TACTICAL DESIGN OF RAIL FREIGHT NETWORKS .1. EXACT AND HEURISTIC METHODS

The tactical planning of rail freight networks is studied with the hel p of non-convex optimization models which are difficult to solve using only exact methods. For this reason it is necessary to use heuristic methods to obtain the solution for realistic networks. In this paper, local search and Branch and Bound methods are compared. In Part I, the model and the methods are defined and tested. In Part II, the methods are compared among one another using statistical analysis. The proble m is to decide the optimal assignment of the trains to the service net work and simultaneously assign the demand of cars to the routes. The f ormulation includes some features such as car transfer and classificat ion, different capacities and a limited fleet of trains available for use. Different heuristics have been developed to obtain the solution f or the proposed model: Simulated Annealing, Tabu Search and a particul ar heuristic that will be mentioned with the name of 'Descending'. The objective function becomes piece-wise linear if the investment cost t o purchase trains is considered. For small size networks a reformulati on of the problem is studied to compare the heuristic approaches with the exact solution provided by Branch and Bound. To solve large networ ks, only heuristic methods can be used.