External Human–Machine Interfaces for Autonomous Vehicle-to-Pedestrian Communication: A Review of Empirical Work

Rouchitsas, Alexandros; Alm, Håkan · 2019 · OpenAlex-citations

DOI: 10.3389/fpsyg.2019.02757

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Summary

This review paper addresses the critical challenge of facilitating communication between autonomous vehicles (AVs) and pedestrians. As AVs replace human drivers, the informal communicative cues currently used in traffic—such as eye contact, gestures, and facial expressions—will disappear, potentially compromising safety and efficiency. The authors aim to provide a comprehensive account of empirical research on external human–machine interfaces (EHMIs) designed to bridge this gap by informing pedestrians of an AV’s state, intentions, and perception of its surroundings. The authors conducted a systematic review of published empirical studies evaluating EHMIs. Studies were identified through manual searches of Google Scholar using specific keywords, supplemented by snowball and citation searches. Inclusion criteria required that studies involve controlled evaluations with human participants. The review categorizes the literature based on methodology, distinguishing between studies using physical prototypes (often employing the "Wizard of Oz" technique to simulate autonomy in real-world settings) and those using laboratory-based simulations via desktop monitors or virtual reality (VR). The latter methods offer greater experimental control and safety, while physical prototypes provide higher ecological validity. The review synthesizes findings from various interface designs, including LED strips, displays, projections, and auditory signals. Key findings indicate that pedestrians generally benefit from the presence of communication interfaces, which enhance feelings of safety and confidence. Specific studies highlight that visual cues, particularly lights and colors, are preferred over text or speech for conveying vehicle intentions. For instance, turquoise light was identified as highly salient and appropriate for AV communication. Research involving physical prototypes, such as Hensch et al. (2019) and Costa (2017), demonstrated that while interfaces can improve pedestrian confidence in crossing, some designs were found to be intuitively incomprehensible or only partially trustworthy. Furthermore, providing information about whether the vehicle has detected the pedestrian was prioritized by users over other data. The significance of this work lies in its identification of current gaps in the field. While empirical evidence supports the utility of EHMIs, the authors conclude that standardized evaluation procedures and optimal interface specifications are still lacking. The review underscores the need for interfaces that are intelligible, unambiguous, and scalable to support multiple road users. It highlights that despite technological advancements, there is no consensus on the best design parameters, and further research is required to establish robust standards for AV-to-pedestrian communication to ensure safety and acceptance in mixed-autonomy traffic environments.

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Topics

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• ehmi external hmi
• vru facing ehmi
• automation
• driver vru interaction

Information type

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• Applied Guidance: design guidelines