Importance of Instruction for Pedestrian-Automated Driving Vehicle Interaction with an External Human Machine Interface -- Effects on Pedestrians' Situation Awareness, Trust, Perceived Risks and Decision Making

An external human machine interface (eHMI) can be viewed as an explicit communication method for providing driving intentions of an automated driving vehicle (AV) to pedestrians. However, the eHMI may not guarantee that the pedestrians will fully recognize the intention of the AV. In this paper, we proposed that the instruction of the eHMI's rationale can help pedestrians correctly understand the driving intentions and predict the behavior of the AV, and thus their subjective feelings (i.e., dangerous feeling, trust in the AV, and feeling of relief) and decision-making are also improved. The results of an interaction experiment in a road-crossing scene indicate that the participants were more difficult to be aware of the situation when they encountered an AV w/o eHMI compared to when they encountered a manual driving vehicle (MV); further, the participants' subjective feelings and hesitation in decision-making also deteriorated significantly. When the eHMI was used in the AV, the situational awareness, subjective feelings and decision-making of the participants regarding the AV w/ eHMI were improved. After the instruction, it was easier for the participants to understand the driving intention and predict driving behavior of the AV w/ eHMI. Further, the subjective feelings and the hesitation related to decision-making were improved and reached the same standards as that for the MV.