At the annual meeting of AASHO in 1924, its Subcommittee on Traffic Control and Safety presented recommendations for standard signs and markings based largely on the work of the Mississippi Valley Association, but incorporating at least one new feature, a color code to distinguish the several types of signs. Acting on an AASHO resolution, the Secretary of Agriculture appointed a Joint Board on Interstate Highways in March 1925 with 21 members from State highway departments and 3 from the Bureau of Public Roads. In October, the Board made its report covering the proposed interstate highway network, the route numbering system, and a comprehensive set of sign designs. The system devised for numbering the interstate network of highways (now called the U.S. Numbered Highways) used even numbers for east and west roads and odd numbers for north and south roads. Long distance routes which might be connected entirely, or nearly so, across the country were given multiple numbers of 10. The principal north and south routes were given numbers such as 1, 5, 11, 15. Other numbered routes could be used for shorter lines between the main designated routes.
The Joint Board sign standards followed closely the 1924 Conference recommendations with the addition of the now familiar “U.S. shield” marker for the new network. A yellow background was adopted for all caution and danger message signs, including the stop sign. There were no recommendations on luminous or reflectorized signs.
The Joint Board report was submitted to the Secretary of Agriculture and approved by him November 8, 1925. It was accepted at the annual AASHO meeting a few days later and subsequently adopted by letter ballot of the State highway departments.
During the following year, AASHO developed detailed sign standards and published the first edition (1927) of the Manual and Specifications for the Manufacture, Display, and Erection of U.S. Standard Road Markers and Signs. This Manual set forth the design and use of each type of sign and illustrated most of the approved signs. It listed a series of working drawings of standard signs and alphabets that had been prepared for distribution by the Bureau of Public Roads. Also, it contained detailed specifications for materials and manufacturing of various types of wood and metal signs. This 1927 Manual was the first national rural manual on traffic control signs and markings. A 1929 second edition authorized the use of a luminous element mounted below a standard sign on the same post or on a separate mounting in advance of the standard sign framed with a background of the same shape and color as the standard sign that it supplemented. A 1931 revised edition added a number of new signs, including a new design for junction markers.
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The standardized U.S. route shield.
Two years after the 1927 AASHO Manual, other officials gathered for urban sign standardization. The National Conference on Street and Highway Safety, recognizing the need for greater uniformity in street traffic signs, signals, and markings, accepted an offer of the American Engineering Council to make a national survey of existing conditions and to prepare a recommended practice. The resulting report accepted most of the AASHO Sign Manual standards, but with some exceptions and qualifications. The recommended “stop” sign was to have a yellow background, but the letters were to be red. Eighteen inches was to be the standard outside dimension instead of 24 inches because the generally slower speeds in cities did not require large signs for visibility and the smaller signs would occupy less space. Parking regulation signs and other signs applicable to city use were added. These parking signs were to be 12 by 18 inches with a white background. Red letters were to be used on “no parking” signs, and green letters where limited time parking was permitted. Pedestrian restrictions were to be shown in blue letters on a white background, and other restrictions in black on white.
The urban recommendations also included subjects not dealt with by AASHO, such as traffic signals, pavement markings and safety zones. The signal recommendations included terms, systems, control types, colors, specifications, beacons, and “wigwag” and flashing light train signals. The marking recommendations included pavement lines, railroads, identification, curve lines, words, pavement inserts, paint, buttons, and markings on vertical elements such as obstructions and railroad gates.
The Council’s report was submitted and approved by the Third National Conference on Street and Highway Safety in 1930. Then there were in existence two national manuals, one for rural use and one for municipal use, with some significant differences between them. It was apparent to all that a single manual covering all traffic control devices would be desirable.
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