Please, Go Ahead! Fostering Prosocial Driving with Sympathy-Eliciting Automated Vehicle External Displays

Road traffic is strongly regulated, however informal communication is essential whenever formal rules are flexibly treated. Consequently, conflict-avoidant automated vehicles (AVs) can be disadvantaged when humans do not behave prosocially towards them. This can lead to disruptions of mixed traffic, where human and automated driving co-exists. Equipping AVs with sympathy-eliciting external Human-Machine Interfaces (eHMI) mimicking informal communication cues could mitigate this challenge by fostering the prosocial behavior of drivers. This work contributes video vignettes that are experimentally validated in an online survey (N=90). While we found participants to not behave differently towards human-controlled and baseline automated vehicles, eHMIs were potent in eliciting sympathy and encouraged yielding behavior. This effect was more pronounced when the interface signaled an urgent situation or indicated prolonged waiting times. Non-yielding behavior was rationalized based on priority rules. These results emphasize how fostering prosocial behavior in traffic can be achieved via sympathy-eliciting external displays.