In conditionally autonomous vehicles, drivers should take over vehicle control when the automated system fails. It is a challenge to perform safely in urgent situations due to critical time constraints and great stress increment. This study conducted a human-in-the-loop driving simulator experiment to identify how driver stress changes during urgent takeovers and the association with driver performance. The urgent takeover request was designed with a time budget of 3s. Stress levels were evaluated through galvanic skin responses (GSR). A moderating effect model was then built between stress levels, minimum time to collision, and brake reaction time. Results showed driver stress was significantly high and peaked from 5s to 10s after the takeover was triggered. Besides, too much stress indicated by GSR data (0.059-0.096mμS) showed significant moderating effects on extending brake reaction time. This study could contribute to improving the takeover strategy with stress traits considered.

automaed driving;driver stress;GSR;urgent takeover;driver performance