The Manchac Swamp Bridge is a twin concrete trestle bridge

Bridge

A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...

 in the US state of Louisiana

Louisiana

Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

. With a total length of 22.8 miles (36.69 km) it is one of the longest bridges in the world over water. The bridge carries Interstate 55

Interstate 55

Interstate 55 is an Interstate Highway in the central United States. Its odd number indicates that it is a north–south Interstate Highway. I-55 goes from LaPlace, Louisiana at Interstate 10 to Chicago at U.S. Route 41 , at McCormick Place. A common nickname for the highway is "double...

 over the Manchac Swamp in Louisiana

Louisiana

Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

, and represents one-third of the highway's approximately 66 miles in Louisiana. Opening in 1979, its piles

Deep foundation

A deep foundation is a type of foundation distinguished from shallow foundations by the depth they are embedded into the ground. There are many reasons a geotechnical engineer would recommend a deep foundation over a shallow foundation, but some of the common reasons are very large design loads, a...

were driven 250 feet (76.2 m) beneath the swamp and with the cost of the span being $7 million per mile to complete.