United States Department of Transportation
i
Freeway Guide Sign Performance at Complex Interchanges: Reducing Information Overload
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2024-07-01
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[PDF-2.96 MB]
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Edition:Final Report
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Abstract:Complex freeway interchanges are difficult to navigate in many cases. Poorly designed signs at such locations, along with contributing roadway and traffic factors, frequently lead to increased crash risks. A sign design issue typically seen on urban freeways is the use of complex guide signs. The 2009 Manual on Uniform Traffic Control Devices sets forth the minimum standards for guide sign design.(1) Though the manual identifies the issue of information overload on signs and the need to spread out information on a sign, it lacks detailed provisions on how to design signs and how to space signing to rectify the issue, including a way to identify the maximum amount of information to provide on freeway guide signs at any one location. During this project, the research team analyzed a large set of the Second Strategic Highway Research Program Naturalistic Driving Study data in an effort to learn the correlations between driver behaviors relevant to safety and freeway guide signs at interchange areas.(2) Based on the correlations, the research team developed sign complexity thresholds at freeway interchange areas to ensure driver safety. The primary sign complexity variable, “Number of Words on Subject Sign,” significantly correlated with a large number of driver behavior variables at the analysis segments. Overall, the sign complexity models showed that sign complexity negatively affected drivers unfamiliar with an interchange much more than it did familiar drivers. Based on the research findings, the research team suggests that a guide sign not contain more than nine words when used for right ramps requiring at least one lane change for exiting traffic to be in the correct exit lane. In addition, the research team suggests that a guide sign not contain more than 10 words for right ramps requiring no lane changes for exiting traffic already in the rightmost lane to be in the correct exit lane. The report also includes a large number of other relevant suggestions that could potentially improve the sign design process for safer freeways.
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