Notes: Mackinac Bridge and Straits of Mackinac, The five-mile bridge, including approaches, and the world's longest suspension bridge between cable anchorages, was designed by the great engineer Dr. David B. Steinman. Merritt-Chapman & Scott Corporation's $25,735,600 agreement to build all the foundations led to the mobilization of the largest bridge construction fleet ever assembled. The American Bridge Division of United States Steel Corporation, awarded a $44,532,900 contract to build this superstructure, began its work of planning and assembly. In U.S. Steel's mills the various shapes, plates, bars, wire and cables of steel necessary for the superstructure and for the caissons and cofferdams of the foundation, were prepared. The bridge was officially begun amid proper ceremonies on May 7 & 8, 1954, at St. Ignace and Mackinaw City.

The bridge opened to traffic on November 1, 1957 according to schedule, despite the many hazards of marine construction over the turbulent Straits of Mackinac. The last of the Mackinac Bridge bonds were retired July 1, 1986. Fare revenues are now used to operate and maintain the Bridge and repay the State of Michigan for monies advanced to the Authority since the facility opened to traffic in 1957.

Facts & Figures

LENGTHS
Total Length of Bridge (5 Miles) 26,372 Ft.
Total Length of Steel Superstructure 19,243 Ft.
Length of Suspension Bridge (including Anchorages) 8,614 Ft.
Total Length of North Approach 7,129 Ft.
Length of Main Span (between Main Towers) 3,800 Ft.

HEIGHTS AND DEPTHS
Height of Main Towers above Water 552 Ft. 168.25 Meters
Maximum Depth to Rock at Midspan Unknown Unknown
Maximum Depth of Water at Midspan 295 Ft. 90 Meters
Maximum Depth of Tower Piers below Water 210 Ft. 64 Meters
Height of Roadway above Water at Midspan 199 Ft. 61 Meters
Underclearance at Midspan for Ships 155 Ft. 47 Meters
Maximum Depth of Water at Piers 142 Ft. 43 Meters
Maximum Depth of Piers Sunk through Overburden 105 Ft. 32 Meters

CABLES
Total Length of Wire in Main Cables 42,000 Miles 67,592 Kilometers
Maximum Tension in Each Cable 16,000 Tons 14,515,995 Kilograms
Number of Wires in Each Cable 12,580
Weight of Cables 11,840 Tons 10,741,067 Kilograms
Diameter of Main Cables 24 1/2 Inches 62.23 Centimeters
Diameter of Each Wire 0.196 Inches .498 Centimeters

pier construction
CONCRETE
Total Concrete in Bridge 466,300 Cu. Yds. 356,512 Cu. Meters
Total Concrete in Substructure 451,000 Cu. Yds. 344,814 Cu. Meters
Total Concrete in One Anchorage (No. 22) 91,600 Cu. Yds. 70,033 Cu. Meters
Total Concrete in One Pier (No. 19) 80,600 Cu. Yds. 61,623 Cu. Meters
Total Concrete in Superstructure 15,300 Cu. Yds. 11,698 Cu. Meters

WEIGHTS
Total Weight of Bridge 1,024,500 Tons 929,410,766 Kilograms
Total Weight of Concrete 931,000 Tons 844,589 Kilograms
Total Weight of Substructure 919,100 Tons 326,931,237 Kilograms
Total Weight of Two Anchorages 360,380 Tons 326,931,237 Kilograms
Total Weight of Two Main Piers 318,000 Tons 288,484,747 Kilograms
Total Weight of Superstructure 104,400 Tons 94,710,097 Kilograms
Total Weight of Structural Steel 71,300 Tons 64,682,272 Kilograms
Weight of Steel in Each Main Tower 6,500 Tons 5,896,701 Kilograms
Total Weight of Cable Wire 11,840 Tons 10,741,067 Kilograms
Total Weight of Concrete Roadway 6,660 Tons 6,041,850 Kilograms
Total Weight of Reinforcing Steel 3,700 Tons 3,356,584 Kilograms

RIVETS AND BOLTS
Total Number of Steel Rivets 4,851,700
Total Number of Steel Bolts 1,016,600
DESIGN AND DETAIL DRAWINGS
Total Number of Engineering Drawings 4,000
Total Number of Blueprints 85,000

MEN EMPLOYED
Total, at the Bridge Site 3,500
At Quarries, Shops, Mills, etc. 7,500
Total Number of Engineers 350

IMPORTANT DATES
Mackinac Bridge Authority Appointed June, 1950
Board of Three Engineers Retained June, 1950
Report of Board of Engineers January, 1951
Financing and Construction Authorized by Legislature April 30, 1952
D.B. Steinman Selected as Engineer January, 1953
Preliminary Plans and Estimates Completed March, 1953
Construction Contracts Negotiated March, 1953
Bids Received for Sale of Bonds December 17, 1953
Began Construction May 7, 1954
Open to traffic November 1, 1957
Formal dedication June 25-28, 1958
50 millionth crossing September 25, 1984
40th Anniversary Celebration November 1, 1997
100 millionth crossing June 25, 1998