Principles for External Human–Machine Interfaces

Wilbrink, Marc; Cieler, Stephan; Weiß, Sebastian L.; Beggiato, Matthias; Joisten, Philip; Feierle, Alexander; Oehl, Michael · 2023 · Crossref

DOI: 10.3390/info14080463

archive: archived pipeline: cataloged verified

Get this paper ↗ (DOI — opens at the source; we link to it, we don't host it)

Summary

This paper addresses the challenge of integrating connected and automated vehicles (CAVs) into mixed-traffic environments where they must interact safely with other road users (ORU). While external human–machine interfaces (eHMIs) have demonstrated benefits for trust and acceptance, current eHMI designs are highly varied and often contradictory, hindering the development of consistent mental models among road users. To resolve this lack of harmonization, the authors propose a set of design guidelines to ensure safe and efficient communication between CAVs and ORU. The authors derived these guidelines through a multi-method approach involving the evaluation of existing literature on human–machine interaction and traffic psychology, focus groups with drivers, and insights from over 40 user studies and expert workshops conducted during the German @CITY-AF project. Over a two-year period, these inputs were iteratively refined in expert workshops to formulate 17 heuristics, termed "eHMI-principles." These principles are structured into two categories: Category A (ten principles) addresses *how* a CAV should communicate, while Category B (seven principles) addresses *in which situations* communication should occur. The principles are designed as application-oriented recommendations rather than normative homologation guidelines. The proposed principles emphasize clarity, consistency, and context-awareness. Key findings include Principle A1, which mandates that signals be clear and unambiguous to avoid accidents, and Principle A5, which requires explicit eHMI signals to align with implicit dynamic HMI (dHMI) signals, such as vehicle acceleration or braking, to prevent contradictory messages. Principle A3 advocates for prosocial communication, suggesting CAVs should signal considerate behaviors like yielding to encourage cooperative traffic flow. Principle A7 highlights the need to adapt sensory modalities (e.g., visual vs. auditory) based on the physical and psychological states of ORU, such as distraction or impairment. Additionally, Principle A8 requires eHMIs to adapt to environmental conditions like lighting and weather to ensure signal salience. The principles also cover consistency across different vehicle types (A4) and the importance of informing passengers about external communications to maintain situational awareness (A9). The significance of this work lies in providing a systematic framework for the design and evaluation of eHMIs, addressing the current fragmentation in the field. By establishing these heuristics, the authors aim to facilitate the harmonization of eHMI signals across manufacturers and scenarios. This harmonization is critical for enabling ORU to build accurate mental models of CAV behavior, thereby enhancing traffic safety, efficiency, and public acceptance of automated vehicles. The paper also identifies open research questions, such as the temporal coordination of dHMI and eHMI and the long-term effects of eHMI use on user trust, guiding future empirical studies.

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed.

Summary generated by qwen3.6-27b-prismaquant on 2026-06-26; verification: verified_with_issues.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• ehmi external hmi
• vru facing ehmi
• automation
• odd communication

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Applied Guidance: design guidelines