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First, we’ll review a few environmental noise basics.

Noise levels are measured in A-weighted decibels, or dBA, and is the relative loudness of sounds in air perceived by the human ear. The figure on the right shows some common noises and their dBA. For example, a whisper is about 30 dBA while thunder is around 120 dBA.

Because noise levels vary from moment to moment, Leq averages the louder and quieter measures of dBA over a time period, but gives much more weight to the louder measures of dBA.

Receptors represent noise-sensitive locations, such as a backyard or an outdoor seating area at a restaurant.

Receivers are representative points where traffic noise levels are measured and/or modeled. An individual receiver may represent multiple receptors. For example, an apartment complex may be modeled as one receiver within a model, but it represents multiple receptors (individual apartment units).

Noise abatement is a set of strategies or techniques to reduce noise impacts.

Noise abatement criteria (NAC) is the limit of acceptable noise levels for different land uses.