Sound Transit West Seattle Link Extension — cost growth from $2.7B (2016) to $4.9–5.3B (2025 dollars)

Sound Transit’s West Seattle Link Extension has ballooned from a voter-approved $2.7 billion estimate in 2016 to a range of $4.9–$5.3 billion after cost cuts — and hit $7.9 billion before those reductions were applied.

What happened

When voters approved Sound Transit’s third mass-transit package (ST3) in 2016, the West Seattle Link Extension was projected to cost approximately $2.7 billion. The estimate grew steadily through 2024 and 2025.

By September 2025, the range had reached $7.1–$7.9 billion. A cost-reduction analysis completed in March 2026 — involving station consolidation and route changes — brought the current estimate back to $4.9–$5.3 billion in 2025 dollars. The board is also weighing a stripped-down alignment ending at Delridge, estimated at $3.3–$3.4 billion.

No fraud allegation has been made. This is a project management and cost-control failure.

The receipts

Sound Transit’s own project page documents the current scope and status. The Urbanist reported in September 2024 that the board voted to continue the project even when the estimate stood at $5.1–$5.6 billion — already roughly double the 2016 voter-approved figure. The cost growth from 2016 baseline to the September 2025 peak represents an increase of between 80% and 192% depending on which estimate is used, before cost-reduction measures were applied.

Status

The project is ongoing. The Sound Transit board has not terminated it. Cost-reduction options remain under consideration. No enforcement action has been taken.

Why it’s in the registry

Voters approved this project at a specific price. The board’s governing structure — composed largely of elected officials from jurisdictions that want the project built — creates an incentive to keep going even as costs escalate. This case documents what happens when there is no independent check on a mega-project’s cost trajectory.

Reform implication

There is no independent, binding cost-control mechanism for regional transit mega-projects in Washington. An outside stage-gate review authority — with real authority to stop or restructure a project when costs cross defined thresholds — would provide the structural check the current board-only model does not. See [reform: transit_governance_reform] and [reform: cost_transparency_reporting].