The Federal Highway Administration is the agency
responsible for administering the Federal-Aid Highway program. Under this program,
federal funds are allotted by Congress to the individual states. However, before
these monies can be used for highway projects, the projects must be approved by
FHWA,
which can only grant its approval for projects that are developed in accordance with
federal statutes and regulations. One of these regulations requires that a noise
study be accomplished to determine what noise impact, if any, will result from the
proposed highway improvement and what measures will be taken to lessen these noise
impacts. If noise impacts are expected, noise reduction measures that are determined
by the state highway agency and the FHWA to be practicable,
reasonable and acceptable to
the affected public, must be incorporated into the highway improvement and are eligible for
federal funding in the same proportion as other aspects of the project.
NOISE ANALYSIS
What is Noise?
Noise is considered unwanted
sound, particularly when the sound causes annoyance. Noise comes from
many sources. One of the most significant sources is from
transportation, particularly traffic noise.
Highway noise comes from three
sources: the engine, the exhaust, and the interaction of the tires and
pavement. Once typical highway speeds are reached, the predominate noise
from light trucks and cars is from the tire/pavement interaction. Heavy
trucks produce a high volume of noise from all three sources even at
high speeds.
Mitigating transportation noise in
the environment is important for the health and welfare of the
surrounding community. Numerous studies have demonstrated the effect of
noise on the health of those suffering under its impact. Effects ranging
from hearing loss to cardiac arrest have been linked to noise. Prolonged
exposure to noise in excess of 75 dBA may initiate hearing loss. Noise
may also negatively impact the quality of life of those who must live
with it. Loss of sleep and the inability to hold conversations are
frequent complaints. Helping to alleviate these negative impacts is the
objective of noise abatement. Table 1, below shows various effects
attributed to exposure to noise.
TABLE
TO BE ADDED
Studies demonstrate a correlation
between the Ldn (a measurement of the average day-night noise
level) and the percentage of people annoyed by noise at a particular Ldn
level. As the average noise level exceeds 50 Ldn the
percentage of people annoyed by the noise increases.
Applicability
Noise analysis projects are
categorized into two types by the ODOT Analysis and Abatement of Highway
Traffic Noise Policy and the Federal Highway Association (FHWA), Highway
Traffic Noise Analysis and Abatement - Policy and Guidance (FHWA,
1995) . A Type I project refers to projects that include Federal funding
for construction of highways in a new location or the alteration of an
existing highway resulting in substantial change in either alignment or
the number of through-traffic lanes. A Type II project refers to
voluntary projects where noise abatement is investigated due to high
average noise levels at a given location. Type II projects are currently
funded by ODOT from regular project funds without Federal assistance.
Analysis Objectives
All noise analysis is conducted in
compliance with Code of Federal Regulations (CFR), Title 23, Part 772,
the United States Department of Transportation, Federal Highway
Administration (FHWA), Highway Traffic Noise Analysis and Abatement -
Policy and Guidance (FHWA, 1995), and The Ohio Department of
Transportation (ODOT) policy concerning analysis and abatement of
highway traffic noise (ODOT, 1997).
The purpose of noise analysis is
to accomplish a number of objectives:
1. Identify existing and potential
noise sensitive areas within the project area.
2. Demonstrate existing noise
conditions through the use of computer modeling.
3. Determine future noise levels
and the impact of future noise levels on sensitive land use activities
for the given design year.
4. Comparison of existing and
projected conditions to determine the projected impact on the
surrounding area.
5. Identify and evaluate
reasonable and feasible noise abatement measures for reducing noise
where impacts are determined to occur.
6. Address potential concerns for
noise occurring during construction and mitigate when possible.
Noise Descriptors
A variety of methods are used to
describe noise. Noise is typically described using the sound level in
decibels (dB). Decibels are a unit of measure on a logarithmic scale
used to demonstrate the amount of sound pressure at a given location
from the general environment or specific sources. The decibel scale
includes a range of 0-120. A change of 10 dB in either direction
constitutes doubling or halving the sound pressure level respectively.
The frequency of sound is measured
in cycles per second or Hertz (Hz). Humans are capable of detecting
sounds in the range of 20 to 20,000 Hertz. The human ear is best attuned
to frequencies in the range of 200 to 5000 Hz. People do not respond
uniformly to frequency ranges perceiving sounds of equal decibel levels
differently when heard at different frequency intervals. For example, a
60 dBA sound at 1000 Hz will be perceived to be much louder than at 100
Hz. The result is that various weighting methods have been developed to
account for the way people hear sounds at varying frequencies. The
purpose of the weighting is to emphasize frequency ranges to which
people are more attuned. The most common measure of noise level is the
A-weighted sound level (dBA). This is the measure most typically used in
community sound ordinances and in traffic related noise measurements.
