Seattle-Tacoma (Sea-Tac) International Airport, one of the fastest growing and busiest airports in the US, served more than 42 million passengers and 332,000 metric ton (mt) of air cargo in 2015. Project Type Airport master plan Location Seattle-Tacoma International Airport, Washington, US Estimated Investment $1.645bn Start of Construction Q1 2017 Expected Completion 2021 Seattle-Tacoma (Sea-Tac)