The customer determined the interchange points between railroads. The problem was getting a favorable tariff in place from origin to destination. In some instances, the ICC required a competing railroad to offer a similar rate regardless of mileage (within reason) or operating considerations.
There was a situation a few years ago between a Canadian and US railroad that went to the STB (successor if the ICC). It was a long haul between Canada and the Gulf. Both railroads quoted the movent to the nearest interchange with the other railroad, but both refused to give a rate for the middle of the trip which they both could have handled. Why didn't either railroad want the long haul? Neither wanted any more liability exposure to hauling chlorine gas than they had to assume while fulfilling their common carrier obligation. What is in the car matters as to rates.