Noise barrier
4049625
226071094
2008-07-16T18:23:07Z
Enoisecontrol
6743417
added case study
[[Image:TullamarineFwy.jpg|thumb|310px|The ''[[CityLink#Western Link|sound tube]]'' in [[Melbourne]], [[Australia]], designed to reduce roadway noise without detracting from the area's aesthetics.]]
A '''noise barrier''' (also called a '''soundwall''', '''sound berm''', '''sound barrier''', or '''acoustical barrier''') is an exterior structure designed to protect sensitive [[land use]]s from [[noise pollution]]. Noise barriers are the most effective method of mitigating [[roadway noise|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, [[Noise_mitigation#Roadway_noise_mitigation|other methods]] of reducing the source noise intensity include encouraging the use of [[Hybrid vehicles|hybrid]] and [[electric vehicle]]s, improving [[Automotive aerodynamics|automobile aerodynamics]] and [[tire]] design, and choosing low-noise [[Pavement (material)|paving material]]. Extensive use of noise barriers began in the [[United States]] after [[noise regulation]]s were introduced in the early 1970s.
==History==
{{Globalize/North America}}
Noise barriers have been built in the [[United States]] since the mid-20th century, when vehicular traffic burgeoned. In the late 1960s, [[acoustics|acoustical]] science technology emerged to mathematically evaluate the efficacy of a noise barrier design adjacent to a specific [[roadway]]. Below, a researcher collects data to calibrate a [[roadway noise]] model for [[County Route G5 (California)|Foothill Expressway]].
[[Image:Noisebarrierm.jpg|thumb|left|290px|Acoustical [[scientist]] measures sound in Noise barrier design study, [[Santa Clara County]], Calif.]]
The best of these early computer models considered the effects of roadway [[geometry]], [[topography]], [[vehicle]] volumes, vehicle speeds, truck mix, [[roadway 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 [[Palo Alto, California]]; the [[Bolt, Beranek and Newman]]<ref>John Shadely, ''Acoustical analysis of the [[New Jersey Turnpike]] widening project between Raritan and East Brunswick'', Bolt Beranek and Newman, 1973</ref> 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]].<ref>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</ref>
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]]<ref>* U.S. [[National Environmental Policy Act]], enacted January 1, 1970</ref> 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|Noise Control Act of 1972]],<ref>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)</ref> demand for noise barrier design soared from a host of [[noise regulation]] spinoff.
By the late 1970s, over a dozen research groups in the U.S. were applying similar [[computer model]]ing 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 [[noise pollution]] from highways. The nature and accuracy of the [[computer model]]s used is nearly identical to the original 1970s versions of the technology.
==Theory of noise barrier design==
The acoustical science of noise barrier design is based upon treating a roadway or railway as a [[line source]]. The theory is based upon blockage of sound ray travel toward a particular [[Sensory receptor|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. Further complicating matters is the phenomenon of [[refraction]], the bending of sound rays in the presence of an [[wiktionary:heterogeneous|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 resulting [[computer model]] is based upon dozens of physics [[equations]] translated into thousands of lines of computer code.
[[Image:noisercrazorback.jpg|thumb|right|310px|Noise barrier earth berm along [[Highway 12]], [[Sonoma County]], California]]
Some noise barriers consist of a masonry wall or earthwork, or a combination thereof (such as a wall atop an earth [[berm]]). Sound abatement walls are commonly constructed using steel, concrete, masonry, wood, plastics, insulating wool, or composites. In the most extreme cases, the entire roadway is surrounded by a noise abatement structure, or dug into a tunnel using the [[cut-and-cover]] method. The noise barrier may be constructed on private land, on a public [[Right-of-way (railroad)|right-of-way]], or on other public land. Because sound levels are measured using a [[logarithmic scale]], a reduction of nine [[decibel]]s is equivalent to elimination of about 80 percent of the unwanted sound.
Noise barriers can be extremely effective tools for [[noise pollution]] abatement, but theory calculates that certain locations and topographies are not suitable for use of any reasonable noise barrier. Cost and [[aesthetics]] play a role in the final choice of any noise barrier.
==Tradeoffs in noise barrier design==
[[Image:Geluidscherm Overschie.jpg|thumb|right|310px|This noise abatement wall in The Netherlands has a transparent section at the driver's eye-level to reduce the visual impact.]]
Disadvantages of noise barriers include:
* Aesthetic impacts for motorists and neighbors, particularly if scenic vistas are blocked.
* Costs of design, construction, and maintenance.
* Necessity to design custom drainage that the barrier may interrupt.
Normally, the benefits of noise reduction far outweigh aesthetic impacts for residents protected from unwanted sound. These benefits include lessened [[sleep disturbance]], improved ability to enjoy outdoor life, reduced [[speech interference]], [[Stress (medicine)|stress]] reduction, reduced risk of [[hearing impairment]], and reduction in [[blood pressure]] (improved [[cardiovascular]] health).
With regard to construction costs, a major factor is the availability of excess soil in the immediate area which could be used for [[berm]] construction. If the soil is present, it is often cheaper to construct an earth berm noise barrier than to haul away the excess dirt, provided there is sufficient land area available for berm construction. Generally a four-to-one ratio of berm cross sectional width to height is required. Thus, for example, to build a six foot high berm, one needs an available width of 24 feet.
Earth berm noise barriers can be constructed solely of excess earth from [[grading pad]]s for a residential development it will protect. Thus its entire construction cost is negligible; arguably, it may pay into the project, since offhaul of earth may have been needed. A further nuance of this particular project is that the residential side of the berm is over-excavated, which gives more privacy between highway and homes and also enhances noise benefit. Finally, note the [[aesthetic]]s of the earth berm which blends with scenic elements of the natural hills of [[Annadel State Park]] in the background. It may be a surprise to find out this berm is over six feet in height, since the aesthetics of earth mounding reduce the visual impact of the structure, compared to a soundwall.
As a minor embellishment to noise barrier design, one may note the concept of constructing a [[louver]] or [[cap]] atop the wall that is directed back toward the noise source. This concept follows the theory that such a design should inhibit shadow zone diffraction filling in sound behind the noise barrier. In actual experience the benefits are slight compared to the benefits of a higher barrier and the costly construction techniques necessary to create and maintain such a device. Variation of the louver design can be found in [[Denmark]], where the designs are also intended to minimize reflected sound. Furthermore some of the Danish soundwalls are made of transparent materials to minimize the visual impact; such material use, however, compromises the efficacy by reducing mass.{{Fact|date=December 2007}}
==See also==
* [[Noise health effects]]
* [[Soundproofing]]
==External Links==
* [http://www.enoisecontrol.com/Air_Cooled_Chiller_Noise_Control_Case_Study.htm Noise Barrier Wall Case Study]
==References==
{{reflist}}
[[Category:Environmental engineering]]
[[Category:Noise pollution]]
[[Category:Noise reduction]]
[[Category:Road infrastructure]]
[[Category:Acoustics]]
[[Category:Sound]]
[[de:Lärmschutzwand]]
[[es:Barrera acústica]]
[[it:Barriera antirumore]]
[[nl:Geluidsscherm]]