ceci n'est pas une pipe
In the ER series the Locomotive (start player marker) moves to the player with the greatest income at the end of each round. In the case of a tie, this is what breaks it: "the greater cash (or least debt)".
The more important question is: Why give the loco to the leading player? This seems to be pure positive feedback. Being start player is simply a big advantage, and no downside.