Page:America's Highways 1776–1976.djvu/441

 caused by normal service load. In the early 1950’s, reports on European use of prestressed-concrete bridges had aroused the interest of engineers and cement producers in this country. The first American prestressed bridge was the Walnut Lane Bridge in Philadelphia, Pennsylvania, built in 1951. Subsequently, in 1955, Public Roads published the Criteria for Prestressed-Concrete Bridges, the only such publication in the United States at the time. With the help of this pamphlet and the standard plans published by the cement industry and Public Roads, the use of prestressed-concrete for bridges rapidly developed and greatly expanded the span range of concrete structures.

The Red Bridge over the Seekonk River between Providence, and East Providence, R.I., a welded plate girder bridge of composite construction.

The desire for separation of grades led to extensive use of long sections of viaduct construction in urban areas on the Interstate as well as on other freeways. Divided roadways, liberal bridge roadway widths and increased pier and abutment clearances under overpasses became normal safety practices.

The mainline and ramps of the Mission Valley Bridge in San Diego, Calif., are prestressed concrete box girders. Architectural treatment gives the piers an old “Spanish flavor.” 435