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

The focus of this study is the future interaction between pedestrians and automated buses. Pedestrians highly depend on the communication with other road users as misunderstandings can have serious consequences. This applies especially for the interaction with a larger sized automated vehicles (AVs), e.g., an automated bus. Current research has shown that pedestrians relied primarily on implicit communication signals, e.g., vehicle dynamics such as speed or deceleration. Additionally, explicit communication signals are needed to clarify misunderstandings before they actually result in accidents. Two possible communication tools exist for AVs: Dynamic Human-Machine Interfaces (dHMIs) for implicit communication and external Human-Machine Interfaces (eHMIs) for explicit communication. The interplay of both means of communication has not yet been sufficiently researched for automated buses as larger AVs. This experimental online study (N=120) addressed pedestrians' interactions with an automated bus on a shared space and focused on possible negative effects on pedestrians’ trust ratings when the eHMI contradicted the dHMI (non-matching conditions). Results revealed that pedestrians' trust was surprisingly high in non-matching conditions which could present a high-risk traffic scenario for pedestrians. These findings provided insights into possible negative effects of eHMIs when they do not match vehicle behavior (dHMI). Implications for pedestrians’ future interactions with different sized AVs will be discussed