The MUTCD is updated and revised periodically to set specific guidelines for roadway transportation. The manual outlines rules pertaining to highway markings, traffic signals and road signage traffic control.
The Federal Highway Administration has set codes for overhead sign positioning, lettering and frequency of use for signs to "promote reasonably safe and efficient operations." Signs are reflective or illuminated to look the same at all times of day.
Signs are classified by purpose. Federal road signs are used to regulate traffic, provide warnings and display directional guides to drivers. Particular shapes and colors are reserved for each type of sign.
Certain shapes are reserved for the category of sign. For example, octagons identify stop signs.
Signs are also classified by color. Green, orange and blue backgrounds are used for guide, construction and information signs, respectively.
