Effect of Driver's Age on Nighttime Legibility of Highway Signs

A field investigation of the effect of driver's age on nighttime legibility of highway signs was performed. Subjects of two age groups (under 25 and over 61 years of age) participated. The results indicate that legibility distances for the older subjects were 65 to 77% of those for the younger subjects with equal high-luminance visual acuity. This finding implies that older drivers are likely to have less distance (and thus less time) in which to act on the information transmitted by highway signs. Consequently, it is argued that (I) legibility standards for highway signs should not be based exclusively on data obtained from young observers and (2) standard (high-luminance) acuity tests have questionable relevance to nighttime visual performance.