Handing control back to drivers: Exploring the effects of handover procedure during transitions from Highly Automated Driving

•During self-paced transitions of authority, drivers benefitted from lateral assistance in the form of a Lane-Keeping Assist.•Assisting the drivers at an operational level did not enhance their capacity for addressing more complex tasks.•Being assisted for longer periods improved both drivers’ performance and comfort. The operational capabilities of automated driving features are limited and sometimes require drivers’ intervention through a transition of control. Assistance at an operational level might be extremely beneficial during transitions but the literature lacks evidence on the topic. A simulator study was conducted to investigate the potential impacts that lateral assistance systems might have while the Automated Driving System (ADS) hands back control to the driver. Results showed that drivers benefitted from a strong Lane Keeping Assist during the first phase of the transfer, helping them to keep the lane centre. However, assisting the drivers at an operational level did not enhance their capability of addressing a more complex task, presented as a lane change. In fact, it was more task-specific assistance (Blind-spot assist) that allowed drivers to better cope with the tactical decision that the lane change required. Moreover, longer exposure to lane-keeping assist systems helped them in gaining awareness of the surrounding traffic and improved the way drivers interacted with the Blind-spot assist.