Roadway noise
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.
Hybrid vehicles are so quiet at low speeds that they create a pedestrian safety issue when reversing or maneuvering when parking etc.
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[citation needed].
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.
Diffraction is usually addressed by establishing secondary emitters at any points of topographic or anthropomorphic “sharpness” (such as noise barriers or building surfaces).
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.
[12] 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 models allowed the court to understand the effects of roadway geometry (width in this case), vehicle speeds, proposed noise barriers, residential setback and pavement types.
The matter was revisited a decade later and a greatly reduced highway design with transit element and extensive noise mitigation was agreed to.
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.
The tighter regulatory requirements of the EU and Japan encourage quieter design even in unregulated countries, because most car manufacturers aspire to international sales.
In developing countries, noise pollution from motor vehicles represents a significant impact, but technologies are not as advanced as in Western nations.
