NTSB Recommends Bridge Collapse Risk Assessments
The National Transportation Safety Board (NTSB) “urgently” recommended March 20 that 30 owners of 68 bridges across 19 states conduct a vulnerability assessment to determine the risk of bridge collapse from vessel hitting it.
“We need action,” NTSB chair Jennifer Homendy said in a press conference held in conjunction with the report’s release. “Public safety depends on it.”
The report was part of NTSB’s investigation into the collapse of the Francis Scott Key Bridge on March 26, 2024, in Baltimore, Md.
The bridges recommended for assessment are all over navigable waterways frequented by ocean-going vessels. They include the Huey P. Long Bridge, Horace Wilkinson Bridge, Sunshine Bridge, Gramercy (Veterans Memorial) Bridge, Greater New Orleans Bridge and Crescent City Connection Bridge over the Mississippi River and the Israel LaFleur Bridge across the Calcasieu River in Louisiana.
Several of the Texas bridges named in the report cross the Houston Ship Channel or the Sabine-Neches Ship Channel. They include the Sidney Sherman Bridge, the eastbound and westbound Fred Hartman Bridge, the Rainbow Bridge, the Veterans Memorial Bridge and the Gulfgate Bridge.
In Washington, the Lewis and Clark Bridge crosses the Columbia River, as does the Astoria-Megler Bridge in Oregon. In Georgia, the Talmadge Bridge is over the Savannah River.
“This vulnerability assessment is essentially a mathematical risk model used to determine how susceptible a bridge is to collapse from a vessel collision, and it’s not new,” Homendy said.
The American Association of State Highway and Transportation Officials (AASHTO) developed and published the vulnerability assessment in 1991 in response to the NTSB’s investigation of the Sunshine Skyway Bridge collapse across the Tampa Bay in Florida. It revised those standards in 2009.
“Included in the 1991 standards was a recommendation from AASHTO that all bridge owners conduct a vulnerability assessment of existing bridges to evaluate the risk of catastrophic collapse in the event of a vessel collision and take action,” Homendy said. AASHTO reiterated that recommendation to states again in 2009 for “all remaining existing bridges over navigable waterways with commercial barge and ship traffic.”
“What we are telling bridge owners is that they need to know the risk and determine what actions they need to take to ensure safety,” Homendy said.
Homendy asked the 30 bridge owners to notify the NTSB whether the calculations they perform determine that risk to them is above the AASHTO threshold and, if so, to develop and implement a comprehensive risk reduction plan that includes guidance and assistance from federal officials. That plan should include both short-term and long-term strategies to reduce the probability of a collapse from a vessel collision, she said.
Since 1994, the Federal Highway Administration has required that new bridges be designed to minimize the risk of a catastrophic collapse from being hit by a vessel, given the size, speed and other characteristics of vessels navigating the channel under the bridge.
The NTSB found that the Key Bridge was almost 30 times above the acceptable risk threshold for critical or essential bridges, according to guidance established by AASHTO.
The 68 bridges the NTSB identified for assessment were all designed before AASHTO guidance was established. The recommendations call for bridge owners to calculate the annual frequency of collapse risk for their bridges using AASHTO’s Method II calculation and to develop and implement a comprehensive risk reduction plan if the calculations indicate a bridge has a risk level above the AASHTO threshold.
The NTSB also recommended that the Federal Highway Administration, U.S. Coast Guard and Corps of Engineers establish an interdisciplinary team to provide guidance and assistance to bridge owners on evaluating and reducing risk, which could mean infrastructure improvements or operational changes.
The full report, titled “Safeguarding Bridges from Vessel Strikes: Need for Vulnerability Assessment and Risk Reduction Strategies,” is available online at https://www.ntsb.gov/investigations/AccidentReports/Reports/MIR2510.pdf.
