Scheduling of maintenance work of a large-scale tramway network

For a public transport network preventive maintenance tasks have to be performed periodically to ensure a functioning system. The tasks include costly ones like replacing rails but also cheaper and more frequent ones like grinding. This paper deals with the strategic scheduling of these tasks for a large-scale network and a planning horizon of up to three decades. This planning also requires the consideration of side-effects like the implementation of replacement services with buses if some segments have to be blocked for the maintenance work, or speed restrictions if the replacement of tracks is overdue. The problem is first formulated as a mixed integer programming model which can be solved via commercial solvers. However, its limitations are revealed when it comes to large real-life problems with a long planning horizon. For this purpose, a metaheuristic based on large neighborhood search is developed. The approach is applied to the Viennese tramway network in a case study.