[tomarr]

Large amount of US popular is clustered around key areas (East Coast corridor, West Coast Corridor, Midwestern cities etc.

No reason these couldn't be linked up and are more populous than many equivalent regions with HSR. It's like power grids, noone is arguing that one big one from SF to NY is the right solution.

[seanmcdirmid]

China is even more densely packed behind the Heihe–Tengchong Line. Oh, don't misunderstand, China has it even harder than we do, if you look at eastern China...where people live, a lot of it is not flat and they are tunneling through lots of mountains to make these HSR lines work. Actually, that might make it easier for them, since their population is much more focused (no room for huge suburbs), and their only real challenge is building tunnels and viaducts.