In addition to a dense network of bus routes, the cities of Seattle and Tacoma in Puget Sound, Washington are served by a rapid transit rail system named Link Light Rail. Designed, built, and operated by Sound Transit, the region's mass transportation agency, the system is currently composed of two lines. The Tacoma Link provides streetcar service in downtown Tacoma, while the Central Link light rail line operates between the University of Washington and the Seattle–Tacoma International Airport. The current system, which covers a total of 27.8 kilometres, is now being extended to connect the Seattle neighbourhoods of Northgate, Roosevelt, and the University District.

Northgate Link Extension map, image via Sound Transit

From University of Washington Station, the northern terminus of the Central Link, Northgate Link will travel in two tunnels. It will stop at U District and Roosevelt underground stations and then continue to Northgate Station via an elevated section. Each tunnel is being dug with a massive tunnel boring machine measuring 6.6 metres in diameter. The machines were named Brenda and Pamela for the northbound and southbound tunnels respectively, but those names have since been eliminated to avoid comparisons to the Bertha machine used for the Alaskan Way Viaduct replacement tunnel project, which has been plagued by delays and construction issues. 

Northgate Link Extension, image via Sound Transit

The second tunnel boring machine, formerly Pamela, broke through to the U District Station site on March 24. One week later, the first tunnel boring machine, previously Brenda, completed the northbound tunnel just north of University of Washington Station. Photos captured by Forum contributor SounderBruce show the cutterhead for Brenda, now above ground, being lifted, while Pamela remains underground to complete the next leg of the southbound tunnel. All tunnel construction is expected to wrap up in early 2017. 

TBM 1, Brenda, being lifted near University of Washington Station, image by SounderBruce via Flickr

The 6.9-kilometre line will boast a speedy 14-minute journey from Northgate to Downtown Seattle. The $1.9 billion project is expected to be complete by 2021, when it will begin providing reliable service to one of the region's most congested areas. 

TBM 2, Pamela, underground at U District Station, image by SounderBruce via Flickr

Additional images and information can be found in the Database file linked below. Want to get involved in the discussion or share your photos? Check out the associated Forum thread or leave a comment at the bottom of this page.