Not a lawyer and might be wrong but as far as I know land rights go all the way to the core in the US, so going underground wouldn't help with right of way. I know, "HN is more than the US," but we seem to have the most trouble with trains.
I think you're referring to the 'all the way to heaven and all the way to hell' bit.
In principle that's true. But in practice mining rights and such have been split off from the right to the land and some reasonable depth underground. And any objection to an easement would be much harder to establish if it doesn't actually affect you. But for those parties that own the underground and mining rights for a given location there could well be a viable opposition to such a development. But that would then risk an eminent domain claim.
It's all pretty complex. But I would still assume that going underground is easier than going above ground where the parcels are small and the interests are immediate due to interference with existing activity.
Even if this is true, the costs of digging are much higher than the costs of above-ground construction + the legal costs of acquiring the land. A hundred kilometer tunnel would be one of the longest tunnels ever built, and the longest train/track tunnel by quite some margin. And it would need copious safety features and auxiliary tunnels leading to the surface, even before the whole vacuum part gets added in. So it won't even completely avoid the need for buying above ground lands.
> the costs of digging are much higher than the costs of above-ground construction
Yes, easily 3 to 10x.
> A hundred kilometer tunnel would be one of the longest tunnels ever built, and the longest train/track tunnel by quite some margin. And it would need copious safety features and auxiliary tunnels leading to the surface, even before the whole vacuum part gets added in. So it won't even completely avoid the need for buying above ground lands.
Indeed, so it's both a technical and economical non-starter. But it's not a 'dumb idea' in the sense that it is impossible. Merely impractical, too expensive and too complex and besides cheaper solutions exist (aircraft, for one, which scale much better with increasing distance than rail ever will).
One thing all of these 'dumb ideas' and the hyperloop, tidal energy and so on all have in common: they are great ways to get your grubby fingers on subsidies.
