Rinse and repeat: behavior change associated with using partial automation among three samples of drivers during a 4-week field trial

September 2024

Introduction: Partial automation is in its infancy. There is a need to understand driver behavior associated with the use of this technology, such as to what extent it differs from manual driving behavior or changes with use over time. In Reagan et al. (2021; Transportation Research Part F, 82), volunteers driving a Volvo S90 with adaptive cruise control (ACC) and Pilot Assist, which couples ACC and continuous lane centering, were more likely to show visual-manual disengagement when using Pilot Assist in the second portion of a 4-week field trial compared with manual driving or relative to driving with Pilot Assist in the first portion. Method: We used the same analytical approach as Reagan et al. with three separate samples of drivers (nA = 10, nB = 10, nC = 9). Using video data, we estimated the odds of conducting a visual-manual secondary activity or driving with both hands off the wheel across three automation modes (manual [no automation], ACC, Pilot Assist) and two study periods (period 1, weeks 1 and 2; period 2, weeks 3 and 4). Results: Participants exhibited higher odds of visual-manual distraction or driving hands-free in period 2 when using Pilot Assist relative to manual driving, but patterns differed noticeably across the groups. Pilot Assist use among groups A and B was associated with higher odds in the second period relative to the first, whereas group C exhibited a high level of visual-manual distraction and hands-free driving when using Pilot Assist throughout the 4 weeks of data collection. Discussion: Our findings suggest that drivers show reliably less attention to the road with the versions of partial automation we tested compared with manual driving that develops with time or is evident relatively early during drivers’ initial trips with the automation. The results support arguments for driver-monitoring solutions that ensure adequate attention to the road. Differences among the samples in patterns of behavior change highlight the need to study factors that may further modify how drivers adapt their behavior when using partial automation such as driving exposure, willingness to use automation, and iterations of partial automation that differ in functional performance.