How Long Does It Take to Stop? Methodological Analysis of Driver Perception-Brake Times
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Summary
Methodological review of perception-brake reaction-time studies that pulls together a much larger set of brake-RT data sets than prior surveys to produce condition-specific estimates rather than a single canonical figure. Green argues that driver expectation is the dominant variable, doubling RT between fully-expected and surprise conditions: ~0.70–0.75 s for fully cued brake signals, ~1.25 s for unexpected but common signals (e.g., a lead car braking), and ~1.5 s for surprise events (e.g., an object suddenly entering the driver's path). Secondary modulators include age, gender, cognitive load, and urgency. The paper critiques regulatory norms (2.5 s in the U.S., 2.0 s in Europe) and prior factor-analytic syntheses that ignored methodological flaws, instead arguing that brake-RT estimates are only meaningful when conditioned on driver expectancy and stimulus type.
Key finding
Driver brake reaction time depends primarily on expectancy: ~0.70–0.75 s when fully expected, ~1.25 s for unexpected common signals, and ~1.5 s for surprise events.
Methodology
literature_review
Sample size: Exp 1: N=10; Exp 2: N=20
Quality score: 5 / 5