自动驾驶安全测试场景生成一直面临计算慢、动作不真实的问题，RiskFlow 用单次前向传播替代迭代去噪，做仿真评估的团队可以直接用，效果比扩散方法更高效更保真。
安全关键交通场景生成对评估自动驾驶系统在罕见但高风险交互下的表现至关重要。现有扩散方法虽在闭环生成中可控性强，但迭代去噪过程计算成本高，且长序列中易累积采样和引导误差，导致抖动、异常加速等不真实运动。RiskFlow 提出一种新框架，将未来轨迹生成建模为动作空间中的传输，通过单次前向传播学习平均速度场，将高斯动作序列转化为加速度和偏航率指令，并利用输出空间引导生成高风险交互，同时保持物理可行性。实验表明，RiskFlow 在多智能体和长时域设置下实现了对抗性与真实性的良好平衡，显著提升真实性并降低推理时间。
RiskFlow: Fast and Faithful Safety-Critical Traffic Scenario Generation
Safety-critical traffic scenario generation is essential for evaluating autonomous driving systems under rare but high-risk interactions. Existing diffusion-based methods offer strong controllability in closed-loop generation, but their iterative denoising process is computationally expensive and may accumulate sampling and guidance errors over long rollouts, causing unrealistic motion artifacts such as jitter, abnormal acceleration, and off-road behavior. To address these issues, we propose RiskFlow, a closed-loop safety-critical multi-agent traffic generation framework that formulates future trajectory generation as transport in the action space. Instead of relying on iterative denoising, RiskFlow learns an average velocity field over a finite interval to transform Gaussian action sequences into future acceleration and yaw-rate commands with a single forward pass, using a JVP-based objective for efficient and stable training. At test time, RiskFlow applies output-space guidance to the generated actions, steering selected critical agents toward risky interactions while regularizing off-road behavior, and reconstructs physically feasible trajectories through vehicle dynamics. Experiments on nuScenes with tbsim closed-loop evaluation show that RiskFlow achieves a strong adversariality-realism trade-off across multi-agent and long-horizon settings. Compared with representative baselines, RiskFlow consistently improves realism while maintaining competitive safety-critical generation capability, and substantially reduces inference time for evaluation.