Nighttime Legibility of Ground-mounted Traffic Signs as a Function of Font, Color, and Retroreflective Sheeting Type

A closed course nighttime legibility study measured legibility distance for 6-in. letters using Highway Series D and two experimental fonts, Clearview Condensed Road and a D-Modified font. The Clearview font has a thinner stroke width than Series D and was used for white-on-green signs. The D-Modified font has a thicker stroke width than Series D and was used for black letters on white, yellow, and orange backgrounds. Three types of retroreflective sheeting were tested: ASTM Types III, VIII, and IX.