Roadway noise
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Roadway noise is the collective
sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...
energy emanating from
motor vehicle A motor vehicle, also known as a motorized vehicle, automotive vehicle, automobile, or road vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on railway track, rails (such as trains or trams), does not fly (such ...
s. It consists chiefly of
road surface A road surface (British English) or pavement (North American English) is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, ...
, tire,
engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...
/transmission, aerodynamic, and braking elements. Noise of rolling
tire A tire (North American English) or tyre (Commonwealth English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineeri ...
s driving on pavement is found to be the biggest contributor of highway noise and increases with higher vehicle speeds. In developed and
developing countries A developing country is a sovereign state with a less-developed Secondary sector of the economy, industrial base and a lower Human Development Index (HDI) relative to developed countries. However, this definition is not universally agreed upon. ...
, roadway noise contributes a proportionately large share of the total societal
noise pollution Noise pollution, or sound pollution, is the propagation of noise or sound with potential harmful effects on humans and animals. The source of outdoor noise worldwide is mainly caused by machines, transport and propagation systems.Senate Publi ...
. In the U.S., it contributes more to
environmental noise Environmental noise is an accumulation of noise pollution that occurs outside. This noise can be caused by transport, industrial, and Sport, recreational activities. Noise is frequently described as 'unwanted sound'. Within this context, envir ...
exposure than any other noise source.


History

Roadway noise began to be measured in a widespread manner in the 1960s, as
computer model Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determin ...
ing of this phenomenon began to become meaningful. After passage of the
National Environmental Policy Act The National Environmental Policy Act (NEPA) is a United States environmental law designed to promote the enhancement of the environment. It created new laws requiring U.S. federal government agencies to evaluate the environmental impacts of ...
and Noise Control Act, the demand for detailed analysis soared, and decision makers began to look to acoustical scientists for answers regarding the planning of new roadways and the design of noise mitigation. Partial bans on motor vehicles from urban areas have been shown to have minimal impacts upon reducing sound levels (as would become clear from later modeling studies); for example, the partial ban in Gothenburg, Sweden resulted in minuscule reduction of sound levels. Noise regulation in the EU and Japan of tire and power-train noise has only sought to reduce noise by approx 3 dB, and will only slowly take effect because a few older noisier vehicles can dominate the soundscape. Small reductions in vehicle noise occurred in the 1970s as states and provinces enforced unmuffled vehicle ordinances. The vehicle fleet noise has not changed very much over the last three decades; however, if the trend in
hybrid vehicle A hybrid vehicle is one that uses two or more distinct types of power, such as submarines that use diesel when surfaced and batteries when submerged. Other means to store energy include pressurized fluid in hydraulic hybrids. Hybrid powertrai ...
use continues, substantial noise reduction will occur, especially in the regime of traffic flow below 35 miles per hour. Hybrid vehicles are so quiet at low speeds that they create a pedestrian safety issue when reversing or maneuvering when parking etc. (but not when travelling forward), Technical Report DOT HS 811 204 and so are typically fitted with electric vehicle warning sounds.


Causes


Speed

Traffic operations noise is affected significantly by vehicle speeds, since sound energy roughly doubles for each increment of ten miles an hour in vehicle velocity; an exception to this rule occurs at very low speeds where braking and acceleration noise dominate over aerodynamic noise.


Vehicles

Trucks contribute a disproportionate amount of noise not only because of their large engines, but also the height of the diesel stack and the aerodynamic drag. Significant interior noise is usually present inside moving motor vehicles; in fact, passengers are generally not aware that these levels are high, because experience has led motorists to expect levels commonly exceeding 65 dBA.


Surfaces

Roadway surface types contribute to different noise levels. Of the common types of surfaces in modern cities, there is a 4 dB difference between the loudest and the softest: chip seal type and grooved roads being the loudest, and
concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
surfaces without spacers being the quietest, and
asphalt Asphalt most often refers to: * Bitumen, also known as "liquid asphalt cement" or simply "asphalt", a viscous form of petroleum mainly used as a binder in asphalt concrete * Asphalt concrete, a mixture of bitumen with coarse and fine aggregates, u ...
ic surfaces being about average. Rubberized asphalt (which uses recycled old tires) is much quieter and is already widely used. Experimental Porous Elastic Road Surfaces (PERS) might cut road noise in half. PERS is made by adding ground up tires to asphalt paving material. Studies have shown that cutting longitudinal grooves in the pavement reduces noise.


