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Roadway noise is the collective sound energy emanating from . It consists chiefly of road surface, tire, engine/transmission, aerodynamic, and Brake elements. Noise of rolling driving on pavement is found to be the biggest contributor of highway noise and increases with higher vehicle speeds.
In developed and developing countries, roadway noise contributes a proportionately large share of the total societal noise pollution. In the U.S., it contributes more to environmental noise exposureSenate Public Works Committee, Noise Pollution and Abatement Act of 1972, S. Rep. No. 1160, 92nd Cong. 2nd session than any other noise source.
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 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.
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.
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 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 (e.g. roadway). Two of the leading research teams were BBN Technologies in Boston and ESL Incorporated of Sunnyvale, California. Both of these groups developed complex mathematical models 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 or building surfaces). Meteorology can be addressed in a statistical manner allowing for actual wind rose and wind speed statistics (along with thermocline data). Recent models have also attempted to predict levels of local air pollution based on an analysis of specific frequencies that are related to tire and engine noise.
Another early case involved the proposed extension of Interstate 66 through Arlington, Virginia. The plaintiff, Arlington Coalition on Transportation sued the Virginia Department of Transportation on the grounds of air quality, 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.
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 from motor vehicles represents a significant impact, but technologies are not as advanced as in Western nations. For example, a recent paper from Iran 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, 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.
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