Simultaneous locomotive and car assignment at VIA Rail Canada

In this paper, we present a sophisticated model and a heuristic solution ap proach based on mathematical optimization for the assignment of locomotives and cars to passenger trains. Given a periodic schedule and a fleet compos ed of several types of locomotives and cars, our approach determines a set of equipment cycles that cover all scheduled trains while satisfying a numb er of operational constraints. We first present a basic formulation that tr anslates maintenance requirements and other fundamental difficulties of the problem. We then discuss several extensions, such as substitution possibil ities and the minimization of switching operations, which are required in a real-life application. The resulting model is optimized through a branch-a nd-bound method in which the linear relaxations are solved by column genera tion. The model and solution strategy were tested on data from VIA Rail in Canada and a complete system based on this approach is now implemented at t he company. (C) 2001 Elsevier Science Ltd. All rights reserved.