Building Mighty Mac

The Mackinac Bridge consists of three segments, with a post-supported truss bridge at each end and a suspension bridge segment in the center. For decades after its construction, it was the longest suspension bridge in the world, though today most of the longest are in China. Designed to withstand crushing ice and winds up to 120 mph, it was built as an engineering and construction triumph for $99.8 million between 1954 and 1957, on time and within budget. The 4.5 million vehicles that safely cross each year reflect the work of dedicated builders and crews who overcame the harsh winters and winds of the Straits. The suspension portion was used because truss bridges supported by posts were far cheaper to build, but the Straits of Mackinac reached depths of up to 300 feet, making deep posts impractical. Engineers placed an anchor block at each edge of the deep water, stretched cables between them across the chasm, and supported those cables with two towers, while the roadbed hangs from the cables. The full weight of the roadbed, vehicles, and cables is carried by the pull of the cables on the anchor blocks. Designers determined the height of the towers by calculating the bridge span and the desired height of the roadbed above the water, which has a minimum clearance of 149 feet to allow freighters and tall ships to pass.

Mackinaw City, Michigan · United States