Experimental results are presented on sign size and brightness and letter-to-sign brightness ratio. This series of experiments was conducted to measure: (1) the effects of sign size, brightness, and letter-to-sign brightness ratio, and (2) the effects of competing signs on highway sign visibility. A typical highway scene for day or night conditions was projected continuously on the screen in front of the subject. From time to time under automatic control, keyed by its own responses to an auxiliary task, four simulated interstate green highway signs were flashed on the screen superposed on the previous highway scene. It was determined that the expected advantage for the largest of four signs was found consistently when the simulated green signs were seen against either day-snow or the night background. It was determined that an advantage for visibility was enhanced by a combination of: (1) greater sign brightness, (2) greater relative sign size, (3) contrast of sign against background, and (4) letter-to-sign brightness. Findings suggest that silhouette seeing is of importance for visibility or attention value where signs are seen against a bright background. Optimum combinations of these variables must be found to obtain best attention value and best legibility.
Abstract