Sounds like amtrak boxes are as big as airline boxes, I used one in the early '90s (only $10 at airport IIRC) to Germany and back, fortunately with a co-worker, for 2 weeks of work training. Only had to turn the handlebars and remove the pedals. But moving the box, what a pain! My boss dropped me off and picked me up from the USA airport in his VW van. In Germany, hauled giant box and suitcase from airport to train, then fortunately at destination town, hailed station-wagon taxi to haul to hotel (needed to fold back seat, my traveling companion then sat in front and I jogged to hotel), then deboxed and assembled, rode every day after work. Really enjoyed, but way too much hassle. Folding bike would have been so much easier. Not sure Bromptons were easily available back then. I think Bike Friday had just barely started up that same year. A couple years later, I had business in Japan, only 4 days, so I just got up early and jogged each day. Brompton would have been cool, that trip they flew me first class, a Brompton in a bag would have easily been allowed there, tons of luggage room in the nose of a 747-400, no seats in front of me, real recliners, choice of japanese cuisine if desired, that was luxury. Way more comfy, even 12 hours(?), than 8 hour flight in coach to Germany.

I'm sold on folders, now that mine has been modified to get the gearing I need. I'll never buy another non-folder.