The back-haul problem is well known to management in many areas of transportation. The problem occurs when using equipment causes its relocation, and it must be relocated before it can be used again. Getting the equipment back to where it is needed is costly. For example, a customer who rents an international freight container or a moving truck may return it at a distant location. The owner may be able to rent it to another customer at its new location. However, if no current demand exists at the return location, the owner may need to back-haul rental units to a location that has sufficient demand. Naturally occurring patterns of trade can create situations in which back-haul is common