Improved perception-reaction time information for intersection sight distance

Hostetter, Robert S.; McGee, H. W.; Crowley, K. W.; Seguin, E. L.; Dauber, G. W. · 2002 · ROSA P / United States. Federal Highway Administration

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Summary

This study addresses the lack of empirical evidence supporting the perception-reaction time (PRT) specifications used in intersection sight distance standards established by the American Association of State Highway and Transportation Officials (AASHTO). Specifically, it evaluates the adequacy of current PRT values for YIELD-controlled (Case II) and STOP-controlled (Case III) intersections. The research was motivated by the finding that existing PRT values, such as the 2.0 seconds prescribed for Case III and the implied 2.5 seconds for Case II, were largely assumed rather than derived from operational data. To generate empirical data, researchers conducted field experiments using an instrumented vehicle driven by 124 licensed subjects across a 3-hour circuit containing 52 intersections. The vehicle recorded brake, accelerator, and steering inputs, while an experimenter logged discrete events such as head movements and the presence of crossing traffic. Subjects drove under both unalerted and alerted conditions. For Case II intersections, PRT was measured from the point of first possible perception to the first reaction (accelerator release or brake application). For Case III intersections, PRT was defined as the interval from the first head movement after stopping to the application of the accelerator to enter the intersection. The results for Case II intersections indicated that drivers initiated their first reaction before reaching the stopping sight distance in over 90 percent of trials, regardless of whether crossing vehicles were present. This finding, combined with prior validation of stopping sight distance PRT, led to the conclusion that current specifications for Case II are adequate. No significant differences in PRT were observed based on age or sex. For Case III intersections, the mean PRT was 1.82 seconds, with the 85th percentile value at approximately 2.7 seconds. Analysis revealed that through movements yielded lower PRT values than turning movements. Consequently, the authors recommended maintaining the current 2.0-second PRT for Case IIIA (through movements) but increasing the PRT to 2.5 seconds for Cases IIIB and IIIC (left and right turns). Similar to Case II, no significant age or sex differences were found for Case III measures. The significance of this research lies in its provision of operational data to refine highway design standards. By distinguishing between through and turning movements at STOP-controlled intersections, the study supports a more nuanced approach to sight distance requirements. The recommendation to increase PRT for turning movements acknowledges the greater complexity and time required for these maneuvers, potentially improving safety at intersections where drivers must yield to cross traffic.

Key finding

Drivers initiated reactions before stopping sight distance in over 90 percent of yield-controlled intersection trials, while stop-controlled turning movements required a longer perception-reaction time of approximately 2.5 seconds compared to 2.0 seconds for through movements.

Methodology

naturalistic

Sample size: 124

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.

• perception reaction time
• crash reconstruction hf
• hazard perception
• pedestrian behavior perception
• visibility analysis litigation
• looked but failed to see

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
• Methodological Resource: measurement protocol