[jtzhou]

The GBT is 94 miles, right? I think the Swiss achieve these costs through economies of scale. There are tunnels throughout the country so they can achieve greater efficiencies at 5-10x of those in specific metro areas in the US. I remember when they were debating a tunnel under Tysons Corner in Virginia, the largest office park in the Washington-Baltimore area, the estimate came in at $800 miles for 4 miles and was considered cost-prohibitive. It'd be great to bundle a number of these projects together to achieve the efficiencies of scale.

[hn9780470248775]

"Economies of scale" when tunneling through solid rock?

[maxerickson]

I would naively expect running a tunnel boring machine 1 mile to cost a lot more per mile than running it 2 miles.

[gsnedders]

FWIW, a surprising amount of the base tunnel was blasted by dynamite, as the geology didn't allow use of TBMs everywhere. (And they hit more cases where they had to blast it than they expected.)