Bridge Collapses and Other Infrastructure Failures

​Bridges and tunnels make our travels possible and more seamless. When these structures are properly designed, built, and maintained, we don’t give them much thought. But when a collapse occurs, we are reminded of the magnitude of engineering, construction, and oversight tasks that are required to ensure their integrity and safety. 

Although the nation’s bridges and tunnels are extremely safe overall, our investigations of major structural failures highlight key safety issues and the changes that are needed to prevent these types of accidents from happening in the future.


​  Notable locations where NTSB has investigated a bridge or tunnel infrastructure failure​​

Infrastructure Investigations: Early Actions

​Infrastructure failures, including bridge and tunnel collapses, have remained one of our primary focus areas since we investigated the 1967 Silver Bridge collapse in West Virginia. The Silver Bridge collapse and investigation generated nationwide concern about bridge safety and led to the establishment of the National Bridge Inspection Standards by the U.S. Department of Transportation in 1970. These standards set the foundation for systematic bridge oversight. 

We continued to see the need to improve infrastructure design, inspection policies, maintenance practices, and safety as we investigated infrastructure failures, such as:

  • 1980 Sunshine Skyway Bridge ​​collapse near Tampa Bay, Florida led to the 1991 adoption of the AASHTO Guide Specification and Commentary for Vessel Collision Design of Highway Bridges.
  • ​​1983 Mianus River Bridge collapse in Connecticut​, which prompted the Federal Highway Administration, through the National Bridge Inspection Standards,​ to require a Fracture Critical Member (FCM) inspection.
  • 1987 Schoharie Creek Bridge collapse in New York and the collapse of the Hatchie River bridge​ in Covington, Tennessee, which prompted the Federal Highway Administration, through the National Bridge Inspection Standards,​ to require a comprehensive underwater inspection.​
  • 2006 Interstate 90 tunnel ceiling collapses in Boston​, which prompted the Federal Highway Administration to develop National Tunnel Inspection Standards in 2008. 

Safety Issues Across Investigations

Structural Design (and Design Review)

<strong>​Pedestrian Bridge Collapse Over SW 8th Street, Miami, Florida</strong><div></div><div><ul><li>​The Florida International University pedestrian bridge design was nonredundant, providing only a single load path. This meant that the failure of a single structural component could lead to full collapse.</li><li>​Design errors included underestimating the demands of the actual bridge and&#160;overestimating the load-carrying capacity of critical members and nodal regions. </li><li>The peer-review process was inadequate—it failed to scrutinize all load paths and did not detect errors in the design or construction plans.<br/></li></ul></div><div> </div><div><br/></div><div><strong>I-35W Mississippi River Bridge Collapse, Minneapolis, Minnesota</strong> </div><div><ul><li>The collapse was directly caused by a design calculation error, specifically gusset plates that had inadequate load capacity to support expected bridge loads.</li><li>The engineering firm responsible for the bridge construction did not have sufficient quality control or independent review practices to identify undersized gusset plates before construction.</li><li>Increases in bridge weight from modifications and extraordinary construction loads placed on the bridge on the day of collapse contributed to this incident.<br/><br/></li></ul></div><div><strong>I-90 Tunnel Ceiling Collapse, Boston, Massachusetts</strong> </div><div><ul><li>The tunnel roof used an epoxy anchoring adhesive that was not capable of sustaining long-term loads, which was a direct cause of the failure. </li><li>There were inadequate reviews of both the tunnel ceiling adhesive anchors and the overall structural design, compounding the risk.<br/></li></ul></div>

