Investigation of Key Automated Vehicle Human Factors Safety Issues Related to Infrastructure: Comparing Intersection Crossing Behaviors of Human Drivers and Automated Vehicles
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Summary
This study investigates the impact of in-vehicle signal countdown timers on human driver behavior at signalized intersections and compares these behaviors with those of automated shuttles. The research addresses safety concerns related to the "dilemma zone," where drivers face uncertainty about whether to stop or proceed during the yellow signal phase. By providing real-time signal phase and timing (SPaT) information via cooperative driving automation (CDA), the study aims to determine if such infrastructure support reduces abrupt braking and improves decision-making consistency compared to automated systems. The methodology involved a field study with 57 licensed human drivers in the Washington, DC, metropolitan area. Participants were assigned to either a countdown group, which received real-time signal phase information on an in-vehicle display, or a control group. Drivers navigated a predefined route approaching a specific intersection, with data collected on speed, acceleration, eye-tracking, and braking patterns. The study also analyzed data from an automated shuttle operating on the same route. Researchers simulated predicted shuttle behaviors at higher speeds to compare against human drivers at lower speeds, aiming to test the hypothesis that automated shuttles would respond more consistently to yellow light onsets than human drivers. Results indicated that the presence of the signal countdown timer regulated human drivers' speed and acceleration within the approach zone, supporting the hypothesis that such information increases the probability of stopping in response to the yellow signal onset. Post-drive questionnaires revealed that participants perceived benefits in safety, trust, usability, and traffic management, with similar response distributions between those who experienced the timer and those who only read about it. However, the study faced significant data limitations: only one of 55 applicable approaches involved a signal change from green to yellow during the approach, preventing a thorough statistical examination of stopping probabilities. Consequently, the hypothesis comparing the consistency of automated shuttles versus human drivers could not be systematically tested. Comparisons of available data suggested human drivers crossed intersections more frequently than shuttles at both lower and higher speeds, though this difference was not statistically significant. The findings highlight the feasibility of comparing human and automated vehicle behaviors across different speeds and underscore the safety benefits of providing real-time signal phase information to drivers. While the study confirms that countdown timers help regulate driver behavior and reduce uncertainty, the lack of sufficient data on yellow-light transitions limits definitive conclusions regarding comparative safety between human and automated vehicles. The research provides a methodological framework for future studies to better evaluate the integration of CDA technologies into mixed traffic environments.
Key finding
The presence of an in-vehicle signal countdown timer regulated human drivers' speed and acceleration during intersection approaches, increasing the likelihood of stopping in response to the yellow signal phase.
Methodology
field_study
Sample size: 57
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. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).
| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | rosap | — | — | 2 | 2026-05-23 |
| archive | success | — | — | — | 1 | 2026-05-23 |
| extract | success | cached | — | — | 2 | 2026-06-10 |
| clean | success | — | — | — | 1 | 2026-06-01 |
| chunk | success | — | — | — | 1 | 2026-06-01 |
| embed | success | — | — | — | 1 | 2026-06-02 |
| enrich | success | — | — | — | 1 | 2026-05-23 |
| promote | success | — | — | — | 1 | 2026-05-23 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 3 | 2026-06-10 |
| tag | success | vector_similarity | — | — | 19 | 2026-06-11 |
| verify | success | — | — | — | 2 | 2026-06-10 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.
Topics
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- ehmi external hmi
- rail grade crossings
- vru facing ehmi
- driver vru interaction
- signaling behavior
- automation
Information type
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- Empirical Findings: behavioral performance data, observational prevalence
- Methodological Resource: tool software