Environmental Noise Guidelines

In some cases, instead of establishing specific noise limits, sound level standards may be expressed as exceedances over existing ambient sound levels. For example, in many instances the Washington State Department of Transportation considers an increase in traffic noise of more than 10 decibels over existing sound levels to be a noise impact for which mitigation is appropriate.

Measurements and Predictions

Measurement of existing levels of environmental noise usually involves monitoring at pre-determined locations for periods of 24 hours to as long as a week. Monitoring of noise levels at major airports may be year-round.

Most noise studies for planned projects include predicted sound levels, often for various project alternatives. For example, the alternatives might include predicted future sound levels without the project, levels with the project at reduced operations, and levels with the project at full operations.

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