Roadway noise is the collective
soundSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
energy emanating from
motor vehicleA motor vehicle or road vehicle is a self-propelled wheeled vehicle that does not operate on rails, such as trains or trolleys. The vehicle propulsion is provided by an engine or motor, usually by an internal combustion engine, or an electric motor, or some combination of the two, such as hybrid...
s. In the USA it contributes more to environmental noise exposure than any other noise source, and is constituted chiefly of
engineAn engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
,
tireA tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
, aerodynamic and braking elements. In other Western countries as well as lesser developed countries, roadway noise is expected to contribute a proportionately large share of the total societal
noise pollutionNoise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...
.
History
Roadway noise began to be measured in a widespread manner in the 1960s, when computer modeling of this phenomenon was perfected. After passage of the
National Environmental Policy ActThe National Environmental Policy Act is a United States environmental law that established a U.S. national policy promoting the enhancement of the environment and also established the President's Council on Environmental Quality ....
and
Noise Control ActThe Noise Pollution and Abatement Act of 1972 is a statute of the United States initiating a federal program of regulating noise pollution with the intent of protecting human health and minimizing annoyance of noise to the general public....
, 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 mitigationNoise mitigation is a set of strategies to reduce noise pollution. The main areas of noise mitigation or abatement are: transportation noise control, architectural design, and occupational noise control...
.
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.
Description of basic variables
The intensity of roadway noise is governed by the following variables: traffic operations (speed, truck mix, age of vehicle fleet), roadway surface type, tire types, roadway geometrics, terrain, micrometeorology and the geometry of area structures.
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. 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 vehicleA hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles , which combine an internal combustion engine and one or more electric motors.-Power:...
use continues, substantial noise reduction will occur, especially in the regime of traffic flow below 35 miles per hour. As a pedestrian safety issue, hybrid vehicles are so quiet at low speeds that the customary warning noise may not alert the pedestrian to nearby danger, creating a potential hazard for visually impaired people, who rely on such noise to navigate in areas of heavy traffic. 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
dBAA Weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. The most commonly known example is frequency weighting in sound level measurement where a specific set of weighting curves known as A,...
.
Roadway surface types contribute differential noise effects of up to 4 dB, with chip seal type and grooved roads being the loudest and concrete surfaces without spacers being the quietest.
AsphaltAsphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...
ic surfaces are about average.
Tire types had considerable design changes in the 1970s, and at this juncture are probably optimized for noise control, given the of safety needs for a significant grip by the tread.
Roadway geometrics and surrounding
terrain are interrelated, since the propagation of sound is sensitive to the overall geometry and must consider
diffractionDiffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
(bending of sound waves around obstacles),
reflectionReflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
, ground wave attenuation, spreading loss and
refractionRefraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
. 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.
Micrometeorology is significant in that sound waves can be
refractedRefraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
by
wind gradientIn common usage, wind gradient, more specifically wind speed gradientor wind velocity gradient,or alternatively shear wind,...
s or
thermoclineA thermocline is a thin but distinct layer in a large body of fluid , in which temperature changes more rapidly with depth than it does in the layers above or below...
s, effectively dismissing the effect of some
noise barrierA noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...
s or terrain intervention.
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 for roadway noise
Because of the complexity of the variables discussed, 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 sourceA line source is a source of air, noise, water contamination or electromagnetic radiation that emanates from a linear geometry...
(e.g. roadway). Two of the leading research teams were
BBNBBN might refer to:* BBN Technologies, formerly Bolt, Beranek and Newman, a technology company in Cambridge, Massachusetts, best known for its work on packet switching technology and its construction of the Interface Message Processor - the first router...
in
BostonBoston is the capital of and largest city in Massachusetts, and is one of the oldest cities in the United States. The largest city in New England, Boston is regarded as the unofficial "Capital of New England" for its economic and cultural impact on the entire New England region. The city proper had...
and
ESLESL Incorporated, or Electromagnetic Systems Laboratory, was a subsidiary of TRW, a high technology firm in the United States that was engaged in software design, systems analysis and hardware development for the strategic reconnaissance marketplace. Founded in January, 1964 in Palo Alto,...
of
Sunnyvale, CaliforniaSunnyvale is a city in Santa Clara County, California, United States. It is one of the major cities that make up the Silicon Valley located in the San Francisco Bay Area...
