Sign Visibility

SIGN VISIBILITY

• Sign visibility refers to the likelihood of a sign being found in the driving environment and is integrally associated  with sign conspicuity. 
• Sign conspicuity is a function of a sign’s capacity to attract a driver’s attention that depends on sign, environmental, and driver variables Sign legibility describes the ease with which a sign’s textual or symbolic content can be read. 
• Sign legibility differs from sign recognizability in that the former refers to reading unfamiliar messages while the latter refers to identifying familiar sign copy. 
• Sign legibility and recognizability in turn differ from sign comprehensibility in that the latter term implies understanding the message while the former merely involve the ability to discern critical visual elements.
• Other measures of sign visibility include blur tolerance and comprehension speed
• Sign visibility is most often assessed by determining threshold distance. 'T'
• The two thresholds used are 
• Detection distance (the distance at which an observer can find a sign in the driving environment) and
• Legibility distance (the distance at which an observer can read a sign’s message).
•  The intent of a sign designer is to provide the sign’s observer with the maximum time to read the sign, and to do that the observer must find it before its maximum reading distance.
• Legibility index (LI) refers to the legibility distance of a sign as a function of its text size