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CarPlanner: Consistent Auto-regressive Trajectory Planning for Large-Scale Reinforcement Learning in Autonomous Driving
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Proposes CarPlanner, a consistent auto-regressive RL planner that conditions a PPO-trained trajectory generator on time-invariant longitudinal-lateral mode representations, achieving state-of-the-art closed-loop scores on nuPlan.
Problem
RL-based trajectory planning for autonomous driving suffers from training inefficiency and poor performance on large-scale real-world datasets such as nuPlan, and vanilla auto-regressive planners produce inconsistent multi-modal trajectories.
Approach
Condition an auto-regressive, model-based RL policy on a consistent (time-invariant) longitudinal-lateral mode representation, use an expert-guided displacement-error plus safety reward, an invariant-view module that makes policy inputs time-agnostic, and a rule-augmented selector at inference.
Key results
- On Test14-Random non-reactive, CarPlanner achieves CLS-NR 94.07 vs. 92.07-level PLUTO 91.92 and PDM-Closed 90.05 (improvement of 4.02 over PDM-Closed).
- On Reduced-Val14 non-reactive, CarPlanner achieves CLS-NR 91.45 and S-PR 95.37, surpassing PDM-Closed (91.21 CLS-NR, 92.68 S-PR) and Gen-Drive finetune (87.53).
- Reactive setting CLS-R 91.1 on Test14-Random, slightly below PDM-Closed (91.64); the authors attribute this to training only in non-reactive settings.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| use CarPlanner instead of PLUTO | CarPlanner · Test14-Random | CLS-NR: 91.92 -> 94.07 | Helped |
| use CarPlanner instead of PDM-Closed | CarPlanner · Test14-Random | CLS-R: 91.64 -> 91.1 | No clear effect |
| use CarPlanner instead of PDM-Closed | CarPlanner · Reduced-Val14 | CLS-NR: 91.21 -> 91.45 | Helped |
| use CarPlanner instead of PDM-Closed | CarPlanner · Reduced-Val14 | S-PR: 92.68 -> 95.37 | Helped |
| use CarPlanner instead of PDM-Closed | CarPlanner · Reduced-Val14 | S-CR: 97.01 -> 96.38 | Hurt |
| add quality reward alongside DE reward (ablation) | CarPlanner RL · Test14-Random non-reactive | S-CR: 97.49 -> 99.22 | Helped |
| add quality reward alongside DE reward (ablation) | CarPlanner RL · Test14-Random non-reactive | S-Area: 96.91 -> 99.22 | Helped |
| add DE reward alongside quality reward (ablation) | CarPlanner RL · Test14-Random non-reactive | CLS-NR: 31.79 -> 94.07 | Helped |
| add coordinate transformation to IVM (ablation) | CarPlanner RL · Test14-Random non-reactive | CLS-NR: 90.78 -> 94.07 | Helped |
| add KNN to IVM (ablation) | CarPlanner RL · Test14-Random non-reactive | CLS-NR: 92.73 -> 94.07 | Helped |
| add ego-history dropout (ablation) | CarPlanner IL · Test14-Random non-reactive | CLS-NR: 91.51 -> 92.72 | Helped |
| add ego-history dropout (ablation) | CarPlanner RL · Test14-Random non-reactive | CLS-NR: 94.07 -> 89.51 | Hurt |
Surprising findings
- Ego-history dropout helps IL training but degrades RL performance by harming advantage estimation.
- Backbone sharing between trajectory generator and selector helps IL but hurts RL training due to gradient interference.
Limitations
- RL relies on expert-guided reward design, which may constrain discovery of solutions beyond human expertise.
- Reactive-setting performance slightly below PDM-Closed because the model was trained only in non-reactive settings.
- RL can overfit training environments and degrade in unseen environments.
Experimental setup
Datasets: nuPlan
Benchmarks: nuPlan Test14-Random nuPlan Reduced-Val14
Metrics: CLS-NR CLS-R S-CR S-TTC S-Area S-PR S-Comfort
Baselines: IDM PDM-Closed PDM-Open RasterModel UrbanDriver GC-PGP GameFormer PlanTF PEP PLUTO Gen-Drive
Builds on: PPO PDM PlanTF PLUTO Gen-Drive
Closest papers by meaning
- GoIRL: Graph-Oriented Inverse Reinforcement Learning for Multimodal Trajectory Prediction (ICML 2025 · similarity 0.88)
- AdaWM: Adaptive World Model based Planning for Autonomous Driving (ICLR 2025 · similarity 0.87)
- Diffusion-Based Planning for Autonomous Driving with Flexible Guidance (ICLR 2025 · similarity 0.87)
- Beyond Self-Play and Scale: A Behavior Benchmark for Generalization in Autonomous Driving (NeurIPS 2026 · similarity 0.87)
- Drive-R1: Bridging Reasoning and Planning in VLMs for Autonomous Driving with Reinforcement Learning (AAAI 2026 · similarity 0.87)
- RAD: Training an End-to-End Driving Policy via Large-Scale 3DGS-based Reinforcement Learning (NeurIPS 2025 · similarity 0.87)
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