The Acela corridor in the north east US connects DC, Philly, NYC, and Boston. Many trains run per day and most of them are full capacity. The Acela corridor revenues support the entire other ~Amtrak routes. Most cities along the Acela have sufficient public transit and density to not require car rentals on arrival.

Funnily enough, the Midwest is pretty much a spoke and hub of medium sized metro areas focused around Chicago.

There’s the Northeast corridor (and its cousin the Southeast corridor going down to Atlanta).

The PNW cities also are clustered like this but have difficult geography.

California and the Central Valley with the Bay and LA also meet this criteria, but CAHSR is run by a mix of incompetents and constrained by the wording of the ballot initiative that got it approved.

> The PNW cities also are clustered like this but have difficult geography.

Not really. It's pretty flat here in the Willamette valley, where the majority of Oregon's population lives, and relatively flat going north into Washington to Seattle... But the best we've got for long distance trains is Amtrak which shares the tracks with commercial traffic, where Amtrak gets basically the lowest priority on the tracks.