Mmm theoretically I think it’s possible because I think there’s an ‘Unload All’ option to add to a line, I’m not sure though because I don’t owe the Beta and never payed attention to it. This was in fact an option in Transport Tycoon.
Actually I hoped that this is done automatically, same as in reallife, when I go from a to b its possible I switch trains multiple times. This way I could get my cities a lot cleaner and also safe me some in game money 🙂