| Railroads have a substantial portion of their investment in freight cars. Hence the study of freight car utilization is important.;We first analyze the freight car cycle to identify strategies for improving freight car utilization. The dispatch policy and blocking policy are identified for further analysis since they affect the utilization. A line policy to study the impact of passenger train operation on freight train operation is also considered.;Three dispatch strategies are compared--the Constant Interval Policy, the Constant Batch Policy and the Modified Constant Interval Policy. The third policy is where a locomotive is not dispatched when no cars are accumulated over an interval.;While considering the mean delay as a measure, it is established that the constant batch policy performs the best and the constant interval policy the worst. While considering variance, the ranking is not so clear. Costs are also considered as a measure.;The blocking policy is modeled on the assumption that train lengths (batches) are constant. We seek to answer how trains should be run so that cars are moved from their origins to destinations with minimum total time for a system. Three components of time are considered--(i) classification, (ii) accumulation and (iii) travel. The resulting formulation is called the Train Blocking Problem (TBP) and is a Fixed Charge Network Design Problem.;The TBP can be solved as a Mixed Integer Program using Bender's Decomposition. It is also established that another formulation of the TBP performs better in generating integer values as solutions when solved as an LP.;Lastly, as we model the Line Policy in the context of a double track railroad, we determine that the loss in capacity is (i) directly proportional to n--the number of blocks between sidings and (ii) increases, remains a constant or decreases as the speed ratio increasing depending on whether n is equal to one, two, or greater than two, respectively. |
