A mathematical programming model to select maintenance strategies in railway networks

A main challenge in railway asset management is the selection of long-term maintenance strategies to effectively manage the railway infrastructure given that performance and safety targets have to be met under budget constraints. Due to economic, functional and operational dependencies between different assets and sections of the network, optimal solutions at network level do not always include the best strategies available for each asset or section. This paper presents an optimisation model to support the selection of the maintenance strategies to implement on different regions of a railway network. The optimisation problem is formulated as a nonlinear integer programming model. The model is performance-oriented, it assumes that decisions are aimed at minimising the impact on service due to speed restrictions, while availability targets for different railway lines have to be met despite sections’ closure, and budget constraints have to be respected. The main contribution is to provide a simple yet effective modelling approach and solution method which are suitable for large networks and make use of standard solvers. Indeed both an heuristic solution and an ad hoc relaxation methods are developed, the latter enabling the quality of the heuristic solution to be estimated. The availability of railway lines is computed by exploiting the analogy with series-parallel networks. By varying the model parameters, a scenario analysis is performed so that the infrastructure manager is provided with a range of solutions for different combination of the available budget and performance targets. The results of the scenario analysis also enable a better understanding of the influence of the system parameters, including those related to the network topology.

This paper presents a nonlinear integer programming model to support the selection of maintenance strategies to implement on different segments of a railway network. Strategies are selected which collectively minimise the impact of sections’ conditions on service, given network availability and budget constraints. Different metrics related to the network topology, sections’ availability, service frequency, performance requirements and maintenance costs, are combined into a quantitative approach with a holistic view. The main contribution is to provide a simple yet effective modelling approach and solution method which are suitable for large networks and make use of standard solvers. Both an ad hoc heuristic solution and relaxation methods are developed, the latter enabling the quality of the heuristic solution to be estimated. The availability of railway lines is computed by exploiting the analogy with series–parallel networks. By varying the model parameters, a scenario analysis is performed to give insight into the influence of the system parameters on the selection of strategies, thus enabling more informed decisions. For its simple structure, the model is versatile to address similar problems arising in the maintenance of other types of networks, such as road and bridges networks, when deciding on the strategic allocation of maintenance efforts.