Tuesday, May 27, 2014

All About the Mackinac Bridge

When I went down state this past weekend for my grandson's first birthday party, I had to drive over the Mackinac Bridge.  As I looked through the photos for this blog posting, I decided to include information about the bridge that has changed the state of Michigan.

Below is a NASA image and map of the Straits of Mackinac, which runs between the Lower Peninsula and Upper Peninsula of Michigan.

I went right to the web page published by the Macinac Bridge Authority to find out more about the bridge:  http://www.mackinacbridge.org/ 

The Mackinac Bridge is currently the fifth longest suspension bridge in the world and the longest in the western hemisphere. In 1998, the Akashi Kaikyo Bridge in Japan became the longest with a total suspension of 12,826 feet. The total length of the Mackinac Bridge is 26,372 feet. The length of the suspension bridge (including anchorages) is 8,614 feet. The length from cable bent pier to cable bent pier is 7,400 feet. Length of main span (between towers) is 3,800 feet.

The width of the roadway is 54 feet. The outside anes are 12 feet wide (2), the inside lanes are 11 feet wide (2), the center mall is 2 feet wide, and the catwalk, curb and rail width is 3 feet on each side - totaling 54 feet. 


The height of the roadway at mid-span is approximately 200 feet above water level. The vertical clearance at normal temperature is 155 feet at the center of the main suspension span and 135 feet at the boundaries of the 3,000 ft. navigation channel. 

All suspension bridges are designed to move to accommodate wind, change in temperature, and weight. It is possible that the deck at center span could move as much as 35 feet (east or west) due to high winds. This would only happen under severe wind conditions. The deck would not swing or "sway" but rather move slowly in one direction based on the force and direction of the wind. After the wind subsides, the weight of the vehicles crossing would slowly move it back into center position.

People first suggested building a bridge across the Straits of Mackinac during the early 1880s.   The dedication of the Brooklyn Bridge in 1883 gave Mackinac Bridge backers encouragement.  On July 1, 1888, a group met at the famous Grand Hotel on Mackinac Island.  The minutes show that Cornelius Vanderbilt said: "We now have the largest, well-equipped hotel of its kind in the world for a short season business. Now what we need is a bridge across the Straits."

In 1923 the Legislature ordered the State Highway Department to establish a ferry service at the Straits. Within five years traffic on this facility became so heavy that the late Governor Fred Green ordered the same agency to make a study of bridge feasibility. The report was favorable and its cost was estimated at 30 million dollars. Some strides to get the project underway were taken but it was eventually dropped.

In the extra session of 1934 the Michigan Legislature created the Mackinac Straits Bridge Authority and empowered it to investigate the feasibility of constructing a bridge and to finance the work by issuance of revenue bonds. The Authority began its studies in May 1934.  Work continued until all the pieces came together and the project was approved in 1951, but financing through the sale of bonds was not completed until 1953.  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. 

There are always seagulls hanging out near the bridge.  Here are some photos I took last Saturday.


Just to summarize, here are the facts from the Bridge Authority's web site:


Total Length of Bridge (5 Miles) 26,372 Ft. 8,038 Meters
Total Length of Steel Superstructure19,243 Ft. 5,865 Meters
Length of Suspension Bridge (including Anchorages)8,614 Ft. 2,626 Meters
Total Length of North Approach 7,129 Ft. 2,173 Meters
Length of Main Span (between Main Towers) 3,800 Ft. 1,158 Meters


Height of Main Towers above Water552 Ft168.25 Meters
Maximum Depth to Rock at MidspanUnknownUnknown
Maximum Depth of Water at Midspan295 Ft.90 Meters
Maximum Depth of Tower Piers below Water210 Ft.64 Meters
Height of Roadway above Water at Midspan199 Ft.61 Meters
Underclearance at Midspan for Ships 155 Ft.47 Meters
Maximum Depth of Water at Piers142 Ft.43 Meters
Maximum Depth of Piers Sunk through Overburden105 Ft.32 Meters


Total Length of Wire in Main Cables42,000 Miles 67,592 km
Maximum Tension in Each Cable16,000 Tons 14,515,995 kg
Number of Wires in Each Cable12,580
Weight of Cables11,840 Tons10,741,067 kg
Diameter of Main Cables24 1/2 Inches62.23 cm
Diameter of Each Wire 0.196 Inches .498 cm

Total Weight of Bridge 1,024,500 Tons 929,410,766 kg
Total Weight of Concrete931,000 Tons844,589 kg
Total Weight of Substructure 919,100 Tons833,793,495 kg
Total Weight of Two Anchorages 360,380 Tons 326,931,237 kg
Total Weight of Two Main Piers 318,000 Tons 288,484,747 kg
Total Weight of Superstructure 104,400 Tons94,710,087 kg
Total Weight of Structural Steel 71,300 Tons 64,682,272 kg
Weight of Steel in Each Main Tower 6,500 Tons5,896,701 kg
Total Weight of Cable Wire 11,840 Tons 10,741,067 kg
Total Weight of Concrete Roadway 6,660 Tons6,041,850 kg
Total Weight of Reinforcing Steel 3,700 Tons3,356,584 kg


Total Number of Steel Rivets 4,851,700
Total Number of Steel Bolts 1,016,600


Total, at the Bridge Site3,500
At Quarries, Shops, Mills, etc. 7,500
Total Number of Engineers 350

Vehicle Traffic Volume

             Traffic 2013   Traffic 2012
January   169,480          168,994
February 177,376          192,287
March      206,728          205,508
April        201,298          230,475
May        308,440          307,260
June        380,202          386,306
July         523,485          538,564
August    556,259          541,843
Sept        393,178          393,023
October  330,610          314,479
Nov        248,003          257,789
Dec         200,602          200,821

Rules & Regulations

  • Maximum speed limit is 45 mph.
  • No U-turns.
  • No stopping on the Mackinac Bridge.
  • In the event of a flat tire or motor failure, please remain in your vehicle. Bridge personnel on duty will investigate and assist.
  • Use four-way flashers while vehicle is disabled.
Truck Regulations
  • Travel in right lane – no passing.
  • 500-foot spacing – no tailgating.
  • Use four-way flashers.
  • Maximum speed is 20 mph.
  • Rules Enforced from toll plaza to Jamet Street exit.
  • Trucks with a gross load of over 40 tons must request escort prior to crossing.
  • Maximum allowable vehicle weight is 72 tons.

Drdpw, http://commons.wikimedia.org/wiki/File:Straits_of_Mackinac_map.png?uselang=en-gb


varnent, http://commons.wikimedia.org/wiki/File:Mackinac_Bridge_from_Straits_of_Mackinac_during_boat_tour_-_0026.jpg?uselang=en-gb

defenseimagery.mil., http://commons.wikimedia.org/wiki/File:Ice_forms_in_the_Straits_of_Mackinac,_underneath_the_Mackinac_Bridge,_near_St_120124-G-JL323-038.jpg?uselang=en-gb

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