CHICAGO (CBS) — Huge chunks of concrete and large sections of twisted steel fell from a viaduct on a railroad bridge over a busy South Side street early Tuesday.

Police blocked off 87th Street between South Chicago and Anthony Avenues, after the collapse from the Norfolk Southern railroad bridge that runs parallel to the Chicago Skyway.

Norfolk Southern said the collapse happened around 3 a.m. Luckily, no one was walking or driving under the bridge at the time, otherwise the incident could have proved deadly.

The railroad’s engineers inspected the bridge after the collapse, and determined it is structurally sound. Trains continued running over the bridge by 4 a.m.

Norfolk Southern said repairs to the damaged section of bridge would take six to eight hours to complete. The street was still closed as of 11 a.m.

“Cleanup of 87th Street is underway at this time. A portion of the street will remain closed to roadway traffic until cleanup is complete. Norfolk Southern is coordinating with local authorities to complete the repairs and reopen the roadway as soon as possible,” the company stated in an email. “Norfolk Southern is investigating why the pieces of concrete fell from the bridge.”

The Illinois Department of Transportation said, along with federal oversight, Norfolk Southern is responsible for inspecting the bridge, and making sure it is structurally safe.

The Illinois Commerce Commission said its Rail Safety Section has not received any complaints about the structure, but a track inspector will look into what caused the collapse.

No injuries have been reported.