Surprise Braking Trials, Time-to-Collision Judgments, and “First Look” Maneuvers Under Realistic Rear-End Crash Scenarios

Kiefer, R. J.; Cassar, M. T.; Flannagan, C. A.; Jerome, C. J.; Palmer, M. D. · 2005 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This report evaluates the effectiveness of Forward Collision Warning (FCW) systems in preventing rear-end crashes, building upon previous Crash Avoidance Metrics Partnership (CAMP) research. The study addresses two primary goals: assessing how various factors influence the robustness of a specific FCW alert timing approach, and understanding driver decision-making and avoidance maneuvers under realistic crash scenarios. The research aims to determine if FCW alerts are effective across different driver characteristics, distraction types, and kinematic conditions, and to validate methods for simulating distracted driving states. The researchers employed a surrogate target, test-track methodology involving 260 participants aged 20–70. This setup used three vehicles: a subject vehicle driven by the participant, a lead vehicle towing a mock surrogate target, and a principal other vehicle controlling the lead vehicle’s braking. The study comprised three experimental phases. First, "surprise braking trials" involved 17 conditions where drivers were intentionally distracted (via head-down or eyes-forward tasks) immediately before an unexpected lead vehicle braking event, triggering an FCW alert. Second, "time-to-collision (TTC) judgment" studies used visual occlusion to block drivers' vision during the final phase of an approach, requiring them to press a button when they perceived a collision was imminent. Third, "first-look" maneuvers occluded drivers' vision during the initial approach phase, then suddenly opened it to simulate a surprised, distracted driver who must immediately execute an avoidance maneuver. Performance was measured by intervention rates from a safety driver, brake reaction times, and maneuver choices. The results indicated that the evaluated FCW alert timing, coupled with a single-stage, dual-modality (auditory and visual) alert, was robust and effective. Intervention rates were 6.8% with FCW alerts versus 13.2% without. However, the benefits of FCW alerts were restricted to tasks involving head-down glance activity; no significant benefit was observed for eyes-forward distraction tasks. All interventions occurred when drivers were looking down at the time of the alert, suggesting that eye-tracking technology could improve alert timeliness and reduce false alarms. TTC judgment studies revealed that drivers can quickly assess collision risk and execute appropriate maneuvers if looking toward the lead vehicle, utilizing an efficient optic flow heuristic. Notably, the probability of overestimating TTC increased with higher relative velocities. Across all conditions, there were generally no significant age or gender effects, suggesting FCW alerts may equalize crash avoidance abilities among diverse drivers. The study concludes that the CAMP FCW alert timing approach is feasible as a "one-size-fits-all" solution for closing alerts. The findings support the use of eye movement sensing to enhance system credibility by tailoring alerts to driver gaze location. Additionally, the "first-look" visual occlusion method was validated as an efficient tool for exploring the consequences of later FCW alert timing, which could help balance crash avoidance effectiveness with the reduction of false alarms. These results provide critical calibration data for comparing real-world driving behavior with simulated environments, such as the National Advanced Driving Simulator, aiding in the development of more effective crash avoidance systems.

Key finding

FCW alerts significantly reduced test driver interventions during head-down distraction tasks but provided no benefit for eyes-forward distraction tasks, with no significant differences observed across age or gender groups.

Methodology

on_road

Sample size: 260

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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

• time to collision looming
• braking response
• temporal
• visual
• following distance
• perception reaction time

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).

• Empirical Findings: behavioral performance data, observational prevalence
• Methodological Resource: measurement protocol