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Westbound traffic, right, slows as eastbound traffic, though heavy, flows consistently on the left during rush hour, Wednesday, December 21, 2016, on Interstate 10 near the Nairn Drive overpass in Baton Rouge, La.

Advocate staff photo by HILARY SCHEINUK

Major traffic backups last weekend on Interstate 10 in the Baton Rouge area stemmed from preliminary work on a $72 million project  to widen the road between Highland Road to La. Hwy. 73 in suburban Ascension Parish, officials said Monday.

However, narrowing the interstate to one lane in part of the construction zone will not be a regular part  of the work, said Shawn Wilson, secretary for the state Department of Transportation and Development.

On Saturday night I-10 westbound was the site of a major traffic backup from near the La. 73 exit, which is the off-ramp for Prairieville and Geismar.

Travelers were forced to move from the outside to the inside lane, sparking delays of 30 minutes or more.

The project will add a new lane in each direction over the 6.5 mile stretch.

Wilson said the work is part of efforts to cut the shoulder on the interstate to create room for a new lane.

"Essentially what  is happening is both lanes have shifted to the right," he said. "Then they can cut the shoulder, and that is where they will start the widening."

Three- or four-foot concrete slabs, called Jersey barriers, will be put in place for both east and westbound travelers.

"Essentially you are narrowing your lanes and putting a positive barrier between the traveling public and the median," Wilson said.

Once the striping is done, he said, two narrowed lanes will remain in place in both directions while workers craft a third lane for eastbound and westbound travelers.

Wilson said the lane closing was done on the weekend rather than grappling with even heavier traffic, and bigger backups, on weekdays. About 95,000 motorists daily use the section of I-10 under construction.

The work is expected to take about 2 1/2 years.

The I-10 widening is something of a rarity amid Louisiana's nearly $14 billion backlog of road and bridge needs.

A separate push for three other projects, including widening I-10 from the Mississippi River bridge to or near the I-10/12 split, would be financed with federal bonds if Gov. John Bel Edwards' push clears all the hurdles.

The pricetag for that work is about $600 million.

Wilson said an accident on Sunday between the exits for La. Hwy, 30 and La. Hwy. 42 contributed to other travel delays in the construction zone.

Follow Will Sentell on Twitter, @WillSentell.