Scheduling of railway track maintenance activities and crews
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Scheduling of railway track maintenance activities and crews A Higgins CSIRO Tropical Agriculture, Australia Before railway track maintenance crews can undertake any work, the allocation of activities to available time intervals in the train schedule as well as to crews must be undertaken. This paper puts forward a model aimed at determining the best allocation of maintenance activities and crews so as to mininise the disruption to and from scheduled trains and to reduce completion time. The model is subject to constraints such as available budget; maintenance activity precedence; track availability; and minimum travel time between track links. Solution to the model is found using the tabu search heuristic for which the neighbourhood is de®ned by swapping the order of jobs, maintenance crews, or both. Application to a 300 km track corridor with a four day planning horizon is discussed along with the impacts of modifying the number of maintenance crews. The optimal schedule achieved an 8% reduction in expected interference delay with the train schedule and a 7% reduction in average completion times, relative to the solution which was constructed manually. Keywords: rail transport; maintenance; integer programming; scheduling; tabu search
Introduction In Australian freight operations, maintenance costs comprise between 25 and 35% of total train operating costs. Therefore, it is important that the track maintenance planning function is undertaken in an effective and ef®cient manner. This applies to short-term planning such as daily scheduling of activities, as well as the medium to long-term planning of required maintenance. The main applicability of a maintenance scheduling model is a decision support tool for track maintenance and train planners. The need for such a model is more pressing under single-track train operations, where trains can only pass or overtake each other at speci®ed locations (sidings). The occupancy of track segments due to maintenance prevents all train movements on those segments. Although urban rail is usually at least double line, the unavailability of a track can cause severe disruptions in peak period or if the other parallel track(s) are not bidirectional. The model of this paper involves scheduling maintenance activities to minimise disruptions to and from train services, and the amount of time a given track segment has a level of service below a speci®ed benchmark (for example speed restrictions imposed on trains due to poor track conditions). This latter aspect is achieved by scheduling each of the activities as early as possible. Different types of routine activities include: visual inspection; replacing sleepers; re-railing; rail grinding; ballast cleaning; and tamping. The resulting model is a 0-1 time dependent integer Correspondence: Dr A Higgins, CSIRO Tropical Agriculture, 306 Carmody Road, St. Lucia 4067, Australia. E-mail: [email protected]
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