The National Transit Safety Board has issued a warning for bridges in New York and New Jersey that need to be checked.
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The report which lists 68 bridges, does not suggest these are in danger of collapsing but need to be checked for safety measures.
Some of the bridges include the Brooklyn Bridge, Manhattan Bridge, Williamsburg Bridge and George Washington Bridge.
Bridges built before 1991 were not required to undergo a vulnerability assessment; such an assessment had not been performed for the Key Bridge, which was constructed in 1977.
Following the Dali collision, the NTSB conducted a vulnerability assessment of the bridge using the AASHTO Method II calculation to understand its level of risk at the time of its collapse.
The calculated AF considered certain factors to assess whether this value was below AASHTO’s acceptable threshold value for a critical/essential bridge’s probability of collapse.
"We calculated and summed the AFs for both inbound and outbound vessel traffic for Piers 16, 17, 18, and 19. These piers provided support to the portion of the bridge over the Fort McHenry Federal Channel.
"A comparison of the AFs of the piers shows that a vessel collision with Pier 17 or Pier 18 was the largest contributor to the Key Bridge’s overall AF."
Since the Key Bridge’s opening in 1977, engineering and shipping advances—such as the 2016 Panama Canal expansion—have led to far larger vessels visiting, andincreased vessel traffic volume to and from, the Port of Baltimore.
Therefore, incorporating current vessel traffic parameters (and other environmental/waterway factors) into the AASHTO Method II vulnerability assessment calculation to evaluate the Key Bridge’s specifications, the NTSB determined that if the MDTA had calculated the AF for the Key Bridge before the collapse, it would have identified that the bridge’s risk level was almost 30 times greater than the AASHTO risk threshold for
critical/essential bridges (0.0001).
Therefore, the NTSB concludes that had the MDTA conducted a vulnerability assessment of the Francis Scott Key Bridge based on recent vessel traffic, as recommended by the 1991 and 2009 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.
For the Key Bridge, factors that contributed to this risk in the calculated vulnerability assessment included the piers adjacent to the main navigation channel and the channel size, which provided off-course vessels with little time for path correction before colliding with the bridge.
Further, the locations and size of the dolphins did not fully protect Pier 17 and Pier 18 from a collision from an off-course vessel, and the speed and size (dimensions and weight) of modern vessels such as the Dali highlighted that the bridge piers were not strong enough to withstand a collision from a large ocean-going vessel.
Like the Key Bridge, other bridges throughout the United States were designed before AASHTO’s 1991 Guide Specification for bridge design was issued.
To understand the scope of the risk posed by bridges nationwide with designs predating AASHTO’s Guide Specification, the NTSB requested that the FHWA identify bridges that cross navigable waterways and are used by ocean-going vessels like the Dali, as well as gather information about protection devices in place for those bridges (if any).
The FHWA coordinated with state DOTs to identify 176 bridges in 26 states that cross waterways used by ocean-going vessels.
The NTSB subsequently filtered the results according to whether a bridge:
• Was built before 1996. "We recognized that although the AASHTO Guide Specification was available in 1991, bridges under design or initial construction at that time were likely not built to its specifications.
"Therefore, we determined that bridges placed into service before 1996 were likely not designed and built to the current specifications.
• Had a vertical clearance of at least 80 feet. We used the typical vertical clearance height for ocean-going vessels (80 feet) based upon the typical minimum mast clearance height of a loaded bulk carrier and
loaded tanker.
• Had substructures (such as piers) in a waterway. The only bridges considered in this report were those with piers in a waterway, because piers on land have natural protection from a horizontal vessel impact. Applying these conditions to the 176 bridges reduced the number to 95.
"Next, we evaluated the vessel traffic transiting under the 101 bridges between January 1, 2019, and September 31, 2024, to determine whether a bridge’s average annual transits by ocean-going vessels were sufficient to result in a measurable amount of risk in the vulnerability assessment calculation.
"This evaluation was accomplished using a similar methodology to the one used to determine the vessel traffic for the Key Bridge.
"As a result, we identified 72 bridges (in 19 states, managed by 30 separate bridge owners) over navigable waterways frequented by ocean-going vessels that were likely not designed and built to the AASHTO Guide Specifications.
"The information that the FHWA collected in coordination with state DOTs regarding protection devices helped us to identify that the owners of 4 of the 72 bridges had performed a recent vulnerability assessment and were either implementing a plan to reduce their bridge’s vulnerability or would be doing so in the near future.
"The remaining 68 bridges that have not undergone a vulnerability assessment based on recent vessel traffic and therefore have an unknown level of risk of collapse from a vessel collision."
The NTSB concludes that 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. ■