Page:America's Highways 1776–1976.djvu/416

 traffic control standards was extended to apply to all streets and highways. The Act provided funds for the improvements, which would ultimately place the Nation under one set of traffic control standards.

New signs, 1971. Many of the signs combine international symbols and word equivalents.

Using the Joint Committee as an advisory board, a new updated revision of the MUTCD was prepared by the FHWA staff. Issued as the 1971 Manual on Uniform Traffic Control Devices for Streets and Highways, it is now the national standard for all highways open to public travel.

The 1971 MUTCD incorporates significant changes in the wider use of symbols, which are international in character, on both regulatory and warning signs. A separate part covers traffic controls for school areas. A pennant shaped “no passing zone” sign and pentagon shaped school signs were added. For construction and maintenance work, the colors for the warning signs were changed to orange. In the pavement marking area, yellow was added as the color to delineate the separation of traffic flowing in opposite directions. Traffic signal updating included recommending a 12-inch signal face instead of 8-inch for arrows. It emphasizes that engineering study always is an important part of the application of detail standards.

The history of the development of highway pavements in the United States to the present stage is a series of incidents that are widespread both in time and place. Once roads advanced beyond the footpaths and horse trails, their improvements into paved highways were successive developmental efforts to match the available manpower, funds and natural resources against the changing needs of the types and extent of vehicular traffic for each area’s expanding commerce.

The first “macadam” surface in this country was constructed in 1823 between Hagerstown and Boonsboro, Maryland. Rocks were broken by hand so as not to exceed 6 ounces in weight or to fail to pass a 2-inch ring. The material was laid in three separate strata, the finished surface being 15 inches deep at the center and 12 inches at each edge. The surface was 20 feet wide.

In the forested sections, plank roads were dominant for a period. The first plank road in the United States was opened to traffic in 1846 in Syracuse, New York. Advocates of plank roads made extravagant 410