Effects of non-driving related postures on takeover performance during conditionally automated driving

In spite of the advancement in driving automation, driver's ability to resume manual control from a conditionally automated vehicle appears as a safety concern. Understanding the impact of various non-driving related tasks (NDRT) on takeover performance is crucial for the development of advanced driver assistance systems. The aim of this study was to investigate how the takeover performance was impacted by non-driving related postures when engaging in different NDRTs. A same takeover scenario with SAE automation level 3 requiring emergency braking was deployed for all test conditions on a static driving simulator under different time budgets. Reaction times, pedal movement and takeover quality were collected from 54 drivers (mean age 34.5 years, 27 females) taking over from two reference postures and 21 non-driving related postures. Results showed that drivers reacted faster given a shorter time budget. Non-driving related postures were found to prolong the takeover time and deteriorate the takeover quality. In particular, the postures with abnormal right foot positions, big trunk deviations and both hands occupation much lowered motoric readiness. Results also revealed that when driver's upper body was engaged in abnormal postures, driver's lower body would react slower, and vice versa. In addition, drivers' takeover performance was affected by their individual reaction capacity, which demonstrated a range of variation. Theoretical and practical implications of the findings are discussed.