Validation study - on-road evaluation of the Cooperative Intersection Collision Avoidance System - Stop Sign Assist sign : (CICAS-SSA Report #5).

Rakauskas, Michael; Creaser, Janet; Manser, Michael P.; Graving, Justin; Donath, Max · 2009 · ROSA P / United States. Department of Transportation. Intelligent Transportation Systems Joint Program Office

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Summary

This study evaluates the Cooperative Intersection Collision Avoidance System – Stop Sign Assist (CICAS-SSA), an infrastructure-based decision support system designed to reduce crash risks at rural, stop-controlled intersections. The research addresses the problem of unsafe gap acceptance by drivers on minor roads attempting to cross or turn onto high-speed major highways. While previous simulation studies suggested the CICAS-SSA sign improved driver decision-making, this validation study aimed to confirm those benefits in a real-world setting and identify any unintended consequences. The system uses sensors to track vehicles on the major roadway and displays yellow or red icons on a roadside sign to warn drivers when approaching vehicles are too close for safe entry, utilizing a 7.5-second safety threshold. The validation field test was conducted at the intersection of US Highway 52 and County Road 9 in Southern Minnesota. The study involved 48 car drivers from three age groups (young, middle-aged, and senior) and 13 truck drivers to assess performance across different vehicle types and viewpoints. Participants drove instrumented vehicles through the intersection while making right turns, left turns, and crossing maneuvers. Data collection focused on performance metrics such as rejected gap size, time-to-contact, safety margins, and wait times, as well as usability metrics including mental effort, comprehension, and perceived usefulness. The experimental design compared driver behavior with the CICAS-SSA sign active versus inactive to isolate the system's impact. Results indicated that the CICAS-SSA sign effectively influenced driver behavior by encouraging the rejection of shorter, unsafe gaps. Specifically, the 80th percentile rejected gap size increased when the sign was active, demonstrating that drivers waited for safer gaps. The system’s 7.5-second warning threshold aligned well with actual driver gap selection performance. However, the sign did not significantly alter accepted gap lengths, lead gap lengths, or time-to-contact metrics, suggesting it reduced decision-making risk without disrupting the fundamental mechanics of how drivers execute maneuvers. Subjective measures revealed that 66% of car drivers and 50% of older drivers used the sign, primarily to validate their own safety perceptions rather than to control their actions. Drivers reported the system as useful, satisfying, and low-stress, with no significant negative effects on comfort or mental effort. The study concludes that the CICAS-SSA sign is a beneficial tool for improving gap decision-making at rural intersections without causing unintended behavioral changes or undue stress. The consistency of findings with previous simulation studies increases confidence in the system's robustness. However, the authors note limitations regarding the short duration of the test and the experimental conditions, which may have altered naturalistic driving behaviors. They recommend a long-term field operational test to understand how drivers adapt to the system over time and to further validate its utility in naturalistic settings. Additionally, the lower adoption rate among older drivers suggests a need for targeted advertising campaigns to promote the technology's benefits to this demographic, who are at higher risk for intersection crashes.

Key finding

The use of the CICAS-SSA sign significantly increased the 80th percentile rejected gap size, indicating that drivers avoided shorter, unsafe gaps more frequently when the system was active.

Methodology

on_road

Sample size: 61

Provenance

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Topics

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• rail grade crossings
• signaling behavior
• gap acceptance
• driver vru interaction
• vru facing ehmi

Information type

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• Empirical Findings: behavioral performance data