Interchange is a routine happening between railroads right up to the time something happens. A big customer, a power plant or something similar, has a breakdown on a carriers property and now the 5 trainloads of coal that are on railroad A cannot be delivered to the plant that is located on railroad B and a train is still blocking the interchange between A and B. The train that is on the interchange has already been charged to B's Car Hire account; the remaining trains in the pipeline are still in A's Car Hire account. With the situation being what it is Railroad A will under take a procedure to 'Reclaim' the per diem charges for the trains in the pipeline against Railroad B. This can be a ticklish situation for the Operating personnel for both carriers. Railroad A has to find someplace to 'hide' the trains they can't Interchange. Railroad B has to work with the big customer to find out what they have to do to assist the customer in getting 'back in business' or undertake the necessary steps to Embargo shipments destined to the customer, wherever the shipments originate - this is an action of last resort. At some point, the situation gets resolved and we will say the plant get back in full scale operation. In theory, Railroad A will get from Railroad B the Car Hire amounts for all the cars and days that the undeliverable cars were held until the interchange reopened. That is the Theory. The reality is that the Car Accounting officials of the carriers will have a meeting and and negotiate a settlement of the claims each carrier has against the other. Per Diem is the 'rental' rate for railroad owned rail cars that is charged in dollars and cents per hour. The Per Diem rate of the car is dependent on its age and purchase price when new with the rate depreciating as the cars age. Private owner cars, those whose initials end in X have their per diem payable toa the private car owner. Car hire and the rules that pertain to it is a rabbit hole most railfans never think of, but it is a very deep rabbit hole that defines how the carriers have to operate with respect to each other. A subset of Car Hire is the Car Repair Rules and what repairs carriers can make on Foreign (railroad cars of other carriers) and Private Owner cars. There are standard prices/payment for the routine repairs that cars need to continue in service. If the cars have more issues than the Car Repair Rules cover, the cars will be sent back to the owner as a 'Home Shop' - before movement back home, the Owner will be contacted so the car(s) can be sent to the proper Home Shop. For cars with more extensive damage the owner will be contacted to see if they want the car shipped back home 'as freight' on another rail car or if the car is to be scrapped in place.
