Photometric measurements of the daytime chromaticity and luminance of retroreflective sign materials were made both in the laboratory and in the field. These instrument measurements were compared with daytime perceptual judgments of color properties made by human observers in the field. Hue, saturation, and brightness were determined for four different types of retroreflective sheeting materials and one diffuse material at four quadrants of each color area for six different colors specified in the Code of Federal Regulations for use on street and highway traffic control signs. Overall, participants’ responses aligned well with the instrument measurements. The introduction of retroreflective properties reduced both the apparent saturation and the brightness of all the colors. The results for the white, green, and blue color areas showed distinct color separations for retroreflective sign materials. The results for the red, orange, and yellow areas showed less color separation but little overlap among contiguous colors in the perceptual color space. This outcome has implications for determining the shape and size of the color areas used to specify the colors that may be employed on traffic control signs. While the present color areas seem to adequately support the daytime perception of the color of retroreflective sign materials for the six colors tested, special attention needs to be paid to the red/orange and orange/yellow color boundaries in any future revisions to the Federal Highway Administration (FHWA) color areas. The results of the present experiment indicate that there is no pressing need to modify the FHWA color areas, but improvements might be made in future iterations so as to enhance separation of those color areas that are more difficult to discriminate. (Author/publisher)
Samenvatting