Signs convey information to travelers not only by their messages and color, but through their shape as well.
Special shapes are specifically assigned to certain types of signs so that travelers can recognize them quickly and react appropriately.
In general, the greater number of sides on a sign, the more critical a message it conveys. This is why a circular shape was adopted for the Railroad Advance warning sign (i.e. infinite number of sides), as a collision between a train and a typical vehicle will nearly always end badly. Then next the octagon shape is used for the Stop sign, since not noticing that sign typically has unpleasant consequences, and so on down the line. There are of course exceptions to this rule - a pentagonal County Route marker isn't (typically) a greater threat than a standard square route marker, and even though they have only 3 sides, the Yield and No Passing Zone signs are still rather important (and the pennant shape of the NPZ sign serves as a sort of "get back over on your own side of the road" arrow).
|Circle||Exclusively for railroad crossing advance warning signs|
|Octagon||Exclusively for Stop signs|
(Equilateral, point down)
|Exclusively for Yield signs|
|Crossbuck||Exclusively for railroad grade crossing signs|
(Isosceles Triangle, point to right)
|Exclusively for No Passing Zone signs|
|Diamond||Warning signs (permanent or temporary)|
(Longer Dimension Vertical)
(Longer Dimension Horizontal)
|Guide signs, some warning signs, and some temporary traffic control signs|
National Forest route marker signs
(was used in past for guide signs for recreational areas)
|Pentagon||School advance warning signs and county route marker signs|
|Other shapes||Route marker signs|
Updated 01 March 2019 (revised into new format)
Scripting: Richard C. Moeur
All text and images on this page © Richard C. Moeur. All rights reserved.
Linked sign layout files in PDF format provided courtesy of FHWA's MUTCD website
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