No one was injured and there are no reports of vehicles being damaged.
Authorities say a chunk of concrete three feet by 10 feet and two inches thick fell from the overpass around 4:30 p.m. on Tuesday.
"We have crews that are on site right now that are inspecting the bridge and will be knocking off any other potential loose concrete from the structure. We'll be working on that for the next couple of hours," said Peter Scales, Chicago Department of Transportation.
The bridge dates back to the 1930s, and last underwent "significant" repairs about five years ago, Scales said. Officials deemed the bridge in fair condition when it was last inspected, sometime within the past two years.
"I was going to get off here and go to Lakeview and I didn't know," said Diego Rocheae, motorist.
There were a lot of surprised motorists trying unsuccessfully to get on and off Lake Shore Drive at North Avenue Tuesday evening. But that's nothing compared to the surprise those driving underneath the overpass here received when a large piece of concrete fell onto the westbound lanes just after 4pm. As a result, CDOT shut down the on and off ramps to both vehicles and pedestrians.
"We have our championship game right now and I need to be through. And I can't get through," said Megan Bearder, pedestrian.
"I guess for public safety they have to do it but I just fought the traffic and didn't know what the reason was. They had the exit blocked off. Drove all the way to Irving Park, turned around and now I have to drive all the way back. Disappointed, yes," said Tony Woods, motorist.
After clearing the debris, CDOT crews worked into the night, prying loose pieces of concrete from the overpass. They also removed a large part of the first layer of concrete around the affected area to ensure its safe to reopen to traffic.
Still, for those who often go through here, news of what happened was hardly encouraging.
"That could kill someone. I hope they inspect all the bridges," said Bearder.
"I think they should spend some more money on rebuilding the bridges," said Matt Grier, runner.
CDOT described the work they did on the bridge Tuesday as "triage," and say they willl need to do more thorough tests on the overpass this week. Officials say the falling concrete was most likely caused by a combination of age, water damage and vibration from vehicles on Lake Shore Drive.
The Sun-Times Media Wire contributed to this report.