As part of its investigation into the collapse of major sections of the 1.6-mile-long Francis Scott Key Bridge outside Baltimore after the 984-foot-long Singapore-flagged container ship Dali hit the structure in March 2024, killing six people, the National Transportation Safety Board is calling for 68 U.S. bridges in 19 states to be assessed regarding the risk of similar scenarios due to maritime vessel strikes.
[Above photo by the NTSB]
During a press conference regarding its investigation, NTSB Chair Jennifer Homendy stressed that those assessments need to “determine whether they [the 30 owners of those bridges] need to implement counter measures and, if warranted, a comprehensive risk reduction plan that includes at a minimum short- and long-term strategies to reduce the probability of a bridge collapse from a vessel collision.”
She added that the agency is also urging the Federal Highway Administration – in coordination with the U.S. Coast Guard and the U.S. Army Corps of Engineers – to provide “guidance and assistance” to those 30 bridge owners on evaluating and reducing the risk of a bridge collapse from a vessel collision.
The NTSB said those 68 bridges should be assessed based on structural guidance established 34 years ago by the American Association of State Highway and Transportation Officials in the wake of the 1980 Sunshine Skyway Bridge incident in Florida, when the 608-foot-long M/V Summit Venture freighter struck one of the bridge’s key support columns, collapsing a 1,200-foot section of that structure and killing 35 people.
NTSB noted that, since 1994, the FHWA has required new bridges to be designed to minimize the risk of a catastrophic collapse from a vessel collision, considering the size, speed, and other characteristics of vessels navigating the waterways under those structures. However, the Francis Key Bridge was built before vulnerability assessments were required by FHWA, the agency said.
Homendy added that the 68 bridges cited in NTSB’s recommendation were built prior to the development of AASHTO’s Method II calculation in 1991.
AASHTO updated that guidance – formally entitled “AASHTO Guide Specifications and Commentary for Vessel Collision Design of Highway Bridges” – in 2009.
Those provisions as they relate to the design of new bridges were also incorporated into the first edition of the “Load and Resistance Factor Design (LRFD) Bridge Design Specifications” which AASHTO published in 1994 and have been updated as needed in subsequent editions, including the current 10th edition, published in December 2024.
Homendy went on to emphasize that bridges with risks above the “acceptable threshold” laid out in AASHTO’s guidance “doesn’t mean a [structural] collapse from a vessel collision is an absolute. Likewise, a bridge designed with a risk level below the acceptable threshold doesn’t guarantee that a collapse from a vessel collision won’t occur. What we are telling bridge owners is that they need to know the risks and determine what actions they need to take.”
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