Level 3 automated vehicles (AVs) issue a request to intervene (RtI) when the automated driving system approaches its system limitations. Although this takeover transition is safety-critical, it is usually invisible to surrounding manually driven vehicle (MV) drivers. This study proposes an external human-machine interface (eHMI) called eHMI C+O that externalizes the RtI-related takeover status of a Level~3 AV using cyan and orange light bars. A driving-simulator experiment with 40 participants examined whether the proposed eHMI supports surrounding MV drivers during AV takeover scenarios. The results showed that, compared with the ADS-status-only eHMI condition, which is similar to ``Automated Driving Marker Lights,'' and the no-eHMI condition, the proposed eHMI C+O significantly improved participants' understanding of the AV's driving intention, their prediction of its behavior, and their perceived sufficiency of the information presented by the AV. It also reduced hesitation, increased confidence, and promoted earlier and larger increases in time headway after the RtI was issued. In the AV accident scenario, eHMI C+O significantly reduced the odds of accident involvement for the following MV compared with the no-eHMI condition, corresponding to a 76.8% reduction in accident odds. Exploratory path analysis suggested that the safety benefit of the proposed eHMI C+O may be associated with improved situation awareness and earlier defensive driving responses. These findings indicate that externalizing RtI-related takeover status can help surrounding drivers better understand Level 3 AVs and respond more safely during safety-critical takeover transitions.

翻译：当自动驾驶系统接近其系统极限时，L3级自动驾驶车辆会发出请求干预（RtI）。尽管这一接管过渡过程对安全性至关重要，但通常对周围手动驾驶车辆（MV）的驾驶员而言是不可见的。本研究提出一种名为eHMI C+O的外部人机界面，利用青色和橙色光条将L3级自动驾驶车辆与RtI相关的接管状态外部化。一项包含40名参与者的驾驶模拟实验考察了所提议的人机界面在自动驾驶车辆接管场景中是否能为周边手动驾驶车辆驾驶员提供支持。结果表明，与仅显示自动驾驶系统状态的人机界面条件（类似于“自动驾驶标记灯”）及无人机界面条件相比，所提议的eHMI C+O显著提高了参与者对车辆驾驶意图的理解、对其行为的预测能力，以及对其所呈现信息充分性的感知。该界面还减少了犹豫，增强了信心，并促使参与者在RtI发出后更早且更大幅度地增加车头时距。在自动驾驶车辆事故场景中，与无人机界面条件相比，eHMI C+O显著降低了后续手动驾驶车辆的事故卷入几率，对应事故几率降低76.8%。探索性路径分析表明，所提议的eHMI C+O带来的安全效益可能与提升的情境意识和更早的防御性驾驶响应有关。这些发现表明，将RtI相关的接管状态外部化有助于周边驾驶员更好地理解L3级自动驾驶车辆，并在安全关键的接管过渡过程中做出更安全的响应。