MACKINAC BRIDGE

Mackinac Bridge, Michigan one of the longest and strongest suspension bridges in the world, spanning the Mackinac Straits from the Upper to the Lower Peninsula of Michigan, U.S. Designed by David B. Steinman in the wake of the failure of the Tacoma Narrows Bridge (1940), the Mackinac Bridge was not constructed until the 1950s because of World War II. The bridge measures 8,344 feet (2,543 m) between the main anchorages. Its 3,800-foot (1,158-metre) main span is stiffened by a truss 38 feet (13 m) deep, with open spaces on either side of the roadway and grid construction of the deck to permit the passage of wind gusts. Heavy pier foundations, the deepest 210 feet (64 m), were necessary to resist the ice masses that accumulate every winter in the Mackinac Straits. In November 1955 the incomplete bridge withstood a 76-mile-per-hour (122-kilometre-per-hour) gale. It was opened to vehicle traffic in 1957.