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In this paper a bottom-up approach of automatic simplification of a railway network is presented. Starting from a very detailed, microscopic level, as it is used in railway simulation, the network is transformed by an algorithm to a less detailed level (macroscopic network), that is sufficient for long-term planning and optimization. In addition running and headway times are rounded to a pre-chosen time discretization by a special cumulative method, which we will present and analyse in this paper. After the transformation we fill the network with given train requests to compute an optimal slot allocation. Then the optimized schedule is re-transformed into the microscopic level and can be simulated without any conflicts occuring between the slots. The algorithm is used to transform the network of the very dense Simplon corridor between Swiss and Italy. With our aggregation it is possible for the first time to generate a profit maximal and conflict free timetable for the corridor across a day by a simultaneously optimization run.
This paper presents a case study on a railway timetable optimization for the very dense Simplon corridor, a major railway connection in the Alps between Switzerland and Italy. Starting from a detailed microscopic network as it is used in railway simulation, the data is transformed by an automatic procedure to a less detailed macroscopic network, that is sufficient for the purpose of capacity planning and amenable to state-of-the-art integer programming optimization methods. In this way, the macroscopic railway network is saturated with trains. Finally, the corresponding timetable is re-transformed to the microscopic level in such a way that it can be operated without any conflicts among the slots. Using this integer programming based micro-macro aggregation-disaggregation approach, it becomes for the first time possible to generate a profit maximal and conflict free timetable for the complete Simplon corridor over an entire day by a simultaneous optimization of all trains requests. This also allows to to undertake a sensitivity analysis of various problem parameters.
Railway Track Allocation
(2012)
This article gives an overview of the results of the author's PhD thesis. The thesis deals with the
mathematical optimization for the efficient use of
railway infrastructure. We address the optimal allocation of the available
railway track capacity - the track allocation problem. This track allocation
problem is a major challenge for a railway company, independent of whether
a free market, a private monopoly, or a public monopoly is given. Planning
and operating railway transportation systems is extremely hard due to the
combinatorial complexity of the underlying discrete optimization problems,
the technical intricacies, and the immense sizes of the problem instances.
Mathematical models and optimization techniques can result in huge gains
for both railway customers and operators, e.g., in terms of cost reductions or
service quality improvements. We tackle this challenge by developing novel
mathematical models and associated innovative algorithmic solution methods
for large scale instances. We made considerable progress on solving track
allocation problems by two main features - a novel modeling approach for the
macroscopic track allocation problem and algorithmic improvements based on the
utilization of the bundle method. This allows us to produce for the first time reliable solutions for a real world instance, i.e., the Simplon corridor in Switzerland.