Enhancing the interaction of railway timetabling and line planning with infrastructure awareness

Planning a railway system is done in multiple stages that are typically intractable to optimize in an integrated manner. This work develops a novel iterative approach to tackle two of these stages jointly: line planning and timetabling. Compared to existing approaches that iteratively ban a whole conflicting line plan when the timetable is found infeasible, our method can accurately identify the smallest set of incompatible services. Besides, by efficiently exploiting the available railway infrastructure, our method accounts for all the possible routing options of trains, a feature commonly neglected to reduce complexity but that helps gaining timetable feasibility. Using real data from a railway company in Switzerland, we find that our approach is (i) practical for solving real-life instances, (ii) an order of magnitude faster than existing benchmarks, and (iii) able to solve more instances. Our insights shed light on the necessity of considering infrastructure and banning conflicts rather than line plans in the joint line planning and timetabling problem.