Around 10 a.m. today, CDOT crews working in the area under North Lake Shore Drive for other purposes discovered the damage to the steel beam under the roadway. About an hour later, engineers determined the northbound lanes needed to be closed “out of an abundance of caution to make immediate repairs to the structure,” Scheinfeld said.

“What they found was cracks in some of the structural steel girders on the underside of the viaduct at the expansion joints. This caused a dip in the driving surface at the expansion joints on the surface of Lake Shore Drive in the northbound lanes,” she said.

Two of the seven girders under the northbound lanes were found to be affected. Crews also discovered some cracking in the ramp to southbound Lake Shore Drive from the lower level south of the bridge, so it has been closed, too.

It’s not clear how long the viaduct structure was compromised. CDOT thinks the cracking was the result of corrosion exacerbated by the recent temperature fluctuations.

“We’re taking immediate corrective action to address this,” Scheinfeld said. “We are now mobilizing the resources needed to erect several steel support towers to stabilize the roadway, so that we can safely reopen while we make permanent repairs.”

Traffic is detoured off northbound Lake Shore Drive at Monroe, sent westbound to Columbus, and northbound to Lower Wacker Drive where it can rejoin northbound Lake Shore Drive, CDOT said.

The affected structure is a viaduct that carries Lake Shore Drive up to Lake Shore Drive Bridge and over the river. It was constructed in 1986 and last inspected in June 2017.

Inspections of the viaduct structure on the approach of northbound and southbound Lake Shore Drive are ongoing, Scheinfeld said, and no further issues have been found. No injuries or damage to vehicles have been reported.

Lake Shore Drive in both directions handles about 120,000 cars a day, according to Scheinfeld.

“We will not reopen this bridge to traffic until we are confident that it is safe to do so,” she said.