Investigation of driving safety in partial driving automation considering driving modes and drivers' pre-drive states

With the release of partial driving automation systems that allow drivers to take their hands off the steering wheel (L2 hands-off), it has become increasingly important to evaluate their implications for driving safety. This study investigated how different driving modes influence driving safety considering drivers' pre-drive states. Using a static driving simulator, two groups of UK drivers participated in the experiment: 19 non-nightshift workers and 19 nightshift workers. Participants in each group completed drives under three driving modes: manual driving, L2 hands-on, and L2 hands-off. The drowsiness, attention behavior, hazard perception performance, and driving performance of the participants were measured. The results suggested that the L2 hands-off mode had adverse effects on drowsiness and attention behaviors in both groups, with detrimental trends also observed for hazard perception performance and driving performance. Moreover, given the adverse effects of the L2 hands-off mode, drivers with different pre-drive states adopted different response strategies. Non-nightshift workers performed more frequent takeovers in the L2 hands-off mode to avoid collisions, whereas nightshift workers responded similarly across all modes but exhibited the highest collision probability in the L2 hands-off mode. In summary, although L2 driving may reduce manual control demands, taking hands off steering wheel increases safety risks, particularly for nightshift workers. Future efforts should adopt strategies to mitigate the safety risks associated with L2 hands-off systems and assess drivers' pre-drive states before permitting the use of such systems.