1205 The Human Factors of Forward Collision Warning Systems : System Performance, Alarm Timing, and Driver Trust

Abe, Genya; Richardson, John · 2005 · Crossref

DOI: 10.1299/jsmetld.2005.14.345

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Summary

This study investigates how alarm timing in Forward Collision Warning Systems (FCWS) influences driver trust and subsequent responses to system malfunctions, specifically false alarms and missing alarms. The research addresses the critical problem that while FCWS aims to reduce accidents caused by driver inattention, system errors can lead to detrimental behaviors such as delayed braking or ignored warnings. The authors hypothesize that the timing of the alarm—whether early or late relative to the collision risk—shapes driver trust, which in turn mediates how drivers react when the system fails. The researchers conducted a driving simulator experiment with 24 licensed drivers (12 male, 12 female). Participants were randomly assigned to one of two groups: an "early alarm" group or a "late alarm" group. The simulation involved a car-following task on a single-lane road at 60 mph (96.6 km/h), maintaining a 2.0-second time headway. The FCWS algorithm used a Stop-Distance Algorithm, with alarm timing manipulated by adjusting the assumed deceleration parameter ($D_f$). Early alarms were triggered approximately 0.02 seconds after the lead vehicle began emergency braking (0.8g), while late alarms were triggered 1.20 seconds after. Each participant completed 11 trials, including baseline conditions, correct alarms, a false alarm (warning without lead vehicle braking), and a missing alarm (no warning during lead vehicle braking). Data collected included brake reaction times and subjective trust ratings on a 10-point scale. The results demonstrated significant differences in driver behavior based on alarm timing. Drivers in the late alarm group showed no significant change in brake reaction times across different trial blocks and were reluctant to respond to false alarms. Their trust levels remained relatively stable and low, making them less susceptible to the negative effects of system malfunctions. In contrast, drivers in the early alarm group exhibited significant changes in behavior. They tended to brake in response to false alarms and suffered from delayed brake reactions following a missing alarm. Trust levels in this group were initially high but dropped sharply after false alarms and again after missing alarms. Furthermore, a positive correlation was found between pre-missing-alarm trust levels and the magnitude of brake reaction delay; drivers with higher trust experienced significantly longer delays when the alarm failed to trigger. The study concludes that alarm timing is a critical factor in determining driver trust and behavioral adaptation to FCWS errors. Early alarms foster higher trust, which can lead to over-reliance and dangerous delays when the system fails to warn. Late alarms, while potentially less effective for immediate collision avoidance, result in lower trust and more consistent driver behavior regardless of system errors. These findings suggest that FCWS design must carefully balance alarm timing to mitigate the negative impacts of false and missing alarms, potentially by manipulating timing to manage driver trust levels appropriately.

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Topics

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• trust calibration
• automation surprise
• warning design
• auditory warnings