Whenever a train is to receive a mandatory directive, the engine number must be used. At other times, the train ID can be used. So if train 510 has the Amtrak 505, whenever a gang foreman reads it through his limits, of the DS flags the train by a stop signal or gives it an unforseen speed restriction, you'll hear "Amtrak 505 South (or whatever) . . . ". Other times you may hear the train number, "Amtrak 510" -- sometimes not even the "Amtrak" part.