Exploration of driver stress when resuming control from highly automated driving in an emergency situation

Kerautret, Laora; Dabic, Stephanie; Navarro, Jordan · 2023 · Crossref

DOI: 10.1016/j.trf.2023.01.016

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Summary

This study investigates the impact of emergency takeovers on driver stress in highly automated vehicles, addressing a critical safety concern where drivers must resume control under time pressure. The research is motivated by the finding that resumption of manual control often occurs in emergency situations automation cannot handle, potentially leading to risky behaviors due to insufficient time for information processing. The authors aim to understand how varying degrees of emergency influence physiological and subjective stress responses, specifically testing whether warning systems can mitigate stress through cognitive preparation. The experiment utilized a driving simulator with 36 participants, measuring heart rate, pupil diameter, and perceived stress. The study design manipulated emergency levels across three scenarios: a non-emergency Optional Driver-Initiated (ODI) transition at a toll area; a moderate emergency Mandatory Automation-Initiated (MAI) transition involving fog and complex maneuvers with a system warning; and an extreme emergency Mandatory Driver-Initiated (MDI) transition in a work zone with no system warning, requiring the driver to detect automation failure. Data were analyzed during pre-takeover (3 seconds prior) and post-takeover (5.5 seconds following) periods, comparing takeover sessions against monitoring control sessions. Results indicated that emergency takeovers significantly increased driver stress compared to non-emergency situations. In both moderate (MAI) and extreme (MDI) emergencies, drivers exhibited pupil dilation, higher perceived stress, and sustained heart rate increases. However, the presence of a warning in the moderate emergency condition led to lower perceived stress and a distinct bi-phasic cardiac pattern: a short-lasting heart rate decrease followed by an increase. This initial deceleration was absent in the extreme emergency condition, where drivers faced no warning. In contrast, the non-emergency ODI condition showed no significant heart rate changes compared to monitoring, though pupil dilation was observed. The findings confirm that time urgency is a primary driver of stress during takeovers. Crucially, the study supports the existence of a warning-induced preparatory response, characterized by cardiac deceleration, which aligns with defensive behavior theories. This preparatory response appears to mitigate stress levels, suggesting that providing drivers with advance warnings allows for active cognitive preparation, thereby reducing the physiological and subjective burden of emergency takeovers. These insights are significant for designing human-machine interfaces that optimize warning systems to enhance safety and reduce driver stress in automated driving contexts.

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Topics

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• takeover transitions
• automation
• automation surprise
• stress driving
• manual
• situational awareness

Information type

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• Empirical Findings: physiological data, behavioral performance data
• Theoretical Contribution: conceptual framework