Mackinac Bridge

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Mackinac Bridge
Mackinac Bridge
Carries 4 lanes of Interstate 75
Crosses Straits of Mackinac
Locale Mackinaw City and St. Ignace, Michigan
Maintained by Mackinac Bridge Authority [1]
Design Suspension bridge
Longest span 3,800 feet (1,158 meters)
Total length 26,400 feet (7,920 m)
Width 54 feet (16.5 m)
Clearance below 155 ft (47 m)
Opening date November 1, 1957
Toll $1.25 per axle for passenger vehicles. $3.00 per axle for commercial vehicles
Connects:
Mackinaw City and St. Ignace

The Mackinac Bridge (pronounced [ˈmækɪˌnɔː], like MACK-in-aw, note the silent "c", and affectionately known as the "Mighty Mac" or "Big Mac"), is a suspension bridge spanning the Straits of Mackinac to connect the non-contiguous upper and lower peninsulas of the U.S. state of Michigan. Envisioned since the 1880s, the bridge was completed only after many decades of struggles to begin construction. Designed by engineer David B. Steinman, it connects the cities of St. Ignace on the north end with Mackinaw City on the south.

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[edit] Longest between anchorages

The bridge opened on November 1, 1957, and a year later was formally dedicated as "the world's longest suspension bridge between anchorages". This designation was chosen because the bridge would not be the world's largest using the customary way of measuring suspension bridges, the length of the center span between the towers—that title already belonged to the Golden Gate Bridge, which has a longer center span. By saying "between anchorage", the bridge could be considered longer than the Golden Gate Bridge, and also longer than the suspended western section of the San Francisco-Oakland Bay Bridge. (That bridge has a longer total suspension but is a double bridge with an anchorage in the middle.)

The Mackinac Bridge is still the longest two tower suspension bridge between anchorages in the western hemisphere, but it is now third longest world-wide. The combined length of the three spans of the bridge (including anchorages) is 8,614 feet (2,626 m). In 1998, the Akashi Kaikyo Bridge in Japan became the longest with a total suspension of 12,826 feet (3,909 m).

The length of main span is 3,800 feet (1,158 m), which makes it the third largest suspension span in the United States and tenth largest worldwide.

[edit] History

Before the construction of the bridge, the typical way to cross the Straits of Mackinac was by ferry. By the 1880s, the area had become a popular resort destination, mainly because of nearby Mackinac Island. Year-round boat service across the straits had been abandoned as impractical because of the cold winters which would often freeze the water across the entire strait. Following the opening of the Brooklyn Bridge in 1883, local residents began to imagine such a structure could span the straits. In 1884, a store owner in St. Ignace published a newspaper advertisement that included a reprint of an artist's conception of the Brooklyn Bridge with the caption "Proposed bridge across the Straits of Mackinac."

A Mackinac Island ferry passing in front of the Mackinac Bridge.
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A Mackinac Island ferry passing in front of the Mackinac Bridge.

The idea of the bridge was discussed in the Michigan Legislature as early as the 1880s. At the time the area was becoming a popular tourist destination, including the creation of Mackinac National Park on Mackinac Island in 1875.

Despite the perceived necessity for the bridge, several decades elapsed with no formal plan. In 1920, the Michigan state highway commissioner advocated the construction of a floating tunnel across the straits. At the invitation of the legislature, C. E. Fowler of New York City put forth a plan for a long series of causeways and bridges across the straits from Cheboygan, 17 miles (27 km) southeast of Mackinaw City, to St. Ignace, using Bois Blanc, Round, and Mackinac Island as intermediate steps.

In 1923, the state legislature ordered the State Highway Department to re-establish ferry service across the strait. By 1928, however, the service had become so expensive to operate that Governor Fred Green ordered the department to study the feasiblity of a bridge. The department deemed the idea feasible, estimating the cost at 30 million dollars.

In 1934, the Michigan Legislature created the Mackinac Straits Bridge Authority of Michigan, to study the feasiblity of the bridge, and authorized it to sell bonds for the project. In the mid 1930s, the Authority twice attempted to obtain federal funds for the project but was unsuccessful, despite the endorsement of the United States Army Corps of Engineers and President Franklin D. Roosevelt. Nevertheless, between 1936 and 1940, a route was selected for the bridge and borings were made for a detailed geological study of the route.

Preliminary plans for the bridge at the time featured a 3-lane roadway, a railroad crossing on the underdeck of the span, and a center-anchorage double-suspension bridge configuration similar to the design of the San Francisco-Oakland Bay Bridge. (Since this would have required sinking an anchorage pier literally in the deepest area of the Straits, the practicality of this design may have been questionable.) A causeway, approximately 4,000 feet, extending from the northern shore, was constructed with concrete road fragments from 1939-1941.

