Do Highway Noise Barrier Walls Work In Reducing Noise?

We all get stuck in bumper to bumper traffic whether it is to commute to work, head out for vacation, or to go to popular events. When you are sitting in traffic, you probably think about the sights and sounds around you.

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If you travel long distances or are frequently on the highway, you may also notice one or several types of noise abatement solutions in the form of large walls aligning the roadway.

Have you ever considered why there are different types of sound walls and if they even work?

How Highway Noise Barriers Work

Believe it or not, highway noise barriers and sound walls are the subject of many federal, state, and local studies and discussions.

Traditionally, these blockades use metal, brick, concrete or wood to minimize the loud noises generated by highway traffic.

These highway sound barrier walls are important to keep offensive freeway sounds from penetrating local neighborhoods and business districts. Studies show the first attempts at blocking the sound creates a couple of problems.

First, the materials used did not sufficiently lower the sound levels in the targeted areas. Highway walls that are not sufficiently tall allow the sound to go over the top of the barrier.

Second, using sound-reflective concrete walls on both sides of the highway often causes the noise to reverberate or bounce back and forth across the Interstate. The noise levels can increase or become higher in frequency when this reflection effect happens.

This is why outdoor noise control is important with residential and commercial businesses being located so close to heavy traffic areas.

Disadvantages of Concrete Highway Barriers

Newer research proves concrete sound barrier walls are some of the worst offenders for creating unwanted and unpredictable reflected noise issues.

The sound waves hit the wall and the reflective surface of the concrete causes the sound wave to go in the opposite direction.

Excessive Noise Contributes to Numerous Health Problems

1. Circulatory issues like high blood pressure, heart attack, and stroke
2. Nervous system problems including irritability, mood swings, depression, and anxiety
3. Lack of sleep or trouble getting restful slumber
4. Immune suppression, problems healing, and chronic health issues

Sound wall construction with acoustic panels help reduce high and low-frequency noise levels that contribute to these health problems. Advancements in noise testing and sound dampening materials offer a tremendous advantage for local municipalities and government entities.

Instead of attempting to block the sound or bounce it to a less populated area, noise dampening materials like mineral wool between layers of perforated fiberglass diffuse and absorb much of the unwanted sound.

Such sound-absorptive panels &#;kill&#; the noise by making the sound wave use up its energy as it passes through strategic openings in the wall.

Benefits of Highway Noise Control

• Fewer headaches and problems hearing
• Better rest
• Improvement in work production
• Better attendance because of a reduction in lack of sleep or noise related health issues

Additional Benefits To Highway Sound Barriers

Absorptive panels are pre-engineered and easily customized for each site and application. Walls designed with the best materials have protective UV coating and will not rust, rot, or deteriorate in extreme temperatures.

Since these walls use lightweight materials, they work extremely well for areas with weight restrictions.

Conversely, concrete noise barriers are dense, hard to recycle, and not mobile. Studies show a sound wall are more effective sound-reflective sound barriers.

Such innovations ensure freeway sound walls reduce sound levels and provide a cost-effective solution to highway noise pollution.

Sources:

https://www.fhwa.dot.gov/Environment/noise/noise_barriers/design_construction/design/design05.cfm
https://www.soundfighter.com/products/retrosorb/
https://undark.org/article/highway-noise-barrier-science/

Exterior structure on infrastructure used to prevent loud sounds from escaping

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 s.

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.[1] In the late s, analytic acoustical technology emerged to mathematically evaluate the efficacy of a noise barrier design adjacent to a specific roadway. By the s, noise barriers that included use of transparent materials were being designed in Denmark and other western European countries.[2]

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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 , 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 ,[5] demand for noise barrier design soared from a host of noise regulation spinoff.

By the late s, 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 , 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 s 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.[dubious &#; discuss] 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.[6] 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.

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.[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 solar photovoltaic panels 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 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.[12]

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.[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 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.[14]

See also

References

• Noise barriers at Wikimedia Commons

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