Hello Ethan, In British English the carriage or coach is one of the main sections of the train and in England you will often hear announcements saying that the first four coaches are for one destination and the remaining coaches for another place. Compartments are the sections within the coach/carriage. 'Car' is American English for 'carriage'. Hope this helps Bob

I think you can use compartment.

It depends on the train, the country, and the train company. I have heard all of these in the US except "carriage," but that is used (I believe) in England. "Coach" can refer to other things and is a bit awkward so I would avoid that. But "car" and "compartment" are about the same, where "car" refers to the entire structure (including the wheels, undercarriage, etc.), and "compartment" is just the inside of the car.