I periodically give Network Rail (or whatever it's called this week) a hard time, and the proposed £30bn+ London-to-Birmingham rail link is economically daft, but today I have to concede that our transatlantic cousins have us beat.
For those of you not following West Coast USA news, the state of California has been planning a high-speed railway link from San Francisco to LA, a journey of 500+ miles. The link will eventually goes from San Francisco itself down to central LA, but the first stretch to be funded will run in the central valley from Modesto through Bakersfield down to Burbank on the coast.
Note that even this first stretch will be horrendously expensive (in the tens of billions of $ even on the current and therefore wildly optimistic plan) and will have no chance of any significant revenue because many of the central valley towns are bankrupt or near bankruptcy, and hence have very few rich business commuters willing to pay significant sums to be able to commute by rail.
Who's going to use this link even when it's complete? Even a 125mph rail link will take 4 hours to travel LA to SFO, best case, and that assumes it doesn't stop anywhere. You can fly the distance in an hour, which will cap the potential ticket prices, and travellers have a wider choice of airport destinations each end than the single railway station endpoints.
I also invite my readers to inspect the current 7-day map of earthquakes \ in the California-Nevada region, and consider the likely impact of a nearby 4+ magnitude quake (which occurs maybe once a month in the Bay Area) on a precisely engineered high-speed railway link.