What Is Noise? By Joe Brodowski, LPG, CESCO
“Noise” is unwanted or excessive sound. Noise can be caused by a variety of sources related to expanded infrastructure that supports modern society. As mobility increases, transportation, in particular, can be a key source of noise across modes, from airports to rail to new roads.
Studies have shown that some of the most pervasive sources of noise in our environment are those associated with transportation. Residences and businesses often are faced with increased highway traffic noise, both from newly constructed highways and from highways that are already in place.
The National Environmental Policy Act (NEPA) of 1969 provided broad authority and responsibility for evaluating and mitigating adverse environmental effects including highway traffic noise. NEPA directed the Federal government to use all practical means and measures to promote the general welfare and foster a healthy environment.
Public concern about noise led to federal legislation in 1970 that authorized the use of federal aid highway funds for measures to abate and control highway traffic noise. The Federal Aid Highway Act of 1970 (23 USC 109(h)) mandated that the Federal Highway Administration (FHWA) develop noise standards for mitigating highway traffic noise. The law required traffic noise-level criteria for various land use activities. The law further provided that FHWA not approve the plans and specifications for a federally aided highway project unless the project included adequate noise abatement measures to comply with the standards.
When describing effects of highway noise and the types of noise mitigation, it is important to understand the principles of noise. Noise is defined as unwanted or excessive sound. Sound becomes unwanted when it interferes with normal activities, such as sleep, work, speech, or recreation. People react to noise differently, based on many emotional and physical factors, such as hearing sensitivity, the degree to which someone is accustomed to noise, or a person’s ability to sleep with noise. A decibel (dB) is the unit used to indicate the intensity of a sound wave. Sound (noise) is often measured in decibels using an A–weighted scale (dBA) because this method approximates the way humans hear sound. Table 1 presents typical sound levels at distances measured from the source of the sound.
Factors That Affect Sound Levels
There are many factors that affect sound levels. Sound levels are influenced by the distance and the path traveled between the source of the sound and receptor(person). There is a natural reduction of sound levels with increasing distance between the source and the receptor. The type of ground cover between the source and the receptor also affects sound levels by disrupting or deflecting the sound wave. Highway-generated sound levels will decrease with the distance from the roadway. This reduction will vary depending upon the ground type (hard or soft). Hard ground (e.g., pavement, dirt, or water) will decrease sound levels by 3 decibels for each doubling of distance. Soft ground (e.g., grass, trees, or vegetation) will decrease sound levels by 4.5 decibels for each doubling of distance. Obstacles between the source and the receptor, such as buildings, hills, and trees, will result in additional noise reductions depending upon their size, density, and location. Additionally, highway noise levels constantly vary with the number, type, and speed of the vehicles that produce the noise.
There are several methods to reduce highway noise. These include vehicle noise control, noise compatible planning, traffic management techniques, alteration of a roadway’s horizontal or vertical alignment, acquisition of property or property rights to create buffer zones, vegetation planting, installing noise insulation in public or nonprofit institutional buildings, or the construction of noise barriers.
Noise Compatible Planning
Noise-compatible planning encourages State and local governments to use their power to regulate land development in such a way that noise-sensitive land uses are either prohibited from being adjacent to a highway, or that the developments are planned, designed, and constructed in such a way that highway traffic noise impacts are minimized.
To promote noise compatible planning, state transportation agencies coordinate with local officials whose jurisdictions are affected by noise from proposed projects. The following information is typically furnished to the local officials:
- Estimated future noise levels for both developed and undeveloped properties in the immediate vicinity of a proposed project.
- Estimated future noise levels shown at various distances from the roadway to allow the public and local officials to understand where local communities should protect future land development from becoming incompatible with anticipated highway noise levels.
- Eligibility for Federal-aid participation for Type II projects as described in the Type II Projects section of this Web site.
Noise Impacts and Noise Abatement Criteria
To help protect public health and welfare from excessive vehicle traffic noise, FHWA established Noise Abatement Criteria (NAC) based upon various land use activities and upon noise levels associated with the interference of speech.
Highway traffic noise impact occurs when the measured or predicted existing or future highway traffic noise levels approach or exceed the NAC or when predicted future highway traffic noise levels substantially exceed existing highway traffic noise level, even though the predicted levels may not exceed the NAC. Typically, state transportation agencies define approaching the criteria as meaning that noise levels are within 1 dBA of the appropriate FHWA noise abatement criterion. State transportation agencies typically define a substantial noise increase as one in which noise levels increase by 10 dBA or greater. FHWA regulations require highway agencies to make every reasonable and feasible effort to provide noise mitigation when the criteria are approached or exceeded. For more information, see FHWA’s Highway Traffic Noise website.
METRIC ENVIRONMENTAL Noise teams can address indoor and outdoor concerns with proper mitigation solutions without compromising common uses or presenting design challenges. We start with a thorough understanding of the project and carefully address all factors along the assessment process. Our field staff demonstrate expertise and professionalism while evaluating and reducing noise impacts.
Some of our Noise Services include:
- Environmental Noise Monitoring
- Noise Modeling and Analysis
- Ambient Sound Level Surveys
- Future Build
- Noise Mapping
For more information contact:
Joe Brodowski, LPG, CESCO
Practice Lead/ Assessment + Remediation
josephb@metricenv.com
