Quantum computing approach to railway dispatching and conflict management optimization on single-track railway lines

We consider a railway dispatching problem: delay and conflict management on a single-track railway line. We examine the issue of train dispatching consequences caused by the arrival of an already delayed train to the segment being considered. This is a computationally hard problem and its solution is needed in a very short time in practice. We introduce a quadratic unconstrained binary optimization (QUBO) model of the problem that is suitable for solving on quantum annealer devices: an emerging alternative computational hardware technology. These offer a scalability of computationally hard problems better than that of classical computers. We provide a proof-of-principle demonstration of applicability through solving selected real-life problems from the Polish railway network. We carry out the actual calculation on the D-Wave 2000Q machine. We also include solutions of our model using classical algorithms for solving QUBO, including those based on tensor networks. These are of potential practical relevance in case of smaller instances and serve as a comparison for understanding the behavior of the actual quantum device.