Learning to drive from naturalistic trajectories: Offline reinforcement learning for safe speed guidance at signalized intersections 

This study proposes an offline reinforcement learning framework based on Critic Regularized Regression (CRR) to optimize speed guidance at signalized intersections under mixed traffic conditions. Using real-world trajectory data combined with signal phase and timing (SPaT) information, the framework learns safe and efficient driving policies without requiring online interactions. A structured data-processing pipeline converts raw vehicle trajectories into Markov Decision Process (MDP) format, effectively encoding vehicle motion states and signal timing information to facilitate realistic decision-making. SUMO simulation experiments demonstrate substantial improvements over rule-based baselines in safety, comfort, and efficiency: time-to-collision increases from 2.75 to 8.53 seconds, jerk is reduced by over 50%, and time headway is consistently maintained at approximately 1.68 seconds. Trajectory visualizations confirm smoother and more adaptive driving behavior. Comparisons with state-of-the-art approaches including Model Predictive Control (MPC), Behavior Cloning (BC), Twin Delayed Deep Deterministic Policy Gradient (TD3), and Batch Constrained Q-learning (BCQ) highlight CRR's stable performance across multiple evaluation metrics. Ablation studies reveal the critical role of different components in ensuring robust policy behavior, while communication loss simulations demonstrate framework resilience. The method's computational efficiency, requiring considerably less time than MPC, and robustness to communication failures reinforce its practicality for real-time deployment.