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，eHMIs）可用于向行人传递自动驾驶车辆（automated vehicle，AV）的行驶意图，但目前尚无定论何种eHMI设计最为有效。本研究通过众包实验，探究了5项因素对行人在面对让行与未让行自动驾驶车辆时的过街感知安全感的影响：(1) 灯光颜色（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、灯带）；(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，受试者需在观看276段搭载eHMI的驶来自动驾驶车辆的随机抽取的40段视频时，于确认过街安全时按下按键。实验结果显示：(1) 搭载绿色与青色eHMI的车辆可使行人产生更高的过街安全感，其效果优于红色eHMI；绿色与青色eHMI的效果无显著差异；(2) 安装于保险杠与车顶的eHMI比挡风玻璃上的eHMI更为有效；(3) 针对让行AV，显示WALK的eHMI所引发的感知安全感高于WILL STOP，其次为灯带；针对未让行AV，红色灯带与红色文本的效果相近；(4) 针对让行AV，提前激活的红色灯带会导致更低的感知安全感，而延迟激活的绿色/青色WALK信号则会提升感知安全感；(5) 环境视觉干扰对过街安全感无显著影响。本研究得出如下结论：行人会采用以自我为中心的视角进行判断；挡风玻璃并非合适的eHMI安装位置；常被推荐的青色eHMI或需避免使用；eHMI的激活距离与激活凸显性存在复杂的关联效应。