This isn't really my kind of writing, so forgive me if my response is somehow impertinent, but there is a very good reason to cross the U.S. by train, which is that this is an enormous, beautiful continent and the train takes you to otherwise untouched parts of it that aren't visible any other way. I took the California Zephyr from Denver to San Francisco (technically Emeryville) a few years ago and it was one of the best experiences of my life. Truly unforgettable.
I hope I get the opportunity to do the Empire Builder and Southwest Chief routes at some point!
I hope I get the opportunity to do the Empire Builder and Southwest Chief routes at some point!