After surveying the defeated Germany after WW ll, General Dwight Eisenhower came to the now legendary conclusion that the enemy had enjoyed a superior road system, the Reichsautobahn, with unusual features like controlled access, on-off ramps and overpasses at diamond interchanges that quickly and efficiently moved men and material about the country and that the United States should have one of these too. A decade later he was signing the National Interstate and Defense Highways Act.
The Interstate-55 from Laplace, LA to Chicago, IL was begun in 1960 but it wasn’t until 1979 when it’s final section, between Ruddock and Ponchatoula, was completed. The initial plan was for a raised viaduct from Laplace to Manchac and a ground-level highway to Ponchatoula until local citizens raised strenuous objections over the environmental harm this would cause, so the more expensive viaduct was continued through the wetlands to Ponchatoula.
At 22.8 miles, the elevated portion of I-55 through the Manchac Swamps became one of the longest bridges over water in the world and cost $159 million out of the total $181 million spent on the rest of I-55 in Louisiana. Reinforced concrete pilings and road sections were cast in Mandeville and floated down the new, wide borrow canal by barge for installation. The need for such a canal has been replaced by newer “build on-end” methods like used on the nearby I-310 viaduct to the Luling-Destrehan Bridge.