Sound Transit CEO Lays Out Approach to Second Seattle Rail Tunnel

Last week, transit advocates had the rare opportunity to hear an in-depth hour-long conversation from Sound Transit’s top officials. Transportation Choices Coalition hosted a “Transit Talk” with Sound Transit CEO Dow Constantine and Deputy CEO Terri Mestas. The conversation centered around getting the Sound Transit 3 (ST3) measure on course after the agency recently revealed a major budget shortfall exceeding $30 billion.

Spurred by an audience question, Constantine also discussed the agency’s latest thinking on Seattle’s second downtown transit tunnel. In short, new technology and system upgrades could allow the agency to operate significantly more trains in the existing tunnel. If successfully implemented, that technology could make running three light rail lines in the existing tunnel conceivable.

The ST3 plans envision those three primary lines as running from Redmond to South Everett, Tacoma to Ballard, and Everett to West Seattle, all passing though a Downtown Seattle tunnel on their way. A fourth line would also operate from Issaquah to South Kirkland, as the final light rail project planned to be built.

As it stands, agency plans would make the second downtown tunnel a key part of the 10-station Ballard Link project, providing the highest ridership stations on the line. Cost estimates for Ballard Link have spiked, jumping from $11.9 billion to upwards of $22 billion.

A viable plan to operate three lines in the existing tunnel could make jettisoning Seattle’s downtown tunnel enticing as a cost-cutting measure — especially to suburban boardmembers from outside Seattle. A few of them have essentially already proposed as much. Sound Transit Boardmember and System Expansion Committee Chair Claudia Balducci put forward the proposal to study the idea of operating the three lines in the existing tunnel.

https://www.theurbanist.org/2025/10/29/sound-transit-approach-to-second-seattle-rail-tunnel/