genejockey 

There's a promotional video that Union Pacific shot back close to the end of the Steam Era on the Big Boys, which if I remember correctly showed not only two big boys double-heading up one of the passes in the Rockies, but also a THIRD Big Boy pushing from the rear. Imagine having to coordinate all that! Three ginormous steam engines, all run with mechanical throttles that really were just valves for the steam, all trying to exert just the right amount of force, so that, for example, the second engine in front wasn't simultaneously pushing the lead engine and pulling the train. Three engine crews, working together, with the last guy in line a mile away. With diesels, as I understand it, you need one engine crew because the other engines are all just slaved to the first.