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The Manual on Uniform Traffic Control Devices (MUTCD) is a document issued by the Federal Highway Administration (FHWA) of the United States Department of Transportation (USDOT) to specify the standards by which traffic signs, road surface markings, and signals are designed, installed, and used. These specifications include the shapes, colors, and fonts used in road markings and signs. In the United States, all traffic control devices must legally conform to these standards. The manual is used by state and local agencies as well as private construction firms to ensure that the traffic control devices they use conform to the national standard. While some state agencies have developed their own sets of standards, including their own MUTCDs, these must substantially conform to the federal MUTCD.
The National Committee on Uniform Traffic Control Devices (NCUTCD) advises the FHWA on additions, revisions, and changes to the MUTCD.
At the start of the 20th century—the early days of the rural highway—each road was promoted and maintained by automobile clubs of private individuals, who generated revenue through club membership and increased business along cross-country routes. However, each highway had its own set of signage, usually designed to promote the highway rather than to assist in the direction and safety of travelers. In fact, conflicts between these automobile clubs frequently led to multiple sets of signs—sometimes as many as eleven—being erected on the same highway.
Government action to begin resolving the wide variety of signage that had cropped up did not occur until the early 1920s, when groups from Indiana, Minnesota, and Wisconsin began surveying the existing road signs in order to develop a standard. They reported their findings to the Mississippi Valley Association of Highway Departments, which adopted the report's suggestions for the shapes to be used for road signs. These suggestions included the familiar circular railroad crossing sign and octagonal stop sign.
In 1927, the American Association of State Highway Officials, or AASHO, published the Manual and Specifications for the Manufacture, Display, and Erection of U.S. Standard Road Markers and Signs to set standards for traffic control devices used on rural roads. This was followed by the Manual on Street Traffic Signs, Signals, and Markings, which set similar standards for urban settings. While these manuals set similar standards for each environment, the use of two manuals was decided to be unwieldy, and so the AASHO began work in 1932 with the National Conference on Street and Highway Safety, or NCSHS, to develop a uniform standard for all settings. This standard was the MUTCD.
The MUTCD was first released in 1935, and set standards for both road signs and pavement markings. Since that time, eight more editions of the manual have been published with numerous minor updates occurring between, each taking into consideration changes in usage and size of the nation's system of roads as well as improvements in technology.
In 1966, Congress passed the Highway Safety Act, P.L. 89-564, 72 Stat. 885 (1966), which is now codified at 23 U.S.C. § 401 et seq. It required all states to create a highway safety program by December 31, 1968, and to adhere to uniform standards promulgated by the U.S. Department of Transportation as a condition of receiving federal highway-aid funds.  The penalty for noncompliance was a 10% reduction in funding. In turn, taking advantage of broad rulemaking powers granted in 23 U.S.C. § 402, the Department simply adopted the entire MUTCD by reference at 23 C.F.R. 655.603. Thus, what was formerly a quasi-official project became an official one. States are allowed to supplement the MUTCD but must remain in "substantial conformance" with the national MUTCD and adopt changes within two years after they are adopted by FHWA.
The 1971 edition of the MUTCD included several significant standards; it required all center lines on two-way roads to be painted in yellow (instead of white, which was to demarcate lanes moving in the same direction), and required that all highway guide signs (not just those on Interstate Highways) contain white text on a green background. Most of the repainting to the 1971 standard was done between 1971 and 1974, with a deadline of 1978 for the changeover of both the markings and signage.
On January 2, 2008, FHWA published a Notice of Proposed Amendment in the Federal Register containing a proposal for a new edition of the MUTCD, and published the draft content of this new edition on the MUTCD website for public review and comment. Comments  were accepted until July 31, 2008. The new edition was published in 2009.
Proposed additions and revisions to the MUTCD are recommended to FHWA by the National Committee on Uniform Traffic Control Devices (NCUTCD), a private, non-profit organization. The NCUTCD also recommends interpretations of the MUTCD to other agencies that use the MUTCD, such as state departments of transportation. NCUTCD develops public and professional awareness of the principles of safe traffic control devices and practices, and provides a forum for qualified individuals to exchange professional information.
The NCUTCD is supported by twenty-one sponsoring organizations, including transportation and engineering industry groups (such as AASHTO and ASCE), safety organizations (such as the National Safety Council and Advocates for Highway and Auto Safety), and the American Automobile Association. Each sponsoring organization promotes members to serve as voting delegates within the NCUTCD.
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The United States is among the majority of countries around the world that have not ratified the Vienna Convention on Road Signs and Signals, and thus the FHWA MUTCD differs significantly from the Vienna Convention. Warning signs (alerting drivers of unexpected or hazardous conditions) tend to be more verbose than their Vienna Convention counterparts. On the other hand, MUTCD guide signs (directing or informing road users of their location or of destinations) tend to be less verbose than their equivalents in Vienna Convention countries, since they are optimized for reading at high speeds on freeways and expressways.
The MUTCD has become widely influential outside the United States; for example, the use of yellow stripes to divide opposing traffic has been widely adopted throughout the Western Hemisphere.
For road signs in Canada, the Transportation Association of Canada (TAC)  publishes its own Manual of Uniform Traffic Control Devices for Canada for use by Canadian jurisdictions. Although it serves a similar role to the FHWA MUTCD, it has been independently developed and has a number of key differences with its US counterpart, most notably the inclusion of bilingual (English/French) signage for jurisdictions such as New Brunswick and Ontario with significant anglophone and francophone population, and a heavier reliance on symbols rather than text legends.
The Ministry of Transportation of Ontario (MTO) also has historically used its own MUTCD which bore many similarities to the TAC MUTCDC. However, as of approximately 2000, MTO has been developing the Ontario Traffic Manual (OTM), a series of smaller volumes each covering different aspects of traffic control (e.g., regulatory signs, warning signs, sign design principles, traffic signals, etc.).
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- Manual on Uniform Traffic Control Devices at FHWA website
- National Committee on Uniform Traffic Control Devices (NCUTCD) website
- MUTCD History