Traffic Sign Legibility for Different Sign Background Colors: Results of an Open Road Study at Freeway Speeds

Abstract

Transportation agencies have been considering the use of a purple sign background color to denote that the roadway is tolled. Prior studies have shown a driver preference for a unique color for the toll road category. Concerns about the legibility of purple signs have been raised due to their brightness and contrast ratio with a white legend. The current study performed an evaluation of the legibility and recognition of purple and green freeway guide signs during daytime and nighttime driving in the Houston, TX area. Forty-eight participants drove an instrumented vehicle in open traffic and read traffic signs along a toll road with purple signs on one segment and green signs on another. Results showed no significant difference in legibility distance between signs with purple and green backgrounds. An analysis of recognition distances for advance guide signs marking ramps to the toll road also showed no difference between purple and green signs. These results support the implementation of this new color without any loss in legibility.

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