Noise barrier

Short description: Exterior structure on infrastructure used to prevent loud sounds from escaping

The sound tube in Melbourne, Australia, designed to reduce roadway noise without detracting from the area's aesthetics

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 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.

## Contents

* 1 History
* 2 Design
* 2.1 Materials
* 3 Disadvantages
* 4 Effects on air pollution
* 5 See also
* 6 References
* 7 External links

## History

Noise barriers have been built in the United States since the mid-twentieth century, when vehicular traffic burgeoned. The first was installed in 1968 along a section of I-680 in Milpitas, California.[1] In the late 1960s, analytic acoustical 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.[2]

Acoustical scientist measures sound in noise barrier design study, Santa Clara County, California.

The best of these early computer models considered the effects of roadway geometry, topography, vehicle volumes, vehicle speeds, truck mix, road surface type, and micro-meteorology. Several U.S. research groups developed variations of the computer modeling techniques: Caltrans Headquarters in Sacramento, California; the ESL Inc. group in Sunnyvale, California; the Bolt, Beranek and Newman[3] group in Cambridge, Massachusetts, 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.[4]

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 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,[5] 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. As of 2006[update], this technology is considered a standard in the evaluation of noise pollution from highways. The nature and accuracy of the computer models used is nearly identical to the original 1970s versions of the technology.

Small and purposeful gaps exist in most noise barriers to allow firefighters to access nearby fire hydrants and pull through fire hoses, which are usually denoted by a sign indicating the nearest cross street, and a pictogram of a fire hydrant, though some hydrant gaps channel the hoses through small culvert channels beneath the wall.

## 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. A barrier's acoustic performance is commonly expressed as its insertion loss \- the reduction in sound level at the receiver produced by inserting the barrier into an otherwise open path. For a thin, rigid barrier, the insertion loss is governed largely by the Fresnel number N=2δ/λ, where δ is the difference between the length of the shortest sound path passing over the top of the barrier and the straight-line distance from source to receiver, and λ is the wavelength. Taller barriers, barriers placed closer to the source or receiver, and higher frequencies all increase δ/λ and therefore the attenuation. The empirical design charts published by Maekawa, which relate the Fresnel number to barrier attenuation, remain a widely used basis for barrier design.[6][7]

Sound waves bend (downward) when they pass an edge, such as the apex of a noise barrier. Barriers that block line of sight will therefore block more sound.[8] Further complicating matters is the phenomenon of refraction, the bending of sound rays in the presence of an inhomogeneous atmosphere. 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.

Noise barrier earth berm along California State Route 12, Sonoma County, California

### Materials

Several different materials may be used for sound barriers, including masonry, earthwork (such as earth berm), steel, concrete, wood, plastics, insulating wool, or composites.[9] Walls that are made of absorptive material mitigate sound differently than hard surfaces.[10] It is also possible to make noise barriers with active materials such as solar photovoltaic panels to generate electricity while also reducing traffic noise.[11][12][13]

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.[14]

Noise barriers can be effective tools for noise pollution abatement, but certain locations and topographies are not suitable for use of noise barriers. Cost and aesthetics 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 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
* An expanded target for graffiti, unsanctioned guerilla advertising, and vandalism
* Creation of spaces hidden from view and social control (e.g. at railway stations)
* Possibility of bird–window collisions for large and clear barriers

* Noise abatement walls often block rail passengers' or road users' view and attract graffiti.

* 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.

* 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.[15]

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.[16]

