The Typography of Traffic Signs in USA

Which typefaces are used in traffic signs in yourCaltrans, formerly California Division of Highways.
county, state or country? Do you have an idea? 
 The idea behind the choice of typefaces used in
 Why is it you are so conscious of the typefacestraffic signs is to maximize on legibility. For example,
you use while typing your work and yet you haveall-uppercase letters are used for ground mounted
never noticed the consistent and largely standardizedtraffic signs with reflective letters while mixed-case
typography of traffic signs all over the roads youletters are used for externally illuminated and
drive through? Because that is basically why thoseprojected overhead guide signs. It is actually common
specific font types are used: To attract the leastfor most local governments, road contractors and
attention and emphasize maximal concentration onairport authorities to fabricate typefaces for traffic
the message, not the orthography.signs besides using the conventional FHWA series, if
 particular isolated cases require such fabrication for
US and Canada predominantly use FHWA alphabetmaximal legibility. Common variations include the use
series with specifics on letter-shape and spacingof Helvetica and Arial typefaces.
detailed in the Standard Alphabets for Traffic Control 
Devices published in 1945 by the Public Roads Bureau. A lot of research has gone into finding out which
These specifics on typefaces design have beentypefaces are ideal to which traffic signs and in which
updated to form Standard Highway Signs.environments. Some specific Street Sign like the
 left-turn prohibition sign which hangs from its gantry
Initially traffic signs were in capitalized letters andmust be well lit for better visibility, especially at night
digits but a revision in 2002 allowed traffic signs toor during inclement weather conditions.
include lowercase extensions. State departments and 
the federal roads agencies have since 1927 usedAnother example of how legibility determines the
uniform fabrication of straight-stroke letters in traffictypefaces adopted, is the Clearview typeface, which
signs.was developed by U.S. government researchers
 exclusively as a typeface that improved legibility. It
Today however, rounded alphabets are used sincehas since been adopted as the predominant typeface
the Pentagon road network constructed in 1942.in poorly illuminated road areas by such states as
Mixed-case alphabets are also standard especially onArkansas, Texas, Illinois, Pennsylvania, Michigan,
freeway guide signs an initiative experiment of theVirginia, among others.