At this time, and with funding for the project still uncertain, further work was delayed because of World War II. The Authority was abolished by the legislature in 1947 but was reauthorized three years later in 1950. Engineers were retained in June 1950. Following a report by the engineers in January 1951, the state legistature authorized the sale of 85 million dollars in bonds construction on April 30, 1952. A weakened bond market in 1953 forced a delay of over a year before the bonds could be issued.

View of the bridge looking north across the Straits of Mackinac
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View of the bridge looking north across the Straits of Mackinac

[edit] Engineering and construction

David B. Steinman was appointed as the design engineer in January 1953. By the end of 1953, estimates and contracts had been negotiated, and construction began on May 7, 1954. The American Bridge Division of United States Steel Corporation was awarded a contract of over 44 million dollars to build the steel superstructure. Construction took two and a half years and cost the lives of five men who worked on the bridge. It opened to traffic on schedule on November 1, 1957, and was formally dedicated on June 25, 1958. The bridge officially achieved its 100 millionth crossing exactly forty years after its dedication, on June 25, 1998.

The design of the Mackinac Bridge was directly influenced by the first Tacoma Narrows Bridge, which failed in 1940 because of its instability in high winds. Three years after that disaster, Steinman had published a theoretical analysis of suspension bridge stability problems which recommended that future bridge designs include deep stiffening trusses to support the bridge deck and an open-grid roadway to reduce its wind resistance. Both of these features were incorporated into the Mackinac Bridge.

[edit] Facts and figures

Mackinac Bridge at night
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Mackinac Bridge at night
Mackinac Bridge during a snowstorm
Enlarge
Mackinac Bridge during a snowstorm
  • Overall length shore to shore: 26,372 feet (8,038 m, or approximately 5 miles).
  • 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 (0.6 m) wide.
Catwalk, curb and rail width: 3 feet (0.9 m) on each side.
  • Width of stiffening truss in the suspended span: 68 feet (20.7 m), making it wider than the roadway it supports.
  • 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 foot (900 m) wide navigation channel.
  • Construction cost: $99.8 million (1957 USD)
  • Height of towers above water: 552 feet (168 m).
  • Max. depth of towers below water: 210 feet (64 m).
  • Total length of wire in main cables: 42,000 miles (68,000 km).
  • Total vehicle crossings, 2005: 4,236,491
  • Speed limit: 45 mph (72 km/h) for passenger cars, 20 mph (32 km/h) for heavy trucks. Heavy trucks are also required to leave 500 feet (152 m) spacing ahead.

[edit] Trivia

  • Travelers across the Mackinac Bridge can listen to a radio broadcast that specifically tells about the history of the bridge. One fact mentioned on the broadcast is that the painting of the bridge takes seven years, and when painting of the bridge is complete, it begins again.
  • Five workers died in the construction of the bridge: three iron workers died in a catwalk collapse, one iron worker fell from the north tower, and one diver surfaced too quickly and died from "the bends." Contrary to folklore, no bodies are buried in the concrete of the bridge.
  • Since the bridge's completion, only one bridge worker has fallen to his death. David Doyle was painting when he fell 60 feet on August 7, 1997. His body was found the next day in 95 feet of water.
  • Two vehicles have gone off the bridge: a 1987 Yugo was blown off the bridge during a particularly bad windstorm in 1989 (high speed may have also been to blame), and a sport utility vehicle drove off the bridge in March 1997 (which may have been a suicide).
  • The Mackinac Bridge Authority has a "Drivers Assistance Program" that provides drivers for those uncomfortable with driving across the Mackinac Bridge. You can arrange, either by phone or with the toll collector, to have your car driven to the other end. There is no additional fee for this service.
  • The bridge is painted green and white, and at night bluish vapor lamps light up the roadway while maize-colored spotlights shine on the main towers. Michigan residents speculate that these colors symbolize the state's two largest universities since green and white are the official colors of Michigan State University and maize and blue represent the University of Michigan.
  • Residents of the Upper Peninsula ("Yoopers") often refer to Lower Peninsula residents as "trolls" because they live "below the bridge."
  • On August 13, 2006, it was reported that hundreds of cellphones purchased by three Palestinian-American men from Texas were intended to be used in a possible terrorist attack on the Mackinac Bridge. The men were apprehended and were charged before such an attempt could take place. [2] On September 06, 2006, a federal judge threw out the conspiracy and money laundering charges against these men, and released them. [3]
  • Before it opened, travel between Michigan's two peninsulas was by car ferry. A fleet of nine ferries could carry up to 9000 vehicles per day. Traffic backups sometimes stretched to Cheboygan, Michigan, 16 miles (26 kilometers) away from Mackinac City.

[edit] External links

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