Perceptual and cognitive factors in legend legibility for large freeway guide signs

Abstract

In the United States, older drivers are increasing in numbers on our public highways; the U.S. Census Bureau predicts the age groups of sixty-five and above will increase their percentage of the population over the next six decades. The Texas Department of Transportation recently revised its design standards for freeway guide signs. These changes may have a significant impact on the ability of all drivers, but especially older drivers, to read and react to guide signs. This study explored ways to increase guide sign legibility through changes in sign alphabets. The study compared two alternative fonts for highway signs to the existing standard alphabet letter series. These alternative fonts, Clearview and British Transport, both had a narrower stroke width than the standard alphabet. This study assessed sign legibility distance in a field experiment using full-sized signs and lettering. Measures of effectiveness were legibility distance and recognition distance. Thirty-two subjects, aged fifty-five and older, participated in the experiment. This study ascertained that for daytime driving, neither of the alternative alphabets performed better or worse than the standard series E(Modified) alphabet. All font legibility values exceeded 60 feet per inch of lowercase letter height. Based on these findings, the study recommended that guide signs use which ever alphabet provides the best nighttime sign legibility and that transportation researchers undertake further studies of daytime sign legibility.