data
Figure 18. Location Name, Coordinates and Sound Level, LAeq
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Figure 19. Spectral quality of sound, Third Octave Bands at LT1, near Calle Joaquin.
Figure 20. Spectral Quality of Sound, Third Octave Bands at LT2 near Los Osos Valley Road
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7 Conclusion
The measured and predicted sound levels impacting the proposed Villaggio project are a mix of
transportation noise along Los Osos Valley Road, the Calle Joaquin interchange with Highway
101, and to a lesser extent, Calle Joaquin west of Los Osos Valley Road. Future noise level from
transportation sources at buildout are predicted to result in an increase in sound level of about
one decibel in 20 years’ time.
Perceived sound level studies reveal the subjective interpretation of sound differences. A one
dBA increase in sound level is barely noticeable to the most sensitive subjects. Sound level must
increase by five (5) dBA before most listeners report a noticeable or significant change in sound
level.
for 45dB Acoustics, LLC
David Lord
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8 Glossary of Acoustical Terms
A-Weighted Sound Level (dBA)
The sound pressure level in decibels as measured on a sound level meter using the internationally
standardized A-weighting filter or as computed from sound spectral data to which A-weighting
adjustments have been made. A-weighting de-emphasizes the low and very high frequency
components of the sound in a manner similar to the response of the average human ear. A-
weighted sound levels correlate well with subjective reactions of people to noise and are
universally used for community noise evaluations.
Air-borne Sound
Sound that travels through the air, differentiated from structure-borne sound.
Ambient Sound Level
The prevailing general sound level existing at a location or in a space, which usually consists of a
composite of sounds from many sources near and far. The ambient level is typically defined by
the Leq level.
Background Sound Level
The underlying, ever-present lower level noise that remains in the absence of intrusive or
intermittent sounds. Distant sources, such as Traffic, typically make up the background. The
background level is generally defined by the L90 percentile noise level.
Community Noise Equivalent Level (CNEL)
The Leq of the A-weighted noise level over a 24-hour period with a 5 dB penalty applied to
noise levels between 7 p.m. and 10 p.m. and a 10 dB penalty applied to noise levels between 10
p.m. and 7 a.m. CNEL is similar to Ldn.
Day-Night Sound Level (Ldn)
The Leq of the A-weighted noise level over a 24-hour period with a 10 dB penalty applied to
noise levels between 10 p.m. and 7 a.m. Ldn is similar to CNEL.
Decibel (dB)
The decibel is a measure on a logarithmic scale of the magnitude of a particular quantity (such as
sound pressure, sound power, sound intensity) with respect to a reference quantity.
DBA or dB(A)
A-weighted sound level. The ear does not respond equally to all frequencies, but is less sensitive
at low and high frequencies than it is at medium or speech range frequencies. Thus, to obtain a
single number representing the sound level of a noise containing a wide range of frequencies in a
manner representative of the ear’s response, it is necessary to reduce the effects of the low and
high frequencies with respect to the medium frequencies. The resultant sound level is said to be
A-weighted, and the units are dBA. The A-weighted sound level is also called the noise level.
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Energy Equivalent Level (Leq)
Because sound levels can vary markedly in intensity over a short period of time, some method
for describing either the average character of the sound or the statistical behavior of the
variations must be utilized. Most commonly, one describes ambient sounds in terms of an
average level that has the same acoustical energy as the summation of all the time-varying
events. This energy-equivalent sound/noise descriptor is called Leq. In this report, an hourly
period is used.
Field Sound Transmission Class (FSTC)
A single number rating similar to STC, except that the transmission loss values used to derive the
FSTC are measured in the field. All sound transmitted from the source room to the receiving
room is assumed to be through the separating wall or floor-ceiling assembly.
Outdoor-Indoor Transmission Class (OITC)
A single number classification, specified by the American Society for Testing and Materials
(ASTM E 1332 issued 1994), that establishes the A-weighted sound level reduction provided by
building facade components (walls, doors, windows, and combinations thereof), based upon a
reference sound spectra that is an average of typical air, road, and rail transportation sources. The
OITC is the preferred rating when exterior façade components are exposed to a noise
environment dominated by transportation sources.
Single Event Noise Exposure Level (SENEL)
The time-integrated A-weighted sound pressure level of a single aircraft flyover (which exceeds
a threshold noise level) which is expressed by the level of an equivalent one-second duration
reference signal.
