The last car ferry to cross the Straits of Mackinac was during the ribbon-cutting, parades and fireworks in June, 1958, celebrating the world’s longest suspension bridge, between two anchorages, in the Western Hemisphere.
The “Mighty Mac” was officially opened for driving on November 1, 1957.  The engineer for this renowned project was a man from New York City, by the name of David B. Steinman, who was also an author and a poet.  The bridge took 48 months to complete, employing 350 engineers and a total of 3,500 workers.  The main towers rise 552 feet above the water & the supporting piers are 210 feet below the water.  The deepest point beneath the bridge is 295 feet.  The main cables are made from 42,000 miles of wire and the expansion joints allow the bridge to move or sway as much as 35 feet, accommodating temperature changes, weight and high winds.
 
Mackinac Bridge Map – Mackinac Bridge Authority Site