Robust Integrated Priority and Speed Control based on Hierarchical Stochastic Optimization to Promote Bus Schedule Adherence along Signalized Arterial

In intelligent transportation systems (ITS), adaptive transit signal priority (TSP) and dynamic bus control systems have been independently developed to maintain efficient and reliable urban bus services. However, those two systems could potentially lead to conflicting decisions due to the lack of coordination. Although some studies explore the integrated control strategies along the arterial, they merely rely on signal replanning to address system uncertainties. Therefore, their performance severely deteriorates in real-world intersection settings, where abrupt signal timing variation is not always applicable in consideration of countdown timers and pedestrian signal design. In this study, we propose a robust integrated priority and speed control strategy based on hierarchical stochastic optimization to enhance bus schedule adherence along the arterial. In the proposed framework, the upper level ensures the coordination across intersections while the lower level handles uncertainties for each intersection with stochastic programming. Hence, the route-level system randomness is decomposed into a series of local problems that can be solved in parallel using sample average approximation (SAA). Simulation experiments are conducted under various scenarios with stochastic bus dwell time and different traffic demand. The results demonstrate that our approach significantly enhances bus punctuality and time headway equivalence without abrupt signal timing variation, with negative impacts on car delays limited to only 0.8%-5.2% as traffic demand increases.