Roads are always going to expand their use… because they are free.
Americans are sheep. If the government says “pay your taxes and we’ll give you free roads and cheaper airfare” the sheep believe it.
The first thing to do is begin taxing fuel based on vehicle being filled. A tractor-trailer should pay more since his vehicle causes a much higher fraction of the damage to the roadway. Second, cancel ALL airline subsidies. If they can’t get enough cash in the market, then obviously the market doesn’t justify the need of that many airlines.
Third, figure your head out and decide what you mean by high speed rail. 110mph direct corridor service like that offered by Amtrak’s North East Corridor? or are you looking for 2xTGV type speeds offering service to all 48 continuous states?
If you are looking for the 2xTGV, then get it through your head AND wallets that the only real answer for us is a HUGE investment, rivalling the Panama Canal, or building the ENTIRE EIH system in one big swoop. A large high-speed maglev loop around the US (dual track to offer service counter & clockwise). Amtrak oversees the construction of a 100% grade-crossing free (being 30’ in the air, hopefully tresspasser free as well.) superhighspeed line and then its operations. Each state that wants to can pay a tap-on fee to have a station/transload facility built. If they want one station in the middle, one fee. Two stations further apart? Two tap-on fees… (multiple purchase discounts could apply?) The Mag-lev cars would in fact be nothing more that glorified intermodal containers. A bit wider than a standard container, and perhaps a bit taller, they would lock into the cars. All passenger bound for Mardi Gras would board one car. Upon the mag-lev’s arrival in Louisiana, the locks are dis-engaged, and a crane would transload the car full of MargiGras-Goers onto a local train, and away they’d go. Another “People-Tainer” would be loaded on as outbound “freight” and away the maglev would go.