A combined simulation-optimization approach for minimizing travel time and delays in railway timetables

•An approach to minimize the weighted sum of scheduled travel time and expected delays for a given timetable.•A macroscopic timetabling model using micro-simulation data to forecast reliability.•The approach extends timetable optimization with reliability estimates in the objective.•Experiments indicate improved benefit by 2–5% and improved punctuality by 8–25%. Minimal travel time and maximal reliability are two of the most important properties of a railway transportation service. This paper considers the problem of finding a timetable for a given set of departures that minimizes the weighted sum of scheduled travel time and expected delay, thereby capturing these two important socio-economic properties of a timetable. To accurately represent the complex secondary delays in operational railway traffic, an approach combining microscopic simulation and macroscopic timetable optimization is proposed. To predict the expected delay in the macroscopic timetable, a surrogate function is formulated, as well as a subproblem to calibrate the parameters in the model. In a set of computational experiments, the approach increased the socio-economic benefit by 2–5% and improved the punctuality by 8–25%.