[jltsiren]

The conventional wisdom is that high speed rail is competitive with flying when travel time is at most 4.5 hours. But China has been challenging that with some ridiculously long routes, such as 2760 km from Beijing to Kunming (10 hours 43 minutes). I think the idea is that if flight time is long enough that you can't travel and work reasonably on the same day, you have to dedicate the entire day for travel. Then the difference between a 3.5-hour flight and a 10-hour train trip is no longer that significant.

[dredmorbius]

"Night trains" (where the train effectively doubles as lodging for 8--12 hours) make even longer-haul routes quite viable. Even without HSR that affords nearly 1,000 mi / > 1,500 km of range (80 mph constant / 130 kph).

At typical HSR speeds of 185 mph / 300 kph, that extends to ~2,200 mi / 3,600 km. That's sufficient for travel from SF to Chicago, or NYC to Salt Lake (with range to spare).

(Both calculations presume 12 hours and operating largely at top speeds, both of which may be atypical in practice, but do satisfy the maximum possible range question.)

Travel within major population corridors, generally the east coast (Boston, Minneapolis, Miami, Houston) or west (San Diego, Phoenix, Seattle, Salt Lake, Denver) should be highly viable.

And as is often noted, rail operates city-centre to city-centre, and typically has fewer security checks and delays.