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CoC-VLA: Delving into Adversarial Domain Transfer for Explainable Autonomous Driving via Chain-of-Causality Visual-Language-Action Model
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Proposes CoC-VLA, an adversarial sim-to-real transfer framework where a simulation-trained teacher VLM and a real-data student VLM (both CoC VLMs built on LLaVA-7b) are aligned via a discriminator, evaluated on nuScenes-VLM.
Problem
Autonomous driving VLMs trained on real-world data miss rare long-tail cases, while simulation-trained models suffer a domain gap and cannot be deployed directly; the paper targets transferring long-tail handling from simulation to real-world driving with explainable chain-of-causality answers.
Approach
Teacher and student CoC VLMs share an architecture, with a lightweight text adapter that feeds the previous frame's simplified answer into the next prompt; a transformer discriminator on their features is trained adversarially in two steps, with gradients passed through the discriminator to update the student VLM.
Key results
- On nuScenes-VLM VQA, the proposed LLaVA-7b model reaches BLEU-4 58.84, ROUGE-L 71.70, CIDEr 23.21 and SPICE 51.88, versus DriveLM's 55.13, 68.32, 3.62 and 48.95 (reproduced).
- Open-loop planning on nuScenes-VLM gives ADE 1.44 and collision rate 1.58%, improving on the FinetuneTwice variant (1.60, 1.73) and on DriveLM (1.71, 1.87).
- Training the teacher only on simulation and testing on real-world data gives ADE 17.33, showing a large sim-to-real gap before adversarial transfer.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use CoC-VLA instead of DriveLM | LLaVA-7b autonomous driving on nuScenes-VLM · nuScenes-VLM | ADE: 1.71 -> 1.44 | Helped |
| Use CoC-VLA instead of DriveLM | LLaVA-7b autonomous driving on nuScenes-VLM · nuScenes-VLM | Collision Rate (%): 1.87 -> 1.58 | Helped |
| Use CoC-VLA instead of DriveLM | VQA on nuScenes-VLM · nuScenes-VLM | BLEU-4: 55.13 -> 58.84 | Helped |
| Use CoC-VLA instead of DriveLM | VQA on nuScenes-VLM · nuScenes-VLM | CIDEr: 3.62 -> 23.21 | Helped |
| Train on simulation and real-world data sequentially, rather than real-world data only (ablation) | Student VLM · nuScenes-VLM | ADE: 1.66 -> 1.60 | Helped |
| Mix-train on simulation and real-world data instead of real-world data only (ablation) | Student VLM · nuScenes-VLM | ADE: 1.66 -> 1.84 | Hurt |
| Add adversarial transfer to the student model (ablation) | Proposed-FinetuneTwice (LLaVA-7b) · nuScenes-VLM | ADE: 1.60 -> 1.44 | Helped |
| Replace MLP projection with Q-former (ablation) | CoC-VLA · nuScenes-VLM | ADE: 1.44 -> 1.47 | Hurt |
| Add temporal information aggregation (ablation) | CoC-VLA · nuScenes-VLM | ADE: 1.53 -> 1.44 | Helped |
| Use 2 cached frames instead of 1 (ablation) | CoC-VLA · nuScenes-VLM | ADE: 1.44 -> 1.47 | No clear effect |
| Use 2 cached frames instead of 1 (ablation) | CoC-VLA · nuScenes-VLM | Collision Rate (%): 1.58 -> 1.56 | No clear effect |
| Transfer simulation-trained capability to the real-world student (ablation) | Student VLM · nuScenes-VLM, challenging subset | ADE: 2.08 -> 1.73 | Helped |
Surprising findings
- Mixing simulation and real-world data for the student slightly degraded performance (ADE 1.84 vs 1.66 for real-only training).
- A straight-line dummy regressor was used to check how much of the challenging-split gains could come from easy cases; the proposed model still improved on the student baseline (ADE 1.73 vs 2.08) on the challenging split.
Limitations
- Relies on LLaVA-7b, which the authors note has high inference cost and is hard to deploy online.
- Maintaining two baseline models and a multi-step adversarial training process raises training cost and optimization difficulty.
- Evaluated only on real-world open-loop data; closed-loop metrics not assessed.
Experimental setup
Datasets: nuScenes nuScenes-VLM CARLA-VLM
Benchmarks: nuScenes-VLM
Metrics: BLEU-1 BLEU-2 BLEU-3 BLEU-4 ROUGE-L CIDEr GPT score Accuracy Match SPICE
Baselines: DriveLM LMDrive Straight Regressor Baseline Proposed-Mix Proposed-FinetuneTwice
Builds on: LLaVA-v1.5 DriveLM LMDrive VAD
Closest papers by meaning
- AutoVLA: A Vision-Language-Action Model for End-to-End Autonomous Driving with Adaptive Reasoning and Reinforcement Fine-Tuning (NeurIPS 2025 · similarity 0.90)
- Impromptu VLA: Open Weights and Open Data for Driving Vision-Language-Action Models (NeurIPS 2025 · similarity 0.90)
- LaST-VLA: Thinking in Latent Spatio-Temporal Space for Vision-Language-Action in Autonomous Driving (NeurIPS 2026 · similarity 0.89)
- DriveAgent-R1: Advancing VLM-based Autonomous Driving with Active Perception and Hybrid Thinking (ICLR 2026 · similarity 0.89)
- Less Language, More Latents: Annotation-Efficient VLAs for Driving (NeurIPS 2026 · similarity 0.89)
- SOLVE: Synergy of Language-Vision and End-to-End Networks for Autonomous Driving (CVPR 2025 · similarity 0.89)
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