I’ve done a significant (30-page paper, presentation before several legislators) project on just this subject.
There’s one real, big, huge problem that has to be overcome.
People will generally travel by the fastest method they can afford. Up to about 250 miles, that is by car, and beyond that it’s by airplane and car. A train that runs at 35 to 65 MPH is never gonna beat the mile-a-minute-door-to-door average of a car, or use the congestion and delay at the airport against the 'plane effectively.
The Acela makes money at roughly a normal rate of return (6-8 percent per year). This is better than any other transportation system in this country - we don’t subsidize the Acela at all, it pays for itself and then subsidizes Amtrak. This is because it runs faster than the car or the airplane over its entire route. If a train averages 100 miles per hour, station to station, it’s always going to be ahead of a car (well, unless I’m driving on a clear, dry day), and up to about 500 miles, it will beat the airplane.
No other passenger rail service in this country makes money. No passenger rail service that doesn’t average over about 80 MPH makes money, in any country. Any slower rail service in Europe is the equivalent of the Greyhound bus - cheap and only good when it has to match pace with whatever else is on the rail line.
In experimental testing, FRA Class 3 track, normally rated for 60 miles per hour, was found to be perfectly fine with a relatively light passenger express at 100 miles per hour, and track wear was not deemed excessive. Those tests were run 30 years ago. Modern Class 2 track (really light, cheap stuff) would be good enough for similar service today thanks to some metallurgical and engineering advances. Amtrak doesn’t run outside of stations on anything lighter-duty than Class 3 east of the Mississippi.
The problem dates back to a rule enacted in 1947 in order to REDUCE excessive passenger traffic on the rails. After World War II, the last steam engines and first-generation diesels hauled new stock at unprecedented speeds, and the public responded by piling onto those trains. Congress, scared by reports that the Pennsylvania Railroad T-1 had been doing 140 miles per hour on the western slopes of the Allegheny mountains while hauling a 1,000 ton (2000 passenger) train, and pressured by Ford and Chrysler to reduce the railroads’ sudden dominance of intercity travel, enacted a law that said, effectively, that no non-electric train could go faster than 79 miles per hour.
It broke passenger rail transportation in this country. Railroads stopped ordering fast, advanced equipment. Passenger rail technology stagnated. Schedules slackened (the premier New York-Chicago services were slowed by more than two hours), and luxuries went away, as did the passengers.
If you want intercity passenger rail here, you need two things. First, American railroads run diesel locomotives outside of the Northeast Corridor. That’s not the problem. What is is sticking them with a ridiculous speed limit. In the 1930s and 1940s, any top-end diesel express boasted beginning-to-end averages in the seventies with rail speeds generally around 100. The railroads’ passenger safety record was better then than it was now. The rails are good for 110. The trains are good for 125. They should run that fast.
Fast diesel expresses over 200-400 mile routes would take out almost all airline traffic over their routes. Would anyone fly from Chicago to St. Louis if the train could get them there in two hours at half the cost? Would anyone fly from St. Louis to Kansas City if there was a three-hour train? Would the Detroit-Chicago highway be undergoing an expensive overhaul if there was a decent train between those cities? These trains would have the equivalent of a 120% present market share - not only would they pick up almost every existing traveler between any of these city pairs, but they’d create additional ridership.
France supports the TGV with similar metropolis-to-metropolis distances. Paris-Lyon, Paris-Calais, Paris- Marseilles, and Paris-Nice are all a few hundred miles long and connect cities no bigger than Chicago-St. Louis, Chicago-Detroit, Chicago-Cleveland, or St. Louis-Kansas City. The insufficient population density argument holds true only once you get out into deep red state territory*. The blue and purple ones will support rail travel just fine.
*Exception - Texas Triangle - Dallas/Houston/San Antonio.