Manchac Swamp Bridge in the U.S

The Manchac Swamp Bridge is a twin concrete trestle bridge in the U.S. state of Louisiana. With a total length of 22.80 miles (36.69 km). 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. Opening in 1979 and with the cost of the span being $7 million per mile to complete.