An eHMI Presenting Request-to-Intervene and Takeover Status of Level 3 Automated Vehicles to Support Surrounding Traffic Safety

Level 3 automated vehicles can drive themselves under certain conditions but must issue a request to intervene (RtI) when limitations are reached. Currently, this handover process is invisible to nearby human drivers, leading to confusion and potential collisions. A team of researchers from Japan’s automotive safety labs proposes eHMI C+O, an external human-machine interface that uses cyan and orange light bars to externalize the AV’s takeover status. The design builds on existing 'Automated Driving Marker Lights' but adds a second color to indicate both the request and the driver’s response state.

In a driving simulator experiment with 40 participants, eHMI C+O significantly outperformed both a no-eHMI baseline and a standard ADS-status-only indicator. Drivers reported better understanding of the AV’s intentions, more confidence, and less hesitation. Most strikingly, the eHMI reduced the odds of a following vehicle being involved in an accident when the AV suddenly decelerated by 76.8%. Path analysis suggested the safety gain came from improved situation awareness and earlier defensive driving actions, such as increasing time headway. The findings make a strong case for making takeover requests externally visible—a key step toward integrating Level 3 AVs safely into mixed traffic.