Soon a Joint Committee on Uniform Traffic Control Devices was established, represented by AASHO for the rural manual and the National Conference for the urban manual. At the first meeting of the Committee, it was agreed that certain details should be thoroughly investigated before completing the joint sign manual. A project to investigate visibility and legibility of several alternative color combinations by day and night, with and without reflector buttons, was arranged with the Bureau of Standards by the Bureau of Public Roads. The Bureau of Public Roads also made delay studies at traffic control signals. With these and other data, Committee compromise adjustments were worked out and a combined manual was developed. The new manual was approved by the Secretary of Agriculture as the standard code for application on Federal-aid highways; it was published in 1935 as the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD).
The new Manual dealt comprehensively with the whole field of traffic control devices. Signs were divided into three classifications—regulatory, warning, and guide. The stop sign retained the yellow background and red letters were accepted as an alternative to the black letters. The railroad crossing sign was a crossbuck to closely resemble the standard railroad advance warning sign. The Manual included new self-evident symbols to indicate crossroads, Y and T intersections and side roads. The section on traffic signals supplied long needed guidance on the number, meaning, and arrangement of signal lenses. Green was specified for go, yellow for caution, and red for stop. The Manual provided that each signal should have three lenses since the function of the yellow light could not be attained with a signal having only two lenses.
In 1938 the Joint Committee reexamined the Manual and recommended numerous updating revisions, and a supplement was issued in February 1939.
As one of the aftermaths of the Pearl Harbor attack on December 7, 1941, problems of wartime traffic loomed, especially the altogether new possibility of having to move traffic under blackout conditions. The Joint Committee was revived, this time including the Institute of Traffic Engineers as a member. The “War Emergency Edition” of the Manual, published at the end of 1942, was a condensed version of the previous edition, modified only to deal with blackouts and make certain wartime concessions, such as permissive use of white pavement markings instead of yellow because of material shortages.
In 1944 the Joint Committee agreed that the Manual must be entirely rewritten to include the needs of changed conditions. In 1948, after a wide review, the final draft was approved by the Joint Committee’s three sponsoring organizations and by the American Standards Association. That year, also, the National Committee on Uniform Traffic Laws and Ordinances was made a member of the Joint Committee replacing the National Conference on Streets and Highway Safety.
Some of the more significant changes in the 1948 Manual were: a diamond-shaped sign was prescribed for all warning signs (except the circle for the railroad crossing); a new intersection route turn symbol sign was provided; a new “advisory speed” sign was included for use with any warning signs; and the growing need for larger signs was recognized and some of the minimum sizes were increased.
A major change and innovation was made in the next Joint Committee Manual revision of 1955. The stop sign was changed from black on yellow to white on red. The yield sign came into being in the now familiar equilateral triangle with one point downward and used black lettering on yellow as were other warning signs.
In 1955 the MUTCD did not include material for the signing and marking of freeways. The National Joint Committee on Uniform Traffic Control Devices began drafting an extensive addition to the existing manual in 1956 to cover expressway signs as called for by the 1956 Federal-Aid Highway Act. Also in 1956, the American Association of State Highway Officials set up a subcommittee of its traffic committee to develop an Interstate Manual that would “incorporate the best experience from all the higher type toll roads and freeways.” The resulting Manual was adopted by AASHO in 1958. In February 1958, the Manual for Signing and Pavement Marking of the National System of Interstate and Defense Highways was approved by the Bureau of Public Roads. A second edition of the Interstate Manual was published in 1961 and a slightly revised edition in 1962.
In the meantime, to provide broader representation, the Joint Committee, in 1960, had enlarged its membership to include the National Association of County Officials (now the National Association of Counties) and the American Municipal Association (now the National League of Cities). The Joint Committee published a new MUTCD in 1961, drawing heavily on the AASHO Interstate Manual for expressway and freeway signing. The new Manual had many refinements, changes in emphasis, and new applications of engineering and psychological research and experience in operations of the substantial mileage of high-speed limited access highways, particularly of toll roads. New features included the use of lowercase letters and green background on freeway directional signs, reflectorization or illumination for the background of overhead signs, and reflectorization of all pavement markings that have amplication at night. The 1961 MUTCD also included, for the first time, an extensive special treatment of traffic control devices for highway construction and maintenance operations and a group of special signs for emergency civil defense applications. Standards for traffic signals were modernized to keep up with technical advances in that field.
The 1966 Highway Safety Act provided for the first time that specific Federal safety funds be spent by local governments as a step toward reducing the number of accidents. The existing devices on all highways and streets were to be continually reviewed and upgraded. The Federal-aid requirement for uni-
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