A Systematic Approach on CMS Messaging Selection During Nonrecurring Events: Decision Tree

Weaver, Starla; Ahmed, Ananna; Jannat, Mafruhatul; Olko, Sarah; Arnold, Michelle · 2024 · ROSA P / United States. Federal Highway Administration. Office of Safety and Operations Research and Development

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Summary

This report, published by the Federal Highway Administration (FHWA) in 2024, addresses the challenge of selecting effective Changeable Message Sign (CMS) messaging during nonrecurring events, such as traffic incidents, roadwork, and adverse weather. The primary motivation is to improve roadway safety and operational efficiency by ensuring CMS messages effectively influence driver behavior. While CMSs are critical for disseminating traveler information, inconsistent or poorly constructed messages can fail to prompt necessary behavioral changes or, worse, cause confusion and safety hazards. The report aims to provide CMS operators with a systematic, research-backed framework for constructing messages that are clear, concise, and trustworthy. The methodology involves synthesizing existing research on driver behavior and CMS provisions outlined in the Manual on Uniform Traffic Control Devices (MUTCD). The core of the approach is a set of decision trees designed to guide operators through the selection of specific message components. These trees help determine the message goal, event type, effect of the event, location, suggested action, intended audience, and event time. The report also introduces a CMS Message Construction Worksheet, which integrates these decision trees into a practical tool for generating final messages. The authors emphasize the Problem-Location-Action (PLA) method as a foundational structure but expand upon it to include additional units of information like event effects and timing, prioritizing content based on its impact on driver behavior rather than simply maximizing information density. Key findings highlight that effective CMS messaging relies on strict adherence to visibility and readability standards, such as limiting messages to three lines of text and using familiar, uppercase phrasing. The report identifies that drivers process information in "units," and overloading a sign with more than three units per phrase can lead to reduced reading speeds and increased braking, which creates traffic bottlenecks and rear-end collision risks. The decision trees provide specific guidance on when to include certain components; for instance, they help operators decide whether to display the event itself (e.g., "CRASH") or its effect (e.g., "LANE CLOSED") as the primary problem, depending on which factor most significantly impacts driver decision-making. The report demonstrates through detailed examples, such as crash and roadwork scenarios, how to navigate these trees to produce optimized messages. The significance of this work lies in its provision of a standardized, evidence-based tool for traffic management center operators. By reducing ambiguity in message construction, the approach aims to cultivate driver trust in CMS information, leading to more consistent and appropriate behavioral responses. This systematic method supports the broader goal of Intelligent Transportation Systems (ITS) by enhancing the reliability of traveler information during unpredictable events, ultimately contributing to safer and more efficient traffic flow. The report serves as a practical guide for transportation engineers and agency leadership to align CMS operations with established safety and operational research.

Key finding

A systematic decision-tree approach enables CMS operators to construct standardized, research-backed messages that effectively influence driver behavior during nonrecurring events.

Methodology

theoretical

Provenance

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

Topics

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• public messaging