Investigating the Interplay between eHMI and dHMI for Automated Buses: How Do Contradictory Signals Influence a Pedestrian's Willingness to Cross?

In future urban traffic, communication abilities of automated vehicles (AVs) are needed to enable a safe interaction with pedestrians as so-called vulnerable road users. Dynamic human-machine interfaces (dHMIs) and external human-machine interfaces (eHMIs) are designed to enable AVs to communicate implicitly, e.g., via vehicle dynamics, and explicitly, e.g., by light signals. To this point, it is neither sufficiently studied how the exact interplay of both communication tools should take place nor how this should be considered for an automated bus. This study aims to shed light on pedestrians' interaction with an automated bus by combining vehicle behavior (dHMI) and different eHMIs. The main focus was on the effect of contradictory communication messages on pedestrians' willingness to cross. Results showed that for non-yielding conditions, a dynamic eHMI that displayed an erroneous yielding intent lead to a significantly higher pedestrians' willingness to cross compared to static eHMI or no eHMI.