When I was with NS I use to lashup several different variations. As long as the leading unit was a NS engine on NS lines then all is well. For every day another railroad's unit is on NS lines, then NS is being billed, so priority goes to lashing up other RR's units to get them back to their owner.
What to look for when creating power for a train: HP (Overall for train tonnage, distance, and grade), Fuel level, hours until dead (Federal maintenance check), and if it needs to be returned to owner.
