Noise Studies

The environmental noise control process typically starts with a noise study that quantifies the noise exceedances. The noise study begins with an evaluation of baseline conditions to determine existing noise levels. If the study is to evaluate proposed changes to the existing environment, the baseline evaluation is followed by the use of predictive models to assess future noise levels. The predicted noise levels are then evaluated with respect to the governing noise code and/or legislative guidelines for acceptable increases over existing levels.

If noise mitigation will be required, the study may recommend a variety of measures depending on the types of noise sources, number and location of noise-sensitive receivers, and the nature of the sound path between sources and receivers. Common measures include enclosures around sources, barriers between sources and receivers, and procedural changes that affect the timing or frequency of noise events.

Noise Limits

Many jurisdictions establish maximum allowable limits that a source property may transmit to a receiving property, with the actual limits based on zoning or land use. This is typical of state codes and not uncommon for county and municipal codes. For example, in the state of Washington and many subordinate jurisdictions, a site designated for Commercial use is subject to a daytime maximum allowable limit of 57 decibels (dBA), and a nighttime limit of 47 decibels (dBA), as measured at an adjacent Residential property; the limits for a residential source and a residential receiver are 55 dBA during the day and 45 dBA at night. (For a discussion of A-weighted decibels, abbreviated dBA, see the Noise Descriptors section.)

A number of city noise codes deal only with noise classified as a nuisance, prohibiting certain specific kinds of noise such as yelling, car stereos, horns, fireworks, etc. at levels which are irritating to residents. Such codes are useful in defining certain prohibited noises or activities, but can be difficult to enforce either because they lack objective criteria or because they are so all-encompassing that normal activities such as lawn mowing constitute a violation.

Click on the following subjects to learn more about environmental noise and how it can be controlled.

Noise Descriptors | Noise Studies and Limits | Environmental Noise Guidelines | Measurements and Predictions | Putting It Together