Mackinac Bridge

The Mackinac Bridge (pronounced MACK-in-aw, 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 the engineer David B. Steinman, it connects the cities of St. Ignace on the north end with Mackinaw City on the south.

Contents

1 Longest between anchorages 2 History 3 Facts and figures 4 External links

Longest between anchorages

The bridge opened in 1957 with the formal dedication taking place a year later 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 would be 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, however it 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 has fallen to the third longest world-wide. The combined length of the three spans of the suspension bridge (including anchorages) is 8,614 feet. In 1998, the Akashi Kaikyo Bridge in Japan became the longest with a total suspension of 12,826 feet.

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

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, in particular at nearby Mackinac Island. Year-round boat service across the straits had been abandoned as impractical after several attempts. 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 took out a newspaper advertisement that included a reprint of an artist's conception of Brooklyn Bridge with the caption "Proposed bridge across the Straits of Mackinac."

On July 1, 1888, at a meeting board of directors of the Grand Hotel on Mackinac Island, the famous entrepreneur Cornelius Vanderbilt advocated the building of a bridge across the straits in order to help lengthen the resort season of the hotel. A similar bridge to the type envisioned was under construction across the Firth of Forth in Scotland and was completed in 1889.

The idea of the bridge was discussed in the Michigan Legislature as early as the 1880s, inspired in part by the construction of the Brooklyn Bridge. At the time the area was becoming a popular tourist destination, including the creation of Mackinac National Park on nearby 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 an 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 deeemed 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 U.S. 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.

The project 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 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.

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 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 catastrophic failure of the first Tacoma Narrows Bridge in 1940 due to 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.

Facts and figures

• The Mackinac Bridge is currently a toll bridge on Interstate 75.

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

• Overall length between 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.

• Total width of the roadway: 54 feet.

Two outside lanes: 12 feet wide each.

Two inside lanes: 11 feet wide each.

Center mall: 2 feet wide.

Catwalk, curb and rail width: 3 feet on each side.

• Width of stiffening truss width in the suspended span: 68 feet wide making it wider than the roadway it supports.

• Height of the roadway at mid-span: approximately 200 feet above water level.

• Vertical clearance at normal temperature:

155 feet at the center of the main suspension span.

135 feet at the boundaries of the 3,000 ft. navigation channel.

External links

• Official site (http://www.mackinacbridge.org/)
• Information and lots of photos. (http://www.pcnate.com/bridges/other/mackinac/index.htm)
• Detroit News archives: The breathtaking Mackinac Bridge (http://info.detnews.com/history/story/index.cfm?id=156&category=locations)
• Length Comparison (http://www.michigan.gov/mdot/0,1607,7-151-9618_11016-22026--,00.html)