Tires

Tire types can cause 10 dB(A) variations in noise, based on a 2001 sample of 100 commercially available tires. As of 2001, there was no correlation between grip and noise. Quieter tires may have slightly lower rolling resistance. Tire labeling for noise, grip, and rolling resistance has been widely introduced in Europe, with noisy tires being taxed.


Geometry

Roadway geometrics and surrounding terrain are interrelated, since the propagation of sound is sensitive to the overall geometry and must consider
diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...
(bending of sound waves around obstacles), reflection,
ground wave Ground wave is a mode of radio propagation that consists of currents traveling through the earth. Ground waves propagate parallel to and adjacent to the surface of the Earth, and are capable of covering long distances by diffracting around the E ...
attenuation, spreading loss and
refraction In physics, refraction is the redirection of a wave as it passes from one transmission medium, medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commo ...
. A simple discussion indicates that sound will be diminished when the path of sound is blocked by terrain, or will be enhanced if the roadway is elevated so as to broadcast; however, the complexities of variable interaction are so great, that there are many exceptions to this simple argument.


Wind

Micrometeorology is significant in that sound waves can be
refracted In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...
by
wind gradient In common usage, wind gradient, more specifically wind speed gradient or wind velocity gradient, or alternatively shear wind, is the vertical component of the gradient of the mean horizontal wind speed in the lower atmosphere. It is the rate of ...
s or
thermocline A thermocline (also known as the thermal layer or the metalimnion in lakes) is a distinct layer based on temperature within a large body of fluid (e.g. water, as in an ocean or lake; or air, e.g. an atmosphere) with a high gradient of distinct te ...
s, effectively dismissing the effect of some
noise barrier 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 effecti ...
s or terrain intervention.


Obstacles

Geometry of area structures is an important input, since the presence of buildings or walls can block sound under certain circumstances, but reflective properties can augment sound energy at other locations.


Computer models

At a macro level, ongoing research is required for national and worldwide responses to road noise pollution - issues include road surface choices, the regulation and taxing of noisy designs, and the ongoing inspecting of individual vehicles. At the micro level of managing particular roads, because of the complexity of the variables discussed above, it is necessary to create a
computer model Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determin ...
that can analyze sound levels in the vicinity of roadways. The first meaningful models arose in the late 1960s and early 1970s addressing the noise
line source A line source, as opposed to a point source, area source, or volume source, is a source of air, noise, water contamination or electromagnetic radiation that emanates from a linear (one-dimensional) geometry. The most prominent linear sources ...
(e.g. roadway). Two of the leading research teams were BBN in
Boston Boston is the capital and most populous city in the Commonwealth (U.S. state), Commonwealth of Massachusetts in the United States. The city serves as the cultural and Financial centre, financial center of New England, a region of the Northeas ...
and ESL of
Sunnyvale, California Sunnyvale () is a city located in the Santa Clara Valley in northwestern Santa Clara County, California, United States. Sunnyvale lies along the historic El Camino Real (California), El Camino Real and U.S. Route 101 in California, Highway 1 ...
. Both of these groups developed complex
mathematical model A mathematical model is an abstract and concrete, abstract description of a concrete system using mathematics, mathematical concepts and language of mathematics, language. The process of developing a mathematical model is termed ''mathematical m ...
s to allow the study of alternate roadway designs, traffic operations and noise mitigation strategies in an arbitrary setting. Later model alterations have come into widespread use among state departments of transportation and city planners, but the accuracy of early models has had little change in 40 years. Generally the models trace sound ray bundles and calculate spreading loss along with ray bundle divergence (or convergence) from refractive phenomena. Diffraction is usually addressed by establishing secondary emitters at any points of topographic or anthropomorphic “sharpness” (such as
noise barrier 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 effecti ...
s or building surfaces). Meteorology can be addressed in a statistical manner allowing for actual wind rose and
wind speed In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer. Wind spe ...
statistics (along with thermocline data). Recent models have also attempted to predict levels of local
air pollution Air pollution is the presence of substances in the Atmosphere of Earth, air that are harmful to humans, other living beings or the environment. Pollutants can be Gas, gases like Ground-level ozone, ozone or nitrogen oxides or small particles li ...
based on an analysis of specific frequencies that are related to tire and engine noise.


