The Manual on Uniform Traffic Control Devices (MUTCD) describes basic principles for evaluating traffic control devices for Streets and Highways.
The MUTCD, published by the Federal Highway Administration (FHWA), standardizes traffic control devices throughout the country to ensure that they mean the same to, and require the same actions by, all motorists anywhere in the country. Compliance with MUTCD standards help to promote the safe, orderly, and efficient movement of traffic. These standards are intended to obtain basic uniformity of traffic control devices, they should be followed consistently. Devices that do not conform to the MUTCD should not be used on roadways.
While some states have adopted the national MUTCD as is, others have either created a similar state-specific MUTCD or simply written a state document to enhance the national MUTCD.