Optimization of service frequency and vehicle size for automated bus systems with crowding externalities and travel time stochasticity

•We develop a total cost minimization model to optimize service frequency and vehicle size for automated bus systems.•Crowding discomfort externalities, time-dependent demand, denied boardings, and stochastic travel times are modeled.•An application-focused study offering an extensive evaluation of the service and cost implications of the deployment of automated buses.•Extensive experiments are performed for two real-life case studies in Germany and Chile, and numerical results are widely analyzed.•In the presence of crowding discomfort externalities, the frequency is increased at a higher rate for automated bus fleets than for human-driven bus fleets.•The deployment of automated bus systems can significantly mitigate crowding-related problems for users. Public transport is considered as one of the most suitable candidates to benefit from autonomous driving technologies. In this research, we develop a mathematical modeling framework to optimize service frequency and vehicle size for automated bus systems, while accounting for both user and operator costs. We explicitly consider travel time stochasticity, time-dependent passenger flows, vehicle capacity limitations (extra waiting time due to denied boarding), and in-vehicle discomfort externalities for both sitting and standing passengers at a microscopic level. We attempt to provide a thorough assessment of the service and cost implications of the deployment of automated buses. Hence, a broad range of experiments are simulated by combining different deployment cases: (i) vehicle technology (human-driven or automated vehicles), (ii) travel time assumptions (deterministic or stochastic travel times), and (iii) crowding externalities (considering or ignoring in-vehicle crowding costs). The model applicability is assessed on two real-world bus corridors in Regensburg (Germany) and Santiago (Chile). Results show that, with crowding externalities, optimal vehicle size is increased at a similar rate for both human-driven and automated bus services, whereas optimal service frequency is increased at a higher rate for automated buses. Thus, under optimal levels of supply, automated vehicles are operated with lower occupancy levels than human-driven vehicles, increasing the quality of service. Besides, the deployment of automated bus systems can significantly alleviate or eliminate denied boardings. The effects of automation on travel time volatility and dwell time regularity are studied. The consideration of stochas