Can External Human–Machine Interfaces Promote Human Drivers’ Prosocial Intentions Toward Automated Vehicles in Mixed Traffic?

External human–machine interfaces (eHMIs) in automated vehicles (AVs) are expected to facilitate harmonious interactions between AVs and human drivers by expressing clear intentions and friendly behaviors. However, whether eHMIs can effectively foster human drivers’ prosocial behaviors in complex mixed traffic remains unclear. We conducted a video-based experiment where 1,172 Chinese drivers were randomly assigned to interact with either an AV (indicating lane-changing intentions via a text-based eHMI or conventional lamp signals) or a human-driven vehicle in lane-changing scenarios. Participants reported their willingness to yield to and attitudes toward the front vehicle. The eHMI did not increase participants’ willingness to yield compared to the HV and AV with conventional lamp signals. Thus, the eHMI failed to promote participants’ prosocial intentions. However, participants who noticed the eHMI held more positive attitudes toward the AV. These findings advance theoretical understanding of human–AV interaction and underscore the complexity of eHMI design.