A multidisciplinary study of vertical road signage effectiveness for traffic safety.

Vertical road signage constitutes the primary means of communication between the infrastructure and the road user. Given the high incidence of human error, the present doctoral research aimed at an integrated analysis of the management, maintenance, and driver perception of vertical road signage. The effectiveness of signage depends on the integration of three successive and interdependent aspects of the communication process between infrastructure and driver: technical compliance, perceptual effectiveness, and legibility. The study employed a combination of field experiments, driving simulations, and behavioral analyses. A core methodology was established based on the integration of eye-tracking techniques, to study visual behavior and cognitive load, and vehicle kinematic data. At a technical level, the research confirmed that retroreflectivity is an essential property for road safety, particularly under night-time or low-light conditions. A comparison between two types of retroreflectometers, manual measurement instrument and automatic vehicle-mounted system, revealed that mobile system provides a more consistent and realistic representation of sign visibility from the driver’s perspective, while also offering a significantly higher inspection capacity. At a perceptual level, the results showed that the surface condition of the sign, such as dirt, deterioration, and water, directly influences visual perception and driving behavior. Dirt was found to be the most significant factor, influencing perceptual effectiveness with a 15% reduction in initial observation distance, 37% fewer fixations, and a 40% increase in the time required for perception compared to a clean sign. Regarding legibility, a study in a simulated scenario was conducted to analyses driver responses, including those with dyslexia, in the presence of variable message signs, varying the type of message and the weather condition. The general conclusions suggest that improvements to the effectiveness of vertical road signage should include increasing the size of the most critical signs and adding visual effects, such as flashing lights.