Generally there is what is called a General Manager's agreement which covers detours. Usually it is a set price per train-mile, but sometimes there is a more complicated billing arrangement by car-mile or a combination of the two. It is not just a matter of calling the dispatcher and getting a signal to go. The host railroad has to provide a pilot that is qualified over the territory. These arrangement are usually made weeks in advance when the reason is a maintenance project. However, when it is a washout, derailment, etc. they are activated in a matter of hours. So the prices are in this pre-negotiated agreement and then the operating departments of the two railroads work together to schedule the trains and pilot crews. The host railroad can take as many trains or as few trains as they feel they can handle based on crew availability and their own traffic congestion concerns. Railroads do have an incentive to work together as the host railroad will likely have a need sometime in the future for reciprocity with the detouring carrier. The rates in the GM agreement is quite a bit higher than trackage rights so the detouring carrier has an incentive to minimize the use of the detours.