NTSB has recommended that owners of 68 bridges across 19 states conduct a vulnerability assessment to determine the risk of collapse from a vessel collision, part of the ongoing investigation into the collapse of the Francis Scott Key Bridge in Baltimore.
The NTSB found that the Key Bridge, which collapsed after being struck by the containership Dali on March 26, 2024, was almost 30 times above the acceptable risk threshold for critical or essential bridges, according to guidance established by the American Association of State Highway and Transportation Officials, or AASHTO.
The 984-foot Singapore-flagged cargo vessel Dali was transiting out of Baltimore Harbor when it experienced a loss of electrical power and propulsion and struck the southern pier supporting the central truss spans of the Francis Scott Key Bridge, which subsequently collapsed. Six construction crewmembers were killed and another was injured, as well as one person onboard the vessel.
Key findings
- Had the Maryland Transportation Authority (MDTA) conducted a vulnerability assessment of the Francis Scott Key Bridge based on recent vessel traffic, as recommended by the 1991 and 2009 American Association of State Highway and Transportation Officials (AASHTO) Guide Specifications, the MDTA would have been aware that this critical/essential bridge was above the AASHTO threshold of risk for catastrophic collapse from a vessel collision when the Dali collision occurred.
- Had the Maryland Transportation Authority (MDTA) conducted a vulnerability assessment of the Francis Scott Key Bridge using the American Association of State Highway and Transportation Officials’ Method II vulnerability assessment calculation, the MDTA would have had information to proactively identify strategies to reduce the risk of a collapse and loss of lives associated with a vessel collision with the bridge.
- The 30 owners of 68 bridges over navigable waterways frequented by ocean-going vessels are likely unaware of their bridges’ risk of catastrophic collapse from a vessel collision and the potential need to implement countermeasures to reduce the bridges’ vulnerability.
Over the last year, the NTSB identified 68 bridges that were designed before the AASHTO guidance was established — like the Key Bridge — that do not have a current vulnerability assessment. The recommendations are issued to bridge owners to calculate the annual frequency of collapse for their bridges using AASHTO’s Method II calculation.
NTSB’s report does not suggest that the 68 bridges are certain to collapse. The NTSB is recommending that these 30 bridge owners evaluate whether the bridges are above the AASHTO acceptable level of risk. The NTSB recommended that bridge owners develop and implement a comprehensive risk reduction plan, if the calculations indicate a bridge has a risk level above the AASHTO threshold.
In 1991, AASHTO developed and published the vulnerability assessment calculation for new bridges on the National Highway System, in response to the NTSB’s investigation of the Sunshine Skyway Bridge collapse in Florida. At the time, AASHTO also recommended that all bridge owners conduct the vulnerability assessment on existing bridges to evaluate their risk of catastrophic collapse in the event of a vessel collision. AASHTO reiterated that recommendation to States again in 2009.
Since 1994, the Federal Highway Administration, or FHWA, has required new bridges be designed to minimize the risk of a catastrophic bridge collapse from a vessel collision, given the size, speed and other characteristics of vessels navigating the channel under the bridge. The Key Bridge was built before vulnerability assessments were required by FHWA.
The NTSB found that had the Maryland Transportation Authority, or MDTA, conducted a vulnerability assessment on the Key Bridge based on recent vessel traffic, MDTA would have been aware that the Key Bridge was above the acceptable risk and would have had information to proactively reduce the bridge’s risk of a collapse and loss of lives associated with a vessel collision with the bridge.
The NTSB is also recommending FHWA, the U.S. Coast Guard and the U.S. Army Corps of Engineers establish an interdisciplinary team to provide guidance and assistance to bridge owners on evaluating and reducing the risk, which could mean infrastructure improvements or operational changes.
Recommendations
To the Federal Highway Administration:
In coordination with the US Coast Guard and US Army Corps of Engineers, an interdisciplinary team should be established—including representatives from the Federal Highway Administration, US Coast Guard, and US Army Corps of Engineers—and guidance and assistance should be provided to bridge owners on evaluating and reducing the risk of a bridge collapse from a vessel collision. (H-25-1) (Urgent)
To the US Coast Guard and the US Army Corps of Engineers:
Support should be provided to the Federal Highway Administration in establishing an interdisciplinary team—including representatives from the Federal Highway Administration, US Coast Guard, and US Army Corps of Engineers—and guidance and assistance should be provided to bridge owners on evaluating and reducing the risk of a bridge collapse from a vessel collision. (H-25-2) (Urgent)
To the Bay Area Toll Authority, the California Department of Transportation, the Golden Gate Bridge Highway and Transportation District, the US Army Corps of Engineers, the Florida Department of Transportation, the Georgia Department of Transportation, Skyway Concession Company LLC, the Louisiana Department of Transportation and Development, the New Orleans Public Belt Railroad, the Maryland Transportation Authority, the Massachusetts Department of Transportation, the Mackinac Bridge Authority, the New Hampshire Department of Transportation, the Delaware River Port Authority, the New Jersey Turnpike Authority, Metropolitan Transportation Authority Bridges and Tunnels, the New York City Department of Transportation, the New York State Bridge Authority, the Ogdensburg Bridge and Port Authority, the Port Authority of New York and New Jersey, the Seaway International Bridge Corporation, the Thousand Islands Bridge Authority, the Ohio Department of Transportation, the Oregon Department of Transportation, the Pennsylvania Turnpike Commission, the Rhode Island Turnpike and Bridge Authority, the Harris County Toll Road Authority, the Texas Department of Transportation, the Washington State Department of Transportation, and the Wisconsin Department of Transportation:
The American Association of State Highway and Transportation Officials (AASHTO) Method II annual frequency of collapse should be calculated for the bridge(s) identified in appendix B of this report for which responsibility is held, and the National Transportation Safety Board should be informed whether the probability of collapse is above the AASHTO threshold. (H-25-3) (Urgent)
If the calculations performed in response to Safety Recommendation H-25-3 indicate that a bridge has an annual frequency of collapse greater than the American Association of State Highway and Transportation Officials threshold, a comprehensive risk reduction plan should be developed and implemented, which includes, at a minimum:
- guidance and assistance from the Federal Highway Administration, US Coast Guard, and US Army Corps of Engineers Interdisciplinary Team identified in Safety Recommendations H-25-1 and H-25-2, and
- short- and long-term strategies to reduce the probability of a potential bridge collapse from a vessel collision. (H-25-4) (Urgent)
