Color and Animation Preferences for a Light Band eHMI in Interactions Between Automated Vehicles and Pedestrians

Dey, Debargha; Habibovic, Azra; Pfleging, Bastian; Martens, Marieke; Terken, Jacques · 2020 · OpenAlex-citations

DOI: 10.1145/3313831.3376325

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Summary

This study addresses the lack of empirical guidance regarding the design of external Human-Machine Interfaces (eHMIs) for automated vehicles (AVs), specifically focusing on how to effectively communicate a yielding intention to pedestrians. While light band eHMIs are a popular form factor due to their simplicity, there is no consensus on which colors or animation patterns are most intuitive or safe. The authors investigate whether specific visual cues—colors and animations—carry innate associations that could lead to ambiguity or danger, particularly concerning the use of red and green, which have established meanings in traffic lights but may be misinterpreted when mounted on moving vehicles. To evaluate user preferences, the researchers conducted an online crowdsourcing survey with 400 participants recruited from Amazon Mechanical Turk, restricted to US residents to ensure cultural homogeneity regarding traffic norms. The study employed a mixed experimental design with three independent variables: Color (green, red, cyan), Animation (flash, pulse, in-sweep, out-sweep, dual-sweep), and Message type (Intention announcement: “I am yielding” vs. Instruction: “Please cross”). Participants viewed videos of a Toyota Prius model with the eHMI displayed on the bumper in a featureless background to isolate visual variables. They rated the intuitiveness of each combination on a 5-point Likert scale. Data from participants who failed manipulation checks or showed insufficient variance in responses were excluded, resulting in final sample sizes of 183 for the intention condition and 192 for the instruction condition. The results revealed significant main effects for both color and animation. Cyan was identified as the most neutral and suitable color for communicating a yielding intention, avoiding the contradictory associations found with red and green. Red and green elicited strong but confusing interpretations; for instance, green was often interpreted as the vehicle’s intention to move rather than to yield, while red was ambiguous regarding whether the vehicle or the pedestrian should stop. Regarding animation, uniformly flashing or pulsing patterns were preferred over lateral sweeping or wiping animations. The sweeping patterns, despite their similarity to human hand gestures, did not score higher in intuitiveness. The type of message (intention vs. instruction) did not significantly alter these preferences, though the perspective from which the eHMI was evaluated (color-focused vs. animation-focused) influenced the scores. The significance of this work lies in providing evidence-based recommendations for the standardization of AV eHMIs. The findings suggest that cyan is the optimal color choice to minimize ambiguity, while simple flashing or pulsing animations are more effective than complex sweeping patterns. These insights help resolve the current lack of consensus in eHMI design, contributing to safer and more intuitive interactions between automated vehicles and vulnerable road users. The study highlights the importance of considering innate user associations and avoiding colors that conflict with existing traffic signal meanings.

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Topics

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• ehmi external hmi
• vru facing ehmi