Effectiveness of Changeable Message Signs in Controlling Vehicle Speeds in Work Zones

Garber, Nicholas J; Patel, Surbhi T · 1994 · ROSA P / Virginia Transportation Research Council

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Summary

This study evaluates the effectiveness of Changeable Message Signs (CMS) equipped with radar units in reducing vehicle speeds within highway work zones. The research was motivated by the rising number of fatalities and accidents in construction zones during the 1980s and early 1990s, with excessive speed identified as a primary contributing factor. Traditional static speed control measures, such as regulatory and advisory signs, were found to be largely ineffective because drivers often ignore them unless immediate hazards are visible. While active methods like law enforcement and flagging are effective, they are costly and resource-intensive for long-term projects. The study aimed to determine if radar-activated CMS, which provides personalized, real-time warnings to speeding drivers, could serve as a more efficient and effective speed control method. The experimental design involved testing four specific CMS messages at seven work zones on two interstate highways in Virginia. The messages tested were: "YOU ARE SPEEDING SLOW DOWN," "HIGH SPEED SLOW DOWN," "REDUCE SPEED IN WORK ZONE," and "EXCESSIVE SPEED SLOW DOWN." Data collection utilized automatic traffic counters to record speed and volume for the entire traffic population, while videotaping was employed to track specific vehicles that triggered the radar-activated display. This allowed for a comparative analysis of speed characteristics—including average speeds, 85th percentile speeds, speed variance, and the percentage of vehicles speeding by various margins—between conditions using only standard Manual on Uniform Traffic Control Devices (MUTCD) signing and those using CMS. Statistical methods, including odds ratios, analysis of variance, and t-tests, were applied to assess significance. The results demonstrated that CMS effectively reduced speeding across all metrics. Odds ratios indicated a significant reduction in the number of vehicles speeding by any amount, as well as by 5 mph or more and 10 mph or more, when CMS was used compared to MUTCD signing alone. Analysis of variance confirmed that all speed characteristics were reduced with any of the four messages, though some reductions did not reach statistical significance at the 0.05 level. The messages were ranked by effectiveness, with "YOU ARE SPEEDING SLOW DOWN" proving the most effective, followed by "HIGH SPEED SLOW DOWN," "REDUCE SPEED IN WORK ZONE," and "EXCESSIVE SPEED SLOW DOWN." Crucially, t-tests revealed that all messages significantly reduced the average speeds of high-speed vehicles (those traveling 59 mph or faster in a 55 mph zone) compared to standard signing. The study concludes that radar-activated CMS is a highly effective tool for controlling vehicle speeds in work zones, particularly for targeting high-speed drivers who are most at risk. By providing dynamic, personalized feedback, CMS overcomes the limitations of static signs and offers a cost-effective alternative to labor-intensive methods like flagging or law enforcement. The findings support the integration of Intelligent Vehicle Highway System (IVHS) technologies into work zone safety strategies, suggesting that real-time information significantly influences driver behavior and enhances safety in construction environments.

Key finding

Changeable message signs with radar units significantly reduced average speeds, 85th percentile speeds, speed variance, and the percentage of vehicles speeding by any amount, 5 mph, or 10 mph compared to standard MUTCD signing, with the message 'YOU ARE SPEEDING SLOW DOWN' proving most effective.

Methodology

field_study

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.

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