Megan McArdle tells us:
…why is America’s high-speed rail so dreadful? The Acela delivers
you, at enormous added expense, to Boston one hour ahead of the
regional. On the DC-to-NY run, the added benefit is 10-15 minutes. The
answer is that the Acela uses existing track, which is twisty, the
better to serve every congressional district between here and Boston.
Real high speed rail needs to be fairly straight, for the same reason
you don’t take hairpin turns at 120 mph in your car.
I had never heard the Congressional district argument before. I’ve also heard that freight railways crowd the lines and Amtrak doesn’t pay a high enough prices for access; the freight services had, way back when, pledged to the government to give Amtrak trains priority but of course that kind of cheap talk is not enough to get the job done; here is some relevant background, and more here. Here is a good summary of Amtrak critiques. It comes from a whole blog devoted to criticizing Amtrak.