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Mackinac Bridge

Mackinac Bridge

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Key Facts
Bridge Name Facility Carried / Feature Intersected Location Structure Type Construction Date / Builder or Contractor Engineer
Mackinac Bridge I-75 Over Straits of Mackinac Mackinaw City and St. Ignace: Emmet County, Michigan and Mackinac County, Michigan Metal Deck Truss Stiffening Cable Suspension Bridge 1957 By: American Bridge Company of New York, New York David Steinman
Technical Facts
Total Structure Length Roadway Width Main Spans Approach Spans
19247.7 Feet / 3.65 Miles (5866.7 Meters / 5.87 Kilometers) 48 Feet (14.6 Meters) 3 57 Warren Deck Truss and Others
Normal Vertical Clearance Under Bridge Tower Height Total Length Between Anchorages Total Suspended Span Length Main Suspended Span Length Approach Suspended Span Lengths
155 Feet (47.2 Meters) 257 Feet (78.3 Meters) 8614 Feet (2625.6 Meters) 7400 Feet (2255.6 Meters) 3800 Feet (1158.2 Meters) 2 at 1700 Feet Each (518.2 Meters)

 Michigan's Bridge King

This bridge is the king of all Michigan Bridges. It held the title of longest bridge in the world for a very long time, and is still the longest bridge in the western hemisphere. This bridge also set records for safety when it was completed, with extensive stiffening truss, as well as air-flow grating, which reduced the chance of dangerous oscillations to nearly zero. It is the largest and most famous bridge on I-75, and is quite a climax for the expressway, which ends (or begins?) a ways north in Sault Ste Marie.

About the Bridge

Compared to other bridges on this website, this is a relatively new bridge, completely finished in 1958. Its relatively new age in the world of historic bridges evidences itself in its simple concrete approach supports, bolted connections on the stiffening truss, and a lack of v-lacing or lattice on any part of the bridge's built-up steel. Guardrails are composed of three steel poles. There is a steel curb that sits in front of the guardrails. Air-flow grating is located on the inside two lanes, which, along with the stiffening truss, prevents dangerous oscillations of the deck due to wind. Traffic is separated by only a large steel curb. The towers of the bridge were designed with aesthetics in mind, and they include attractive pierced openings in them, in addition to the large openings, which are arched. Approaches to the bridge are deck truss. There is also a significant causeway built of rubble-type stones on the St. Ignace side of the bridge. A small (ugly) steel beam bridge is located at one spot on this causeway, to allow water to pass through.

One thing that makes the Mackinac Bridge a winner is its location. Since it is the only large man-made object in the area, it really sticks out and shows off its size. Also, the way I-75 is curved, if you are heading north, you will not see the bridge at all until you round one final curve and, assuming it is a fairly clear day, then you can see those towers immediately. For a first-time experience it is quite a dramatic event. As if that were not enough, there are some nice t-beam overpasses in that area... which results in some very cool pictures with the curved t-beams in the foreground and the towers of the Mackinac Bridge in the background.

Mackinac Bridge Photography

This bridge is so big that it is impossible to get a detailed picture of exactly what the bridge looks like. You can take pictures of the whole bridge from a long way away, but you have to zoom your camera out so far that the bridge becomes quite tiny. You can fill the bridge into the picture by zooming in when you are closer to the bridge, but that makes the bridge look shorter than it is!

On the other hand there are countless places where photos of this bridge can be taken. There are parks on both sides, as well as some lookouts and high spots that offer views of the bridge. If you are like me, and like a mid-span shot of the bridge without getting in a boat (although a ferry to Mackinac Island offers some good bridge photos) you should take a drive down Boulevard Drive, which is a tiny dirt road that wanders tight along the shore west from St. Ignace. There are excellent photo opportunities all the way along that road, and no houses are in your way.

Condition of the Bridge

This is probably the most cared for bridge in Michigan. Tolls provide a solid source of income for the bridge. The tolls help keep paint on this bridge and any other repairs that may become necessary. An extensive painting and renovation project has been going on for the past few years, and maintenance of some sort always seems to be happening on this bridge. If only the smaller, yet also important, historic bridges in Michigan got the same treatment!

