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Noise barrier
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<h2 id="history">History</h2> <p>Noise barriers have been built in the United States since the mid-twentieth century, when vehicular traffic burgeoned. I-680 in <a href="/facts/Milpitas%2c_California/kjUVfUXV">Milpitas, California</a> was the first noise barrier.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> In the late 1960s, analytic <a href="/facts/Acoustics/2GpQUymy">acoustical</a> technology emerged to mathematically evaluate the efficacy of a noise barrier design adjacent to a specific <a href="/facts/Roadway/fjEkVMx5">roadway</a>. By the 1990s, noise barriers that included use of transparent materials were being designed in Denmark and other western European countries.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <p>The best of these early computer models considered the effects of roadway <a href="/facts/Geometry/wTQf5ffQ">geometry</a>, <a href="/facts/Topography/SS8Bx4t9">topography</a>, <a href="/facts/Vehicle/jSIEqANL">vehicle</a> volumes, vehicle speeds, truck mix, <a href="/facts/Road_surface/m80ermWq">road surface</a> type, and micro-<a href="/facts/Meteorology/xblFr28q">meteorology</a>. Several U.S. research groups developed variations of the computer modeling techniques: <a href="/facts/Caltrans/9lpl5qBV">Caltrans</a> Headquarters in <a href="/facts/Sacramento%2c_California/L2BulyUg">Sacramento, California</a>; the ESL Inc. group in <a href="/facts/Sunnyvale%2c_California/ghnntvr1">Sunnyvale, California</a>; the <a href="/facts/Bolt%2c_Beranek_and_Newman/9kA7axL3">Bolt, Beranek and Newman</a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> group in <a href="/facts/Cambridge%2c_Massachusetts/k9UMIJ7U">Cambridge, Massachusetts</a>, and a research team at the <a href="/facts/University_of_Florida/zGg0HXXs">University of Florida</a>. Possibly the earliest published work that scientifically designed a specific noise barrier was the study for the <a href="/facts/Foothill_Expressway/n1zoFp2Y">Foothill Expressway</a> in <a href="/facts/Los_Altos%2c_California/HoJN8QHu">Los Altos, California</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p><p>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. <a href="/facts/National_Environmental_Policy_Act/USw6zahb">National Environmental Policy Act</a>, enacted in 1970, effectively mandated the quantitative analysis of <a href="/facts/Noise_pollution/dVwYwHMM">noise pollution</a> from every <a href="/facts/Federal-Aid_Highway_Act/veFDG3b8">Federal-Aid Highway Act</a> Project in the country, propelling noise barrier model development and application. With passage of the <a href="/facts/Noise_Control_Act/AyPSJquu">Noise Control Act of 1972</a>,<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> demand for noise barrier design soared from a host of <a href="/facts/Noise_regulation/qbMQuCxb">noise regulation</a> spinoff. </p><p>By the late 1970s, more than a dozen research groups in the U.S. were applying similar <a href="/facts/Computer_model/Re6o8vzN">computer modeling</a> technology and addressing at least 200 different locations for noise barriers each year. As of 2006, this technology is considered a standard in the evaluation of <a href="/facts/Noise_pollution/dVwYwHMM">noise pollution</a> from highways. The nature and accuracy of the <a href="/facts/Computer_model/Re6o8vzN">computer models</a> used is nearly identical to the original 1970s versions of the technology. </p><p>Small and purposeful gaps exist in most noise barriers to allow <a href="/facts/Firefighter/483TlnYB">firefighters</a> to access nearby <a href="/facts/Fire_hydrants/p0FITWJg">fire hydrants</a> and pull through <a href="/facts/Fire_hose/aPIMpnKt">fire hoses</a>, which are usually denoted by a sign indicating the nearest cross street, and a <a href="/facts/Pictogram/6HmoV1u6">pictogram</a> of a fire hydrant, though some hydrant gaps channel the hoses through small <a href="/facts/Culvert/J7DTG3BK">culvert</a> channels beneath the wall. </p> <h2 id="design">Design</h2> <p>The acoustical science of noise barrier design is based upon treating an airway or railway as a <a href="/facts/Line_source/E84Yhgyf">line source</a>.