Optimization Of Locomotive Utilization

Locomotive utilization is mainly concerned with assigning a set of locomotives to scheduled trains to meet both the horsepower and tonnage requirements.An optimized locomotive movement is crucial to transportation production efficiency,especially in the situation where the locomotives are insufficient,which is common in many developing countries.At Zambia Railways Limited(ZRL),the locomotive problem is caused by the daily movement of locomotive between ODs to pull freight cargo,due to several related constraints.Currently,planners at ZRL assign the locomotive manually through a timeconsuming process without considering their optimization and other factors such as tonnage requirement,horsepower requirement,and the imbalance created by onedirectional locomotive movement.In some instances,the single locomotive coupled to a freight train can develop a fault that ends up blocking other trains.The travel time and costs related will eventually increase resulting in customers opting for the alternative road freight transport in turn ZRL losing customers and revenues.To solve this problem,this study introduced a mixed linear integer programming model to optimize the locomotives utilization using ZRL as a case study.A network model is constructed that depicts the locomotive utilization that flows between origin and destination stations in the active and light traveling train arcs.The objective function of the model is to minimize the costs associated with an active and light traveling locomotive and the penalty for assigning a single locomotive to pull a loaded freight train between stations.The proposed MILP has been encoded into CPLEX12.1 optimizer and solved with data from ZRL for a period of 24 hrs.Using CPLEX,a solution approach that was developed solved the problem within 2minutes of computational time.The optimized results from the MILP model are compared with the manual operation currently being practiced,a saving of locomotive utilized,and an efficient way of assigning locomotives to trains was obtained.The savings realized can be translated into a considerable amount of money for the organization.