Hitting the Apex Highly Automated? – Influence of Trajectory Behaviour on Perceived Safety in Curves

There is not yet sufficient knowledge on how people want to be driven in a highly automated vehicle. Currently, trajectory behaviour as one part of the driving style is mostly implemented as a lane-centric position of the vehicle in the lane, but drivers show quite different preferences, especially with oncoming traffic and in curves. A driving simulator study was conducted to investigate seemingly natural reactive driving trajectories in curves on rural roads in an oncoming traffic scenario to better understand people’s preferences regarding driving styles. 46 subjects experienced different lateral offsets in curves in three different oncoming traffic scenarios either on a 3.00 m or on a 3.50 m lane width. The test track consisted of 12 right and 18 left curves with an oncoming truck, car or none oncoming vehicle in balanced order. Results show that reactive trajectory behaviour and wider lane widths lead to significantly higher perceived safety. Even though drivers tend to shift their lateral position in curves in manual driving situations, they do not want the automated vehicle to cut curves and hit the apex. On the other hand, they also do not wish to get close to the road side, as seen in manual driving, too. We recommend an adaptive driving trajectory, which modifies trajectory behaviour on different lane widths and adjusts its behaviour on type and position of oncoming vehicles. The results of the study help to design an accepted, preferred and trustfully trajectory behaviour for highly automated vehicles.