An Optimization Approach to Freight Car Allocation Under Time-Mileage Per Diem Rental Rates

The paper proposes the use of linear programming to "solve" a specific freight car allocation situation wherein a choice of freight cars is available for shipper shipments, and the railroad's car allocation objective is to maximize the expression (freight car rental receivables-freight car rental payables). The freight car rental payment structure which is applicable is that of "time-mileage per diem" rates proposed in the United States by the Interstate Commerce Commission. The paper first describes the problem and its background, and then a model and various extensions are formulated. An example illustrates how costly to a railroad the difference between good and bad car allocation may be. Although the proposed linear programming approach may be manually tractable for small volume car allocation situations, the paper concludes that in most car allocation situations, the approach requires a computerized data base with a "real-time" information and communications system which includes order entry, car rental, routing-distance, and train travel time and yard delay time information.