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