Emergency, Automation Off: Unstructured Transition Timing for Distracted Drivers of Automated Vehicles

In future automated driving systems, drivers will be free to perform other secondary tasks, not needing to stay vigilant in monitoring the car's activity. However, there will still be situations in which drivers are required to take-over control of the vehicle, most likely from a highly distracted state. While highly automated vehicles would ideally accommodate structured takeovers, providing ample time and warning, it is still very important to examine how drivers would behave when they are subjected to an unstructured emergency transition of control. In this study, we observed how participants (N=30) in a driving simulator performed after they experienced a loss of automation. We tested three transition time conditions, with an unstructured transition of control occurring 2 seconds, 5 seconds, or 8 seconds before the participants encountered a road hazard that required the drivers' intervention. Participants were given a passive distraction (watching a video) to do while the automated driving mode was enabled, so they needed to disengage from the task and regain control of the car when the transition occurred. Few drivers in the 2 second condition were able to safely negotiate the road hazard situation, while the majority of drivers in the 5 or 8 second conditions were able to navigate the hazard safely. Similarly, drivers in the 2 second condition rated the vehicle to be less trustworthy than drivers in the 5 and 8 second conditions. From the study results, we are able to narrow down a minimum amount of time in which drivers can take over the control of vehicle safely and comfortably from the automated system in the advent of an impending road hazard.