Line Change Considerations Within a Time-Space Network Based Multi-Depot Bus Scheduling Model

Abstract

The vehicle scheduling problem, arising in public transport bus companies, addresses the task of assigning buses to cover a given set of timetabled trips. It considers additional requirements, such as multiple depots for vehicles and vehicle type groups for timetabled trips as well as depot capacities. An optimal schedule is characterized by minimal fleet size and minimal operational costs including costs for unloaded trips and idle time spent outside the depot. This paper discusses the multi-depot, multi-vehicle-type bus scheduling problem for timetabled trips organized in bus lines. We use time-space-based networks for problem modeling. The cost-optimal vehicle schedule may involve several line changes for a given bus within a working day which might not be desirable from the practical point of view. Some bus companies prefer to pose a restriction for bus line changes as well. Because the network flow based model works with trips and not lines, it does not explicitly take into account line changes. In this contribution, we discuss several methods to find schedules with an acceptable number of line changes.