The $10.5 million project, which will end in the elevation of just more than 3 miles of Highway 23, will prevent the road from being flooded by tidal surges, Plaquemines Parish President Billy Nungesser said.
Hurricane Isaac swamped this section of the highway.
"After the storm, we saw the need and we saw the frustration in everybody's eyes of this happening year after year," Plaquemines Parish President Billy Nungesser said during a news conference.
The closure stretches from Alliance to Point Celeste, the Louisiana Department of Transportation and Development said.
Traffic has been diverted to the northbound lanes, which will become two-way until November, the agency said.
Construction, which began last month, is expected to be complete in the fall of 2014, according to the state.
The work will elevate Louisiana 23 from 2 inches to 2 feet, DOTD Secretary Sherri LeBas said.
"Local, state and federal money is being used on the project, according to the transportation department. Barriere Construction of Metairie has the contract.