Computers & Operations Research 34 (2007) 1121 – 1140 www.elsevier.com/locate/cor Maintenance routing for train units: The interchange model Gábor Maróti a , ∗ , Leo Kroon b a CWI, Amsterdam and NS Reizigers, Utrecht, P.O. Box 94079, 1090 GB Amsterdam, The Netherlands b NS Reizigers, Utrecht and Erasmus University, Rotterdam, P.O. Box 1738, 3000 DR Rotterdam,The Netherlands Available online 29 June 2005 Abstract 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 this paper, we present an integer programming model for solving this problem, give complexity results, suggest solution methods, and report our computational results based on practical instances of NS Reizigers, the main Dutch operator of passenger trains.  2005 Elsevier Ltd. All rights reserved. MSC: 90B06; 90B10; 90C35 Keywords: Railway transportation; Maintenance routing 1. Introduction The Dutch passenger railway operator NS Reizigers runs a number of train units in order to carry out its timetable services. These train units need regular preventive maintenance checks, say every 30,000km: units that traveled that far since their previous maintenance check must go to the maintenance facility. These checks are arranged by maintenance routing planners. They modify the regular rolling stock schedule so that the train units that need maintenance in the next couple of days arrive in time at a maintenance facility. As yet, NS Reizigers does not use a decision support system for supporting this maintenance routing process. The goal of this research is to provide mathematical programming models and solution methods ∗ Corresponding author. E-mail addresses: g.maroti@cwi.nl (G. Maróti), L.Kroon@fbk.eur.nl (L. Kroon). 0305-0548/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.cor.2005.05.026