Core Viewpoint - The article discusses the application of reinforcement learning (RL) fine-tuning in trajectory planning for autonomous driving, emphasizing the transition from open-loop to closed-loop training methods to enhance the effectiveness of training models [3][4]. Group 1: Training Methodology - The mainstream planning modules based on learning typically use imitation learning, which can struggle with out-of-distribution scenarios during real-world testing [3]. - A closed-loop training approach is proposed, which simulates real vehicle testing environments, making it more effective than open-loop training [4]. - The article introduces a network structure based on Waymo's previous work, MotionLM, which outputs trajectories in an autoregressive manner, ensuring causal relationships are maintained [4][6]. Group 2: Input and Output Structure - The network's input is designed to be scene-centered, summarizing static information over a specified time frame rather than relying on the current frame alone, which helps prevent the vehicle from navigating outside the perceived road [6]. - Many imitation learning methods combine single-frame perception with ground truth (GT) data over several seconds, which can lead to causal inconsistencies if the perception range is limited [7]. Group 3: Reward Function and Training Phases - The training process consists of two phases: pretraining and reinforcement learning, with a simple reward function that balances efficiency and safety by considering both GT fitting and collision avoidance [11]. - The reward function is calculated by normalizing the rewards across all samples and time steps, allowing for the omission of a critic network, similar to the GRPO method [13]. Group 4: Challenges and Future Directions - The article notes that many imitation learning methods introduce auxiliary losses that can lead to undesirable model outputs, highlighting the limitations of open-loop training [14]. - The core value of reinforcement learning lies in closed-loop learning, which can significantly enhance model capabilities even with smaller datasets [14].