May I really go first or you? The effect of right-of-way on pedestrians’ trust for the interaction with automated vehicles

Abstract

In the near future, automated vehicles (AVs) will have to communicate with other traffic participants. This leads to the challenge that AVs need to be able to communicate successfully to increase safety and, in particular, with vulnerable road users, e.g., pedestrians, as they highly depend on the communication with their surrounding traffic environment. The use of communication tools for AVs can enhance the efficient external communication between AVs and pedestrians, e.g., external HMI (eHMI) and dynamic HMI (dHMI). External HMIs transmit explicit communication signals whereas dHMIs transmit implicit communication signals via the vehicle’s behavior. Research showed promising results of both communication tools separately and in combination when it is well-coordinated. However, some studies also manifested negative effects of eHMIs, i.e., over-trust. As limitation, this was investigated mostly in traffic scenarios where the pedestrians had the right-of-way which might have affected pedestrians’ subjective assessment and, therefore, needs further investigation. In this experimental online study, pedestrians interacted in pre-recorded video sequences with AVs approaching from the right-hand side, i.e., from the non-privileged side. The interaction took place on a shared space traffic scenario which is defined by interactions in low-speed and low-distance and, thus, this traffic scenario not only demands implicit communication signals by the dHMI but also explicit information signals by the eHMI. In the experimental conditions, the vehicle size (car vs. bus), the vehicle’s dynamics, i.e., dHMI (yielding vs. non-yielding), and the eHMI condition (no eHMI vs. static eHMI vs. dynamic eHMI) was varied. Moreover, a major focus was placed on the experimental conditions in which the eHMI contradicted the dHMI, i.e., when the dynamic eHMI showed a yielding intent by a slow pulsation although the vehicle was not yielding (non-matching conditions). The results revealed that pedestrians' trust was surprisingly high in those non-matching conditions which could present a high-risk traffic scenario for pedestrians as vulnerable road users. Overall, findings of this study provided insights into possible negative effects of eHMIs when they do not match the vehicle’s dynamics.