Category: History & Politics Key figures: Tim Pawlenty (Minnesota Governor); Mark Rosenker (NTSB Chairman); Carol Molnau (Minnesota Commissioner of Transportation); Sverdrup & Parcel (original 1967 design firm)
Summary
At 6:05 p.m. on August 1, 2007, the Interstate 35W highway bridge spanning the Mississippi River in Minneapolis, Minnesota collapsed without warning during the evening rush hour. The eight-lane steel deck truss bridge, built in 1967 and carrying approximately 140,000 vehicles per day, fell approximately 60 feet into the river and onto its banks over a 1,907-foot span. Thirteen people were killed and 145 were injured. The disaster was the deadliest bridge collapse in the United States in four decades and the first catastrophic failure of a major American interstate highway bridge since the Silver Bridge collapse in West Virginia in 1967.
At the time of the collapse, the bridge was undergoing a repaving project. Heavy construction equipment — including two full truckloads of sand, gravel, and concrete stored above one of the weakest points — and the weight of added anti-skid concrete overlay contributed to the load on a structure already compromised by a previously undetected design flaw. Among the survivors was a school bus carrying 52 students from an after-school program, which came to rest on a broken section of the deck; all 52 children survived, evacuated by their bus driver and first responders.
The Collapse
Timeline of Events
The collapse unfolded in seconds at 6:05 p.m. Central Daylight Time. Security camera footage from a nearby rail yard — the most widely viewed footage of the event — captured the entire central span dropping vertically into the river, followed immediately by the flanking truss sections. Traffic on the bridge at the moment of collapse included an estimated 111 vehicles. The deck hit the water and the exposed riverbed simultaneously.
Minneapolis Fire Department crews arrived within minutes. Divers from multiple jurisdictions entered the Mississippi River before dark, and water temperatures of approximately 77°F (25°C) aided early search efforts. Minnesota Governor Tim Pawlenty declared a state of emergency within hours. President George W. Bush visited the site on August 4, three days after the collapse, and pledged federal disaster assistance. The last victim’s body was recovered from the river on August 20, 2007, nearly three weeks after the collapse.
Victims
The 13 fatalities included workers in the construction zone, motorists, and a child. Ages ranged from 23 to 60. The 145 injured included survivors with traumatic brain injuries, spinal injuries, and severe burns from vehicle fires that ignited on the deck. Minnesota’s Hennepin County Medical Center treated the most critically injured.
Investigation and Cause
NTSB Findings
The National Transportation Safety Board conducted a 14-month investigation and released its final report on November 14, 2008. The board determined that the probable cause of the collapse was an inadequate design of the gusset plates — the large flat steel connectors joining the main truss members — which had been undersized since the bridge’s original 1967 design by the engineering firm Sverdrup & Parcel. The gusset plates at nodes U10 east and west were approximately half the thickness required to support the bridge’s design loads.
The NTSB concluded that the load imposed by construction equipment and materials — estimated at 578,000 pounds (about 289 tons) of sand and gravel near the southern end — pushed the structurally insufficient gusset plates beyond their yield strength, initiating the collapse. Contributing factors included corrosion of the gusset plates over the bridge’s 40-year life and the progressive addition of weight from deck overlays applied in 1977 and 1998.
History of Inspections
The bridge had been rated structurally deficient by the Federal Highway Administration (FHWA) every year since 1990 — a designation applied when a structure’s key components are in poor condition but which does not by itself require closure or immediate repair. Inspection reports from 2001 noted cracking and fatigue in the approach spans, and a 2006 report by the University of Minnesota identified the need for more detailed monitoring. Neither inspection explicitly flagged the gusset plates as the critical failure risk. The NTSB’s investigation concluded that no inspection since 1967 had caught the undersized plate design because inspectors lacked the original design calculations, which Sverdrup & Parcel had not provided to MnDOT.
At the time of the collapse, approximately 77,000 bridges in the United States — about 12 percent of the total — carried a structurally deficient rating. The FHWA estimated the cost of repairing all such bridges at over $140 billion.
Response and Recovery
Emergency Legislation
Within days of the collapse, the U.S. Congress passed and President Bush signed emergency legislation providing $250 million in federal funds to assist Minnesota in replacing the bridge. The measure bypassed normal FHWA programming requirements, reflecting the political urgency of the disaster. Congressional leaders from both parties also called for a broader review of bridge safety funding.
State and Legal Accountability
A 2008 Minnesota legislative report found that MnDOT had systematically underfunded bridge maintenance for more than a decade. In 2008, the state of Minnesota and its contractors reached a $36.4 million settlement with the victims and their families — at the time the largest infrastructure disaster settlement in state history. The subcontractor that supplied and positioned the construction equipment, Progressive Contractors Inc., contributed to the settlement under a liability share.
Minnesota Commissioner of Transportation Carol Molnau, who also served as Lieutenant Governor, faced intense legislative criticism; the Minnesota Senate voted to remove her from the transportation role in February 2008, though the removal required gubernatorial action that Governor Pawlenty declined to take.
Replacement Bridge
Construction of the replacement structure, the St. Anthony Falls Bridge (officially designated I-35W Saint Anthony Falls Bridge), began in late 2007 under an accelerated design-build contract with the firm Flatiron-Manson. The new bridge opened on September 18, 2008 — just 13.5 months after the collapse — more than three months ahead of the contracted deadline. The contractor received a $27.5 million bonus for early delivery. The new bridge incorporated advanced sensor technology including over 323 embedded sensors monitoring load, stress, temperature, and traffic, making it one of the most heavily instrumented highway bridges in the United States.
Significance
The I-35W collapse became the defining infrastructure safety event of the 2000s and a lasting symbol of the consequences of deferred maintenance in American public works. Its significance operated at multiple levels:
Engineering and inspection reform: The NTSB report prompted the FHWA to launch a national review of fracture-critical bridges — those where a single element’s failure could cause catastrophic collapse. By 2008, federal and state agencies had identified and begun reviewing thousands of similar steel truss bridges.
Infrastructure funding debate: The disaster injected urgency into the debate over the Highway Trust Fund’s solvency. Congress included significant bridge funding in the subsequent SAFETEA-LU reauthorization discussions and eventually the Moving Ahead for Progress in the 21st Century Act (MAP-21, 2012), which established new condition standards requiring states to repair bridges in poor condition.
Public awareness: Public polling following the collapse showed a significant increase in support for higher fuel taxes or other mechanisms to fund infrastructure maintenance — a shift that had been politically impossible before August 1, 2007. The event is widely cited in subsequent policy discussions as the moment when infrastructure deferred maintenance became a mainstream political concern.
Design record gaps: The investigation revealed a systemic problem: many states lacked original design calculations for bridges built before computerized record-keeping. The NTSB recommended that all states obtain and archive original design documents for fracture-critical bridges.