Seattle-based Sound Transit pushed through the wall into the future Capitol Hill station site to complete a two-mile light rail tunnel from the University of Washington (UW). The 21-foot diameter tunnel boring machine (TBM) emerged within three millimeters of its target as part of the University Link light rail expansion.

When complete, the University Link project will connect UW and Capitol Hill to downtown Seattle with 3.1 miles of new underground light rail service.

The overall $1.9 billion project is about halfway complete and scheduled open in 2016. The expansion, with stations in the heart of Capitol Hill and UW, will provide unparalleled speed and reliability through Seattle's most dense neighborhoods. A trip from Husky Stadium to Westlake will take six minutes and is expected to add 70,000 riders to the system, which today runs from downtown to south Seattle and Sea-Tac International Airport by 2030.

The corridor includes three major universities /colleges —UW, Seattle University and Seattle Central Community College (SCCC) — with a combined enrollment of more than 50,000 students.

The contractor launched the TBM on its two-mile underground journey from the University of Washington Station site near Husky Stadium in May, 2011. The machine, nicknamed "Togo" passed beneath the Montlake Cut and Montlake, Interlake, Volunteer Park and north Capitol Hill neighborhoods. A second TBM, named "Balto," is still mining the second tunnel between UW and Capitol Hill and is expected to arrive in April. Meanwhile, a third TBM is mining the second tunnel between Capitol Hill and downtown. That machine is expected to arrive in June.

Each of the TBMs:

• Weighs over one million pounds.

• Stretches more than 500 feet long including the conveyor system that removes spoils from the cutterhead to the surface.

• Places 21-foot diameter pre-cast concrete tunnel liners as it mines through the earth.

• Was built specifically for this job.

The U-Link project has become a major construction jobs driver with almost 1.5 million direct construction work hours into the project. Sound Transit estimates the project will create about 20,000 direct and indirect jobs over the life of the project.

With major tunneling work wrapping up, contractors have begun mining 20 cross passages between the north and southbound tunnels. With that work complete, contractors will build a new track bed in the tunnels and begin laying the rail and communications systems for light rail operations. At the same time, contractors will finish the stations at Capitol Hill and UW.