Abstract
Abstract External Human-Machine Interfaces (eHMIs) are expected to bridge the communication gap between an automated vehicle (AV) and pedestrians to replace the missing driver-pedestrian interaction. However, the relative impact of movement-based implicit communication and explicit communication with the aid of eHMIs on pedestrians has not been studied and empirically evaluated. In this study, we pit messages from an eHMI against different driving behaviors of an AV that yields to a pedestrian to understand whether pedestrians tend to pay more attention to the motion dynamics of the car or the eHMI in making road-crossing decisions. Our contributions are twofold: we investigate (1) whether the presence of eHMIs has any objective effect on pedestrians’ understanding of the vehicle’s intent, and (2) how the movement dynamics of the vehicle affect the perception of the vehicle intent and interact with the impact of an eHMI. Results show that (1) eHMIs help in convincing pedestrians of the vehicle’s yielding intention, particularly when the speed of the vehicle is slow enough to not be an obvious threat, but still fast enough to raise a doubt about a vehicle’s stopping intention, and (2) pedestrians do not blindly trust the eHMI: when the eHMI message and the vehicle’s movement pattern contradict, pedestrians fall back to movement-based cues. Our results imply that when explicit communication (eHMI) and implicit communication (motion-dynamics and kinematics) are in alignment and work in tandem, communication of the AV’s yielding intention can be facilitated most effectively. This insight can be useful in designing the optimal interaction between AVs and pedestrians from a user-centered design perspective when driver-centric communication is not available.
Highlights
There are different schools of thought when it comes to effectively facilitating the interactions between an automated vehicle (AV) and Vulnerable Road Users (VRU) such as pedestrians
The other school of thought posits that the motion dynamics of the vehicle can act as a form of ‘implicit communication’ through movement patterns, and are enough to convey the intentions of an AV in traffic: Some works suggest that such forms of implicit communication is enough and further augmentation with External Human-Machine Interfaces (eHMIs) is discouraged due to potential ‘griefing behavior’ from bystanders [19], especially in the early stages of integration of automated driving technology in traffic
Two different dependent variables were used as measures to evaluate the effect of eHMIs on pedestrians’ road crossing behaviors
Summary
There are different schools of thought when it comes to effectively facilitating the interactions between an automated vehicle (AV) and Vulnerable Road Users (VRU) such as pedestrians. The other school of thought posits that the motion dynamics of the vehicle can act as a form of ‘implicit communication’ through movement patterns, and are enough to convey the intentions of an AV in traffic: Some works suggest that such forms of implicit communication is enough and further augmentation with eHMI is discouraged due to potential ‘griefing behavior’ (mild form of bullying) from bystanders [19], especially in the early stages of integration of automated driving technology in traffic. Given the empirical evidence supporting arguments both for eHMIs, and against eHMIs in favor of vehicle behavior-based communication, it is important to understand the relative impact of both in order to design an effective and usable interaction experience for AV-pedestrian interaction.
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