Framing the comparison as cost-per-passenger-mile is unfair to Amtrak, though. Amtrak on the NE corridor enables many trips between nearby cities in ranges of tens of miles that are too short for an airline to serve. Using passenger-miles as the denominator misframes Amtrak's strength as a downside. Amtrak is serving a very useful service there in displacing those trips from cars or buses.
It's true that Amtrak isn't all that useful beyond the NE corridor, although that's as much a function of the scale of the US as of Amtrak itself.
It's true that Amtrak isn't all that useful beyond the NE corridor, although that's as much a function of the scale of the US as of Amtrak itself.