Impacts of Using Dynamic Features to Display Messages on Changeable Message Signs

Dudek, Conrad L.; Schrock, Steven D.; Ullman, Gerald L. · 2005 · ROSA P / United States. Federal Highway Administration. Operations Office of Travel Management

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Summary

This study, conducted by the Texas Transportation Institute for the Federal Highway Administration, investigates the human factors impacts of using dynamic display features on Changeable Message Signs (CMS). The research was motivated by the widespread but unverified practice among state Departments of Transportation of using dynamic features—such as flashing entire messages, flashing single lines, or alternating text with redundancy—to attract driver attention and emphasize message importance. The primary objective was to determine whether these features improve communication effectiveness or adversely affect reading times, comprehension, driver preference, and driving performance. The researchers employed a driving simulator study involving 64 subjects from the Bryan–College Station, Texas area, selected to represent the Texas driving population in terms of age, education, and gender. To simulate realistic driving workload, participants followed a lead vehicle that varied its speed significantly during message presentation, forcing drivers to divide attention between the driving task and reading the CMS. The study evaluated three specific dynamic features against static or non-redundant alternatives: (1) flashing an entire one-phase, three-line message; (2) flashing only the top line of a one-phase, three-line message; and (3) alternating the bottom line of a two-phase message while keeping the top two lines constant (creating redundancy). Measures of effectiveness included reading times, message comprehension, driver preference, and seven driving performance metrics, such as acceleration noise and lane position stability. The results indicated mixed effects depending on the dynamic feature used. For flashing entire one-phase messages, average reading times were not significantly higher than static messages, but comprehension suffered for unfamiliar drivers, with only 78% understanding the bottom line. Furthermore, 61% of subjects preferred static displays, citing easier readability and more time to process information. Flashing a single line significantly increased reading times and negatively impacted comprehension, particularly for the non-flashing lines, though driver preference was evenly split between flashing and static options. For alternating messages with redundancy, reading times were significantly longer than for non-redundant messages, yet comprehension levels remained similar. Notably, 59% of subjects preferred the redundant alternating message, suggesting that while it slowed reading, it was perceived as more effective or acceptable by drivers. No significant differences were found in driving performance metrics across the different message modes, nor were there significant effects based on age, education, or gender. The study concludes that while dynamic features do not necessarily impair vehicle control, they often hinder message comprehension and increase reading times, particularly for flashing single lines and redundant alternating messages. The findings suggest that flashing entire messages may be detrimental to understanding for drivers unfamiliar with the format, while redundancy, despite increasing reading time, is preferred by a majority of drivers. These results provide empirical evidence to guide the Manual on Uniform Traffic Control Devices, recommending caution in the use of flashing features and highlighting the trade-offs between reading speed and driver preference in CMS design.

Key finding

Flashing a single line of a message significantly increased reading times and reduced comprehension of non-flashing text, while alternating redundant lines increased reading times but was preferred by 59 percent of drivers.

Methodology

simulator

Sample size: 64

Provenance

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

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• external distraction

Information type

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• Empirical Findings: behavioral performance data