Preliminary Investigation of System Transparency and System Failure on Driver Trust in Partial Vehicle Automation

Trust in automation is a key determinant for the usage of vehicle automation (Beggiato & Krems, 2013). In the context that contemporary automated vehicles based on SAE (2018) level 2 still demand human supervision for driving safety despite dynamic vehicle controls instead of human drivers, system transparency and system failure are considered to be important factors influencing driver trust in automation. First, system transparency leads to a positive relationship with trust in automated vehicles (Helldin et al., 2013). Providing supplemental information in terms of driving automation before interacting with the automation can prompt driver trust and prevent decreased trust, keeping the driver to use automation. Second, the occurrence of system failures is critical for shaping driver trust as the driver is responsible for supervisory control, such as monitoring both external and internal environments and intervention in vehicle control. System failures can be categorized into two types: systemlimitation and -malfunction. The system-limitation can be considered as a designed failure by automation designers, however, the system-malfunction can be regarded as unexpected hardware or mechanical error. The objective of the present study was to explore how system transparency and failures changes driver trust in partial driving automation with preliminary results from vehicle automation simulations. Twenty-eight participants (15 females, 14 males) drove in a driving simulator in which generated partial vehicle automation with adaptive cruise control, lane keeping assistance system, and lane changing system on highway. Subjective ratings of trust were collected to examine the impact of two factors: system transparency (Detailed vs. Less) and type of system failure (by Limitation vs. Malfunction). Drivers for the detailed group received additional information in terms of why system failure occurs and what will be projected in a situation where the system encountered system failures. Both system failures occurred on a curve road, however system limitation occurred with a deep fog, whilst system malfunction occurred without the fog. We examined trust ratings at three points: before and after driver intervention in the automated vehicle, and after subsequent experience of flawless vehicle automation. Our preliminary result found no interaction between system transparency and system failures on driver trust change from before to after the intervention, F(1, 24) = 2.906, p = 0.101, and main effect of each factor was not observed. Qualitative observation indicates that drivers in the Detailed group kept trusting automation after the issue of intervention task, whilst the trust ratings of drivers in the Less group was decreased by experiencing the intervention task. Similar to this trend, the exposure to system limitation did not lead decrease of trust ratings. Contrary to the system-limitation group, drivers who experienced system-malfunction showed decreased trust ratings, but the subsequent error-free automation reestablished the decreased trust levels. In addition, when the system-limitation occurred to drivers who have detailed information about the system, trust was fostered in spite of the experience of intervention. This preliminary study noted the finding that driver’s trial-and-error experience of the partial driving automation is effective on rebuilding decreased trust by system failure as well as maintaining driver trust to a certain level. These changes remain implication that additional experiments with a larger sample size may help to characterize the relationship between driver trust and system transparency, and system failure.