The expected price to build West Seattle’s light rail extension has soared $800 million, reaching a possible $7.9 billion for 4 track miles and four stations, Sound Transit executives reported Thursday.

Reasons for that spike include continued construction industry inflation, adjusting old figures to reflect 2025 dollars and more extensive engineering work to design the route from Sodo to Alaska Junction. Newer numbers bring the nitty-gritty prices of time, labor and materials, such as bridge pilings in weak Sodo soil, into better focus, instead of basing projections on per-mile costs years ago.

Thursday’s cost range, of $7.1 billion to $7.9 billion, exceeds the $6.7 billion to $7.1 billion range that shocked the region last September, disclosed then by new Deputy CEO Terri Mestas. Those

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