Identifying User Needs and Current Challenges of External Interface Design for AV-VRU Communications: Insights from an Expert Survey Data Analysis

The recent deployment of highly automated vehicles (AVs) in various cities highlights the potential improvement of transportation safety but also reveals the need for improved interaction between AVs and other road users, particularly vulnerable road users (VRUs). The reduction of driver involvement in this AV-VRU interaction results in the absence of human-to-human communication cues and thus calls for new system designs. Researchers have proposed designing external human-machine interfaces (e-HMIs) to replace these communication cues and improve the AV-VRU interaction. However, designing e-HMIs is complex and requires consideration of various factors, such as stakeholder responsibilities, context of use, user needs, implementation, design principles, and usability testing. This paper examines potential e-HMI design solutions from the perspective of experts to determine user needs and identify challenges. An online survey was conducted with 47 experts in the AV and VRU field to gather their opinions on anticipated issues in AV-VRU interaction, preferred e-HMI design options, and related concerns. Both quantitative and qualitative analyses of the data revealed that experts view "Awareness" and "Intent" as the most important information to be communicated through visual e-HMIs placed on AVs. Open-ended questions also showed that there were fewer experts concerned about "Awareness" and "Intent" compared with other information types, and more experts concerned about auditory cues compared with visual cues and about VRU wearable or handheld devices installation locations compared with other locations. These findings provide insights into the efficiency, feasibility, effectiveness, and challenges in developing e-HMIs for improved and safer communication between AVs and VRUs.