Analyzing Driver Strategy for Scheduled Takeovers Under the Effect of Multi-stage Takeover Request Design

For scheduled takeover events in conditional driving automation, a longer lead time of takeover request (ToR) up to 60 seconds was recommended for drivers’ better situation awareness and subjective evaluations. However, the long ToR lead time could impair drivers’ estimation of the urgency of situation, which potentially results in risky takeover behavior. Four multi-stage ToR designs varying in warning modality that communicate the urgency within a long lead time were thus proposed to mitigate the negative effects. The present study involved a driving simulator experiment with 32 participants performing 12 takeover tasks for exiting a freeway with the aim to analyze driver strategy for scheduled takeover events and evaluate the multi-stage ToR designs. Eight driver strategies for attention management and takeover were identified. Using multi-stage ToR designs advanced drivers’ takeover actions by decreasing the likelihood of alternating attention between non-driving activities and road and reducing the duration of takeover preparation.