The 1 Line is a light rail line serving Seattle, Washington, United States, and its surrounding suburbs. It is operated by Sound Transit as part of the Link light rail system and runs 25 miles (40 km) from Northgate in Seattle to the city of SeaTac, passing through the University of Washington campus, Downtown Seattle, the Rainier Valley, the city of Tukwila, and Seattle–Tacoma International Airport. Construction on the system began in 2003 after decades of shelved transit plans and trains began operating from Downtown Seattle to Tukwila in 2009. Since then, the line has been expanded four times; it carried an average of 80,000 daily passengers in 2019 and is slated to be extended further into the suburbs in the 2020s.