One person was injured after a concrete railing section fell from a bridge in Chattanooga, Tennessee, on Monday, shutting down two interstate ramps at one of the busiest intersections in the country.

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 Tennessee Department of Transportation.

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 said on Twitter the ramps to both interstates were expected to open Monday night, but 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.

Investigators are trying to determine what caused the collapse. Officials told CNN affiliate WTVC-TV that it’s possible an oversized truck hit the railing and knocked it off, but so far no such vehicle has been found.

A ‘once in a lifetime accident’

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

TDOT officials told 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.”