Why are some intermodal stack larger containers on top and smaller ones on the bottom?
You can’t put the smaller ones on top because there are no IBC (inter box connector) sockets in the middle of 40,45,48,53 foot containers.
Another reason is that on some cars, the 48’ and 53’ containers won’t fit in the well, so you have to have a 40’ or 2 20’ containers in the well and longer containers on top. On any container over 40’, the IBC sockets are located at the point where they would line up with a 40’ container; i.e., 4 feet in from each end on a 48’ container.