Consisting of parallel, 24-mile-long spans, the Lake Pontchartrain Causeway is the world’s longest verwater highway bridge and one of the oldest prestressed concrete bridges built in the United States.
Serving as a vital link between New Orleans and communities to the north, the 24-mile long Lake Pontchartrain Causeway supports traffic loads of up to 30,000 vehicles a day and serves as a primary evacuation route for coastal areas in the event of hurricanes or other severe storms. Construction of the causeway, listed by Guinness World Records 2004 as the world’s longest bridge, was funded by a 1952 amendment to the Louisiana constitution. The amendment dedicated approximately half of one of its two state highway funds to construction and operation of the causeway, toll bridge, and approach roads.
The Greater New Orleans Expressway Commission (GNOEC) was established as the project’s governing body and compiled $46 million in bond and $5 million in highway funds to construct the causeway and ancillary projects. The GNOEC chose Palmer and Baker, Inc., to serve as consulting engineers. William H. Smith, P.E., was chief structural engineer for the original span, and he was assisted by Kenneth C. Roberts, P.E.
On Jan. 20, 1955, construction on the causeway began. An onsite precast, prestressed concrete plant manufactured the various components which were then barged to the bridge site where large cranes were used for installation. The assembly line process resulted in high levels of quality control and rapid production. Construction of the structure, from first pile to completion, was a mere 14 months.
The causeway opened to traffic on Aug. 20, 1956. A decade later, daily traffic exceeded 5,300 vehicles, and the GNOEC authorized a feasibility study for a second, parallel bridge.
On May 10, 1969, a second bridge opened at a cost of $33 million. As part of the construction project, low-level bascules on the original bridge were removed and replaced with both a high-level, fixed-span at the south navigation channel and a high-level bascule at the north navigation channel. Seven crossovers were built to allow access from one bridge to the other and to accommodate vehicle emergencies.
Each of the Lake Pontchartrain Causeway ’s two bridges have 28-footwide roadways with 18-inch curbs on either side. The two spans are approximately 84 feet apart.
The original bridge—now the southbound bridge—has 56-foot spans, while the northbound bridge was designed with 84-foot spans. The new bridge consists of precast, prestressed segments that are monolithically-cast to incorporate the girders, deck, and bridge railing. This type of span is used throughout the structure with the exception of the end spans and the North Channel Bascule. Those spans are built from steel girders with conventional concrete deck and bridge rail. The spans are supported on precast pile bents resting on top of 54-inch diameter hollow precast, post-tensioned concrete piles.
In 1995, the GNOEC established a rehabilitation program to provide systematic repairs on the aging structures. The commission increased causeway tolls by $0.50 to pay for repair and maintenance. The $79 million program is currently underway and is scheduled to be finished in 2008.
Precast concrete plant: Prior to construction of the original bridge, a precast, prestressed concrete plant was built on Lake Pontchartrain’s north shore. Virtually the entire causeway was manufactured at this plant. The deck and girders were monolithically cast and prestressed, forming one unit for each span.
Piles: The twin bridges are supported by more than 9,000 hollow, precast, concrete pilings that are 54 inches in diameter. At the time of the first span’s construction, they were the largest piles ever driven. Plans are underway to restore damaged pilings. Details and anecdotes