I have often wondered, when I see a freight train with many upfront pulling engines (two or more; sometimes up to five) how those engines are coordinated by the engineer in the lead engine? Are they somehow wired together, or via radio waves, or? to have them coordinate their pulling movements together? Taking it a step further, when I see a pusher engine or two way back on the train in the middle of a stream of cars, or pushing from the very rear of the train; again, how are they being controlled by the engineer? I assume those pushers are unstaffed? Have there been any problems where a pusher engine a mile away from the lead engine doesn't 'follow orders'?