Cooperative Adaptive Cruise Control Human Factors Study : Experiment 4 : Preferred Following Distance and Performance in An Emergency Event
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Summary
This study, the fourth in a series on Cooperative Adaptive Cruise Control (CACC) human factors, investigates how drivers’ preferred following distances influence workload and performance during emergency events. CACC systems use vehicle-to-vehicle communication to maintain smaller gaps than conventional adaptive cruise control, potentially increasing roadway capacity. However, shorter gaps may cause driver discomfort or impair takeover performance. The research aimed to determine if individual preferences for following distance affect crash avoidance, workload, and reactions to merging vehicles or emergencies. The experiment utilized a driving simulator with 98 licensed drivers. It was divided into two parts. Part 1 established each participant’s preferred following distance by having them drive at both comfortable and minimum safe distances behind a lead vehicle at varying speeds. The median preferred gap was determined to be 0.91 seconds. In Part 2, participants were assigned to either a "near" (0.6 s) or "far" (1.1 s) CACC following gap, creating congruent or incongruent conditions relative to their preferences. Participants drove in a dedicated lane within a platoon, experiencing a vehicle merge and a simulated emergency crash event requiring driver intervention. Workload was measured using the NASA Task Load Index (NASA-TLX) at three points: after the merge, during steady cruising, and after the crash event. Results indicated that driver workload did not vary significantly between the cruise period and the merge event, but it increased substantially after the emergency crash event. Crucially, workload levels were unaffected by either the assigned following distance or the driver’s preferred following distance. Regarding performance, participants assigned to the near following distance were significantly more likely to hover their foot over the brake pedal during the merge event and reacted faster to the emergency crash event compared to those in the far distance group. However, a driver’s personal preference for following distance did not significantly affect their ability to avoid collisions or their reaction times. The data suggest that performance depends more on the system’s assigned gap settings than on individual driver preferences. The findings imply that CACC systems can effectively implement standardized following distance gaps based on vehicle physics rather than accommodating individual driver preferences, as personal preferences do not correlate with crash avoidance performance. However, the study highlights that drivers in closer following distances remain vigilant, evidenced by brake hovering and faster emergency reactions. The authors conclude that clear alerts for takeover situations are critical for safety, as reduced arousal from automation could otherwise impair performance. This supports the feasibility of widespread CACC implementation while emphasizing the need for robust human-machine interface designs to ensure timely driver intervention.
Key finding
Drivers following at a shorter assigned distance reacted faster to an emergency event and were more likely to hover over the brake during a merge, while preferred following distance did not affect performance.
Methodology
simulator
Sample size: 93
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.
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- Empirical Findings: behavioral performance data