Manchac Swamp Bridge
The Manchac Swamp Bridge is a twin concrete trestle bridge in the U.S. state of Louisiana. With a total length of it is one of the longest bridges in the world over water and is the longest bridge on the Interstate Highway System. Some claim it is the longest toll-free road bridge in the world. The bridge carries Interstate 55 and U.S. Route 51 over the Manchac Swamp in Louisiana, and represents one-third of the highway's approximately 66 miles in Louisiana. Opening in 1979, its piles were driven beneath the swamp and with the cost of the span being $7 million per mile to complete.
