Express What I Think: The Impact of External Human-Machine Interfaces on the Performance of Lane Change Maneuvers
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Summary
This study investigates the impact of External Human-Machine Interfaces (eHMIs) on vehicle-to-vehicle interactions, specifically focusing on lane-change maneuvers. While prior research has extensively examined eHMIs in autonomous vehicle-pedestrian contexts, this work addresses a gap in understanding how explicit intention communication affects human drivers in dynamic, vehicle-to-vehicle scenarios. The researchers aimed to determine whether displaying lane-changing intentions via eHMIs improves safety and efficiency, and whether the tone of the message (command, polite, or explanatory) influences driver yielding behavior and subjective usability. The study employed a within-subject driving simulation experiment with 32 licensed participants (aged 20–35). Participants drove an 8-kilometer, three-lane highway scenario with moderate congestion. During four lane-changing events per drive, a cutting-in vehicle accelerated and merged into the participant’s lane. The cutting-in vehicle displayed one of three text-based eHMIs on its rear and sides: a command message ("Changing lanes, slow down immediately"), a polite message ("Changing lanes, please yield to me"), or an explanatory message ("About to exit ramp, preparing for lane change"). A baseline condition with no eHMI was also included. Participants were not informed of the eHMIs beforehand to avoid priming effects. Objective metrics included yield rate and minimum time-to-collision (minTTC), while subjective usability was measured using the System Usability Scale (SUS). Statistical analyses utilized Poisson regression for yield rates and Linear Mixed Models for minTTC and SUS scores. The results demonstrated that all three eHMI types significantly increased both yielding rates and minTTC compared to the baseline condition, indicating improved safety and cooperation. However, the tone of the message produced distinct outcomes. The polite eHMI yielded the highest performance, resulting in significantly higher yield rates and greater minTTC than both the command and explanatory conditions. In terms of subjective evaluation, the polite eHMI received the highest usability scores. Interestingly, while the command and explanatory eHMIs did not differ significantly in safety metrics, participants perceived the explanatory eHMI as more usable than the command eHMI, likely because the latter’s authoritarian tone triggered psychological resistance. Gender did not significantly affect behavioral or subjective outcomes. The findings underscore that explicitly expressing lane-changing intentions through eHMIs enhances traffic safety and efficiency among human drivers. Crucially, the study highlights that message framing matters: polite requests foster greater compliance and safety margins than direct commands or simple explanations. This suggests that eHMI design should prioritize cooperative social cues over mere informational clarity to optimize driver cooperation. The study provides foundational evidence for integrating eHMIs into human-driven vehicles to improve interaction transparency, while noting limitations such as the simulator environment and the need for future research on multimodal interfaces and diverse demographic groups.
Key finding
Polite external human-machine interfaces resulted in the highest yielding rates, greatest minimum time to collision, and highest perceived usability compared to command, explanatory, and baseline conditions during simulated lane-change maneuvers.
Methodology
simulator
Sample size: 32
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | — | — | — | 1 | 2026-05-28 |
| archive | success | canonical_url | — | — | 1 | 2026-06-06 |
| extract | success | cached | — | — | 3 | 2026-06-10 |
| clean | success | clean | — | — | 1 | 2026-06-07 |
| chunk | success | chunk | — | — | 1 | 2026-06-07 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-06-07 |
| enrich | success | semantic_scholar | — | — | 4 | 2026-06-15 |
| promote | success | — | — | — | 1 | 2026-06-04 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 2 | 2026-06-10 |
| tag | success | vector_similarity | — | — | 15 | 2026-06-11 |
| verify | success | — | — | — | 2 | 2026-06-10 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.
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