Sound Transit Board Sets Aside Idea of Skipping Second Downtown Tunnel

Sound Transit will likely not spend any more time studying the idea of cutting a planned second light rail tunnel under Downtown Seattle, following a surface-level discussion this week at the Sound Transit board.

The concept could have potentially saved the agency up to $4.5 billion, reducing an the estimated $34 billion shortfall that it’s facing over the coming decades, as it builds out the Sound Transit 3 (ST3) system approved by voters in 2016. However, overhauling expansion plans would also have come with significant risks and potential long-term impacts on the rest of the light rail system.

Building the Ballard Link Extension project without its downtown tunnel component was put forward this past summer by King County Councilmember Claudia Balducci, who argued that the agency should study the idea of instead utilizing the existing light rail tunnel to handle future increases in train volumes. The move was in reaction to the revelation that Ballard Link had jumped from the previous price estimate of $11.9 billion to upwards of $22 billion.

The agency determined the tunnel, which opened in 1990, needs extensive ventilation upgrades and upgraded tracks and platforms to be able to handle more trains, cutting into savings. While fitting a third light rail line in the existing tunnel would certainly be a heavy lift, it could save the agency enough to avoid having to push off other elements of the planned system by years, or to truncate lines well short of where voters signed off on.

https://www.theurbanist.org/2025/12/19/sound-transit-board-sets-aside-idea-of-skipping-second-downtown-tunnel/