Forward collision warning requirements project : refining the CAMP crash alert timing approach by examining "last second" braking and lane change maneuvers under various kinematic conditions

Kiefer, Raymond J.; Cassar, M.T.; Flannagan, C.A.; LeBlanc, D.J.; Palmer, M.D.; Deering, R.K.; Shulman, M.A. · 2003 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This study, conducted by the Crash Avoidance Metrics Partnership (CAMP) for the National Highway Traffic Safety Administration, addresses the refinement of crash alert timing requirements for Forward Collision Warning (FCW) systems. Building upon previous CAMP research, the project aimed to validate and expand the understanding of driver deceleration behavior under a wider range of vehicle-to-vehicle kinematic conditions. Specifically, the research sought to determine if existing alert timing models remained robust when applied to scenarios involving lead vehicles moving at constant speeds, and to assess the potential for nuisance alerts during intentional lane-change maneuvers. By examining both "last-second" braking and steering behaviors, the study aimed to define the kinematic envelopes that distinguish normal driving from emergency avoidance, thereby improving the accuracy of FCW alert triggers. The experimental design utilized a closed-course methodology at the Transportation Research Center in Ohio, employing a "surrogate target"—a mock vehicle rear end mounted on an impact-absorbing trailer—to safely simulate rear-end crash threats. Seventy-two participants, stratified by age (20–70) and gender, performed last-second braking and steering maneuvers in a 1997 Ford Taurus SHO. Drivers were instructed to execute maneuvers using either "normal" or "hard" intensity levels across three scenario types: stationary lead vehicles, lead vehicles moving at constant slower speeds, and decelerating lead vehicles. Data collection included detailed kinematic metrics such as speed, acceleration, and range. The resulting database comprised 3,536 braking trials and 790 steering trials, which were analyzed to model driver response thresholds. The study yielded two primary modeling outcomes. First, it validated the previously established "Required Deceleration Model," finding it robust and largely unaffected by the expanded kinematic conditions. Second, the researchers developed a new "3-Tiered Inverse Time-to-Collision (TTC) Model." This logistic regression-based model predicts the probability of a hard braking onset based on an inverse TTC threshold that decreases linearly with speed. A key advantage of this new model is its reliance on only coarse knowledge of lead vehicle deceleration, addressing technological challenges in real-time sensing. Comparative analysis showed the 3-Tiered Inverse TTC Model performed comparably to, and in some cases better than, the Required Deceleration Model. Additionally, the study found that last-second steering onsets often occurred later than hard braking onsets at higher speeds, suggesting that FCW systems based solely on braking data might trigger nuisance alerts during intentional lane changes. The significance of this work lies in providing a more flexible and technologically feasible framework for FCW alert timing. The 3-Tiered Inverse TTC Model offers a probabilistic approach that can be adjusted for driver characteristics and environmental conditions, potentially reducing false alarms. The findings highlight the necessity of considering steering behaviors in alert timing algorithms to avoid annoying drivers during normal lane changes. However, the authors note that further field operational testing is required to determine the acceptable level of nuisance alerts in real-world driving contexts. This research contributes critical human factors data to the development of effective collision avoidance systems, balancing safety efficacy with user acceptance.

Key finding

The 3-Tiered Inverse Time-To-Collision Model provided comparable or more favorable performance than the Required Deceleration Model while requiring only coarse knowledge of lead vehicle deceleration, and last-second steering onsets occurred later than braking onsets at 60 MPH, indicating potential for nuisance alerts during lane changes.

Methodology

on_road

Sample size: 72

Provenance

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

Topics

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

Information type

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• Empirical Findings: behavioral performance data