Robust Optimal Control Method to Improve Bus Schedule Adherence Considering Stochastic Bus Operations under Mixed Traffic

Mixed traffic often results in large deviations in bus schedules due to the influence of stochastic factors on bus operations. In order to improve bus schedule adherence, signal priority is often employed at signalized intersections by adjusting signal timing. However, traditional deterministic optimization methods that treat bus travel time as a constant are not effective in meeting the challenges posed by changes in bus operations. To address these limitations, this paper proposes a robust signal priority control method that aims to improve the reliability of bus operations. However, because of the limited adjustable range of signal timing, signal control used independently only works a little in large bus headways. In order to further enhance control performance, bus holding is introduced in this study, leading to the development of an integrated robust signal priority and holding control (RHC) method. The RHC method improves bus schedule adherence and reliability in bus operations and is designed based on a bus schedule deviation model that takes stochastic bus speed and the number of queuing vehicles at intersections into account under mixed traffic. Through simulation experiments, the effectiveness of the proposed calculation models is verified. Furthermore, the RHC method can boost bus schedule adherence by 38% while limiting the negative impact on car delays to only 3%.