Communicating minimal risk maneuvers to passengers in highly automated vehicles: Ensuring hedonic user experience with media rich in-vehicle HMIs

With the introduction of highly automated vehicles (HAV; SAE Level 4) driverless mobility systems may fundamentally change public transportation. For potential passengers of these systems, new situations may arise, leaving them without a driver to directly communicate with. This can be problematic when the driving automation is confronted with situations it might be unable to manage by itself, which would cause a minimal risk maneuver (MRM), e.g. a complete standstill of the vehicle. Some concepts enhance these systems with a remote assistant who can support the HAV, adding novelty to the transportation process. This increased novelty may result in user discomfort for passengers, causing a need for information systems that address this. One possibility to do so and to thus improve hedonic quality and thus comfort for passengers is by providing system transparency via a media rich in-vehicle Human-Machine Interface (iHMI), which provides information to passengers about the ADS and its processes. However, there is still a gap in research on the ideal communication mechanism to ensure good hedonic quality and comfort during these situations. We conducted a simulator study in virtual reality (VR), investigating interfaces based on media richness theory to address this issue. The interface provided a multi-layered iHMI consisting of transparency information presented with varying levels of media richness. In a block design, participants experienced three versions of an iHMI, one presenting information via text, another combining text and auditive presentation and a third adding a human avatar simulating Face-to-Face communication. After each scenario, participants completed questionnaires regarding understanding, predictability, trust and user experience. Study results reveal significant increases in the hedonic quality of user experience and trust towards the system for interfaces with increased media richness, providing a first step towards enhancing user comfort with iHMI in automated mobility systems during challenging situations for the automation system, such as MRM.