what is the difference between lead and controlling locomotive?
The lead locomotive is the engine that leads in the engine consist’s direction of movement. The controlling locomotive is the one that the engineer is operating from. If a multiple unit engine consist pulls West on #1 track with the engineer in the Westmost unit, the engineer is on the lead & controlling locomotive. If the that engine consist then backs East against the train on #2 track without the engineer changing ends, the Eastmost engine is the lead engine but the Westmost engine is the controlling engine.