Control of robotic mobility-on-demand systems: A queueing-theoretical perspective

In this paper we present queueing-theoretical methods for the modeling, analysis, and control of autonomous mobility-on-demand (MOD) systems wherein robotic, self-driving vehicles transport customers within an urban environment and rebalance themselves to ensure acceptable quality of service throughout the network. We first cast an autonomous MOD system within a closed Jackson network model with passenger loss. It is shown that an optimal rebalancing algorithm minimizing the number of (autonomously) rebalancing vehicles while keeping vehicle availabilities balanced throughout the network can be found by solving a linear program. The theoretical insights are used to design a robust, real-time rebalancing algorithm, which is applied to a case study of New York City and implemented on an eight-vehicle mobile robot testbed. The case study of New York shows that the current taxi demand in Manhattan can be met with about 8,000 robotic vehicles (roughly 70% of the size of the current taxi fleet operating in Manhattan). Finally, we extend our queueing-theoretical setup to include congestion effects, and study the impact of autonomously rebalancing vehicles on overall congestion. Using a simple heuristic algorithm, we show that additional congestion due to autonomous rebalancing can be effectively avoided on a road network. Collectively, this paper provides a rigorous approach to the problem of system-wide coordination of autonomously driving vehicles, and provides one of the first characterizations of the sustainability benefits of robotic transportation networks.