Seattle is hemmed in by mountains. Anything heavy that comes from the rest of the country has to climb over the Cascades, and the main crossings are slow, steep, and shut down repeatedly through the winter. The I-90 corridor over Snoqualmie Pass closes around 29 times a winter, and a single multi-day closure has been measured at tens of millions of dollars in lost output. That is a permanent tax on a region that has to import most of what it builds with.
The Twin Tunnels are a proposed pair of highway mega-bores through the Cascade Range, turning that chokepoint into a weatherproof, closure-free link for freight. The model is Switzerland's Gotthard: the Swiss bored under the Alps so a mountain pass would stop being a seasonal tax on a trading nation. A flat trans-Cascade bore would do the same thing for the Pacific Northwest.
It is also the supply line behind the material standard. Dimensional stone, brick, steel, cement, and aggregate are dense, low-value-per-ton freight, exactly the cargo the mountain crossing punishes most. A reliable flat corridor lowers the delivered cost and the schedule risk of every heavy building material that has to reach Seattle. The standard says build with durable materials. The tunnel is part of how the durable materials get here affordably.
Incorrect passphrase.
This initiative is in development. Sign up to follow it, and tell us if you want to help, whether you are an engineer, a contractor, a freight operator, an investor, or a resident who is tired of the pass shutting down.
The Standard Seattle Forgot - the material standard the tunnel is built to supply.
Building the Supply - the plan to manufacture lime, pozzolan, and terra cotta regionally.