Simulator Study of Signs for a Complex Interchange and Complex Interchange Spreadsheet Tool

Fitzpatrick, Kay; Chrysler, Susan T.; Brewer, Marcus A.; Nelson, Alicia A.; Iragavarapu, Vichika · 2013 · ROSA P / United States. Federal Highway Administration. Office of Safety Research and Development

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Summary

This report documents a Federal Highway Administration project aimed at improving safety and navigation at complex highway interchanges. The research was motivated by the need to understand motorist expectations, determine how those expectations influence driving behavior, and identify effective signing and marking practices to mitigate safety risks. The project was divided into two primary studies: a driving simulator evaluation of various sign treatments and the development of a metric tool to quantify interchange complexity. The first study utilized a driving simulator to evaluate driver responses to six specific signing scenarios. Topic 1 tested signing for option lanes, finding that while participants made correct exit decisions, they frequently executed unnecessary lane changes across all sign sets. Topic 2 examined signing for closely spaced exits with three destinations; the arrow-per-lane design resulted in correct lane change decisions for all participants. Topic 3 evaluated Y-split exits, determining that split exit signs at all bridge locations produced the fewest incorrect lane changes and were judged superior to shared exit signs. Topics 4 and 5 assessed information spreading, revealing that distributing information across multiple signs on a single bridge could cause confusion if signs for other exits were present, and highlighting the importance of lateral sign positioning. Topic 6 found minimal differences in driver understanding between two variations of left exit signs. The second study developed a spreadsheet decision tool to score interchange complexity based on geometric design factors affecting driver expectancy and workload. The tool incorporates 32 weighted factors derived from site characteristics. To validate the tool, researchers applied it to 28 existing interchange sites in 11 states, selected by state transportation departments based on perceived complexity. The results provided a general sense of the relative complexity of these interchanges, demonstrating the tool's utility in categorizing sites. The significance of this work lies in its provision of evidence-based guidance for engineers and planners. The simulator findings offer specific recommendations for optimizing sign designs, such as using arrow-per-lane signs for complex exit sequences and split exit signs for Y-splits, while cautioning against certain information-spreading techniques. The complexity spreadsheet tool provides a standardized method for quantifying interchange complexity, aiding in the identification of sites requiring enhanced signing treatments. Together, these outputs support improved public safety by aligning signing practices with driver cognitive processes and geometric realities.

Key finding

Arrow-per-lane sign designs and split exit signs at all sign bridge locations resulted in the fewest incorrect lane changes and were judged superior to other signing arrangements for complex interchange scenarios.

Methodology

simulator

Sample size: 42

Provenance

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

Topics

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• signage environment
• intersection design