Pedestrians' perceptions, fixations, and decisions towards automated vehicles with varied appearances

Future automated vehicles (AVs) are anticipated to feature innovative exteriors, such as textual identity indications, external radars, and external human-machine interfaces (eHMIs), as evidenced by current and forthcoming on-road testing prototypes. However, given the vulnerability of pedestrians in road traffic, it remains unclear how these novel AV appearances will impact pedestrians' crossing behaviour, especially in relation to their multimodal performance, including subjective perceptions, gaze patterns, and road-crossing decisions. To address this gap, this study pioneers an investigation into the influence of AVs' exterior design, in conjunction with their kinematics, on pedestrians' road-crossing perception and decision-making. A video-based eye-tracking experimental study was conducted with 61 participants who were exposed to video stimuli depicting a manipulated vehicle approaching a predefined road-crossing location on an unsignalized, two-way road. The vehicle's kinematic pattern was manipulated into yielding and non-yielding, and its external appearances were varied across five conditions: with a human driver (as a conventional vehicle), with no driver (as an AV), with text-based identity indications, with roof radar sensors, with dynamic eHMIs adjusted to vehicle kinematics. Participants' perceived clarity, crossing initiation time (CIT), crossing initiation distance (CID), and gaze behaviour during interactions were recorded and reported. The results revealed that AVs' yielding patterns play a dominant role in pedestrians' road-crossing decisions, supported by their subjective evaluations and CID. Furthermore, it was found that both textual identity indications and roof radar sensors had no significant effect on pedestrians' CIT and CID but did negatively impact their visual attention, as evidenced by heightened fixation counts and prolonged fixation durations. In contrast, the deployment of eHMIs helped mitigate the visual load and perceptual confusion associated with AV's identity features, expedite road-crossing decisions in terms of both time and space, and thus improve overall communication efficiency. The practical and safety implications of these findings for future external interaction design of AVs are discussed from the perspective of vulnerable road users.