A practical system is needed to evaluate the nighttime visibility of existing signs and provide data for making decisions about signreplacement or refurbishment. Laboratory methods and portable instruments are available for measuring the retroreflectance of traffic signs, but easy-to-use mobile systems are not. Research is currently under way to develop a system that can measure the average retroreflectance of sign legend and background, irrespective of color, size, and placement, and that can be operated during daylight from a moving vehicle. Based on the use of a charge-coupled device video camera to acquire sign images, a xenon flash as a source of light, and a portable personal computer to analyze the images, experiments and analyses indicate that such a system is feasible, is well suited for making measurements from a moving vehicle, and can be built from commercially available components. This paper appears in transportation research record no. 1247, Visibility criteria for signs, signals, and roadway lighting.
Abstract