Which partially automated driving function do drivers prefer? Results from two field studies on public highways

Partial driving automation consists of several subsystems that drivers need to trust to an appropriate level and interact with in a secure manner. To investigate whether drivers adapt their trust functional specific, how they experience the subsystems, and what their preferences are, we conducted two field studies with two partially automated (SAE level 2) vehicles and involving a total of 132 drivers. In both studies, participants drove on a public highway with support from partial driving automation systems for longitudinal control (adaptive cruise control, ACC) and lateral control (lane-keeping assistance, LA). Participants in Study 2 were additionally able to use a lane change assistance (LC) system. The drivers' trust generally increased over time and reflected in how much a participant used the automation (Study 1). Hereby, in both studies drivers had functional specific trust: in Study 1 drivers trusted the ACC more than the LA. In Study 2 drivers in addition had lower trust in the LC than in the LA and the ACC. In their thinking-aloud statements, drivers were more positive about ACC and more critical about LA but reported more interaction difficulties with the ACC (Study 1). In Study 2 participants on average preferred the ACC over the LA and the LA over the LC. The interview responses suggest that the lower preference was due to the perceived reliability (LA) and usefulness (LC). In summary, our results indicate that drivers adapt their trust functional specific when using partial driving automation and have an overall preference for ACC that persists despite a higher number of interaction problems.