Public bus transit service modeling and optimization: from conventional to autonomous vehicles

• Main Author: Tian, Qingyun
• Other Authors: Wang Zhiwei
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Civil engineering::Transportation
• Online Access: https://hdl.handle.net/10356/154698
• Institution: Nanyang Technological University

Public transit is a cost-efficient and sustainable travel mode because of its huge capacity. A well-designed transit network can not only reduce the operation costs of operators but also reduce the travel time of passengers. This thesis mainly focuses on how to model and optimize the public transit service to improve system performance. In particular, this thesis studies the modeling and optimization of the transit system from three aspects: conventional transit service, mixed conventional and autonomous transit service, and autonomous modular transit service. In the first part, this thesis proposes a novel tri-level model for a transit service operation design problem that primarily determines the optimal bus line frequency setting. Unlike the existing studies, the strategy choices of passengers in presence of congested common lines are explicitly considered. To solve this problem, this thesis proposes two solution methods. One is to transform the originally nonconvex problem into a mixed-integer linear program, which can be solved to derive the global optimal solution of the linearized problem. Another is to adopt the surrogate optimization algorithm to solve more complex cases efficiently. The impacts of different parameters on the determination of transit frequencies are investigated. Motivated by the emerging autonomous vehicles, this thesis investigates the integration of autonomous vehicles into bus transit systems in the second part. Two studies are conducted. The first one proposes a multi-stage model to optimize the deployment of autonomous vehicles. The passengers' adoption rate is considered in the transit assignment problem, and the problem is formulated as a bi-level programming model. A metaheuristic approach is adopted to search for the optimal plan strategy. In the second study, this thesis proposes a modeling framework to determine the optimal bus fleet size and its assignment onto multiple bus lines in a bus service network considering uncertain demand. This study demonstrates that the introduction of autonomous buses would enable further reduction of the required fleets and total cost. The model formulation and solution methods proposed in this part can be used to provide bus transit operators with operational guidance on including autonomous buses into current bus services. The third part of this thesis focuses on a conceptually new autonomous transit service using modular vehicles. It first studies the optimal planning and the operational design of public transit services with modular vehicles. The planning decisions are to determine the locations of the specially constructed stations enabling station-wise assembling/dissembling of modular units. Meanwhile, the capacity of these stations will also be determined. Then this thesis extends the problem to consider the optimal scheduling and vehicle formation problem of a modular-vehicle transit service enabling docking/undocking operation corresponding to the dynamic demand. A mathematical model is proposed to determine the timetable and modular-vehicle formation/capacity on a single transit line in a dynamic demand environment, wherein, both vehicle formation-based operating costs and passengers' waiting costs under the over-saturated condition are considered. The numerical results demonstrate its service performance in significantly reducing the operating cost and passengers' travel time costs in the modular-vehicle transit system. In summary, this thesis contributes to the comprehensive modeling and optimization approaches for a sustainable bus transit system, providing decision support frameworks for both practitioners and researchers in the design and operation of public transit services.