Evaluation of diagrammatic signing at Capital Beltway exit no. 1.

Hanscom, Fred R · 1971 · ROSA P / Virginia Transportation Research Council (VTRC)

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Summary

This 1971 pilot study by Fred R. Hanscom evaluates the effectiveness of diagrammatic signing in reducing driver confusion and erratic maneuvers at Exit No. 1 of the Capital Beltway (I-495) in Virginia. The research was motivated by high accident rates and driver confusion at high-speed interchanges, particularly those with complex geometries and close spacing. The study served as a precursor to a broader statewide testing program by the Virginia Highway Research Council, aiming to establish criteria for evaluating signing effectiveness and defining erratic maneuvers. The study employed a "comparative erratic maneuver" method, comparing driver behavior before and after the installation of a diagrammatic sign on the westbound approach. The conventional sign was replaced on March 29, 1971. Data were collected through manual observation and time-lapse photography across three designated zones. Researchers classified erratic maneuvers into four types: weaving (including across gore areas), hesitating (slowing to ~15 mph), stopping/backing, and partial weaving. The analysis covered 19 days, observing 56,326 vehicles in the "before" phase and 91,423 vehicles in the "after" phase. Statistical tests, including t-tests and F-tests, were used to compare means and variances, while regression analysis examined the relationship between weave-to-volume ratios and traffic volume. Key findings indicated a significant reduction in dangerous weaving maneuvers across the gore area, decreasing from 8.16 to 6.92 weaves per thousand vehicles. While the total number of erratic maneuvers increased by 27%, largely due to an influx of tourist traffic during the spring, the nature of these maneuvers shifted favorably. There was a 22.5% reduction in stopping and backing maneuvers, which are considered highly dangerous, accompanied by increases in hesitations (+196%) and partial weaves (+135%). Statistical tests revealed that driver behavior patterns became more consistent (less variable) after the sign installation. Additionally, no accidents were reported in the four months following the sign's installation, compared to an average of 10 accidents per month in the preceding 27 months. Driver interviews suggested that while the unfamiliar diagrammatic sign caused initial confusion, motorists found the information helpful. The study concludes that diagrammatic signing improves safety by providing better advance warning, thereby reducing critical gore-area weaving and stopping maneuvers. Although the signs may initially confuse motorists unfamiliar with the format, the tradeoff toward less dangerous erratic behaviors suggests a net safety benefit. The results support further research and the potential statewide implementation of diagrammatic signs to address driver confusion at complex interchanges.

Key finding

Installation of a diagrammatic sign significantly reduced weaving maneuvers over the gore area and decreased dangerous stopping and backing events, resulting in more consistent driver behavior and zero reported accidents over four months.

Methodology

on_road

Sample size: 147749

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
• signaling behavior
• perceptual countermeasures
• rail grade crossings