Disrupting the smooth flow of traffic increases the probability of accidents. Erratic traffic operation may be caused by vehicles stopping or slowing in the roadway, passing and weaving maneuvers, or surprise elements. For example, unwarranted traffic signals, unreasonably low speed limits, and too many signs may cause driver confusion and indecision. Slower speed does not necessarily mean safer traffic operation. Traffic control devices are all signs, signals, markings, and devices placed on, or adjacent to, a street or highway by a public body having authority to regulate, warn, or guide traffic.
Uniformity means treating similar situations in the same way.
This simplifies the task of the driver because it aids in instant recognition and understanding. Uniformity aids police, courts and road users by giving everyone the same interpretation. It aids public highway officials through economy in manufacture, installation, maintenance, and administration. The Manual on Uniform Traffic Control Devices is the publication that sets forth the basic principles which govern the design and usage of traffic control devices. The Manual was prepared by a National Committee which included state, county, and municipal representation.