While I like the idea of high-speed rail, I wonder how the economics for it will look if/when autonomous cars become common. Sure the train would still be much faster, but personally I wouldn't be that concerned about having a 3-hour travel time vs. 1.5 hours by train if I could relax in the car while watching a movie/reading a book/surfing the web/catching up on email/etc. And if you include the total end-end time it probably wouldn't be much different when including the time to get to the station, wait for the train, get a rental car at the other end, and drive to the destination.
Wouldn't even need fully autonomous cars to seriously dent the demand for long distance trains since only limited-access highway travel would have to be autonomous and that's an easier technological problem to solve.