How a 40-Year-Old Mistake Brought Down the I-35W Bridge

On August 1, 2007, the I-35W bridge over the Mississippi River in Minneapolis collapsed during rush hour, killing 13 people and injuring 145 more. The National Transportation Safety Board's investigation revealed something more unsettling than sudden mechanical failure: the bridge's critical gusset plates had been undersized since its original 1967 design, a calculation error that went undetected for forty years because gusset plates were routinely excluded from standard bridge load rating procedures nationwide. This video traces the full story of the I-35W collapse — the design flaw baked into the bridge from day one, the decades of added weight nobody was tracking, and the systemic blind spot that let it go unnoticed until the exact moment the math finally ran out. 0:00 The Blueprint Mistake Hidden for Decades 1:01 Anatomy of a Non-Redundant Design 3:52 Accumulated Weight and Procedural Blind Spots 5:59 The Moment the Structure Gave Way 9:26 Lessons Learned and the New Bridge Design