Applying the sign luminance computation model to study the effects of other vehicles on sign luminance

Ye, Fan; Carlson, Paul J.; Brimley, Bradford K. · 2014 · DOAJ

DOI: 10.3846/16484142.2014.927396

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Summary

This study addresses the lack of comprehensive research regarding the contribution of adjacent vehicle headlamps to the luminance of retroreflective traffic signs. As transportation agencies increasingly consider removing overhead sign lighting to reduce costs, relying solely on vehicle headlamps for illumination, it is critical to quantify the light provided by the entire traffic stream rather than just the driver’s own vehicle. Previous studies were limited by outdated technology or restricted field measurements. This paper develops and applies a computational model to simulate sign luminance under various traffic scenarios, evaluating the effects of vehicle position, vehicle type, sign type, and sheeting material. The authors extended the Exact Roadway Geometry Output (ERGO) model to include headlamps from multiple vehicles in the traffic stream. The model calculates total observed luminance by summing the contributions from all potential headlamps, accounting for geometric relationships, retroreflectivity matrices for specific sheeting types (ASTM III and XI), and modern headlamp profiles (US2011). The calculation process involves determining illumination and viewing distances, calculating angles for retroreflection, and applying inverse square laws for illuminance. The model also incorporates windshield and atmospheric transmissivity factors. Simulations were conducted for overhead guide signs and street-name signs, using passenger cars and trucks/SUVs as vehicle types, with varying longitudinal and lateral positions relative to the target driver. The results indicate that headlamps from other vehicles significantly enhance sign luminance, particularly at greater distances from the sign. While the target vehicle’s own headlamps provide the baseline luminance, their contribution diminishes as distance increases due to observation angles and illumination patterns. In contrast, the relative contribution of other vehicles increases with distance. For instance, when the target vehicle is 400 ft from an overhead sign, a vehicle 100 ft behind in the same lane increases luminance by nearly 50%. At 700 ft, a vehicle 100 ft in front can increase luminance by approximately 80%. Vehicles in the same lane as the target driver contribute more luminance than those in adjacent lanes. Additionally, larger vehicles like trucks and SUVs provide greater luminance contributions than passenger cars due to higher headlamp placement and intensity. The study also addressed occlusion, calculating minimum distances required to prevent vehicles from blocking headlamp light or the driver’s view. The findings suggest that the cumulative effect of stream traffic headlamps provides substantial illumination for retroreflective signs, supporting the feasibility of removing overhead sign lighting in many contexts. The computational model offers a tool for transportation agencies to evaluate sign visibility under realistic traffic conditions, aiding decisions on lighting infrastructure. By quantifying the additive nature of luminance from multiple sources, the study highlights that ignoring adjacent vehicle headlamps underestimates sign brightness, particularly for drivers at longer viewing distances. This work provides a methodological framework for future studies on sign visibility and lighting requirements.

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Topics

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• sign visibility legibility
• visibility analysis litigation
• vehicle conspicuity
• roadway lighting effects
• headlamp performance