Bus holding control strategies: a simulation-based evaluation and guidelines for implementation

Transit operations involve several inherent sources of uncertainty including dispatching time from the origin terminal, travel time between stops and dwell time at stops. Bus holding control strategies are among the prominent methods applied by transit operators in order to improve transit performance and level of service. The common practice is to regulate departures from a limited number of stops by holding buses until the scheduled time. An analysis of the performance of a high-frequency bus line in Stockholm based on Automatic Vehicle Location (AVL) data shows that this control strategy is not effective in improving service regularity along the line. It also indicates that drivers adjust their speed based on performance objectives. Implications of a control strategy that regulates departures from all stops based on the headways from the preceding bus and the following bus were evaluated using BusMezzo, a transit operations simulation model. The results suggest that this strategy can improve service performance considerably from both passengers and operators perspectives. In addition, it implies cooperative operations as the decisions of each driver are interdependent of other drivers with mutual corrections. The difficulties in realizing the benefits of the proposed strategy in practice such as dispatching from the origin terminal, driver scheduling and compliance are discussed. The implications of several practical considerations are assessed by conducting a sensitivity analysis as part of the preparations to a field experiment designed to test the proposed control strategy.