[breakerbox]

I still think the US has hope for rail and high speed rail that won’t bankrupt everyone. If, and this is a huge if (bc people love their cars), the US can replace a lane or two of major highways between cities with a rail. This would avoid forcing people to leave their homes or have massive payouts for stubborn landowners. The highway infrastructure is a pretty reasonable layer to build on as many highways already take close to the hypotenuse between major cities.

Anybody know why this concept isn’t talked about more?

[beerandt]

It doesn't work like that- the geometric design of high speed rail and interstate highways are significantly different. The same is true for heavy rail vs high speed rail. You need much larger curves, and much smaller gradients for high speed rail.

Also clear space requirements for interstates would likely be infringed, which is one of the biggest factors of safety.

A more workable approach would be to reclaim abandoned rail ROW, and purchased additionally required ROW to extend curve length, where required. However much of this ROW has already been reclaimed by landowners and built upon.