Simulation-Based Optimization in a Bidirectional $A/B$ Skip-Stop Bus Service

A two-way bus corridor system always suffers severe demand imbalance between their two operational directions during the peak hours. This paper intends to minimize the average passenger travel time by applying the A/B skip-stop strategy in such an imbalance situation. This strategy defined three types of stations: A, B, and AB. In the service, the buses depart alternately from the original station as type A and B, and A (or B) buses serve A (or B) stations, as well as AB stations. Then the problem becomes determining the skip-stop patterns for both directions. A heuristic genetic algorithm is adopted to solve this problem with a kernel of a precise simulation model depicting the bus system. Finally, we apply the optimization method to a realistic bus corridor of BRT line 1 in Beijing, China. Results demonstrate that the bidirectional A/B skip-stop service prevails over the unidirectional services applying A/B skip-stop only on one direction, and the common used regular service visiting all stations. It is certificated that the bidirectional skip-stop service reduces bus bunching, yields a more balanced bus load and provides a smooth bus service with lower cycle time and variability. Moreover, a sensitivity analysis is conducted to show the impacts of some key attributes on potential benefits of bidirectional skip-stop service. Finally, the elastic demand case where transferring passengers may change their origins or destinations has been discussed.