> existing real estate and infrastructure would have to be bulldozed,

You mean like they've done with every beltway and interstate? They claim eminent domain, take whatever strip of land they need from you, and bulldoze anything in it's path to build nice fancy exits full of the same features: a few hotels/motels, gas stations, couple of fast food chains, and, perhaps, if you are fancy enough, a strip mall with a Department store, Sporting Goods, and a fine dining establishment from one of America's most recognized brands: Bloomin' or Darden

There was a push for something like that and it would have been great...it fell afoul of NIMBY and Toll road haters. https://en.wikipedia.org/wiki/Trans-Texas_Corridor Everyone in Austin hated SH-45 & 130 when they were built, they were practically empty for a few years to my delight as I could travel the entirety of Austin in a fraction of the normal time even during rush hours. After MOPAC was added residents began to see the light and the tollways are now congested. Many are regretting their opposition to Perry's lost/last road project but, that train has left the station unless Elon can get the Boring project going or Virgin is able to implement their version of Hyperloop. Hell, I'd have settled for elevated wire gondolas over the roads, works well enough for Australia.

The majority of the costs of passenger rail is in the land-costs of placing those statins (and rail-lines) somewhere important.

The US Freight Rail network is just the right place to deploy this technology right now. We may have crappy passenger systems, but our freight is world class.

EDIT: It should be noted that PTC sensors cost $50,000 per train. But each train costs $2+ million, so the PTC sensors aren't that much compared to the overall system. The idea of having a similar suite of $50,000+ sensors / radios on every car is clearly too costly in contrast.