Maryland officials failed to conduct risk assessment that would have prevented Francis Scott Key Bridge collapse: NTSB

The report stated that the bridge, which opened to traffic in 1977, was designed according to the 1969 edition of the American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges, including the 1970 and 1971 Interim Specifications.

As a result of safety efforts in the wake of the 1980 collapse of Tampa Bay’s Sunshine Skyway Bridge, AASHTO adopted the Guide Specification and Commentary for Vessel Collision Design of Highway Bridges in 1991. A second version was released in 2009.

Requirements from the Federal Highway Administration (FHWA) were adapted from the guide, requiring that new bridges on the National Highway System be designed to minimize the risk of bridge collapses due to vessel collisions using a vulnerability assessment calculation.

The report stated, "Neither the FHWA nor AASHTO can require a bridge owner to complete a vulnerability assessment for a bridge designed before the release of the 1991 guidelines," and the MDTA did not perform such an assessment on the bridge, but an assessment was recommended, according to the NTSB.

In the wake of the collision of the Dali vessel into the Francis Scott Key Bridge, the NTSB conducted a vulnerability assessment of the bridge using the updated AASHTO Method II calculation, which takes into consideration vessel transit speeds, waterway and navigable channel geometry, pier protection systems, and other characteristics of the vessels, waterway, and bridge.

"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, and increased 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)," the report stated.

"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."

The NTSB has identified 72 bridges, located in 19 states and operated by 30 bridge owners, that were "likely not designed and built to the AASHTO Guide Specifications." Of those 72 bridges, 68 have not undergone vulnerability assessments.

The NTSB concluded 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," and recommended that the 30 owners conduct such vulnerability assessments.

NTSB chair Jennifer Homendy told CBS News, "We conclude in our report that had the MDTA conducted a vulnerability assessment of the Key Bridge based on recent vessel traffic, the MDTA would have been able to proactively identify strategies to reduce the risk of a collapse and loss of lives associated with a vessel collision with the bridge." She added, "We've been sounding the alarm since this tragedy."