Abstract
This paper concerns a case study for optimal planning and coordination of railway maintenance windows and train traffic. The purpose is to validate a previously presented optimization model on a demanding real-life problem instance and to obtain results that apply in similar planning situations. A mixed integer linear programming model is used for a 913 km long, single-track railway line through the northern part of Sweden, with traffic consisting of 82 trains per day, most of which are freight trains. Cyclic 1-day schedules are produced, which show that 2 h long maintenance windows can be scheduled with small adjustments of the train traffic. The sensitivity for cost changes is studied, which shows that the train costs must increase by more than 30% in order to change the structure of the window solutions. Resource efficient window schedules are obtained by assigning maintenance teams to all windows while respecting crew work and rest time restrictions. A comparison with manually constructed plans from the Swedish Transport Administration indicates that larger window volumes can be scheduled at a lower cost and with solution structures which are deemed reasonable and useful as guidance for constructing the real window patterns. Finally, we estimate that using an integrated planning approach (where maintenance and trains are jointly planned) instead of a sequential approach (where a train timetable has precedence over the maintenance windows), will give maintenance cost savings of 11–17%, without incurring any large cost increases for the train traffic. The paper also presents a method for achieving cyclic schedules without any period-deciding variables, and discusses the consequences of the aggregated capacity usage model that has been adopted.
Highlights
Introduction and motivationRailway infrastructure maintenance consumes large budgets, is complicated to organize and has numerous challenging planning problems (Lidén 2015)
From previous computational results (Lidén et al 2018), we got an indication of the solution times that can be expected in our case study
We address the coordination of maintenance windows and train traffic as an optimization problem for a railway network
Summary
Railway infrastructure maintenance consumes large budgets, is complicated to organize and has numerous challenging planning problems (Lidén 2015). The monetary volumes cited above indicate a large potential for a more efficient use of maintenance spendings if the coordination with train traffic can be improved, there are few research publications that treat such joint scheduling problems. We present a case study for a real-life problem instance concerning the main railway line through the northern part of Sweden, which is over 900 km long, mostly single-track, and has over 80 trains per day, predominantly freight trains. The purpose of the case study is to (a) validate the model on a real and demanding planning problem, and to (b) obtain results that apply for similar railway lines.
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