Maintenance routing for train units: The transition model

Train units need regular preventive maintenance. Given the train units that require maintenance in the forthcoming 1–3 days, the rolling stock schedule must be adjusted so that these urgent units reach the maintenance facility in time. In an earlier paper Maróti and Kroon propose a model that requires a large amount of input data. In this paper we describe a less involved multicommodity flow type model for this maintenance routing problem. We study the complexity of the problem. It turns out that the feasibility problem for a single urgent train unit is polynomially solvable but the optimisation version is NP-hard. Finally, we report our computational experiments on practical instances of NS Reizigers, the main Dutch operator of passenger trains.