Legibility Distances of Fluorescent Traffic Signs and Their Normal Color Counterparts

It is well known that fluorescent traffic sign have a daytime conspicuity that is far superior to that of normal color signs. This study was conducted in order to test the hypothesis if adding the property of fluorescence while leaving all (or in practical terms most) other sign features the same, does in fact increase the legibility distance. Six diamond shaped signs were fabricated and laminated with the normal colors on one side and their fluorescent color counterparts on the other side. The investigated sign background colors included yellow, fluorescent yellow, fluorescent yellow-green, pink, fluorescent pink, purple, and fluorescent purple. Four of the six signs used Landolt rings to avoid word familiarity issues. A pedestrian crossing symbol sign and a PLANT ENTRANCE warning sign were used in addition to the Landolt ring signs. It was found that fluorescence actually did statistically significantly increase the legibility distances. However, the actual increases were fairly small from a practical point of view, ranging from 5.3% to 15.9% when adding the property of fluorescence. In general, for negative contrast signs and for positive contrast signs where both the legend and the background are fluorescent, a slight increase in the legibility distance can be expected. It should be noted, that the illumination conditions that were present in this study (fair day) represent somewhat of a worst-case scenario for fluorescent colors. Larger percent increases in legibility distance may be expected when using fluorescent colors during the time of twilight, during overcast days, and during daytime in inclement weather. Schnell, Bentley, Hayes, and Rick 4