Pedestrians' Perceptions of Autonomous Vehicle External Human-Machine Interfaces

The objective of this work was to better understand pedestrians' understanding, trust, comfort, and acceptance of autonomous vehicle (AV) external human-machine interfaces (eHMIs). A link between mechanical engineering (i.e., automotive engineering) and civil engineering (i.e., multimodal transportation systems) is necessary to understand the effectiveness of varying AV-to-human communication strategies. Using a within-subject experiment design, 47 participants interacted with AVs possessing one of four eHMIs in a virtual reality (VR) environment. We administered a Likert scale survey to measure participants' perceptions of the eHMIs and used ordinal logistic regressions to analyze the results. We also accounted for participants' gender and stated interest in AVs, novel contributions to this field of research. The presence of an eHMI was found to improve participants' perceptions of AVs. Although females generally reported higher levels of understanding, trust, comfort, and acceptance, males' scores increased more significantly with the introduction of an eHMI. Text eHMIs outperformed nontextual interfaces, with participants noting the best perceptions with the text eHMI located on the AV's grille. Participants' understanding and identification of right-of-way (ROW) were most improved by the eHMIs while trust and comfort were most impacted by the participants' stated interest in AVs. Acceptance had little response to the eHMIs or stated AV interest and gender had little impact in the statistical models. This research supports the development of a standard, uniform AV-pedestrian communication strategy and strengthens the connection between humans and AVs.