Freeway Guide Sign Performance at Complex Interchanges: Reducing Information Overload

Li, Yingfeng (Eric); Kassing, Andrew; Perez, Miguel; Medina, Alejandra; Gibbons, Ronald B. · 2024 · ROSA P / United States. Federal Highway Administration. Office of Safety Research and Development

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Summary

This study addresses the safety risks associated with information overload at complex freeway interchanges, where drivers must process large amounts of navigation data within short timeframes. While the Manual on Uniform Traffic Control Devices (MUTCD) acknowledges the need to avoid information overload, it lacks specific guidelines for the maximum amount of information permissible on guide signs. Previous research relied heavily on simulations or limited experimental studies that failed to capture real-world driving dynamics. This project aimed to fill that gap by analyzing naturalistic driving data to establish evidence-based sign complexity thresholds and design recommendations. The researchers utilized data from the Second Strategic Highway Research Program (SHRP2) Naturalistic Driving Study, which records actual vehicle operator behavior. They identified specific interchange locations and analyzed driver behavior variables, including longitudinal and lateral acceleration and jerk, to correlate these metrics with guide sign complexity. The primary variable for sign complexity was the number of words on the subject sign. The analysis distinguished between drivers familiar with an interchange and those unfamiliar, as well as varying roadway conditions such as lane change requirements and visual background complexity. Statistical modeling, including linear mixed-models, was employed to determine significant correlations between sign design features and unsafe driver maneuvers. The findings revealed that sign complexity significantly correlates with adverse driver behaviors, particularly among drivers unfamiliar with the interchange. The "Number of Words on Subject Sign" was the most impactful variable, negatively affecting driver performance more severely for unfamiliar users than for familiar ones. Based on these correlations, the study established specific complexity thresholds: guide signs for right ramps requiring at least one lane change should contain no more than nine words. For right ramps where exiting traffic is already in the correct lane and requires no lane changes, signs should contain no more than ten words. The study also identified other factors, such as visual background complexity and sign lighting, that influence driver behavior. The significance of this research lies in its provision of concrete, data-driven guidelines for roadway designers and safety professionals. By defining maximum word counts for specific interchange scenarios, the study offers a practical method to mitigate information overload and reduce crash risks. These recommendations aim to improve the design process for freeway guide signs, ensuring that signing strategies align with human cognitive limits and vehicle dynamics. The findings support the development of safer infrastructure by moving beyond general MUTCD provisions to specific, implementable standards for complex interchange environments.

Key finding

Sign complexity negatively affects drivers unfamiliar with an interchange much more than familiar drivers, leading to recommendations that guide signs contain no more than nine words for ramps requiring lane changes and ten words for those that do not.

Methodology

naturalistic

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.

• signage environment
• road complexity
• sign visibility legibility
• rail grade crossings
• external distraction
• traffic density

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).

• Applied Guidance: design guidelines
• Empirical Findings: behavioral performance data
• Methodological Resource: dataset resource