I'm with Dave, any CONUS location/railroad would be possible. I would imagine that the preponderance would be east of the Rockies though.
The route could be heavily influenced on where a load was going. Say, a packer needs to send a load to St. Louis or Atlanta. Since the packer is assumed to be ON the NYC, whatever connecting road to StL or ATL that had the best agreement with the NYC or allowed the NYC the greater mileage charge would be the preferred road. The packer could influence what car the load would be using - if they had CNW and NYC cars, he would load the easiest for him. The fly in the ointment would be if the shipper specified what route would be used. And that, then, goes back to the first comment - anyplace could be possible.