Beep and Show, Don’t Tell: Multimodal Feedback Strategies for Driver-Automation Coordination in Critical Driving Situations

In level-3 automated driving, control shifts between the system and the human driver, making timely and effective communication crucial in conflict situations. To explore how different communication modalities affect the driver’s understanding, trust, and performance in such situations, we conducted two complementary studies: a focus group and an interactive user study. The focus group revealed a preference for multimodal, tailored feedback, with visual information most frequently favored. The interactive user study tested these findings in practice by asking participants to confirm the system suggestion or take over. The results from the interactive study showed the importance of a pre-explanation signal that draws attention to the situation, and a clear visual marking of the proposed resolution. While most participants stated a preference for speech-augmented feedback, spoken and written explanations were frequently overlooked or reported as distracting during active conflict scenarios, suggesting a gap between stated preference and in-task utility. These results indicate that in urgent conflict situations, concise visual cues are more effective than detailed verbal explanations, offering guidance for the design of future level-3 vehicle interfaces.