Safe and scalable planning under uncertainty for autonomous driving

Autonomous driving has the potential to significantly improve safety. Although progress has been made in recent years to deploy automated driving technologies, many situations handled on a daily basis by human drivers remain challenging for autonomous vehicles, such as navigating urban environments. They must reach their goal safely and efficiently while considering a multitude of traffic participants with rapidly changing behavior. Hand-engineering strategies to navigate such environments requires anticipating many possible situations and finding a suitable behavior for each, which places a large burden on the designer and is unlikely to scale to complicated situations. In addition, autonomous vehicles rely on on-board perception systems that give noisy estimates of the location and velocity of others on the road and are sensitive to occlusions. Autonomously navigating urban environments requires algorithms that reason about interactions with and between traffic participants with limited information. This thesis addresses the problem of automatically generating decision making strategies for autonomous vehicles in urban environments. Previous approaches relied on planning with respect to a mathematical model of the environment but have many limitations. A partially observable Markov decision process (POMDP) is a standard model for sequential decision making problems in dynamic, uncertain environments with imperfect sensor measurements. This thesis demonstrates a generic representation of driving scenarios as POMDPs, considering sensor occlusions and interactions between road users. A key contribution of this thesis is a methodology to scale POMDP approaches to complex environments involving a large number of traffic participants. To reduce the computational cost of considering multiple traffic participants, a decomposition method leveraging the strategies of interacting with a subset of road users is introduced. Decomposition methods can approximate the solutions to large sequential decision making problems at the expense of sacrificing optimality. This thesis introduces a new algorithm that uses deep reinforcement learning to bridge the gap with the optimal solution. Establishing trust in the generated decision strategies is also necessary for the deployment of autonomous vehicles. Methods to constrain a policy trained using reinforcement learning are introduced and combined with the proposed decomposition techniques. This method allows to learn policies with safety constraints. To address state uncertainty, a new methodology for computing probabilistic safety guarantees in partially observable domains is introduced. It is shown that the new method is more flexible and more scalable than previous work. The algorithmic contributions present in this thesis are applied to a variety of driving scenarios. Each algorithm is evaluated in simulation and compared to previous work. It is shown that the POMDP formulation in combination with scalable solving methods provide a flexible framework for planning under uncertainty for autonomous driving

Keywords: Aeronautics and Astronautics.
Advisor: Kochenderfer Mykel J.
Pavone Marco
Sadigh Dorsa