A noise barrier (also called a soundwall, noise wall, sound berm, sound barrier, or acoustical barrier) is an exterior structure designed to protect inhabitants of sensitive
land use areas from
noise pollution
Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
. Noise barriers are the most effective method of mitigating
roadway, railway, and industrial noise sources –
other than cessation of the source activity or use of source controls.
In the case of surface transportation noise,
other methods of reducing the source noise intensity include encouraging the use of
hybrid and
electric vehicles, improving
automobile aerodynamics and
tire design, and choosing low-noise
paving material. Extensive use of noise barriers began in the United States after
noise regulations were introduced in the early 1970s.
History
Noise barriers have been built in the United States since the mid-twentieth century, when vehicular traffic burgeoned. I-680 in
Milpitas, California was the first noise barrier. In the late 1960s, analytic
acoustical
Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician ...
technology emerged to mathematically evaluate the efficacy of a noise barrier design adjacent to a specific
roadway. By the 1990s, noise barriers that included use of transparent materials were being designed in Denmark and other western European countries.
The best of these early computer models considered the effects of roadway
geometry
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
,
topography,
vehicle
A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles ( motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles ( trains, trams ...
volumes, vehicle speeds, truck mix,
road surface type, and micro-
meteorology
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...
. Several U.S. research groups developed variations of the computer modeling techniques:
Caltrans
The California Department of Transportation (Caltrans) is an executive department of the U.S. state of California. The department is part of the cabinet-level California State Transportation Agency (CalSTA). Caltrans is headquartered in Sacra ...
Headquarters in
Sacramento, California
)
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, mapsize = 250x200px
, map_caption = Location within Sacramento C ...
; the ESL Inc. group in
Sunnyvale, California; the
Bolt, Beranek and Newman group in
Cambridge, Massachusetts
Cambridge ( ) is a city in Middlesex County, Massachusetts, United States. As part of the Greater Boston, Boston metropolitan area, the cities population of the 2020 United States Census, 2020 U.S. census was 118,403, making it the fourth most ...
, and a research team at the
University of Florida. Possibly the earliest published work that scientifically designed a specific noise barrier was the study for the
Foothill Expressway in
Los Altos, California.
Numerous case studies across the U.S. soon addressed dozens of different existing and planned highways. Most were commissioned by state highway departments and conducted by one of the four research groups mentioned above. The U.S.
National Environmental Policy Act, enacted in 1970, effectively mandated the quantitative analysis of
noise pollution
Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
from every
Federal-Aid Highway Act Project in the country, propelling noise barrier model development and application. With passage of the
Noise Control Act of 1972, demand for noise barrier design soared from a host of
noise regulation spinoff.
By the late 1970s, more than a dozen research groups in the U.S. were applying similar
computer modeling technology and addressing at least 200 different locations for noise barriers each year. , this technology is considered a standard in the evaluation of
noise pollution
Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
from highways. The nature and accuracy of the
computer models used is nearly identical to the original 1970s versions of the technology.
Design
The acoustical science of noise barrier design is based upon treating an airway or railway as a
line source. The theory is based upon blockage of sound ray travel toward a particular
receptor; however,
diffraction of sound must be addressed.
Sound waves bend (downward) when they pass an edge, such as the apex of a noise barrier. Barriers that block line of sight of a highway or other source will therefore block more sound. Further complicating matters is the phenomenon of
refraction, the bending of sound rays in the presence of an
inhomogeneous atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. ...
.
Wind shear and
thermocline produce such inhomogeneities. The sound sources modeled must include
engine noise,
tire noise, and
aerodynamic noise, all of which vary by vehicle type and speed.
The noise barrier may be constructed on private land, on a public
right-of-way, or on other public land. Because sound levels are measured using a
logarithmic scale, a reduction of nine
decibels is equivalent to elimination of approximately 86 percent of the unwanted sound power.
Materials
Several different materials may be used for sound barriers. These materials can include masonry, earthwork (such as earth
berm), steel, concrete, wood, plastics, insulating wool, or composites. Walls that are made of absorptive material mitigate sound differently than hard surfaces. It is also possible to make noise barriers with active materials such as solar
photovoltaic panels to generate electricity while also reducing traffic noise.
A wall with porous surface material and sound-dampening content material can be absorptive where little or no noise is reflected back towards the source or elsewhere. Hard surfaces such as masonry or concrete are considered to be reflective where most of the noise is reflected back towards the noise source and beyond.
Noise barriers can be effective tools for
noise pollution
Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
abatement, but certain locations and topographies are not suitable for use of noise barriers. Cost and
aesthetics
Aesthetics, or esthetics, is a branch of philosophy
Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, Epistemology, knowledge, Ethics, values, Philosophy of ...
also play a role in the choice of noise barriers. In some cases, a roadway is surrounded by a noise abatement structure or dug into a tunnel using the
cut-and-cover
A tunnel is an underground passageway, dug through surrounding soil, earth or rock, and enclosed except for the entrance and exit, commonly at each end. A pipeline is not a tunnel, though some recent tunnels have used immersed tube cons ...
method.
Disadvantages
Potential disadvantages of noise barriers include:
* Blocked vision for motorists and rail passengers. Glass elements in noise screens can reduce visual obstruction, but require regular cleaning
* Aesthetic impact on
land- and townscape
* Tendency to get sprayed on with
graffiti
Graffiti (plural; singular ''graffiti'' or ''graffito'', the latter rarely used except in archeology) is art that is written, painted or drawn on a wall or other surface, usually without permission and within public view. Graffiti ranges from s ...
* Creation of spaces hidden from view and
social control (e.g. at railway stations)
* High bird mortality (glass collisions)
LSW Graffiti wm.jpg, Noise abatement walls often block rail passengers' or road users' view and attract graffiti.
Geluidscherm Overschie.jpg, This noise abatement wall in the Netherlands has a transparent section at the driver's eye-level to reduce the visual impact for road users.
Rieder 360° - die niedrige Lärmschutzwand (3).jpg, Low walls close to the track avoid optical impact.
Effects on air pollution
Roadside noise barriers have been shown to reduce the near-road air pollution
concentration levels. Within 15–50 m from the roadside, air pollution concentration levels at the
lee side of the noise barriers may be reduced by up to 50% compared to open road values.
Noise barriers force the pollution plumes coming from the road to move up and over the barrier creating the effect of an elevated source and enhancing vertical
dispersion of the plume. The deceleration and the deflection of the initial flow by the noise barrier force the plume to disperse horizontally. A highly
turbulent shear zone characterized by slow velocities and a re-circulation cavity is created in the lee of the barrier which further enhances the dispersion; this mixes ambient air with the pollutants downwind behind the barrier.
[Bowker, G.E., Baldauf, R., Isakov, V., Khlystov, A., and Petersen, W. (2007). The effects of roadside structures on the transport and dispersion of ultrafine particles from highways. Atmos. Environ. 41, 8128–8139]
See also
*
Health effects from noise
*
Noise control
*
Safety barrier
*
Soundproofing
References
External links
*
{{Authority control
Environmental engineering
Noise pollution
Noise control
Road infrastructure
Acoustics
Sound