​Inspection Programs

<strong>​Fern Hollow Bridge Collapse, Pittsburgh, Pennsylvania ​</strong> <div><ul><li>Significant problems identified in inspection reports were not acted upon, contributing to the collapse.</li><li>Inspections lacked thoroughness in identifying fracture-critical members and assessing localized deterioration and loss of section.<br/><br/></li></ul></div><div> <strong>Failure of Overhead Electrical Conduit Support Systems in Lehigh Tunnel, East Penn Township, Pennsylvania</strong></div><div><ul><li>​The electrical conduit support system in Lehigh Tunnel no. 2 likely failed due to the fracture of extensively corroded polyvinyl chloride-coated steel support struts, allowing the electrical conduit to drop into the path of the oncoming truck-tractor.</li><li>Inspections conducted after the National Tunnel Inspection Program was implemented, documented the deficiencies in the electrical conduit support system as “priority repair items”―conditions in which further investigation, design, and implementation of interim or long-term repairs should take precedence over other scheduled work.</li><li>Although the steps taken by the Pennsylvania Turnpike Commission to replace the overhead electrical distribution system in Lehigh Tunnel no. 2 before the crash were consistent with available guidance, the Commission did not sufficiently prioritize repair of the previously documented deficiencies in the system to protect the safety of the motoring public traveling on the roadway below.<br/><br/></li> <strong>I-35W Mississippi River Bridge Collapse, Minneapolis, Minnesota</strong> <li>Although inspections were conducted following National Bridge Inspection Standards, visual inspections alone were inadequate to detect the design errors and to assess gusset plate condition; nondestructive evaluation methods should have been used for such critical structural elements. <br/> <br/></li></ul></div><div> <strong>I-90 Tunnel Ceiling Collapse, Boston, Massachusetts</strong> </div><div><ul><li>The Massachusetts Turnpike Authority failed to implement a timely tunnel inspection program, which likely would have identified the anchor creep before the accident occurred.<br/></li></ul></div>

​Load Rating and Testing

<strong>​Fern Hollow Bridge Collapse, Pittsburgh, Pennsylvania</strong><div rtenodeid="19"><ul><li>Load ratings failed to account for essential variables (such as section loss), and further ratings should have been recommended given the bridge’s documented deterioration.<br/><br/></li></ul></div><div rtenodeid="21"><strong>I-35W Mississippi River Bridge Collapse, Minneapolis, Minnesota</strong></div><div rtenodeid="23"><ul><li>​The load-carrying capacity of new bridges may not be verified before they open to traffic. The American Association of State Highway and Transportation Officials directed owners to perform load ratings only after major changes, not at initial service.</li><li>The failure occurred due to the combination of increased dead load from bridge modifications and high temporary loads on the day of collapse.</li><li>Critical gusset plates were neither included in load rating guidance nor specified as separate inspection elements, increasing risk that unsafe conditions could go undocumented.<br/><br rtenodeid="36"/></li></ul></div><div rtenodeid="29"><strong>I-90 Tunnel Ceiling Collapse, Boston, Massachusetts</strong></div><div rtenodeid="31"><ul><li>​Ultimate load tests should have been performed on adhesive anchors before installation to validate their performance, which did not occur.</li><li>The use of an epoxy that could not sustain long-term loads was causal to the collapse.<br/></li></ul></div>

​State and Federal Oversight

<div><strong>I-5 Skagit River Bridge Collapse, Mount Vernon, Washington </strong></div><div rtenodeid="38"><ul><li>The Washington State Department of Transportation inadequately evaluated oversize load permit requests, and failed to warn of low-clearance hazards through signage. <br/><br/></li></ul></div><div rtenodeid="40"><strong>Fern Hollow Bridge Collapse, Pittsburgh, Pennsylvania</strong> </div><div rtenodeid="42"><ul><li>Oversight of the city’s bridge inspection program was insufficient, and opportunities for data-driven Federal Highway Administration oversight were not realized.<br/><br/> </li></ul></div><div rtenodeid="44"><strong>Pedestrian Bridge Collapse Over SW 8th Street, Miami, Florida</strong> </div><div rtenodeid="46"><ul><li>The Florida Department of Transportation did not adequately confirm the qualifications of the independent peer review firm, nor did it provide sufficient oversight for a unique, nonredundant bridge design.<br/><br/> </li></ul></div><div rtenodeid="48"><strong>I-35W Mississippi River Bridge Collapse, Minneapolis, Minnesota</strong> </div><div><ul><li>State and federal authorities failed to sufficiently evaluate critical gusset plate designs and their procedures were inadequate for detecting design errors, such as bowing, and excluding gusset plates in load rating analyses.​<br/><br/></li></ul></div><div><strong> </strong></div>