[<i>dubious – discuss</i>] The theory is based upon blockage of sound ray travel toward a particular <a href="/facts/Sensory_receptor/EwY1m2bV">receptor</a>; however, <a href="/facts/Diffraction/Mk80xXHT">diffraction</a> of sound must be addressed. <a href="/facts/Sound_waves/DlKXlPuF">Sound waves</a> 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.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> Further complicating matters is the phenomenon of <a href="/facts/Refraction/S8kvSKzM">refraction</a>, the bending of sound rays in the presence of an inhomogeneous <a href="/facts/Atmosphere/oUpLaGRF">atmosphere</a>. <a href="/facts/Wind_shear/3d3Qkma9">Wind shear</a> and <a href="/facts/Thermocline/0p0cKR3B">thermocline</a> produce such inhomogeneities. The sound sources modeled must include <a href="/facts/Engine/p0m7aXaW">engine</a> noise, <a href="/facts/Tire/TUgHKMQb">tire</a> noise, and <a href="/facts/Aerodynamic/Cn6Lnl3H">aerodynamic</a> noise, all of which vary by vehicle type and speed. </p><p>The noise barrier may be constructed on private land, on a public <a href="/facts/Right-of-way_(railroad)/Vzbfroo1">right-of-way</a>, or on other public land. Because sound levels are measured using a <a href="/facts/Logarithmic_scale/CvIGK5TQ">logarithmic scale</a>, a reduction of nine <a href="/facts/Decibel/0LyxAPXh">decibels</a> is equivalent to elimination of approximately 86 percent of the unwanted sound power. </p> <h3>Materials</h3> <p>Several different materials may be used for sound barriers, including masonry, earthwork (such as earth <a href="/facts/Berm/uGkUpHcH">berm</a>), steel, concrete, wood, plastics, insulating wool, or composites.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> Walls that are made of absorptive material mitigate sound differently than hard surfaces.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> It is also possible to make noise barriers with active materials such as solar <a href="/facts/Photovoltaic/5Xefaayl">photovoltaic</a> panels to generate electricity while also reducing traffic noise.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>A wall with porous surface material and sound-dampening content material can be absorptive where little or no noise is <a href="/facts/Reflection_(physics)/BhcjDs79">reflected</a> 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.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p><p>Noise barriers can be effective tools for <a href="/facts/Noise_pollution/dVwYwHMM">noise pollution</a> abatement, but certain locations and topographies are not suitable for use of noise barriers. Cost and <a href="/facts/Aesthetics/FSD8f7oF">aesthetics</a> 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 <a href="/facts/Cut-and-cover/PJNSaSIw">cut-and-cover</a> method. </p> <h2 id="disadvantages">Disadvantages</h2> <p>Potential disadvantages of noise barriers include: </p> <ul><li>Blocked vision for motorists and rail passengers. Glass elements in noise screens can reduce visual obstruction, but require regular cleaning</li> <li>Aesthetic impact on <a href="/facts/Landscape/pU9HneR0">land-</a> and townscape</li> <li>An expanded target for <a href="/facts/Graffiti/xE9oqKsk">graffiti</a>, unsanctioned <a href="/facts/Guerilla_marketing/kY5T9J8B">guerilla advertising</a>, and vandalism</li> <li>Creation of spaces hidden from view and <a href="/facts/Social_control/TaKTLlr9">social control</a> (e.g. at railway stations)</li> <li>Possibility of <a href="/facts/Bird%25E2%2580%2593window_collisions/A6mDYART">bird–window collisions</a> for large and clear barriers</li></ul> <h2 id="effects-on-air-pollution">Effects on air pollution</h2> <p>Roadside noise barriers have been shown to reduce the near-road <a href="/facts/Air_pollution/zmk9Dy7S">air pollution</a> <a href="/facts/Concentration/wqBmz5od">concentration</a> levels. Within 15–50 m from the roadside, air pollution concentration levels at the <a href="/facts/Windward_and_leeward/7LebHsNX">lee side</a> of the noise barriers may be reduced by up to 50% compared to open road values.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p><p>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 <a href="/facts/Dispersive_mass_transfer/dJt9hb4W">dispersion</a> of the plume. The deceleration and the deflection of the initial flow by the noise barrier force the plume to disperse horizontally. A highly <a href="/facts/Turbulence/NpgFUhG5">turbulent</a> <a href="/facts/Wind_shear/3d3Qkma9">shear</a> 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.