Improving Street Name Sign Legibility for Older Drivers

Abstract

Reading street name signs is an important part of the navigation task of driving a vehicle. Older drivers, in particular, often have trouble reading street name signs because of poor sign design and because of vision problems associated with aging. Past research has shown that older drivers can benefit in sign detection by either increasing the size of the sign or by increasing the retro-reflectivity of the material used to make the sign. The present study examined the effects of reflective material on the legibility distance for a standard size shoulder mounted street name sign. ASTM Types I, III, VII, and IX were used for the white on green signs with legend consisting of a 6“ initial upper case letter and 4.5” lower case Highway Series C. The effects of intersection complexity were examined by conducting the study at three different intersections in an urban area that varied in traffic volumes, commercial lighting and geometric design. An additional variable was which side of the street the signs appeared. Older drivers, with a mean age of 71, drove an instrumented vehicle in real traffic at night and were asked to read traffic signs temporarily erected for purposes of the study. The results showed an interaction between sign reflectivity and intersection complexity, suggesting that brighter signs aid legibility more in complex traffic situations. The differences between the reflective material types at low-complexity intersection were small compared to the differences observed at the high-complexity intersection where ASTM Types VII and IX showed greater legibility distances than Types I and III. Likewise, when signs were mounted on the left side of the street, the reflectivity of the material showed more of an effect than when they were mounted on the right side of the street. Overall, sign legibility distances were improved 21–30 % by changing from ASTM Types I and III to the higher reflectivity materials, Types VII and IX.