I mean flatcars are still used today (not just historically) for things like tanks, farm equipment, lumber, semi-trailers, and sometimes even standard container

I mean flatcars are still used today (not just historically) for things like tanks, farm equipment, lumber, semi-trailers, and sometimes even standard containers (https://en.wikipedia.org/wiki/Flatcar https://en.wikipedia.org/wiki/Flatcar) Cars that carry containers are now mostly referred to as well cars (https://en.wikipedia.org/wiki/Well_car https://en.wikipedia.org/wiki/Well_car) An intermodal chassis or frame usually refers to the highway version used to pull a container behind a truck (https://en.wikipedia.org/wiki/Container_chassis https://en.wikipedia.org/wiki/Container_chassis)