Road warning signs are traffic calming devices used to alert drivers about an upcoming or possible hazard that will affect their driving. On the other hand, regulatory traffic signs remind drivers about traffic laws and regulations. There are also significant differences in the design and layout of warning and regulatory signs, as governed by the MUTCD guidelines.
The MUTCD Chapter 2C covers warning signs and object markers. The manual provides information regarding the purpose of warning signs and the need for an engineering study or judgment to determine the use of these signs. According to the chapter, warning signs are divided into roadway-related signs, traffic-related signs, and supplemental plaques.
The MUTCD guidelines are rather comprehensive and provide details about the design of different warning signs, size requirements, and placement of the signs and well-crafted diagrams and images.
As with regulatory signs such as stop signs that must be a certain shape, the MUTCD (section 2C.03) guidelines require road warning signs to be diamond-shaped. The only deviation allowed is for larger warning signs may be rectangular or square in shape.
Standard, uniform shapes, sizes, and designs of traffic signs facilitate easy and efficient communication of traffic rules and limit the chances of non-compliance.
The use of traffic warning signs is usually governed by state traffic authorities, and local jurisdictions may also have rules or recommendations regarding these traffic calming devices. At the federal level, the MUTCD requires that warning signs be installed only after an engineering study or judgment warrants their use.
As per the MUTCD guidance (Section 2C.02), warning sign use should be kept to a minimum or it may foster disrespect for all signs.
Most warning signs are required to be yellow, with the warning message in black. The fluorescent yellow-green background color is used primarily for warning signs and plaques meant for traffic control in school areas. Pedestrian and bicycle warning signs may also use this background color.