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Blake Pontchartrain: How the Causeway was built 

The bridge over Lake Pontchartrain was put together "like an erector set"

click to enlarge The southbound span of the Causeway was the first large-scale project that used prestressed concrete.

Photo by Glenn/Creative Commons

The southbound span of the Causeway was the first large-scale project that used prestressed concrete.

Hey Blake,

When you cross the Lake Pontchartrain Causeway south to north, you can feel the expansion joints somewhat, but traveling north to south, it is much worse. Why is that?

David

Dear David,

  The answer is in the engineering. The southbound bridge is the older of the two spans and was the original bridge, which opened Aug. 30, 1956. As current Causeway general manager Carlton Dufrechou points out, while many people know the Causeway is the longest bridge over water in the world, some may not realize it also was the first large-scale use of prestressed concrete, or concrete with tensioned steel reinforcement.

  "The Causeway was built much like an erector set," Dufrechou told Gambit. "The components were fabricated in a facility specifically built to manufacture the bridge's piles, pile caps and decks on the Northshore in Mandeville. The components were then barged into Lake Pontchartrain, where mounted cranes drove piles into the lake's bottom, set caps on the piles and finally placed 56-foot roadway deck sections on the caps."

  Traffic on the original bridge (which featured two lanes of traffic, one northbound and one southbound) increased steadily over the first 10 years, demonstrating the need for a second span. Today's northbound bridge opened May 10, 1969 and was the second span built. By then, Dufrechou explains, engineers had more experience with prestressed concrete. "As a result, the deck sections are longer — 84 feet — and have slightly less tension in the reinforcing cables, so the ride is much smoother."

  If you've been in one of the 12 million vehicles that drive the Causeway annually, you know the toll (originally $2 for a round trip or $1 one way in 1956) was raised in May to $5 (or $3 with a toll tag). The extra money will help pay for safety improvements, including higher guard rails on the southbound bridge and shoulders on both spans of the Causeway.

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