Modeling and Solving the Rail Fleet Sizing Problem with Multiple Objectives and Heterogeneous Fleet Using Metaheuristic Algorithms

In the rail fleet Sizing problem, it is aimed to determine the optimal number of each vehicle type in transportation fleet, while optimizing system objectives. This issue has been investigated as a single-objective problem in the context of rail transportation with the assumption of homogeneity in the fleet, despite the existence of different goals in real systems. In this paper, a dual objective function is adopted after studying real-world consideration. According to the experts at the IslamicRepublic of Iran Railway Company (IRIR), reduction of the number of delays in response to requests during the course of planning is an important additional objective function, which is included in our model. The solved problem is dynamic and demands for wagons and the transportation times are assumed to be deterministic. In this paper, after presenting the mathematical model, the importance factor of each objective function is calculated taking into account theprescriptions of the experts at the IRIR Research Center and based on aggregate weighting method. In order to solve the model and find the solutions on the Pareto front, three methods based on Genetic Algorithms, Simulated Annealing, and a hybrid of those are designed and their parameters tuned, by which the rail transportation system of the IRIR is solved and the results are discussed.