Public services began the following morning on the $US 1.9bn extension, which runs in twin-bored tunnels for its entire length and includes one intermediate station at Capitol Hill. The line has reduced the journey time between the University of Washington and the city centre to eight minutes and Seattle-Tacoma International Airport to less than an hour.
The line is expected to increase ridership on Sound Transit's light rail network by 71,000 to 114,000 passengers per day by 2030.
Construction began in 2012 on a further 6.9km extension from University of Washington to Northgate, which is due to open in 2021.
