An old college friend went to work for CSX (I think), and we caught up after he'd worked there for a few years. He said that most of his job consisted of digging into old COBOL code to explain why a train was routed a certain way (e.g. Reno -> Phoenix -> LA -> SF instead of Reno -> SF), and that he rarely ever changed the code. They just made summary documents saying "there was rail congestion on the normal route".

I've always hoped that he was just yanking my chain and that they did...well, anything really.