Optimization modelling and methods for freight transportation in scheduled railways

Abstract: In the planning process of a freight railway transportation company, a number of optimization problems arise. In this thesis, we study two of them; empty freight car distribution and line planning.The empty freight car distribution process is the planning and realization of empty freight car movement in order to remedy spatial imbalances of cargo flows. An efficient utilization of empty cars helps keeping investment costs low. One objective of the empty freight car distribution process is to group empty cars in suitable blocks. In this context, the multicommodity network flow problem with fixed path costs is applicable. The problem is a difficult mixed integer programming problem, and we develop and implement a Lagrangean heuristic for solving the problem. Numerical results are also presented.Line planning is the first stage in the process of making a time table. The aim is to decide paths for trains to follow, and frequencies with which trains run in the paths. A model for the line planning problem for freight transportation in scheduled railways is presented. We also present a mode! for a special case of this problem where only direct trains are used. For the mode! in the direct train case of line planning. two heuristics are developed and evaluated: the first one is a rounding heuristic and the other is a tabu search algorithm.