[erispoe]

Yes, that works in the Central Valley, where it is already relatively easy to build HSR. It doesn't in urba areas. The constraint on the profile of the infrastructure, both horizontal and vertical, in a function of the speed. In the end what you need in an infrastructure with the right profile, and that is where the bulk of the cost is, not in the system that runs on it.

I'm ready to be convinced that the Hyperloop system is cheaper than HSR, but the problem is building the right of way. Viaduct is not a magical answer, we could have a HSR viaduct with soundproof walls. Peninsula NIMBYs successfully killed building new tracks for HSR, where Caltrain already runs (with almost no additional nuisance). Somehow, I don't imagine them (or any californias suburban community) being OK with a viaduct going through their towns. A viaduct that couldn't be laid on top of existing roads to have the right profile for high speed.

There are very few existing roads that are compatible in profile with high speed. And they are located where the right of way is already cheap.

Solving the right of way problem sounds maybe less sexy than supersonic travel, but this is where we can gain the most efficiency. I think this is a harder problem than the hypersonic technology.