From the Amtrak website:

Only true folding bicycles (bicycles specifically designed to fold up into a compact assembly) are acceptable. Generally, these bikes have frame latches allowing the frame to be collapsed, and small wheels. Regular bikes of any size, with or without wheels, are not considered folding bikes, and may not be stored as folding bikes aboard trains.

I said upthread I didn't know why Amtrak cares how your bike gets into their 34" x 15" x 48" (860 x 380 x 1120 mm) "folding bike for carry-on" envelope. Seems arbitrary. But based on what Amtrak's website says, I can not assure cycletourists that their coupler or rinko'ed bike will be accepted as a carry-on by each and every one of Amtrak's conductors.