Robust Control for Regulating Frequent Bus Service: Supporting the Implementation of Headway-Based Holding Strategies

Reliability is a key determinant of the quality of a transit service. Control is needed to deal with the stochastic nature of high-frequency bus services and to improve service reliability. This study focuses on holding control, both schedule- and headway-based strategies. An assessment framework is developed to systematically assess the effect of different strategies on passengers, the operator, and the transport authority. This framework can be applied by operators or authorities to determine which holding strategy is most beneficial to regulate headways, and thus solve related problems. In this research knowledge is gained about what service characteristics affect the performance of holding strategies and the robustness of these strategies in disrupted situations, by using scenarios. The framework is applied to a case study of a high-frequency regional bus line in the Netherlands. Based on the simulation results, the study identified the line characteristics that are important for the performance of schedule- and headway-based strategies and determined how robust different strategies are in the case of disruptions. Headway-based control strategies better mitigate irregularity along the line, especially when there are disruptions. However, schedule-based control strategies are currently easier to implement, because they do not require large changes in practice, and the performance of both strategies is generally equal in regular, undisrupted situations. In this paper, insights into what the concerns are for operators with respect to technical adaptations, logistical changes, and behavioral aspects when using a headway-based strategy are given.