Training and Guidance

<p> <strong>Fern Hollow Bridge Collapse, Pittsburgh, Pennsylvania</strong></p><ul><li>​Inspectors did not have adequate technical guidance from Federal Highway Administration or American Association of State Highway and Transportation Officials on identifying localized tension zones and critical components.</li><li>This collapse should be used as a case study in training courses for the need to complete maintenance, perform inspections properly, identify fracture-critical members, and correctly calculate load ratings.<br/></li></ul><p> <strong>Failure of Overhead Electrical Conduit Support Systems in Lehigh Tunnel, East Penn Township, Pennsylvania</strong></p><ul><li>​The Federal Highway Administration’s Tunnel Operations, Maintenance, Inspection, and Evaluation Manual; its Specifications for the National Tunnel Inventory; and its tunnel inspection training courses did not identify significant corrosion in nonstructural tunnel elements, such as overhead electrical distribution systems, as a critical finding or “Condition State 4” that required immediate action.</li><li>Insufficient guidance led to the Pennsylvania Turnpike Commission’s delay in repairing previously documented deficiencies in the support system.</li><li>Failure of the electrical conduit support system, due to long-term corrosion, resulted in displacement of the electrical conduit into the travel path of the truck-tractor.<br/><br/></li> <strong>I-90 Tunnel Ceiling Collapse, Boston, Massachusetts</strong> <li>​Engineers and builders lacked understanding about the long-term behavior of epoxies in tension applications, underscoring a need for better protocols and standards on testing and design of tunnel finishes.<br/><br/></li></ul> <strong>Pedestrian Bridge Collapse Over SW 8th Street, Miami, Florida</strong>&#160; <div><ul><li>​Florida Department of Transportation’s plan preparation guidance did not require verification of all significant nodal forces by independent peer review for category 2 bridges.</li><li>Design specification publications for concrete/pedestrian bridges need explicit redundancy guidance.&#160;<br/><br/></li></ul></div> <strong>I-5 Skagit River Bridge, Mount Vernon, Washington</strong>&#160; <div><ul><li>​There was minimal standardization or required training for pilot/escort vehicle drivers, despite clear risks around high load strikes and mandatory communication of bridge clearance information.<br/></li></ul></div>

Safeguarding Bridges from Vessel Strikes

​​Francis Scott Key Bridge Collapse, Baltimore, Maryland

  • ​Contributing to the collapse of the Key Bridge and the loss of life was the lack of countermeasures to reduce the bridge’s vulnerability to collapse due to impact by ocean-going vessels, which could have been implemented if a vulnerability assessment had been conducted by the Maryland Transportation Authority as recommended by the American Association of State Highway and Transportation Officials (AASHTO).
  • The Key Bridge was almost 30 times greater than the AASHTO threshold of risk for catastrophic collapse from a vessel collision when the Dali collision occurred.
  • Owners of numerous 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.

Sunshine Skyway Bridge Collapse, Tampa Bay, Florida
  • ​Contributing to the loss of life and to the extensive damage was the lack of a structural pier protection system which could have absorbed some of the impact force or redirected the vessel.
  • ​At the time, there were no federal standards or guidelines for the location and protection of critical bridge piers.

Hazard Detection and Alert Systems

​Francis Scott Key Bridge Collapse, Baltimore, Maryland

  • ​​​​Contributing to the loss of life was the lack of effective and immediate communications to notify the highway workers to evacuate the bridge.
  • In lieu of police officers or highway workers capable of quickly stopping traffic, motorist warning systems preventing motorists from entering onto a bridge are a critical countermeasure that can save lives and may be a component of an effective bridge protection strategy.
  • Owners of bridges over navigable waterways frequented by ocean-going vessels would benefit from updated guidance on motorist warning systems including incorporation of hazard alert and sensing technologies capable of detecting errant vessels and bridge movements that would indicate a need for bridge closure and systems that would both warn and prevent motorists from entering a bridge once a threat is detected. 
  • Effective and immediate communication to evacuate the bridge during an emergency is critical to ensuring the safety of bridge workers.

Sunshine Skyway Bridge Collapse, Tampa Bay, Florida

  • ​Contributing to the loss of life was the lack of a motorist warning system which could have warned the highway vehicle drivers of the danger ahead. 
  • Use of a bridge span failure detection and warning system could have saved lives. ​

Key Safety Recommendations

​​Open Recommendations Representing Critical Safety Priorities

H-25-31​:To the American National Standards Institute Accredited Standards Committee on Safety in Construction and Demolitions Operations A10: ​

  • ​Revise ANSI/ASSP A10.47, Work Zone Safety for Roadway Construction to include an effective and immediate means of emergency communications to alert workers performing roadway work on bridges over navigable waterways, which should consider the presence of law enforcement for traffic control.  ​

