Tree-structured Policy Planning with Learned Behavior Models

TL;DR

This paper introduces Tree Policy Planning (TPP), a scalable, interpretable policy planning method for autonomous vehicles that accounts for multimodal agent behaviors and improves over existing approaches.

Contribution

We propose TPP, a novel tree-structured policy planner compatible with deep learning models, enabling multistage motion planning and interaction-aware decision making for AVs.

Findings

TPP scales effectively to realistic AV scenarios.

TPP significantly outperforms non-policy baselines.

Demonstrated success in real-world nuScenes dataset simulations.

Abstract

Autonomous vehicles (AVs) need to reason about the multimodal behavior of neighboring agents while planning their own motion. Many existing trajectory planners seek a single trajectory that performs well under \emph{all} plausible futures simultaneously, ignoring bi-directional interactions and thus leading to overly conservative plans. Policy planning, whereby the ego agent plans a policy that reacts to the environment's multimodal behavior, is a promising direction as it can account for the action-reaction interactions between the AV and the environment. However, most existing policy planners do not scale to the complexity of real autonomous vehicle applications: they are either not compatible with modern deep learning prediction models, not interpretable, or not able to generate high quality trajectories. To fill this gap, we propose Tree Policy Planning (TPP), a policy planner that is compatible with state-of-the-art deep learning prediction models, generates multistage motion plans, and accounts for the influence of ego agent on the environment behavior. The key idea of TPP is to reduce the continuous optimization problem into a tractable discrete Markov Decision Process (MDP) through the construction of two tree structures: an ego trajectory tree for ego trajectory options, and a scenario tree for multi-modal ego-conditioned environment predictions. We demonstrate the efficacy of TPP in closed-loop simulations based on real-world nuScenes dataset and results show that TPP scales to realistic AV scenarios and significantly outperforms non-policy baselines.