Bridges

The crossing of the Delaware River at Easton, Pennsylvania, provided a central link in travel from the northeastern seaboard to America's inland territories throughout the 18th and early 19th centuries. From 1806 to the mid-1890s, travelers used a landmark wooden structure built by noted bridge-builder Timothy Palmer. By the 1880s, however, Palmer's three-span covered bridge could no longer handle the demands of traffic generated by new trolley lines.

The Northern Pacific High Line Bridge No. 64, built between 1907 and 1908, has continued to perform yeoman service in the uninterrupted flow of the Nation's commerce. Nearly, 100 years after this bridge officially opened, it still carries 125-ton car unit coal trains, double stack container trains, lumber, and refined products at train speeds of 50 m.p.h.

Navajo Bridge spans Marble Canyon, 470 feet above the Colorado River in Grand Canyon National Park. It was considered the highest steel arch bridge in America when completed.

The Navajo Bridge (also known as the Grand Canyon Bridge) was built in 1929 by the Arizona Highway Department and provided a vital transportation link over the Grand Canyon between northern Arizona and southern Utah. Construction commenced by building on one side of the canyon, then on the other, until the two sides met in the middle.

Designed, patented, and built by Thomas W.H. Moseley, this arched 96-foot span bridge preceded by years the standard use of wrought iron for bridges. For the first time in the United States, Moseley incorporated the use of riveted wrought-iron plates for the triangular-shaped top chord.

The Memphis Bridge (now called the Frisco Bridge) comprises three spans across the Mississippi River. With a main span measuring over 790 feet, it was one of the longest railroad bridges in the world upon completion. The renowned George Morison, after whom the bridge is unofficially named, served as Chief Engineer.

The Rogue River Bridge was the most advanced concrete bridge in America when it was built. Distinguished bridge engineer Conde McCullough employed the techniques of Frenchman Eugene Freyssinet to create thin, graceful concrete arches for this seven-span structure.

Pre-compression of the concrete arch was achieved and, as a result of its success, pre-stressing became one of the hallmarks of American bridge building techniques.

When opened in 1909, the 1,470 foot long main span of the Manhattan Bridge was the third longest suspension bridge span in the world, after the nearby Brooklyn and Williamsburg Bridges. The Manhattan Bridge has two 725 foot long suspended side spans for an overall length of 2,920 feet. The bridge deck is supported by 4 main cables of 20.75 inch diameter, each composed of more than 35,000 individual wires. The bridge deck is stiffened by four parallel trusses of 24 foot depth, hinged at the towers.

The Mackinac (pronounced "Mack-in-awe") Bridge (1957) spans the Straits of Mackinac between Lake Michigan and Lake Huron, connecting the Lower and Upper peninsulas of Michigan.   Prior to the construction of the bridge, a fleet of nine ferries would carry as many as 9,000 vehicles per day, with traffic backups stretching as long as 16 miles.

Ancient Chinese literature refers to the Zhaozhou Bridge as a "crescent moon rising from the clouds" or a "rainbow in the sky."  Throughout its history, it has been known as the Anchi or Anji Bridge (literally "safe crossing"), the Dashi Bridge ("big stone"), and the Dashiqiao ("great stone") Bridge.

In the 1850s, the Lexington and Danville Railroad began building a suspension bridge over the Kentucky River. The bridge was designed by John A Roebling. Due to unforeseen increases in train loads, the Roebling bridge was never completed. The High Bridge would then be built 20 years later on the existing foundations.