The typical person is unable to detect changes in sound pressure level
of less than 3 dBA. In general, a change of 5 dBA can be readily
detected.
When quantifying environmental
noise, consideration must be given to the fluctuation in noise levels
over a period of time. To properly measure environmental noise it is
best to measure an equivalent sound level over a period of interest. The
Leq(h) measure is widely accepted for calculating
environmental noise based on an hourly value (h).
Noise Abatement
Noise from transportation sources
in the surrounding community depends on a number of factors. Among these
factors are the volume and vehicle mix of the traffic, specifically, the
number of heavy trucks in the mix, the proximity of the receiver to the
traffic, the speed of the traffic, and the nature of the intervening
terrain. Large hills or other buildings between a receiver and the
roadway help reduce the amount of noise experienced at a receiver.
Vegetation may also serve to reduce traffic noise provided it is dense
enough (at least 100 feet) and tall enough (at least 30 feet).
Otherwise, vegetation only serves to provide psychological relief.
There are several methods
considered for abatement of highway noise:
Traffic Management Measures:
This involves restrictions on the speed and type of vehicles permitted
to use a particular roadway. Prohibiting heavy trucks from using a road
or providing strict limits on speed can greatly reduce to noise from a
road. This measure is not feasible for use in many projects due to the
nature of the roadway in question. For example, the purpose of an
interstate highway is to move large volumes of traffic at high speeds.
Restricting the type and speed of vehicles using the highway is counter
to the purpose of the highway.
Alteration of horizontal and
vertical alignments:
Alignment of the road refers to the physical layout of the roadway.
Placing the road at an elevated grade will typically result in greater
noise than a road at grade or below grade.
Quieter Pavement:
Much research is currently underway to develop quiet pavement. In
general, asphalt pavement is quieter than concrete pavement, but
concrete pavement is believed to have greater durability. Open-graded
asphalt is a quiet pavement that depends on voids in the surface to
reduce the area of the tire interacting with the pavement, resulting in
less noise. The pavement requires cleaning to remain effective. The
voids are subject to being filled with dust and other particles, thereby
reducing the effectiveness of the pavement in providing noise abatement.
Land Use Planning and Control:
State and local governments are encouraged by the FHWA and other federal
agencies to practice land use planning and control near highways. Local
governments should use their authority to encourage development near
highways in such a way that noise sensitive land uses are developed in
areas away from the highway potentially eliminating the need for such
abatement measures as noise barriers. This is a highly complex issue due
to the numerous agencies involved and the various layers of legislative
authority with control over land use issues.
Noise Barrier Construction:
Noise barriers reduce noise by blocking the path of sound between the
source of the noise and the receiver. To be effective, a noise barrier
should be located adjacent to either the source or the receiver. They
must also be long, continuous and break the line-of-sight from the
highway to the receiver. A noise barrier must generally extend four
times the distance between the barrier and the last receiver to be
effective at reducing noise for the last receiver. Noise barriers are
typically designed to achieve a minimum reduction of 5 dBA for at least
one receiver and 3 dBA for other receivers to be considered effective. A
minimum reduction of 3 dBA must be achieved for a particular receiver to
be considered as benefiting from a barrier. Noise barrier construction
is considered reasonable if the construction cost is less than $35,000
per receiver. Per the ODOT noise policy, construction of natural noise
barriers will be explored where feasible.
Ohio entered the noise barrier arena in 1975
with the construction of the great Gahanna Wall, a concrete noise barrier along I-270 in
northeast Columbus. The barrier was acoustically effective but not very
aesthetically appealing. At that time, ODOT allowed the contractor to choose
the type of barrier material. Since then, ODOT's noise barrier procedure has been
revised to include community's choice of color, texture and material type. Brick barriers can be found along I-75 north of Dayton and textured concrete barriers, with
concrete posts, can be found along I-75 in Tipp City. ODOT's noise barrier program
continues to evolve.
Bibliography
ODOT
NOISE POLICY AND PROCEDURE
NOISE ANALYSIS REVIEW CHECKLIST (ADDED 3-10-2008)
(Effective 08/01/2006)
ODOT Standard Procedure for Analysis and Abatement of Highway Traffic Noise
POLICY
STATEMENT 21-001(P)
NOISE ANALYSIS PROCESS FLOW CHART (ADDED 3-03-2009)
NOISE PUBLIC INVOLVEMENT PROCESS FLOWCHART (ADDED 2-21-2008)
23 CFR 772 (ADDED 2-21-2008)
THESE PDF'S WORK WITH
Adobe Acrobat
reader V.5.
NOISE BARRIER SPECIFICATIONS, MATERIALS, CONSTRUCTION METHODS, ETC.
LANDSCAPING GUIDELINES
MOT-75-13.11 NOISEWALL ZIP FILE OF VIDEO FOR DOWNLOAD
