Optimal Scheduling of Connections in Railway Systems

Complex railway networks typically consist of widely diffused OD-pairs by which it is impossible to provide direct trips only. Therefore, passengers often have to change trains at transfer stations. Guaranteeing scheduled connections is complicated by delays during operation. To improve and maintain the quality of transfers requires optimal scheduling and control of connections at transfer stations. For this, feeder and distributing lines are identified that have to be synchronized to give good connections. Here, synchronization is the mutual adjustment of the arrival and departure times of individual trains of connecting lines at a transfer station. Optimal synchronization is obtained when the average waiting time of the transferring passengers is as small as possible. This paper deals with the computation of optimal buffer times in timetables at scheduled connections. These connection buffer times reduce arrival delays of trains at transfer stations during operation and improves the reliability of the connections. The optimal buffer time is computed by minimization of the total expected transfer waiting time of passengers at a transfer station. Both the uncertainty in the trip times between stations and the operational control of connections is explicitly incorporated. Additionally, several transfer quality measures are derived from the obtained expressions for the optimal connection buffer time.