Mackinac Bridge - Facts and Figures

Facts and Figures

The Mackinac Bridge is currently a toll bridge on Interstate 75 (I-75). Prior to the coming of I-75, the bridge carried US Highway 27 (US 27). It is one of only three segments of I-75 that are tolled, the others being the American half of the International Bridge near Sault Ste. Marie, Michigan, and Alligator Alley in Florida. The current toll is $4.00 for automobiles and $5.00 per axle for trucks. The Mackinac Bridge Authority recently raised the toll to fund a $300 million renovation program, which would include completely replacing the bridge deck.

Every Labor Day, two of the lanes of the bridge are closed to traffic and open to walkers for the Mackinac Bridge Walk.

Painting of the bridge takes seven years, and when painting of the bridge is complete, it begins again.

The bridge celebrated its 150 millionth vehicle crossing on September 6, 2009.

• Length from cable bent pier to cable bent pier: 7,400 feet (2,256 m).

• Total width of the roadway: 54 feet (16.5 m)

Two outside lanes: 12 feet (3.7 m) wide each

Two inside lanes: 11 feet (3.4 m) wide each

Center mall: 2 feet (0.61 m)

Catwalk, curb and rail width: 3 feet (0.91 m) on each side

• Width of stiffening truss in the suspended span: 68 feet (20.7 m).
• Depth of stiffening truss: 38.1 feet (11.6 m)
• Height of the roadway at mid-span: approximately 200 feet (61 m) above water level.
• Vertical clearance at normal temperature:

155 feet (47 m) at the center of the main suspension span.

135 feet (41 m) at the boundaries of the 3,000 feet (914 m) wide navigation channel.

• Construction cost: $99.8 million (1957 USD; adjusted for inflation, approximately $732 million, 2007 USD)
• Height of towers above water: 552 feet (168 m)
• Max. depth of towers below water: 210 feet (64 m)
• Depth of water beneath the center of the bridge, 250 feet (76 m)
• Total length of wire in main cables: 42,000 miles (68,000 km).
• Total vehicle crossings, 2005: 4,236,491 (average 11,608 per day)
• Speed limit: 45 miles per hour (72 km/h) for passenger cars, 20 miles per hour (32 km/h) for heavy trucks. Heavy trucks are also required to leave 500 feet (150 m) spacing ahead.