## See also

* Health effects from noise
* Noise control
* Safety barrier
* Soundproofing

## References

1. ↑ Wagner, Kate (8 December 2016). "Building the Wall: Highway Sound Barriers and the Evolution of Noise". 99 Percent Invisible. http://99percentinvisible.org/article/building-wall-highway-sound-barriers-evolution-noise/.
2. ↑ Benz Kotzen and Colin English (1999) Environmental Noise Barriers: A Guide to Their Acoustic and Visual Design, Published by Taylor & Francis, ISBN 0-419-23180-3, 165 pages
3. ↑ John Shadely, Acoustical analysis of the New Jersey Turnpike widening project between Raritan and East Brunswick, Bolt Beranek and Newman, 1973
4. ↑ C.M. Hogan and Harry Seidman, Design of Noise Abatement Structures along Foothill Expressway, Los Altos, California, Santa Clara County Department of Public Works, ESL Inc., Sunnyvale, California, October, 1970
5. ↑ Public Law No. 92-574, 86 Stat. 1234 (1972)Noise Pollution and Abatement Act of 1972, codification amended at 42 U.S.C. 4901-4918 (1988)
6. ↑ Maekawa, Zyun-iti (1968). "Noise reduction by screens". Applied Acoustics 1 (3): 157–173.
7. ↑ Bies, David A.; Hansen, Colin H.; Howard, Carl Q. (2018). Engineering Noise Control (5th ed.). CRC Press.
8. ↑ PublicResourceOrg (2010-07-31), Highway Noise Barrier Design, https://www.youtube.com/watch?v=cZcvlCpuD8I&index=3&list=PL9BADB8ACC34C0404, retrieved 2017-02-04
9. ↑ "4. Noise Barrier Types - Design - Design Construction - Noise Barriers - Noise - Environment". U.S. Federal Highway Administration. https://www.fhwa.dot.gov/environment/noise/noise_barriers/design_construction/design/design04.cfm.
10. ↑ Reflective and Non-reflective Highway Barriers K. Polcak (MD, SHA) and R.J. Peppin (Scantek, Inc.) case study: Reflective and Non-Reflective Highway Barriers MD SHA) TRB ADC 40 Summer Meeting, Denver, CO
11. ↑ Wadhawan, Siddharth R.; Pearce, Joshua M. (2017). "Power and energy potential of mass-scale photovoltaic noise barrier deployment: A case study for the U.S". Renewable and Sustainable Energy Reviews 80: 125–132. doi:10.1016/j.rser.2017.05.223. Bibcode: 2017RSERv..80..125W. https://hal.archives-ouvertes.fr/hal-02113456/file/Power_and_Energy_Potential_of_Mass-Scale.pdf.
12. ↑ "How Solar Panels Work: Solar Power Science Explained". 7 July 2021. https://www.ecowatch.com/solar-powered-noise-barriers-quiet-traffic-while-generating-electricit-1882082739.html.
13. ↑ Djunisic, Sladjana (September 1, 2022). "Switzerland's 2.2-MW alpine solar farm fully operating | Solar Power News | Renewables Now". https://renewablesnow.com/news/switzerlands-2-2-mw-alpine-solar-farm-fully-operating-796667/.
14. ↑ Federal Highway Administration "Highway Traffic Noise" 6/05
15. ↑ Bowker et al., 2007; Baldauf et al., 2008; Heist et al., 2009; Ning et al., 2010; Finn et al., 2010
16. ↑ 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

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Noise (physics and telecommunications)

General|

* Acoustic quieting
* Distortion
* Noise cancellation
* Noise control
* Noise measurement
* Noise power
* Noise reduction
* Noise temperature
* Phase distortion

Noise in...|

* Audio
* Buildings
* Electronics
* Environment
* Government regulation
* Human health
* Images
* Radio
* Rooms
* Ships
* Sound masking
* Transportation
* Video

Class of noise|

* Additive white Gaussian noise (AWGN)
* Atmospheric noise
* Background noise
* Brownian noise
* Burst noise
* Cosmic noise
* Flicker noise
* Gaussian noise
* Grey noise
* Jitter
* Johnson–Nyquist noise (thermal noise)
* Pink noise
* Quantization error (or q. noise)
* Shot noise
* White noise
* Coherent noise
* Value noise
* Gradient noise
* Worley noise

Engineering
terms|

* Channel noise level
* Circuit noise level
* Effective input noise temperature
* Equivalent noise resistance
* Equivalent pulse code modulation noise
* Impulse noise (audio)
* Noise figure
* Noise floor
* Noise shaping
* Noise spectral density
* Noise, vibration, and harshness (NVH)
* Phase noise
* Pseudorandom noise
* Statistical noise

Ratios|

* Carrier-to-noise ratio (C/N)
* Carrier-to-receiver noise density (C/kT)
* dBrnC
* Eb/N0 (energy per bit to noise density)
* Es/N0 (energy per symbol to noise density)
* Modulation error ratio (MER)
* Signal, noise and distortion (SINAD)
* Signal-to-interference ratio (S/I)
* Signal-to-noise ratio (S/N, SNR)
* Signal-to-noise ratio (imaging)
* Signal to noise plus interference (SNIR)
* Signal-to-quantization-noise ratio (SQNR)
* Contrast-to-noise ratio (CNR)

Related topics|

* List of noise topics
* Acoustics
* Colors of noise
* Interference (communication)
* Noise generator
* Radio noise source
* Spectrum analyzer
* Thermal radiation

Denoise
methods|

| General|

* Low-pass filter
* Median filter
* Total variation denoising
* Wavelet denoising

|

2D (Image)|

* Gaussian blur
* Anisotropic diffusion
* Bilateral filter
* Non-local means
* Block-matching and 3D filtering (BM3D)
* Shrinkage Fields
* Denoising autoencoder (DAE)
* Deep Image Prior

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