Sound Transit completes tunneling for Northgate Link extension

Sound Transit's contractors have finished mining the last tunnel segment for the Northgate Link light-rail extension, the agency announced late last week.

A tunnel boring machine holed through the wall of a retrieval shaft at the University of Washington Station, completing the last of six tunnel segments mined by joint venture JCM Northlink LLC.

Between the extension's twin tunnels, JCM is continuing to dig 23 cross passages that will serve as emergency evacuation routes and contain controls for electrical and mechanical systems. JCM is expected to complete the work in 2018, Sound Transit officials said in a press release.

Construction of the Northgate Station will start this fall, while work on the route's two underground stations will begin next year, Sound Transit officials said.

Slated to open for passenger service in 2021, the $1.9 billion Northgate Link project extends light rail 4.3 miles north from the University of Washington to a station next to Northgate Mall.