Investigating Pedestrians’ Interactions with Automated Buses: How Do External and Dynamic HMIs Affect Trust?

Abstract

Pedestrians as vulnerable road users highly depend on the communication with other road users. This also applies to their future interaction with automated vehicles (AVs), especially with larger sized AVs, as miscommunication can have serious consequences. Current research manifested that pedestrians need implicit communication, e.g., vehicle dynamics. Additionally, explicit communication is needed to clarify misunderstandings before they actually result in accidents. Two communication tools exist for AVs and stand in focus of this study: Dynamic Human-Machine Interfaces (dHMIs) for implicit communication and external Human-Machine Interfaces (eHMIs) for additional explicit communication. The interplay of both means of communication has not yet been sufficiently researched for larger sized vehicles. 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 condition). Results revealed that pedestrians' trust ratings were surprisingly high in the non-matching condition which represented a high-risk traffic scenario for them. These findings provided insights into possible negative effects of eHMIs when they do not match vehicle behavior (dHMI). An outlook on possible derivations for the design of a safe human-machine interaction between pedestrians and larger AVs is given.