External Human–Machine Interfaces for Automated Vehicles in Shared Spaces: A Review of the Human–Computer Interaction Literature
DOI: 10.3390/s23094454
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Summary
This review paper addresses the critical safety and communication challenges arising from the integration of automated vehicles (AVs) into shared spaces, focusing specifically on interactions with vulnerable road users (VRUs) such as pedestrians and cyclists. The research is motivated by the fact that VRUs account for more than half of global road fatalities and are particularly at risk in environments lacking formal traffic controls. While AVs are touted for reducing human error, their lack of visible drivers removes conventional non-verbal cues like eye contact, creating ambiguity in negotiation situations. The authors identify a significant gap in existing literature regarding how external human–machine interfaces (eHMIs) can facilitate clear communication in shared spaces—areas where priority is determined by social interaction rather than traffic signals. The study aims to synthesize current knowledge on eHMI design, evaluation, and application in these specific contexts to identify research gaps and guide future development. The authors conducted a critical review of the human–computer interaction (HCI) literature, analyzing studies on eHMI technologies, VRU-AV communication, and the unique characteristics of shared spaces. The review categorizes shared spaces into three types: Pedestrian Prioritized Streets, Informal Streets, and Enhanced Streets, noting that the level of "sharedness" affects user behavior and safety perceptions. The analysis covers various eHMI concepts designed to inform VRUs of vehicle states and intentions, as well as evaluation methodologies, including the innovative use of Virtual Reality (VR) to assess user responses in controlled scenarios. The paper examines how eHMIs resolve ambiguity, influence trust, and impact crossing decisions, while also reviewing the broader context of active transport increases post-pandemic and the specific risks associated with low-speed automated pods in urban environments. Key findings indicate that while eHMIs generally improve pedestrian safety and trust by clarifying vehicle intentions, there are significant limitations in current research. The review highlights that most studies focus on conventional roads, leaving a lack of empirical evidence regarding eHMI effectiveness in shared spaces where interaction norms differ. Furthermore, the literature predominantly focuses on pedestrians, with insufficient research on cyclists, who are an increasingly vulnerable group. The authors also note potential negative effects, such as VRUs over-relying on eHMIs after repeated exposure, which could lead to dangerous situations. Additionally, technical challenges in implementation and the absence of standardized eHMI designs remain unresolved. The review underscores that misinterpretation of traffic situations contributes significantly to collisions, and without clear communication tools, AVs may cause increased "standstill" interactions and frustration for VRUs. The significance of this work lies in its identification of specific directions for future research to ensure the safe integration of AVs. The authors conclude that further investigation is needed into the effects of eHMIs on cyclists, the potential negative consequences of interface reliance, and the technical hurdles of deployment. Crucially, the paper argues for more research into eHMIs within shared spaces, where the absence of formal rules makes clear communication even more vital. By bridging the gap between human factors and emerging technology literature, this review provides a structured overview for researchers and industry stakeholders to develop standardized, effective communication interfaces that enhance safety for all road users in complex, shared urban environments.
Provenance
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | OpenAlex-citations | — | — | 1 | 2026-06-25 |
| archive | success | core_acuk | — | — | 3 | 2026-06-26 |
| extract | success | cached | — | — | 2 | 2026-06-26 |
| clean | success | clean | — | — | 1 | 2026-06-25 |
| chunk | success | chunk | — | — | 1 | 2026-06-25 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-25 |
| promote | success | — | — | — | 1 | 2026-06-25 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 1 | 2026-06-26 |
| tag | success | vector_similarity | — | — | 6 | 2026-06-25 |
| verify | partial | — | — | — | 1 | 2026-06-26 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified_with_issues.
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- Synthesis & Review: research agenda