    • H-25-30: To California Department of Transportation, the Golden Gate Bridge Highway and Transportation District, the US Army Corps of Engineers, the Skyway Concession Company LLC, the Louisiana Department of Transportation and Development, the Maryland Transportation Authority, the Mackinac Bridge Authority, the New Hampshire Department of Transportation, the Delaware River Port Authority, the New Jersey Turnpike Authority, the New York State Bridge Authority, the Ogdensburg Bridge and Port Authority, the Seaway International Bridge Corporation, the Thousand Islands Bridge Authority, the Ohio Department of Transportation, the Oregon Department of Transportation, the Rhode Island Turnpike and Bridge Authority, the Texas Department of Transportation, the Washington State Department of Transportation, and the Wisconsin Department of Transportation:
  • ​As part of your short-term bridge risk reduction and mitigation strategies to protect the traveling public, evaluate the need for and, if appropriate, incorporate motorist warning systems capable of activating when a threat is identified and immediately warn and stop motorists from entering onto the bridge. Status: Open – Awaits Response

H-25-29:To the American Association of State Highway and Transportation Officials (AASHTO):

  • ​Update your Guide Specifications and Commentary for Vessel Collision Design of Highway Bridges to include guidance in the selection of motorist warning systems. Evaluated changes should include Federal Highway Administration research on hazard alert and sensing technologies capable of detecting errant vessels and bridge movements that would indicate a need for bridge closure, and would both warn and prevent motorists from entering a bridge once a threat is detected. • Status: Open – Awaits Response

H-25-28: To the Federal Highway Administration:

  • Research hazard alert and sensing technologies capable of detecting errant vessels and bridge movements that would indicate a need for bridge closure, and would both warn and prevent motorists from entering a bridge once a threat is detected. Provide the results of your research to the American Association of State Highway and Transportation Officials.

H-25-3: ​​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:

  • Calculate the American Association of State Highway and Transportation Officials (AASHTO) Method II annual frequency of collapse for the bridge(s) identified in appendix B of this report for which you are responsible and inform the National Transportation Safety Board whether the probability of collapse is above the AASHTO threshold. (Urgent) • Status: Open – Acceptable Response

H-25-4: To recipients of H-25-3​​

  • If the calculations that you 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, develop and implement a comprehensive risk reduction plan that 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.​​

Summary of Bridge Owner Responses to Safety Recommendat​ions H-25-3 and H-25-4​


H-25-2: To the US Coast Guard and US Army Corps of Engineers

  • Support the Federal Highway Administration in establishing an interdisciplinary team—including representatives from Federal Highway Administration, the US Coast Guard, and the US Army Corps of Engineers—and provide guidance and assistance to bridge owners on evaluating and reducing the risk of a bridge collapse from a vessel collision. ​

H-25-1: To the Federal Highway Administration

  • In coordination with the US Coast Guard and US Army Corps of Engineers, establish an interdisciplinary team—including representatives from FHWA, the US Coast Guard, and the US Army Corps of Engineers—to provide guidance and assistance to bridge owners on evaluating and reducing the risk of a bridge collapse from a vessel collision. 

H-24-4: To the Federal Highway Administration

  • Establish a process for conducting targeted reviews of the safety issues identified in the Pittsburgh, Pennsylvania investigation, including at a minimum:
    1. ​an evaluation of bridge owners’ determinations of the need for new load ratings of deteriorating bridges, and 
    2. an evaluation of inspection reports on bridges with advanced deterioration to confirm load rating assumptions and methods. Incorporate the results as needed into the National Bridge Inspection Program Compliance Review Manual.

H-20-23: To the Federal Highway Administration

  • Revise your Tunnel Operations, Maintenance, Inspection, and Evaluation Manual; your Specifications for the National Tunnel Inventory; and your inspection training courses to classify significant corrosion in nonstructural tunnel elements, such as overhead electrical distribution systems, as a critical finding that requires immediate action.

H-19-30: To the American Association of State Highway and Transportation Officials

  • ​​Develop a requirement that concrete bridge structures be designed with reasonable estimates for interface shear demand, cohesion and friction contributions to shear capacity, and the clamping force across the interface shear surface.

H-19-24: To the Federal Highway Administration
  • ​Develop a requirement that concrete bridge structures be designed with reasonable estimates for interface shear demand, cohesion and friction contributions to shear capacity, and the clamping force across the interface shear surface.

​H-14-25: To Nokia HERE and Google Inc.

​Develop reliable clearance data for highway structures and incorporate that data into commercial vehicle navigation systems to improve routing and permitting of oversize loads.


​Updated December 10, 2025  ​​​


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