West Seattle and Ballard Link Extensions

Alignment

The project consists of two branches extending from a new downtown Seattle tunnel. The West Seattle branch (4.7 miles, 3 stations) would run from the existing International District/Chinatown station south to a Sodo elevated guideway, cross the Duwamish River on a new movable bridge, and terminate at a station near the Alaska Junction. The Ballard branch (7.7 miles, 7 stations) would depart from a reconstructed Westlake hub station, run through South Lake Union and Uptown, cross the ship canal via a new high-level bridge or bored tunnel (still under study), and terminate at a station in the heart of Ballard.

The new downtown Seattle tunnel would serve both branches and relieve pressure on the existing downtown transit tunnel shared with buses and future Link expansion.

Updates

2025-08 — Ship canal crossing type still unresolved

Sound Transit’s board continues to deliberate between a high-level fixed bridge and a bored tunnel under the Lake Washington Ship Canal for the Ballard crossing. The tunnel option is preferred by the City of Seattle for neighborhood compatibility but adds approximately $2B to the cost.

2025-01 — Revised cost estimate: $20–27 billion

An updated program estimate raised the range significantly above the 2021 ST3 baseline, driven by inflation, updated labor costs, and scope refinements. The board directed staff to identify cost-reduction strategies while preserving core project scope.

2024-06 — Board adopts preferred alternative

The Sound Transit board voted to adopt the preferred alternative for the full corridor, including station locations and general alignment. This decision advances the project into NEPA environmental review.

2022-11 — Scope and schedule revised under ST3 realignment

As part of a broader Sound Transit 3 package realignment driven by COVID-era revenue shortfalls, the West Seattle and Ballard extensions were restructured: West Seattle opening moved to ~2032 (later revised further), Ballard to ~2039.