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Diffusion-Based Planning for Autonomous Driving with Flexible Guidance
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Proposes Diffusion Planner, a DiT-based transformer that jointly generates ego and neighbor trajectories via a diffusion objective and uses training-free classifier guidance for safe, adaptable closed-loop planning on nuPlan and a 200-hour delivery-vehicle dataset.
Problem
Learning-based autonomous driving planners struggle to model multi-modal human driving behavior, rely on rule-based refinement for safety, and are hard to adapt post-training to safety or personalized driving preferences.
Approach
Model planning and neighbor prediction jointly as a diffusion trajectory generation task with a DiT-style transformer, and inject safety/comfort/speed preferences at inference via differentiable energy-based classifier guidance, without retraining or rule-based post-processing.
Key results
- Achieves 89.19 non-reactive score on nuPlan Test14 and 82.93 reactive on Test14 among learning-based planners, outperforming PLUTO w/o refine. (89.90 NR) is close but PlanTF scores lower.
- With refinement module, Diffusion Planner w/ refine. reaches 94.80 NR on Test14, surpassing rule-based and hybrid baselines.
- On the delivery-vehicle dataset, Diffusion Planner scores 92.08 versus 90.89 for PlanTF and 87.77 for PLUTO w/o refine.
- Inference runs at about 20 Hz on a single A6000 GPU with 10 denoising steps.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add post-processing refinement | Diffusion Planner · nuPlan closed-loop benchmarks | score: 89.87 -> 94.26; 82.80 -> 92.90; 75.99 -> 78.87; 69.22 -> 82.00; 89.19 -> 94.80; 82.93 -> 91.75 | Mixed |
| Remove z-score normalization (ablation) | Diffusion Planner · nuPlan | closed-loop planning performance | Hurt |
| Remove data augmentation (ablation) | Diffusion Planner · nuPlan | closed-loop planning performance | Hurt |
| Remove interpolation after perturbing the current state (ablation) | Diffusion Planner · nuPlan | closed-loop planning performance | Hurt |
| Retain ego velocity, acceleration, and yaw rate (ablation) | Diffusion Planner · nuPlan | planning capability | Hurt |
| Use a state dropout encoder instead of directly discarding ego velocity, acceleration, and yaw rate (ablation) | Diffusion Planner · nuPlan | planning capability | Hurt |
| Remove current state information from the decoder (ablation) | Diffusion Planner · nuPlan | planning capability | Hurt |
| Increase the number of predicted neighboring vehicles too much (ablation) | Diffusion Planner · nuPlan | ego vehicle performance | Hurt |
| Use low-temperature sampling (ablation) | Diffusion Planner · nuPlan inference | trajectory stability | Helped |
Surprising findings
- Learning-based Diffusion Planner without refinement does not clearly beat PLUTO w/o refine. on the nuPlan Test14 non-reactive score (89.19 vs 89.90).
- Existing diffusion planners such as STR2-CPKS-800M and Diffusion-es degrade substantially without LLM filtering or rule-based refinement.
Limitations
- Relies on vectorized map and detected neighbor inputs rather than end-to-end sensor inputs.
- Weak lateral flexibility and lane-change behavior due to straight-driving-dominated data.
- Multiple denoising inference steps reduce sample efficiency compared with single-pass planners.
Experimental setup
Datasets: nuPlan delivery-vehicle driving dataset (200 hours)
Benchmarks: nuPlan Val14 nuPlan Test14 nuPlan Test14-hard delivery-vehicle driving dataset
Metrics: nuPlan closed-loop score collisions TTC drivable area compliance comfort progress
Baselines: IDM PDM-Closed PDM-Hybrid PDM-Open UrbanDriver GameFormer PlanTF PLUTO Diffusion-es STR2-CPKS-800M
Builds on: DiT classifier guidance DPM-Solver PDM diffusion posterior sampling
Closest papers by meaning
- Diffusion-ES: Gradient-free Planning with Diffusion for Autonomous and Instruction-guided Driving (CVPR 2024 · similarity 0.91)
- Flow Matching-Based Autonomous Driving Planning with Advanced Interactive Behavior Modeling (NeurIPS 2025 · similarity 0.88)
- SAH-Drive: A Scenario-Aware Hybrid Planner for Closed-Loop Vehicle Trajectory Generation (ICML 2025 · similarity 0.88)
- ChainFlow-VLA: Causal Flow Planning with Vision-Language Models (NeurIPS 2026 · similarity 0.88)
- DiffusionDrive: Truncated Diffusion Model for End-to-End Autonomous Driving (CVPR 2025 · similarity 0.88)
- Beyond Self-Play and Scale: A Behavior Benchmark for Generalization in Autonomous Driving (NeurIPS 2026 · similarity 0.87)
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