On Aug. 1, 2007, Lindsay Walz was stuck in traffic, frustrated and anxious to get home after a long day and missing her exit. As she neared the middle of the Interstate 35 bridge in downtown Minneapolis, she heard a clank.

Walz said she knew it was the sound of metal breaking. After Walz realized what was happening, the fall became a blur.

“My car went in and the water came up just as quickly as the car went in,” Walz said. “By the time the car stopped moving, I was drowning. I didn’t have a chance to grasp another breath of air.”

Walz’s Volkswagen Passat nose-dived more than 100 feet – the height of a 10-story building – into the Mississippi River.

“I ended up getting into the backseat and pushed and pushed and pushed, and then my body started to instinctually gasp for air,” Walz said. “Each time that happened I kind of started to shift my focus from fighting to live to accepting that that was where I was going to die.”

To Walz’s surprise, she lived. She started to float, slowly, reaching the surface of the water. But that’s when she noticed the scale of the destruction.

“A construction worker saw me and fished me out of the water with a broom that had fallen with the bridge,” Walz said. “I sat for about 45 minutes. I remember flames, I remember tangled beams, and I remember the Taystee [bakery] truck on fire. I remember the people on the island with me, the rubble…”

The 911 calls from that day describe the catastrophic scene.

“The whole bridge over the river fell down,” said one caller. “There’s cars all over the place.”

“Where sir?” asked the dispatcher.

“35W over the Mississippi,” the caller said. “There’s hundreds of cars in the river. Bring everything you got, and I’m not kidding.”

A formal investigation of the Interstate 35W Mississippi River bridge collapse took more than a year to complete. What was discovered was that the bridge was listed as “structurally deficient” in 2005. At the time of the collapse, it was categorized the same way. Engineers acknowledged the bridge – opened in 1967 – was in need of critical maintenance, but still considered it “safe enough” to remain open.

The National Transportation Safety Board said the cause of the tragedy was a simple design flaw in the bridge’s gusset plates – the metal squares that connect one steel beam to another were not technically safe enough. The plates failed under the weight of bridge modifications, traffic and a concentration of construction equipment and materials on the bridge.