This image shows the truss beam section of the Mackinaw Bridge, under construction with the main suspension towers in the background.
The description states:
Showing approaches and Center Span under construction. The Mackinac Bridge is a structure across the Straits of Mackinac, connecting Michigan’s two Peninsulas at Mackinaw City in the Lower and St. Ignace in the Upper Peninsula. The Length overall will be more than five miles and will take about ten minutes to cross. The Towers are 752 feet high, 552 feet of which are above water. Clearance at the center will be 150 feet. Bridge will carry four lanes of traffic. Construction was started in May, 1954 and is scheduled to be open for traffic in November 1957. Engineered to withstand many times any possible weight, ice pressure or wind velocity, this masterpiece of overwater structurer was disjoined by Dr. D. B. Steinman.
–As indicated in the description, this card dates from the 1950s, during the construction.