Modelling aspects of rail track maintenance scheduling

There are significant productivity gains to be realised in track maintenance through capital expenditure in both the maintenance task itself ( e.g. mechanisation), and by moving to higher quality, lower maintenance track. However, there is also a need to ensure that maintenance of existing networks is undertaken according to a plan which maximises overall net benefit to the rail operator. In Australian freight operations, maintenance costs comprise between 25 -35 percent of total train operating costs. Therefore, it is important that the track maintenance planning function is undertaken in an effective and efficient manner. This applies to short-term planning such as daily scheduling of projects; as well as the medium to long-term planning of required maintenance projects. Maintenance activities can be conveniently classified into routine, spot and production activities. Routine activities are those which are insensitive to volume of the traffic. They are usually carried out at regular intervals and include the following: vegetation control; repair of fences, gates, signs and posts; herbicide application; and routine inspections. The main purpose of spot maintenance is to maintain track in its existing state. The activities are usually carried out whenever defects are identified by manual or automated inspections. They include the following: spot replacement of minor track components, sleepers and short rail sections; repair of joints and weldings; spot ballast packing; and spot stone blowing. Production maintenance refers to activities which have a significant impact on track condition. They include the following: tamping; stone blowing; ballast regulation, stabilization and cleaning; rail grinding; re-sleepering; and re-railing. Track maintenance policies have traditionally been viewed as engineering led decisions. There is a need to focus effort into the development of tools to assist track maintenance planning in the context of maximising the overall net financial benefit to rail users. This overall aim can be achieved by using well established Operations Research techniques, together with engineering judgement. The track maintenance scheduling problem, which involves the allocation of maintenance projects to time windows and crews to projects, is formulated here as an integer programming model. The model presented here was applied to a 89 km track corridor on the eastern coast of Australia. A four day planning horizon was used for which the model was used to test proposed changes including re-scheduling trains and changing the number of maintenance crews. Increasing the time window by moving less important trains was shown to reduce potential delays significantly. The model is mainly aimed at providing for an 'off-line' planning function. However, the same model could be used by local track managers and train planners in real-time so that adjustments could be made to a planned schedule of projects in the light of unplanned train services or train cancellations. Such a system would need to be integrated into a train dispatching real-time database