A model developed by the Washington State Department of Transportation to be used by biologists to determine the action area for highway construction projects is presented. The model conservatively estimates the distance at which construction noise would match ambient background sound levels. The model propagates the combined maximum sound level (Lmax) for project construction equipment spherically over the soft and hard site characteristics to a point where it would converge with the ambient hourly equivalent (Leq) sound level. The ambient Leq sound level can be input into the model from actual measurements, documented reference sources, or from a table based on population density [Federal Transit Authority (FTA) Noise Assessment Guidance (2006)]. The model then combines the ambient sound level with the traffic sound level based on the national mean emission curves. The input for traffic volume, vehicle type, and speed is propagated cylindrically from the source until the traffic source drops to the ambient level. A macro, that applies a general atmospheric and molecular absorption adjustment to the calculated distances, produces the action area circumference both graphically and numerically as it relates to each of the sound sources. [Work supported by the Federal Highway Administration (FHWA) (1978).]