Brambor from Windham, Maine on 5/11/2021 7:34:04 AM:
We also have a tandem and AFAIK there is no provision for tandem on Amtrak ... not officially when you look into their rules for length of the bike. Some cars even make You to take the front wheel off on a single bike in order to hang it.
In theory, if You find a benevolent operator in a good mood I see no reason why one could not just lean the bike in a bike car with roll on service - those cars are for bikes and cargo only and do not have people in it. But, I digress... do not count on it.
If Your tandem has couplers You can just split it in two and treat each piece as 1 bike, buy 2 bike passes and hang it separately as if it was a single bike.
FWIW we have just completed the Erie Canal and Empire State Trail and in our case we rented an SUV one way, folded the back seats and put our cargo in there.