Sound Transmission Class (STC)
STC is a single number rating, specified by the American Society for Testing and Materials,
which can be used to measure the sound insulation properties for comparing the sound
transmission capability, in decibels, of interior building partitions for noise sources such as
speech, radio, and television. It is used extensively for rating sound insulation characteristics of
building materials and products.
Structure-Borne Sound
Sound propagating through building structure. Rapidly fluctuating elastic waves in gypsum
board, joists, studs, etc.
Subjective Loudness Level
In addition to precision measurement of sound level changes, there is a subjective characteristic
which describes how most people respond to sound:
A change in sound level of 3 dBA is barely perceptible by most listeners.
A change in level of 6 dBA is clearly perceptible.
A change of 10 dBA is perceived as being twice (or half) as loud.
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9 Sound Level Modeling and Measurement
9.1 Sound level modeling
Sound level contours compared to the measured sound level values were generated for
assessment using SoundPlan noise simulation software. The software calculates sound
attenuation of environmental noise around buildings. For this project, the land between the
sources (road and airport operations) and receiver project boundary, is generally flat and partially
paved. The modeling software calculates the sound field in accordance with ISO 9613-2
“Acoustics - Attenuation of sound during propagation outdoors, Part 2: General Method of
Calculation.” This standard states that “this part of ISO 9613 specifies an engineering method for
calculating the attenuation of sound during propagation outdoors in order to predict the levels of
environmental noise at a distance from a variety of sources. The method predicts the equivalent
continuous A-weighted sound pressure level under meteorological conditions favorable to
propagation from sources of known sound emissions.”
9.2 Sound Level Measurement
The protocol used for the sound level measurements is prescribed in detail by the American
Society for Testing and Materials (ASTM) in their E 1014 publication. The procedures and
standards in that document were met or exceeded for sound level measurements shown in this
report. The standards of ASTM E 1014 are exceeded by using Type 1 (Class 1) sound level
meters for all measurements in this report instead of less accurate Type 2 meters. Therefore, the
precision of the measurements in this report is likely to be better than +/- 1 dB. The sound level
meters used for measurements shown in this report are Norsonic Nor140 Sound Analyzers, with
synchronized time settings. These sound level meters meet all requirements of ANSI s1.4, IEC
651 for Class 1 accuracy. The sound level meters were calibrated before and after each sound
level measurement. The measurement results from both sound level meters running
simultaneously were compared and found to be in close agreement.
10 References
1. American Association of State Highway and Transportation Officials. 2011. A Policy on
Geometric Design of Highways and Streets.
2. American National Standards Institute, Inc. 2004. ANSI 1994 American National
Standard Acoustical Terminology. ANSI S.1.-1994, (R2004), New York, NY.
3. American Society for Testing and Materials. 2004. ASTM E 1014 - 84 (Reapproved
2000) Standard Guide for Measurement of Outdoor A-Weighted Sound Levels.
4. Bolt, Beranek and Newman. 1973. Fundamentals and Abatement of Highway Traffic
Noise, Report No. PB-222-703. Prepared for Federal Highway Administration.
5. State of California Department of Transportation. 2011. California Airport Land Use
Planning Handbook.
6. California Department of Transportation (Caltrans). 1982. Caltrans Transportation
Laboratory Manual.
7. ______. 1998. Caltrans Traffic Noise Analysis Protocol for New Highway Construction
and Highway Reconstruction Projects
8. California Resources Agency. 2007. Title 14. California Code of Regulations Chapter 3:
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Guidelines for Implementation of the California Environmental Quality Act Article 5.
Preliminary Review of Projects and Conduct of Initial Study Sections, 15060 to 15065.
9. City of San Luis Obispo, California. 1996. Noise Guidebook Measurement and
Mitigation Techniques.
10. City of San Luis Obispo, California, General Plan Noise Element.
11. City of San Luis Obispo, California, Public Works, Traffic Data. https://goo.gl/aRJIRq
12. Federal Highway Administration. 2006. FHWA Roadway Construction Noise Model
User’s Guide Final Report. FHWA-HEP-05-054 DOT-VNTSC-FHWA-05-01
13. Federal Highway Administration. 2011. Measurement of Highway-Related Noise.
https://goo.gl/dKlwZk
14. Harris, Cyril M., editor. 1979 Handbook of Noise Control.
15. Transportation Research Board. 2016. Highway Traffic Manual, a guide for multimodal
mobility analysis.
16. Interactive Sound Level Calculator, MAS Environmental https://goo.gl/23zTnQ