. Both of these groups developed complex
mathematical modelA mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
s to allow the study of alternate roadway designs, traffic operations and
noise mitigationNoise mitigation is a set of strategies to reduce noise pollution. The main areas of noise mitigation or abatement are: transportation noise control, architectural design, and occupational noise control...
strategies in an arbitrary setting. Later model alterations have come into widespread use among state
Departments of TransportationThe Department of Transportation is the most common name for a government agency in North America devoted to transportation. The largest is the United States Department of Transportation, which oversees interstate travel. All U.S. states, Canadian provinces, and many local agencies also have...
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 barrierA noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...
s or building surfaces). Meteorology can be addressed in a statistical manner allowing for actual
wind roseA wind rose is a graphic tool used by meteorologists to give a succinct view of how wind speed and direction are typically distributed at a particular location. Historically, wind roses were predecessors of the compass rose , as there was no differentiation between a cardinal direction and the wind...
and
wind speedWind speed, or wind velocity, is a fundamental atmospheric rate.Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications....
statistics (along with thermocline data).
Case studies
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
BBNBBN Technologies is a high-technology company which provides research and development services. BBN is based next to Fresh Pond in Cambridge, Massachusetts, USA...
and
ESLESL Incorporated, or Electromagnetic Systems Laboratory, was a subsidiary of TRW, a high technology firm in the United States that was engaged in software design, systems analysis and hardware development for the strategic reconnaissance marketplace. Founded in January, 1964 in Palo Alto,...
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 barrierA noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...
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 66Interstate 66 is an Interstate Highway in the eastern United States. As indicated by its even route number, it runs in an east–west direction. Its western terminus is at Middletown, Virginia, at an intersection with Interstate 81; its eastern terminus is in Washington, D.C., at an...
through Arlington, Virginia. The
plaintiffA plaintiff , also known as a claimant or complainant, is the term used in some jurisdictions for the party who initiates a lawsuit before a court...
,
Arlington Coalition on TransportationThe Arlington Coalition on Transportation is a citizens group formed to oppose the construction of Interstate 66 through Arlington, Virginia. The focal activity of ACT was the conduct of a lawsuit filed against the Virginia Department of Transportation in 1971 in district court...
sued the
Virginia Department of TransportationThe Virginia Department of Transportation is the agency of state government responsible for transportation in the state of Virginia in the United States. Headquartered in Downtown Richmond, VDOT is responsible for building, maintaining, and operating the roads, bridges and tunnels in the...
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.
Worldwide perspective
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 pollutionNoise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...
from motor vehicles represents a significant impact, but technologies are not as advanced as in Western nations. For example, a recent paper from
IranIran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...
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.
See also
- Noise barrier
A noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...
for a deeper insight to roadway noise mitigation using physical barriers
- Noise cancellation
Active noise control is a method for reducing unwanted sound.- Explanation :...
for a discussion of methods to actively reduce unwanted sound
- Noise health effects
Noise health effects are the health consequences of elevated sound levels. Elevated workplace or other noise can cause hearing impairment, hypertension, ischemic heart disease, annoyance and sleep disturbance. Changes in the immune system and birth defects have been attributed to noise exposure...
for a discussion of physiological and psychological impacts
- Noise pollution
Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...
for a broader discussion of environmental noise
- Noise regulation
Noise regulation includes statutes or guidelines relating to sound transmission established by national, state or provincial and municipal levels of government. After the watershed passage of the United States Noise Control Act of 1972, other local and state governments passed further regulations...
for the history of noise statutes governing roadway and other noise
External links