Safety Articles

NTSB Warns U.S. Bridge Owners of Uncoated, Weathering Steel

NTSB investigators at the site of the collapsed Fern Hollow Bridge in Pittsburgh, Pa. Photo by James Anderson, NTSB.

In a news bulletin published May 18, 2023, the U.S. National Transportation Safety Board (NTSB) is recommending that federal and state authorities review inspection reports and identify incomplete follow-up actions that need to be resolved for bridges made of uncoated weathering steel. 

This recommendation is being made amid the ongoing investigation of a 2022 bridge collapse in Pittsburgh, Pa. On January 28, 2022, the 447-foot-long (136.2 m) Fern Hollow Bridge experienced a structural failure and fell approximately 100 feet (30.5 m) into the park below. Six vehicles were on or near the bridge when it collapsed, and four people were injured. 

NTSB investigators found corrosion, deterioration, and section loss on all four of the bridge’s legs due to the continual accumulation of water and debris. Some of the section loss was so severe that it resulted in holes. 

Uncoated weathering steel requires periods of dryness to form a protective oxide coating, or patina, that resists corrosion over time, according to the NTSB. In this case, debris, dirt, and leaves were blocking 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.

NTSB investigators found that 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. NTSB investigators found other Pennsylvania bridges with similar issues with drainage, debris accumulation, and corrosion. 

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

While the Fern Hollow bridge investigation is not yet complete, the NTSB is making this early recommendation due to the immediate implications for bridge safety nationwide. The final report with a probable cause, other findings, and recommendations will be issued in the coming months.

The NTSB is also releasing new documents, including a NTSB Materials Laboratory report with photos and three-dimensional (3-D) laser scans of the deterioration on the bottoms of all four bridge legs. The interim report and a summary of the investigative actions taken so far are available on the NTSB’s website.

For more information, contact: NTSB,

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