Historic Significance Rating (HSR)

Information and Findings From MDOT

MDOT Historic Bridge Emmet County I-75 / Straits of MackinacThe five-mile stretch of water separating Michigan's two peninsulas, the result of glacial action some twelve thousand years ago, has long served as a major barrier to the movement of people and goods. The three railroads that reached the Straits of Mackinac in the early 1880s, the Michigan Central and the Grand Rapids & Indiana Railway from the south, and the Detroit, Mackinac and Marquette from the north, jointly established the Mackinac Transportation Company in 1881 to operate a railroad car ferry service across the straits. The railroads and their shipping lines developed Mackinac Island into a major vacation destination in the 1880s. Improved highways along the eastern shores of Michigan's lower peninsula brought increased automobile traffic to the straits region starting in the 1910s. The state of Michigan initiated an automobile ferry service between St. Ignace and Mackinaw City in 1923 and eventually operated eight ferry boats. In peak travel periods, particularly during deer season, five mile backups and delays of four hours or longer became common at the state docks at Mackinaw City and St. Ignace. With increased public pressure to break this bottleneck, the Michigan legislature established a Mackinac Straits Bridge Authority in 1934, with the power to issue bonds for bridge construction. The bridge authority supported a proposal first developed in 1921 by Charles Evan Fowler, the bridge engineer who had previously promoted a Detroit-Windsor bridge. Fowler's plans called for an island-hopping route from the city of Cheboygan to Bois Blanc, Round, and Mackinac islands, thence to St. Ignace, along a twenty-four-mile route. The Public Works Administration flatly rejected a request for loans and grants to implement this project. A plan was then drawn up for a direct crossing from Mackinaw City to St. Ignace, but they were again denied funds. In 1940, a plan was submitted for a suspension bridge with a main span of 4600 feet. This design was a larger version of the ill-fated Tacoma Narrows Bridge in Washington State, a structure destroyed by high winds on November 7, 1940. Although the disaster delayed any further action, the activities of 1938-1940 nevertheless produced some important results. The bridge authority conducted a series of soundings and borings across the straits and built a causeway extending out 4200 feet from the St. Ignace shore. The Second World War ended any additional work, and the Legislature abolished the bridge authority in 1947. William Stewart Woodfill, president of the Grand Hotel on Mackinac Island, almost singlehandedly resuscitated the dream of a bridge across the Straits of Mackinac. Woodfill formed the statewide Mackinac Bridge Citizens Committee in 1949 to lobby for a new bridge authority, which the legislature created in 1950. A panel of three prominent engineers conducted a feasibility study and made recommendations to the bridge authority on the location, structure, and design of the bridge. The State Highway Department, which had just placed a $4.5 million ferryboat, Vacationland, into service at the straits in January 1952, remained hostile to the bridge plan. In April 1952, the Michigan legislature authorized the bridge authority to issue bonds for the project, choose an engineer, and proceed with construction. The authority selected David B. Steinman as the chief engineer in January 1953 and tried unsuccessfully to sell the bridge bonds in April 1953, but by the end of the year, the authority had sold the $99.8 million in revenue bonds needed to begin construction. The major construction achievement of 1954 was the erection of the bridge's six principal piers, including those for the two towers, the anchorages, and the backstay spans. Enormous steel caissons were sunk into the mud under the straits and then driven to bedrock. After removing all the mud and loose rock, two reinforced concrete piers, which extended to bedrock, more that 200 feet below the water's surface, were poured. In 1955, the remaining twenty-eight piers were built and the anchorage was completed. The Mackinac Bridge began to take shape in 1956, when the main cables were strung and the twenty-eight truss spans that made up the approaches were built. The four-year construction effort ended in 1957, with the erection of the main suspension span and paving of the roadway. The new bridge opened to traffic on November 1, 1957, although the contractors did not complete all the work until September 1958. The official bridge dedication ceremonies began on June 25, 1958, with the first "Governor's Walk" across the bridge, and ended four days later. The annual Mackinac Bridge Walk began as a walking race sanctioned by the International Walkers Association. The first walk, in June 1958, involved only sixty walkers. Later bridge walks took place on Labor Day and the number of participants increased rapidly from about 2500 in 1962 to more than 15,000 in 1966-1968. Since the first "Governor's Walk" at the bridge opening, it has become a mandatory political event for governors and gubernatorial candidates. In 1970, more than 20,000 completed the walk and the numbers reached 70,000 in 1990. The Mackinac Bridge Walk is as much an integral part of Labor Day in Michigan as parades and picnics. The sheer size and beauty of the Mackinac Straits Bridge still impress first-time viewers. The bridge's total length, 8614 feet, the longest in the world, combined with towers standing 552 feet above the water line, a 155 feet clearance under the bridge, and a total weight of 11,840 tons, is indeed an impressive sight.

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