Comprehensibility and Perceptibility of Vehicle Pitch Motions as Feedback for the Driver During Partially Automated Driving

During assisted and partially automated driving, having awareness of the automation system's functionality is essential for drivers to fulfill their supervising task adequately. Feedback on state transitions and intentions of the automation system is necessary to obtain, as well as increase the driver's awareness of the automation. In this contribution, feedback for drivers is communicated via active vehicle pitch motions, and not visually, as is usually the case. Comprehensibility and perceptibility are important criteria regarding the effectiveness of feedback. To evaluate these two criteria, a driving study (N = 36) is conducted in real traffic on a motorway in which vehicle guidance is performed by an automation system. The results reveal that 89% of the participants perceive active pitch motions and do not regard them as passive pitch motions induced by the vehicle's acceleration or deceleration. Following, these nonexpert participants were expected to determine the meaning of these pitch motions and report using the think-aloud method. A total of 84% of the participants who were given the chance to understand the meaning of these motions were able to do so. Active vehicle motions, therefore, present a feedback approach that is independent of the driver's viewing direction. These can complement visual feedback, thus resulting in multimodal feedback.