It’s Amtrak. https://www.amtrak.com/home
Most of the service is concentrated in the Northeast corridor, as well as running from Chicago across the country. Anything outside the NE is sparse and they’ve recently cut the cross-country routes to 3X a week instead of daily.
The auto train is DC to Sanford FL only. There is no other location in the US that does it. Suspect it has something with getting people from the NE to their Florida snowbird destination and/or Disney.
If I wanted to take Amtrak from say, Houston TX to DC, I would have to ride the Sunset Limited from Houston to New Orleans, then take the Crescent from New Orleans to DC.
Nashville doesn’t have Amtrak service. I would have to drive to Atlanta, Memphis or St. Louis to even get started.
And yes, It has everything to do with getting folks to Disney......!
.....so it’s a win/win for us living close to Orlando to take this train to DC!