Our regional transit agency is getting better at building subways.

Two tunnel boring machines digging routes for a future light-rail line between Capitol Hill and Husky Stadium "have finished their tunneling three months ahead of their original schedule," says Sound Transit spokesman Bruce Gray. The second machine broke through soil and cement at the future Capitol Hill station late last month, as was widely reported, but a Sound Transit schedule from February shows the tunnels weren't slated to be done until June 30.

"Mining is always the always the highest risk part of the project in terms of cost and unknowns," Gray says. It speaks well for the project "any time you can get the tricky part out of the way."

The advanced schedule doesn't yet change the project's overall timeline or guarantee taxpayer savings—Gray explains that many other project components must fall into place before the line is expected to be open in 2016—but it bodes well for accelerating the project's pace.

"The sooner they are done mining, the sooner the contractor building the station can get to work," Gray says. Currently, three of the four 21-foot-wide tunnels that terminate in the Capitol Hill station are complete: both lines to the University District, northbound and southbound, and one of two lines to downtown. The second tunnel between downtown and Capitol Hill, being dug by a machine named Brenda, is arguably less risky now that the parallel line is complete and engineers are familiar with the soil conditions.

Indiana-based tunnel contractor Traylor/Frontier-Kemper, which has a $339 million deal with Sound Transit, has had a "very smooth operation and had very few hiccups," Gray says.