The Slash Obscures the Symbol on Prohibitive Traffic Signs

The problem of whether drivers should be told what they can do (permissive message) or what they cannot do (prohibitive message) is discussed as it relates to traffic sign symbols. A widely used version of the prohibitive message (symbol surrounded by a red ring with a slash through the symbol) was found to have limited legibility because the slash obscures the symbol. Two experiments examined the glance legibility of 15 symbols under each of four conditions-slash over symbol, slash under symbol, partial slash, and no slash. The results indicated that the glance legibility of traffic sign symbols is better when no slash or a partial slash is used to convey the prohibitive message.