Noise barrier
Anoise barrier(also called asoundwall,noise wall,sound berm,sound barrier,oracoustical barrier) is an exterior structure designed to protect inhabitants of sensitiveland useareas fromnoise pollution.Noise barriers are the most effective method of mitigatingroadway,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 methodsof reducing the source noise intensity include encouraging the use ofhybridandelectric vehicles,improvingautomobile aerodynamicsandtiredesign, and choosing low-noisepaving material.Extensive use of noise barriers began in the United States afternoise regulationswere introduced in the early 1970s.
History
[edit]Noise barriers have been built in the United States since the mid-twentieth century, when vehicular traffic burgeoned. I-680 inMilpitas, Californiawas the first noise barrier.[1]In the late 1960s, analyticacousticaltechnology emerged to mathematically evaluate the efficacy of a noise barrier design adjacent to a specificroadway.By the 1990s, noise barriers that included use of transparent materials were being designed in Denmark and other western European countries.[2]
The best of these early computer models considered the effects of roadwaygeometry,topography,vehiclevolumes, vehicle speeds, truck mix,road surfacetype, and micro-meteorology.Several U.S. research groups developed variations of the computer modeling techniques:CaltransHeadquarters inSacramento, California;the ESL Inc. group inSunnyvale, California;theBolt, Beranek and Newman[3]group inCambridge, Massachusetts,and a research team at theUniversity of Florida.Possibly the earliest published work that scientifically designed a specific noise barrier was the study for theFoothill ExpresswayinLos 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 ofnoise pollutionfrom everyFederal-Aid Highway ActProject in the country, propelling noise barrier model development and application. With passage of theNoise Control Act of 1972,[5]demand for noise barrier design soared from a host ofnoise regulationspinoff.
By the late 1970s, more than a dozen research groups in the U.S. were applying similarcomputer modelingtechnology 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 ofnoise pollutionfrom highways. The nature and accuracy of thecomputer modelsused is nearly identical to the original 1970s versions of the technology.
Small and purposeful gaps exist in most noise barriers to allowfirefightersto access nearbyfire hydrantsand pull throughfire hoses,which are usually denoted by a sign indicating the nearest cross street, and apictogramof a fire hydrant, though some hydrant gaps channel the hoses through smallculvertchannels beneath the wall.
Design
[edit]The acoustical science of noise barrier design is based upon treating an airway or railway as aline source.[dubious–discuss]The theory is based upon blockage of sound ray travel toward a particularreceptor;however,diffractionof sound must be addressed.Sound wavesbend (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.[6]Further complicating matters is the phenomenon ofrefraction,the bending of sound rays in the presence of aninhomogeneousatmosphere.Wind shearandthermoclineproduce such inhomogeneities. The sound sources modeled must includeenginenoise,tirenoise, andaerodynamicnoise, all of which vary by vehicle type and speed.
The noise barrier may be constructed on private land, on a publicright-of-way,or on other public land. Because sound levels are measured using alogarithmic scale,a reduction of ninedecibelsis equivalent to elimination of approximately 86 percent of the unwanted sound power.
Materials
[edit]Several different materials may be used for sound barriers. These materials can include masonry, earthwork (such as earthberm), steel, concrete, wood, plastics, insulating wool, or composites.[7]Walls that are made of absorptive material mitigate sound differently than hard surfaces.[8]It is also possible to make noise barriers with active materials such as solarphotovoltaicpanels to generate electricity while also reducing traffic noise.[9][10][11]
A wall with porous surface material and sound-dampening content material can be absorptive where little or no noise isreflectedback 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.[12]
Noise barriers can be effective tools fornoise pollutionabatement, but certain locations and topographies are not suitable for use of noise barriers. Cost andaestheticsalso 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 thecut-and-covermethod.
Disadvantages
[edit]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 onland-and townscape
- An expanded target forgraffiti,unsanctionedguerilla advertising,and vandalism
- Creation of spaces hidden from view andsocial control(e.g. at railway stations)
- Possibility ofbird–window collisionsfor 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
[edit]Roadside noise barriers have been shown to reduce the near-road air pollutionconcentrationlevels. Within 15–50 m from the roadside, air pollution concentration levels at thelee sideof the noise barriers may be reduced by up to 50% compared to open road values.[13]
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 verticaldispersionof the plume. The deceleration and the deflection of the initial flow by the noise barrier force the plume to disperse horizontally. A highlyturbulentshearzone 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.[14]
See also
[edit]References
[edit]- ^Wagner, Kate (8 December 2016)."Building the Wall: Highway Sound Barriers and the Evolution of Noise".99 Percent Invisible.Retrieved21 March2017.
- ^Benz Kotzen and Colin English (1999)Environmental Noise Barriers: A Guide to Their Acoustic and Visual Design,Published by Taylor & Francis,ISBN0-419-23180-3,165 pages
- ^John Shadely,Acoustical analysis of theNew Jersey Turnpikewidening project between Raritan and East Brunswick,Bolt Beranek and Newman, 1973
- ^C.M. Hogan and Harry Seidman,Design of Noise Abatement Structures along Foothill Expressway,Los Altos, California,Santa Clara CountyDepartment of Public Works,ESL Inc.,Sunnyvale, California,October, 1970
- ^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)
- ^PublicResourceOrg (2010-07-31),Highway Noise Barrier Design,archivedfrom the original on 2021-12-19,retrieved2017-02-04
- ^"4. Noise Barrier Types - Design - Design Construction - Noise Barriers - Noise - Environment".U.S.Federal Highway Administration.Retrieved2017-01-16.
- ^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
- ^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"(PDF).Renewable and Sustainable Energy Reviews.80:125–132.doi:10.1016/j.rser.2017.05.223.S2CID114457016.
- ^"How Solar Panels Work: Solar Power Science Explained".7 July 2021.
- ^"Solar power generating noise barriers go up in the Netherlands".
- ^Federal Highway Administration"Highway Traffic Noise" 6/05
- ^Bowker et al., 2007; Baldauf et al., 2008; Heist et al., 2009; Ning et al., 2010; Finn et al., 2010
- ^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
External links
[edit]
Media related toNoise barriersat Wikimedia Commons
