U.S. 231, a major commuter four-lane highway south of Huntsville, will be closed for about 12 months to repair a dramatic landslide beneath the roadway’s surface.

John Cooper, director of Alabama Department of Transportation, made the announcement Thursday night at a public meeting at Arab High School and described the repair timeline as a “working estimate.” Cooper said he hoped that it would be completed sooner than a year.

Curtis Vincent, ALDOT engineer for the region, said in a presentation that the plan is for bridges to be built over the damaged area on both the northbound and southbound lanes. The columns supporting the bridge will be built atop solid limestone and remove dependence on the soil where the slide occurred.

Vincent put the estimated cost at about $18 million. The bridges will be about 1,000 feet long -- the length of the damaged section of road. The bridges will be low to the ground and will essentially be dropped into the damaged area with seamless connection to the existing road.

A 3-D rendering of twin bridges proposed on U.S. 231 over the slide area in Morgan County that led to the road being closed last month.

The damaged road, located on the side of Brindlee Mountain in Morgan County and about 7 miles south of Huntsville, closed Feb. 12 after ground shifting under the road opened large cracks so severe that they could not be patched by road crews as they had done in the same area last year.

The highway averages about 15,000 vehicles per day in the area where the repairs are ongoing, according to a traffic count conducted last year by ALDOT.

ALDOT began excavation at the site of the repairs last weekend, a project that will take two months that's needed before repairs can begin. The excavation is intended to remove excess material at the site to reduce weight on the ground that contributed to the slide, ALDOT said.

ALDOT said it has all but eliminated an option to move the roads further up Brindlee Mountain because the landslide would still need repair even after shifting the lanes. The highway is still be a stair-step design with the northbound lane at a slightly higher elevation than the southbound lane on the side of the mountain.

A detour has been in place since the closure on a series of two-lane roads through Morgan County.

Updated today, March 12, 2020, at 7:21 p.m. with new information throughout.