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Health_effects_from_noise/6A2Fz81a">Health effects from noise</a></li> <li><a href="/facts/Noise_control/0PvCloyB">Noise control</a></li> <li><a href="/facts/Safety_barrier/XI4u8FyY">Safety barrier</a></li> <li><a href="/facts/Soundproofing/hKbTnCMq">Soundproofing</a></li></ul> <h2 id="external-links">External links</h2> <ul><li> Media related to Noise barriers at Wikimedia Commons</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Wagner, Kate (8 December 2016). "Building the Wall: Highway Sound Barriers and the Evolution of Noise". 99 Percent Invisible. Retrieved 21 March 2017. <a href="http://99percentinvisible.org/article/building-wall-highway-sound-barriers-evolution-noise/" target="_blank">http://99percentinvisible.org/article/building-wall-highway-sound-barriers-evolution-noise/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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 <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>John Shadely, Acoustical analysis of the New Jersey Turnpike widening project between Raritan and East Brunswick, Bolt Beranek and Newman, 1973 <a href="/wiki/New_Jersey_Turnpike" target="_blank">/wiki/New_Jersey_Turnpike</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>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 <a href="/wiki/Los_Altos,_California" target="_blank">/wiki/Los_Altos,_California</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>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) <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>PublicResourceOrg (2010-07-31), Highway Noise Barrier Design, archived from the original on 2021-12-19, retrieved 2017-02-04 <a href="https://www.youtube.com/watch?v=cZcvlCpuD8I&index=3&list=PL9BADB8ACC34C0404" target="_blank">https://www.youtube.com/watch?v=cZcvlCpuD8I&index=3&list=PL9BADB8ACC34C0404</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"4. Noise Barrier Types - Design - Design Construction - Noise Barriers - Noise - Environment". U.S. Federal Highway Administration. Retrieved 2017-01-16. <a href="https://www.fhwa.dot.gov/environment/noise/noise_barriers/design_construction/design/design04.cfm" target="_blank">https://www.fhwa.dot.gov/environment/noise/noise_barriers/design_construction/design/design04.cfm</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>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 <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>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. Bibcode:2017RSERv..80..125W. doi:10.1016/j.rser.2017.05.223. S2CID 114457016. <a href="https://hal.archives-ouvertes.fr/hal-02113456/file/Power_and_Energy_Potential_of_Mass-Scale.pdf" target="_blank">https://hal.archives-ouvertes.fr/hal-02113456/file/Power_and_Energy_Potential_of_Mass-Scale.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"How Solar Panels Work: Solar Power Science Explained". 7 July 2021. <a href="https://www.ecowatch.com/solar-powered-noise-barriers-quiet-traffic-while-generating-electricit-1882082739.html" target="_blank">https://www.ecowatch.com/solar-powered-noise-barriers-quiet-traffic-while-generating-electricit-1882082739.html</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>"Solar power generating noise barriers go up in the Netherlands". <a href="https://www.treehugger.com/solar-technology/solar-power-generating-noise-barriers-go-netherlands.html" target="_blank">https://www.treehugger.com/solar-technology/solar-power-generating-noise-barriers-go-netherlands.html</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Federal Highway Administration "Highway Traffic Noise" 6/05 <a href="/wiki/Federal_Highway_Administration" target="_blank">/wiki/Federal_Highway_Administration</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Bowker et al., 2007; Baldauf et al., 2008; Heist et al., 2009; Ning et al., 2010; Finn et al., 2010 <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>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 <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> </ol>