Here they need the engine on site all the time when they get cars dropped off.  I think they could do about 15 cars when full but a 27 car setup was too big for the old engine.  When the unit trains come in they will leave the engines like you commented on.  Sometimes they have left only two engines which at times can be a struggle.  Now with the new engine, they can hook up and use their own engine as the controller and have the other tow (or three) as the controlled. 

Ed, that steamer that went by your place and mine was newer than that blue engine that the coop was using.