Evaluation of Data From Test Application of Optical Speed Bars to Highway Work Zones [Final Report]

Meyer, Eric · 2004 · ROSA P / K-TRAN (Research program)

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Summary

This study evaluates the effectiveness of optical speed bars—transverse pavement markings with gradually decreasing spacing—in reducing vehicle speeds and speed variations within highway work zones. The research was motivated by the critical safety concerns associated with the proximity of workers to moving traffic and the tendency of drivers to underestimate speed, particularly after prolonged highway driving. While optical speed bars had demonstrated success at roundabout approaches and freeway exit ramps, their application to work zones required specific design adaptations because drivers are expected to maintain reduced speeds over long distances rather than stopping completely. The research, conducted by Eric Meyer at the University of Kansas and sponsored by the Kansas Department of Transportation, involved developing a specialized three-component pattern: a leading pattern of uniformly spaced bars, a primary pattern with graduated spacings, and an intermittent work zone pattern consisting of groups of six bars separated by large gaps. Simulations were utilized to visualize design parameters before implementation. Data collection employed pneumatic hose counters to record vehicle speeds at multiple points before and after the installation of the markings. The analysis focused on mean speeds, 85th percentile speeds, and standard deviations, comparing daytime and nighttime performance across different vehicle classifications. The results indicated that the optical speed bars caused small but measurable reductions in mean and 85th percentile speeds, as well as in speed standard deviations. The study identified two distinct mechanisms for these reductions: warning effects and perceptual effects. Warning effects, which persisted downstream of the pattern, contributed to sustained speed reductions. In contrast, perceptual effects were limited to the area with graduated spacings; drivers increased their speed once they exited this specific section. Notably, the intermittent work zone pattern designed to maintain speed reductions downstream proved ineffective, having no significant impact on speeds or speed variations. The effectiveness of the bars was greatest for passenger cars during daylight hours. The findings suggest that while optical speed bars are effective at reducing speed variation and mean speeds in work zones, their impact is modest and dissipates quickly once the visual stimulus ends. The persistence of reduced speed variation downstream indicates a lasting benefit in traffic uniformity, even if absolute speed reductions fade. The study concludes that the intermittent pattern is not a viable method for maintaining speed control over long distances. These results provide specific guidance for transportation agencies considering perceptual countermeasures, highlighting the limitations of optical bars in maintaining long-term speed compliance without additional enforcement or geometric changes.

Key finding

Optical speed bars with graduated spacings reduced mean and 85th percentile speeds and speed variations, with warning effects persisting downstream while perceptual effects dissipated after the pattern.

Methodology

field_study

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).

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.

• perceptual countermeasures
• work zones
• speed management
• emergency work zone conspicuity
• speed choice