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CNN —  

The collapse of a concrete beam from a bridge in Chattanooga, Tennessee was likely caused when a vehicle carrying an oversized load hit the bottom of the bridge, a state transportation official said Tuesday.

The vehicle went under the bridge and sliced through some of the steel reinforcement strands in the exterior beam, Paul Degges, the department’s chief engineer, told reporters. A concrete rail helped support the damaged beam but ultimately it collapsed, he said.

“We don’t believe that the failure of the beam was an issue with the design of the bridge or maintenance activity,” Degges said.

He said officials don’t know who hit the bridge. The department’s cameras don’t keep a recorded history of footage, he said.

One person was injured after the concrete railing section fell from the bridge on Monday, shutting down two interstate ramps.

The bridge collapse took place at the Interstate 75 North and I-24 West split, according to Chattanooga police. The railing from I-75 fell onto the I-24 ramp, according to the state DOT.

Chattanooga Mayor Andy Berke said on Twitter the I-75 and I-24 split is “one of the most heavily trafficked intersections in the country.”

TDOT tweeted that permanent repairs “will take weeks.”

The Tennessee Highway Patrol said Monday evening the I-24 westbound lanes at the interstate split had been reopened. TDOT spokeswoman Jennifer Flynn said crews opened one lane of I-75 southbound Monday night.

A ‘once in a lifetime accident’

The Chattanooga Fire Department shared photos that showed a blue car crushed by giant slabs of concrete.

TDOT officials told CNN affiliate WTVC the bridge collapse was a “once in a lifetime accident.”

The bridge was built in 1959 and was last inspected in July 2018, according to a TDOT National Bridge Inventory and Appraisal Report obtained by WTVC.

Aside from being one of the busiest intersections in the country, as the city’s mayor said, former Tennessee Transportation Commissioner John Schroer said in November 2017 that the intersection was “probably the worst intersection we got in the state at the moment.”

A spate of recent overpass problems

The Chattanooga accident follows two recent high-profile collapses of overpasses.

In March 2018, a newly installed pedestrian bridge fell onto a busy street at Miami International University, killing six people.

And in March 2017, part of Interstate 85 in Atlanta collapsed after a massive fire broke out beneath the overpass. No one was killed nor injured.

CNN’s Darran Simon contributed to this report.