Yeah, I tried it with another guy, if I uncoupled from the head end he could couple onto the train, but then I couldn't couple back on until he uncoupled. Problem is any "train" can only have one driver, and multiplayer is no exception to that rule. In single player try coupling onto the back of an AI train, the minute the couplers engage you lose control because your engine is now part of the AI train and is controlled by the AI driver. Like I said you can get behind and push, and we tried it on some grades that made it obvious the pusher was actually helping, but if the back guy slows down or the lead guy speeds up you separate since the couplers just won't couple.