  Level 3 automated driving systems (ADS) have attracted significant attention
and are being commercialized. A Level 3 ADS prompts the driver to take control
by requesting to intervene (RtI) when its operational design domain (ODD) or
system limitations are exceeded. However, complex traffic situations may lead
drivers to perceive multiple potential triggers of RtI simultaneously, causing
hesitation or confusion during take-over. Therefore, drivers must clearly
understand the ADS's system limitations to understand the triggers of RtI and
ensure safe take-over. In this study, we propose a voice-based HMI for
providing RtI trigger cues to help drivers understand ADS's system limitations.
The results of a between-group experiment using a driving simulator showed that
incorporating effective trigger cues into the RtI enabled drivers to comprehend
the ADS's system limitations better and reduce collisions. It also improved the
subjective evaluations of drivers, such as the comprehensibility of system
limitations, hesitation in response to RtI, and acceptance of ADS behaviors
when encountering RtI while using the ADS. Therefore, enhanced comprehension
resulting from trigger cues is essential for promoting a safer and better user
experience using ADS during RtI.
