A new recommendation by a the National Transportation Safety Board (NTSB) urges federal and state authorities across the U.S. to review inspection reports and identify incomplete follow-up actions that need to be resolved for bridges made of uncoated weathering steel, citing the ongoing investigation of a 2022 bridge collapse in Pittsburgh, Pa.

On Jan. 28, 2022, the 447-foot-long Fern Hollow bridge experienced a structural failure and fell approximately 100 feet into the park below.

Six vehicles were on or near the bridge when it collapsed, injuring four.

Investigators found corrosion, deterioration and section loss on all four of the bridge’s legs — the result of accumulating water and debris.

Some of the section loss was so severe, it resulted in holes.

Uncoated weathering steel requires periods of dryness to form a protective oxide coating, or patina, that resists corrosion over time, the NTSB reported.

Debris blocked the drainage systems on the Fern Hollow Bridge, allowing water to drain onto areas not intended for water flow and preventing the protective patina from forming.

Prior inspections of the Fern Hollow bridge performed on behalf of the Pennsylvania Department of Transportation identified problems with drainage, but maintenance was not regularly performed to resolve the issue, the NTSB found.

Investigators found other Pennsylvania bridges with similar issues with drainage, debris accumulation and corrosion.

The NTSB is now asking the Federal Highway Administration to develop a process for bridge owners nationwide to perform necessary follow-up actions on bridges with uncoated weathering steel components.

The Fern Hollow bridge investigation is not yet complete. The final report will be issued in the coming months.