Light-Based External Human Machine Interface: Color Evaluation for Self-Driving Vehicle and Pedestrian Interaction
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Summary
This study addresses the critical need for standardized External Human-Machine Interfaces (eHMI) in self-driving vehicles (SDVs) to facilitate safe interactions with pedestrians. As SDVs lack human drivers, traditional communication methods like eye contact are unavailable, creating discomfort and safety risks for vulnerable road users. While eHMIs can signal vehicle status, design guidelines remain undefined. This research specifically evaluates the suitability of two colors—white and turquoise—for eHMI lamps indicating that an Automated Driving System (ADS) is engaged. The study aims to determine which color better supports pedestrian perception, safety, and trust, and whether these evaluations remain consistent across different traffic scenarios. The researchers conducted a Wizard-of-Oz experiment with 59 participants at Daimler AG’s testing center in Germany. A Mercedes-Benz E-Class was modified with fake sensors and LED strips on the roof to simulate an SDV. Participants were divided into two groups encountering either an intersection scenario or a parking lot scenario. In both cases, the vehicle used a steady light to signal ADS engagement. Participants experienced both white and turquoise lights in a randomized within-subject design. Data were collected via questionnaires rating visibility, saliency, discriminability, recognition, suitability, attractiveness, safety, and trust on a 7-point scale, followed by structured interviews. Qualitative content analysis was performed on interview transcripts to identify specific benefits and limitations of each color. The results demonstrated that turquoise was significantly rated higher than white across all measured subjective factors (p < .001). Pedestrians perceived turquoise as more visible, salient, and distinctive from other vehicle lights and traffic signals. It also elicited higher levels of recognition, suitability, attractiveness, sense of safety, and trust. Qualitative analysis revealed that 55 of 55 participants who expressed a preference chose turquoise. Participants noted that white is an "occupied" color, commonly used for headlights and daytime running lights, leading to potential confusion and lower discriminability. In contrast, turquoise was viewed as an unoccupied, informative, and noticeable color. While visibility and saliency ratings were higher in the parking lot scenario than at the intersection, likely due to proximity, the preference for turquoise remained consistent across both contexts. The study concludes that turquoise is a superior color for eHMI lamps indicating ADS engagement compared to white. Its distinctiveness prevents confusion with existing vehicle lighting and traffic signals, thereby enhancing pedestrian awareness and trust. These findings provide evidence-based design guidelines for the automotive industry and standardization bodies like SAE and ISO. By adopting turquoise, manufacturers can improve the clarity of communication between SDVs and pedestrians, contributing to safer urban traffic environments and greater public acceptance of automated driving technologies.
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.
| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | Crossref | — | — | 1 | 2026-08-09 |
| archive | success | openalex | — | — | 5 | 2026-08-09 |
| extract | success | pdftotext | — | — | 4 | 2026-08-10 |
| clean | success | clean | — | — | 2 | 2026-08-10 |
| chunk | success | chunk | — | — | 2 | 2026-08-10 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 2 | 2026-08-10 |
| promote | success | — | — | — | 1 | 2026-08-09 |
| summarize | success | llm | qwen3.6-27b-nvidia | summ-v5 | 2 | 2026-08-10 |
| tag | success | vector_similarity | — | — | 17 | 2026-08-11 |
| verify | partial | — | — | — | 2 | 2026-08-10 |
Summary generated by qwen3.6-27b-nvidia on 2026-08-10; verification: verified_with_issues.
Topics
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- ehmi external hmi
- vru facing ehmi
- emergency work zone conspicuity
- vru conspicuity
- roadway lighting effects
- vehicle conspicuity
Information type
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- Applied Guidance: design guidelines