Study Warns of Increased Risk of Ship Collisions with US Bridges

A new study has revealed a concerning trend regarding the vulnerability of U.S. bridges to ship collisions, suggesting that such incidents are more likely to occur than previously understood. The study, conducted by Johns Hopkins University, comes a year after the collapse of Baltimore’s Francis Scott Key Bridge, which was struck by a cargo ship. The findings indicate that several of the nation’s busiest bridges face a significant risk of being hit by vessels in the coming decades, highlighting the urgent need for preventative measures.

The study’s authors emphasize that the increasing size of ships and the growing volume of shipping lane traffic are major contributing factors to this heightened risk. Michael Shields, the lead investigator of the study, stated that the results confirm that the Key Bridge collapse was not an isolated incident but rather a symptom of a broader systemic vulnerability. He stressed the importance of implementing appropriate corrective measures to mitigate this risk.

The study’s preliminary findings align with a recent update from the National Transportation Safety Board (NTSB) regarding its investigation of the Key Bridge disaster. The NTSB chair, Jennifer L. Homendy, criticized Maryland officials for failing to recognize the bridge’s vulnerability to collisions, which she noted was significantly higher than the federal standard.

The MV Dali, the container ship responsible for the Key Bridge collapse, struck a pier after losing power, causing the structure to collapse into the Patapsco River. The tragic event resulted in the deaths of six road workers and the temporary closure of the Port of Baltimore. The incident served as a stark reminder of the fragility of critical infrastructure and the potential for catastrophic consequences.

Funded by the National Science Foundation’s Rapid Response Program, the Johns Hopkins study focused on assessing the likelihood of similar disasters occurring elsewhere in the U.S. The study identified the nation’s 20 most at-risk bridges, with several facing a probability of being struck by ships within the next 50 years. These include the Huey P. Long Bridge outside New Orleans, the San Francisco-Oakland Bay Bridge, the Crescent City Connection in New Orleans, the Beltway 8 Bridge in Houston, and the Hale Boggs Memorial Bridge west of New Orleans.

The findings have raised concerns among commuters and residents who regularly travel across these bridges. Darby Li Po Price, a professor at Oakland’s Merritt College, expressed his surprise and unease upon learning that the San Francisco-Oakland Bay Bridge was among the most at-risk spans. While acknowledging the low probability of a collision on any given day, Price emphasized the potential for devastating consequences.

Shields reassured the public that the risk to individual commuters remains low, but he cautioned that the overall risk to society and communities is significant. He emphasized the need to address the factors contributing to this increased risk, particularly the growing size of ships and the higher volumes of traffic.

The study highlights that many large bridges were built decades ago when ship traffic was significantly lower, and ships were much smaller. As a result, existing infrastructure may not be adequate to withstand the impact of modern-day vessels.

The Johns Hopkins study focused on major bridges with high traffic and ships exceeding 150 meters in length. The researchers evaluated various factors, including traffic patterns, the probability of ships veering off course, and the likelihood of collisions with bridge piers. They analyzed U.S. Coast Guard data on ship positions, velocities, and headings, cross-referencing this information with port and bridge data from the National Bridge Inventory. The study also considered potential causes of ship deviations, such as pilot error, weather conditions, and loss of power.

Abi Aghayere, a professor of structural engineering at Drexel University, emphasized the importance of protecting bridge piers from ship strikes, particularly in light of the increasing size of vessels. He cited data indicating a significant number of engine failures near U.S. coasts and waterways, highlighting the potential for ships to lose control and collide with bridges. Aghayere also noted that a substantial number of bridges lack adequate protective measures, such as dolphins, fenders, or islands.

He warned that many unprotected bridges are "fracture critical," meaning that the failure of a single component could lead to the collapse of the entire structure. This was the case with the Key Bridge, which lacked effective pier protection.

Historical incidents underscore the potential for catastrophic consequences resulting from ship collisions with bridges. The collapse of the Sunshine Skyway Bridge in Florida in 1980 resulted in 35 fatalities, while the derailment of an Amtrak passenger train in Alabama in 1993, caused by a barge collision with a bridge, claimed 47 lives.

Following the Sunshine Skyway collapse, new federal standards were issued in 1994 requiring bridge designs to have a low probability of collapse due to ship collisions. However, these standards did not mandate retroactive protection for existing bridges.

Shields emphasized that there is no one-size-fits-all solution to mitigate the risk of ship collisions with bridges. Each bridge requires a tailored approach, taking into account its unique characteristics and the surrounding environment. He suggested that local authorities could consider measures such as requiring large vessels to be towed under certain bridges.

Christopher Higgins, a professor of structural engineering at Oregon State University, highlighted the importance of tugboats in preventing ship collisions, particularly in cases where vessels experience electrical difficulties or loss of power.

Aghayere noted that the cost of protecting bridge supports is relatively small compared to the potential consequences of a collapse. He cited the estimated cost of installing dolphins to protect the Delaware Memorial Bridge, which pales in comparison to the estimated cost of replacing the Key Bridge.

Ryan Zamarripa, who manages grants under the U.S. Economic Development Administration’s Build Back Better Regional Challenge, expressed concern that recent federal budget cuts could impact the ability of ports to prevent future tragedies.

Shields concluded by emphasizing the need for proactive measures to protect bridges from ship collisions. He stated that while it may not be possible to build bridges that can withstand the impact of the largest ships, effective protections can be implemented to prevent ships from getting too close to bridge piers in the first place.

The NTSB has urged bridge owners and operators nationwide to conduct risk assessments, identifying numerous U.S. spans for which evaluations have not been performed. The Johns Hopkins study and the NTSB recommendations serve as a call to action for port authorities, bridge owners, and government agencies to prioritize the safety and resilience of critical infrastructure.