Free empty return

I have a question. I understand the policy of railroads where a private car pays a freight charge from A to B, and gets a free empty return. Generally, the free empty return goes from B to A for the car to be loaded again. If the car is reconsigned and diverted on its return from B to A and now goes B to C for loading, is the return still free? What if A to B was in a certain railroad (say BNSF) but B to C is BNSF with a junction to say UP? Does UP charge me because they were not originally on the revenue move? Any help is greatly appreciated. Thanks,

I don't know if this will help but you might find what your looking for here
http://www.bnsf.com/customers/equipment ... ments.html