Mackinac Bridge

The Mackinac Bridge is a massive suspension bridge in Michigan.

It spans the Straits of Mackinac, which connect Lake Michigan and Lake Huron. This structure links the Upper and Lower peninsulas of the state. People often call it the "Mighty Mac" or the "Big Mac." It is a vital part of Interstate 75. The bridge connects the city of St. Ignace to the village of Mackinaw City. It is an iconic symbol of the state of Michigan.

Building a suspension bridge requires careful engineering to handle massive weight and wind. The bridge features a main span of 3,800 feet. This makes it the 29th longest suspension span in the world. It is also the third-longest suspension span in the United States. In the Western Hemisphere, it is the longest suspension bridge between anchorages.

This means the distance from one end's support to the other is unmatched in this part of the world. The bridge is also one of the longest bridges overall.

To keep the bridge stable, engineers used specific designs to fight wind. The design was influenced by the failure of the Tacoma Narrows Bridge in 1940. That bridge failed because it was unstable in high winds. To prevent this, designer David B. Steinman included a stiffening truss. This is a deep, strong frame that supports the road deck. The roadway itself is shaped like an airfoil, which is a shape used by wings. This shape provides lift in crosswinds. Additionally, the center two lanes use an open-grid design. This allows air to flow upward through the road. This upward airflow cancels out the lift from the wind. These features keep the bridge stable in winds up to 100 miles per hour.

For many decades, people had to cross the straits using ferries. In 1881, railroads used car ferries to connect the peninsulas. By 1923, the state of Michigan started an official automobile ferry service. Eventually, the service used nine different boats. These ferries could carry as many as 9,000 vehicles every day. However, traffic grew so large that backups were common. Some drivers had to wait in line for five hours to reach the ferry.

Ideas for a bridge appeared as early as the 1880s. In 1884, a store owner even published an artist's drawing of a proposed bridge. In 1888, Cornelius Vanderbilt II suggested a bridge to help local hotels. However, formal construction took many years to begin. During the 1930s, the Mackinac Straits Bridge Authority tried to get federal funds. They were unsuccessful because of the Great Depression. Even though President Franklin D. Roosevelt endorsed the project, Congress did not provide money. Construction was also delayed by the outbreak of World War II. Finally, the state authorized $85 million in bonds in 1952 to fund the work.

Construction finally began on May 7, 1954. David B. Steinman served as the design engineer. The project was split into two major contracts. One company handled the substructure work for $25.7 million. Another company built the steel superstructure for more than $44 million. The work took three and a half years to complete. This included four summers of work, as no construction happened in the winter. The total cost was approximately $100 million.

During this time, five workers lost their lives. The bridge opened to traffic on November 1, 1957. On that same day, the ferry service stopped running.

Today, the bridge remains a busy and important landmark. It is a toll bridge to help pay for its upkeep. In 2007, the toll was raised to fund a $300 million renovation program. This program includes replacing the bridge deck.

Travelers can see large freighters passing underneath the structure on the water.

Every Labor Day, the governor leads a traditional bridge walk. The bridge is also part of the U.S. North Country National Scenic Trail. In 2010, it was named a National Historic Civil Engineering Landmark.