Case studies of road design

An interesting early case where two of the leading models were pitted against each other involved a proposed widening of the New Jersey Turnpike from six to twelve lanes. The BBN and ESL models were on opposing sides of a matter decided in New Jersey Superior Court. This case in the early 1970s was one of the first U.S. examples of acoustical scientists playing a role in the design of a major highway. The models allowed the court to understand the effects of roadway geometry (width in this case), vehicle speeds, proposed
noise barrier 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 effecti ...
s, residential setback and pavement types. The outcome was a compromise that involved substantial mitigation of noise pollution impacts. Another early case involved the proposed extension of
Interstate 66 Interstate 66 (I-66) is a 76.32 mile east–west Interstate Highway in the East Coast of the United States, eastern United States. The highway runs from an interchange with Interstate 81 in Virginia, I-81 near Middletown, Virginia, on its w ...
through
Arlington, Virginia Arlington County, or simply Arlington, is a County (United States), county in the U.S. state of Virginia. The county is located in Northern Virginia on the southwestern bank of the Potomac River directly across from Washington, D.C., the nati ...
. The
plaintiff A plaintiff ( Π in legal shorthand) is the party who initiates a lawsuit (also known as an ''action'') before a court. By doing so, the plaintiff seeks a legal remedy. If this search is successful, the court will issue judgment in favor of the ...
, Arlington Coalition on Transportation sued the
Virginia Department of Transportation The Virginia Department of Transportation (VDOT) is the agency of the U.S. state, state government responsible for transportation in the state of Virginia in the United States. VDOT is headquartered at the Virginia Department of Highways Buildin ...
on the grounds of
air quality Air pollution is the presence of substances in the Atmosphere of Earth, air that are harmful to humans, other living beings or the environment. Pollutants can be Gas, gases like Ground-level ozone, ozone or nitrogen oxides or small particles li ...
, noise and neighborhood disruption. To analyze roadway noise, the ESL model was used by the plaintiff, who won this case partially due to the credibility of the computer model. The matter was revisited a decade later and a greatly reduced highway design with transit element and extensive noise mitigation was agreed to. Later cases have occurred in every state, both in contentious actions and in routine highway planning and design. The public as well as governmental agencies have become aware of the value of acoustical science to provide useful insights to the roadway design process.


Worldwide perspective

Even without regulation, there are strong individual economic pressures for quieter vehicles, because owners and employers see quieter vehicles as more luxurious and less stressful. The tighter regulatory requirements of the EU and Japan encourage quieter design even in unregulated countries, because most car manufacturers aspire to international sales. On the other hand, individual owners of motorbikes, 'boom-box' cars (with very loud music systems), and 'muscle-cars' may prefer their vehicle to be louder (at least at idling or low speeds), and such noise (often from modified exhaust systems) can only be controlled by on-going inspection and sanctions. Several studies have concluded that reducing traffic noise pollution is low-cost or cost-effective. Such studies include consideration of the reduced value of noise-affected real-estate, the costs of supporting a dispersed population 'trying to get away from all the noise', and the increased healthcare costs statistically attributable to a noisier environment. European technology began to emulate the United States treatment of roadway noise by the 1980s, although the national requirements of noise studies generally remain less stringent than the U.S. In developing countries,
noise pollution Noise pollution, or sound pollution, is the propagation of noise or sound with potential harmful effects on humans and animals. The source of outdoor noise worldwide is mainly caused by machines, transport and propagation systems.Senate Publi ...
from motor vehicles represents a significant impact, but technologies are not as advanced as in Western nations. For example, a recent paper from
Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
illustrates a level of technology that the United States encountered in the 1960s. The European Union has recently proposed a set of vehicle tire requirements, similar to those introduced in the U.S. in the 1970s. In
Mumbai Mumbai ( ; ), also known as Bombay ( ; its official name until 1995), is the capital city of the Indian state of Maharashtra. Mumbai is the financial capital and the most populous city proper of India with an estimated population of 12 ...
, India, excessive honking and road noise is seen as a significant nuisance. The local police launched an experimental program in 2020 to link the time-length of red lights to an ambient noise sensor, increasing red light times if ambient noise from traffic exceeds limits. This acts as a deterrent to use of the horn.


See also

*
Active noise control Active noise control (ANC), also known as noise cancellation (NC), or active noise reduction (ANR), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. The concept was first deve ...


References


External links


FHWA Traffic Noise Model

Norway noise profile showing roadway noise accounts for 78% of all noise annoyance

NoiseOFF - The Coalition Against Noise Pollution - Home
{{Authority control Noise pollution Sounds by type Road transport