Research and recommendations were produced on the basis of a study on the development of minimum retroreflectivity values for overhead guide signs and street name signs. The research reviewed the literature and available photometric models. A photometric model was created to develop minimum retroreflectivity values for overhead guide signs and street name signs. One model input was the minimum luminance required for legibility. To obtain minimum luminance requirements for overhead guide signs and street name signs, a field evaluation was performed. Accommodating older drivers was specifically emphasized. After the minimum luminance values were determined, the minimum retroreflectivity model was used to study the impacts of (and determine appropriate values for) factors that affect retroreflectivity, such as distance, headlights, and vehicle speed. After the appropriate values were determined, the minimum retroreflectivity model was executed for the final runs. The recommended minimum retroreflectivity values were grouped into one table that includes overhead guide signs, postmounted street name signs, and overhead (mast-arm- or span-wire-mounted) street name signs. The values depend on type of sheeting, speed, and sign position.
Abstract