TRAFFIC SIGNAL VISIBILITY: A SYNTHESIS OF HUMAN FACTORS AND VISUAL SCIENCE LITERATURE WITH RECOMMENDATIONS FOR REQUIRED RESEARCH

This paper synthesizes the key human factors and visual science literature related to the visibility and conspicuity of round and symbolic traffic signals. Topics covered are color; daytime intensity and luminance, including the effects of signal size, backplates, depreciation, environmental conditions (such as sky luminance, background complexity, and weather), and driver characteristics such as age and color-vision deficiency; nighttime intensity and luminance, including minimums, maximums, dimming and the effects of environmental conditions and driver characteristics; distribution of intensity and luminance; luminance uniformity; phantom; and shape, size, and recognizability of symbols. The intensity topics normally relate to round signals, and the luminance topics relate to symbols.