Revised traffic analysis for air quality conformity review of Sea-Tac Master Plan Update

A 1996 traffic analysis prepared for the Airport Communities Coalition by SMITH Engineering & Management identifies several critical flaws in the Sea-Tac Airport Master Plan Final EIS, arguing that the traffic modeling unfairly favored the proposed North Unit Terminal Alternative over the Do Nothing Alternative. Key concerns include inconsistent use of the Traffix simulation model, the omission of a south access road from the Do Nothing scenario, and failure to account for increased staffing and peak-hour passenger traffic that a new terminal would generate. The report presents revised traffic forecasts intended to provide a more balanced comparison of the two alternatives for air quality conformity purposes.

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A technical report prepared for the Airport Communities Coalition by SMITH Engineering & Management reviewing ground transportation elements of the Sea-Tac Airport Master Plan Final EIS. The report identifies fundamental flaws in the traffic analysis, including inconsistencies in the Traffix forecast model between the Do Nothing Alternative and the North Unit Terminal (Preferred) Alternative that biased outcomes in favor of the latter. The report presents revised analyses addressing these inconsistencies, including the treatment of a south access road, weather-impaired flight operations, and increased passenger traffic under the North Unit Terminal Alternative.

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