How Resource Demands of Nondriving-Related Tasks and Engagement Time Affect Drivers' Physiological Response and Takeover Performance in Conditional Automated Driving

Drivers are allowed to perform a nondriving-related task (NDRT) in the Level-3 (L3) automated driving, which inevitably promotes a variety of complex NDRTs. Hence, investigating the effect of NDRTs on drivers' behavior is necessary to ensure a safe transition from automated to manual driving. The main aim of this study is to examine the effect of resource demands of NDRTs and its engagement time on drivers' physiological responses, takeover performance, and subjective ratings. A total of 42 participants were recruited to conduct a driving simulator study. Results showed that visual and physical resource demands significantly increased participants' response time and deteriorated their takeover quality. Engagement time significantly affected participants' drowsiness and response time to the takeover request. In addition, participants rated the physical-visual-cognitive task as the most challenging task and the cognitive task as the least demanding task, which matches the takeover performance. Moreover, pupil diameter responds significantly to visual resource demands rather than physical resource demands. Physical resource demands had a significant tendency to elevate heart rate. This study suggested that tasks with a certain level of cognitive resource demand may be more appropriate for L3 automated driving. The findings of this study make it possible to use physiological responses to identify NDRT types or even predict drivers' takeover performance in automated driving. Based on this, the time budget could be dynamically adjusted to ensure a safe transition.