Let us remind all that at one time the US was well on it's way to developing high speed rail in the 1930's with 100 mph consists pulled by steam locomotives, and all accomplished via the private sector. Then came along the FRA with it's 79 mph max sans ABS, the airlines which made most long distance surface transportation pale by comparison per trip speed, and of course GM with it's new-fangled diesels which were most efficient at the lower speed ranges, and suddenly railroads were stuck in a no man's land of being much slower than air travel and much less flexible than highway travel.

As much as we want to blame the Interstate system for destroying private sector HSR, we have to acknowledge that freeways have a max practical speed @ 70 mph give or take. And air travel tends not to be all that practical in the medium distance markets. If the railroads had been allowed by the regulatory agencies to continue incremental speed increases as steam technology advanced there still might be private sector HSR rail travel today. When we consider that Pennsy's T1 were capable of 140 mph using 1940's technology, it is apparent that HSR could have managed that niche high speed market between those new Interstate highways and the airlines.

If the railroads had focused on increased velocity rather than increased axle loadings to improve efficiency, who knows what today might look like? But when the government put that artificial cap on max speeds, it was inevitable that increased axle loadings (something that is anethema to HSR concepts) would take the evolutionary lead.