Supplementary data for the paper 'How should external Human-Machine Interfaces behave? Examining the effects of colour, position, message, activation distance, vehicle yielding, and visual distraction among 1,434 participants'

External human-machine interfaces (eHMIs) may be useful for communicating the intention of an automated vehicle (AV) to a pedestrian, but it is unclear which eHMI design is most effective. In a crowdsourced experiment, we examined the effects of (1) colour (red, green, cyan), (2) position (roof, bumper, windshield), (3) message (WALK, DON’T WALK, WILL STOP, WON’T STOP, light bar), (4) activation distance (35 or 50 m from the pedestrian), and (5) the presence of visual distraction in the environment, on pedestrians' perceived safety of crossing the road in front of yielding and non-yielding AVs. Participants (N = 1434) had to press a key when they felt safe to cross while watching a random 40 out of 276 videos of an approaching AV with eHMI. Results showed that (1) green and cyan eHMIs led to higher perceived safety of crossing than red eHMIs; no significant difference was found between green and cyan, (2) eHMIs on the bumper and roof were more effective than eHMIs on the windshield, (3) for yielding AVs, perceived safety was higher for WALK compared to WILL STOP, followed by the light bar; for non-yielding AVs, a red bar yielded similar results to red text, (4) for yielding AVs, a red bar caused lower perceived safety when activated early compared to late, whereas green/cyan WALK led to higher perceived safety when activated late compared to early, and (5) distraction had no significant effect. We conclude that people adopt an egocentric perspective, that the windshield is an ineffective position, that the often-recommended colour cyan may have to be avoided, and that eHMI activation distance has intricate effects related to onset saliency.

外部人机交互界面（external human-machine interfaces，eHMI）可用于向行人传递自动驾驶车辆（automated vehicle，AV）的行驶意图，但目前尚不明确哪种eHMI设计最为有效。在一项众包实验中，我们探究了以下五项因素对行人在面对让行与不让行自动驾驶车辆时的过街感知安全性的影响：(1) 颜色（红、绿、青）；(2) 安装位置（车顶、保险杠、挡风玻璃）；(3) 显示信息（WALK、DON’T WALK、WILL STOP、WON’T STOP、光条）；(4) 激活距离（距行人35米或50米）；(5) 环境中是否存在视觉干扰。本次实验共有1434名受试者参与：受试者在观看276段搭载eHMI的即将驶来的自动驾驶车辆视频中随机抽取的40段时，若认为可以安全过街，则需按下按键。实验结果表明：(1) 采用绿色与青色的eHMI相比红色eHMI，可使行人获得更高的过街感知安全性，而绿色与青色eHMI之间无显著差异；(2) 安装于保险杠与车顶的eHMI相比挡风玻璃处的eHMI，效果更优；(3) 针对让行自动驾驶车辆，显示WALK信息的eHMI的过街感知安全性高于WILL STOP，光条显示形式次之；针对不让行自动驾驶车辆，红色光条与红色文本的效果相近；(4) 针对让行自动驾驶车辆，红色光条提前激活时的过街感知安全性低于延迟激活时，而绿色/青色WALK信息延迟激活时的过街感知安全性则高于提前激活时；(5) 视觉干扰对过街感知安全性无显著影响。本研究得出结论：行人在过街决策中会采用以自我为中心的视角；挡风玻璃并非eHMI的有效安装位置；常被推荐的青色eHMI或应避免使用；eHMI的激活距离与启动显著性存在复杂关联效应。