The National Transportation Safety Board (NTSB) cited a design flaw as the likely cause of the collapse, noting that an excessively thin gusset plate ripped along a line of rivets.

[23] Construction on the bridge began in 1964 and the structure was completed and opened to traffic in 1967[24][25] during an era of large-scale projects to build the Twin Cities freeway system.

In February and December 1996, the bridge was identified as the single most treacherous cold-weather spot in the Twin Cities freeway system, because of the almost frictionless thin layer of black ice that regularly formed when temperatures dropped below freezing.

The bridge's proximity to Saint Anthony Falls contributed significantly to the icing problem and the site was noted for frequent spinouts and collisions.

The report also noted a concern about lack of redundancy in the main truss system, which meant the bridge had a greater risk of collapse in the event of any single structural failure.

Although the report concluded that the bridge should not have any problems with fatigue cracking in the foreseeable future, regular inspection, structural health monitoring, and use of strain gauges had been suggested.

However, the project was canceled in January 2007 in favor of periodic safety inspections, after engineers realized that drilling for the retrofitting would, in fact, weaken the bridge.

[50] The construction taking place in the weeks prior to the collapse included joint work and replacing lighting, concrete and guard rails.

[59][60][61][62] Sequential images of the collapse were taken by an outdoor security camera located at the parking lot entrance of the control facility for the Lower Saint Anthony Falls Lock and Dam.

[69] President Bush pledged support during a visit to the site on August 4 with Minnesota elected officials and announced that United States Secretary of Transportation (USDOT) Mary Peters would lead the rebuilding effort.

[66][70] Local authorities were assisted by the Federal Bureau of Investigation (FBI) evidence team,[71] and by United States Navy divers who began arriving on August 5.

The children were returning from a field trip to a water park as part of the Waite House Neighborhood Center Day Camp based in the Phillips community.

Twenty divers organized by the Hennepin County Sheriff's Office (HCSO) used side-scan sonar to locate vehicles submerged in the murky water.

The United States Army Corps of Engineers (USACE) lowered the river level by two feet (61 cm) downriver at Ford Dam to allow easier access to vehicles in the water.

[62][85][86][87] The Minneapolis Fire Department[83] (MFD) created the National Incident Management System command center in the parking lot of the American Red Cross and an adjacent printing company[8] on the west bank.

At the request of the NTSB Chairman Mark Rosenker, the U.S. Navy sent 17 divers and a five-person command-and-control element from its Mobile Diving and Salvage Unit Two.

Minneapolis Police Captain Mike Martin stated that, "The public safety divers are trained up to a level where they can kind of pick the low-hanging fruit.

He coordinated site location and staffing arrangements with the city's Department of Health and Family support and relevant Hennepin County offices.

Much of the bridge debris was temporarily stored at the nearby Bohemian Flats as part of the ongoing investigation of the collapse; it was removed to a storage facility in Afton, Minnesota, in fall 2010.

[113][114] Immediately following the collapse, Governor Pawlenty and Mn/DOT announced that the Illinois-based engineering firm of Wiss, Janney, Elstner Associates, Inc. had also been selected to provide essential analysis that would parallel the investigation being conducted by the NTSB.

[119] FHWA advised states to inspect the 700 U.S. bridges of similar construction[120] after identifying a possible design flaw related to large steel sheets called gusset plates, which connect girders in the truss structure.

Contributing to that design or construction error was the fact that 2 inches (51 mm) of concrete had been added to the road surface over the years, increasing the static load by 20%.

[140][non-primary source needed] Thirty-five people lost their jobs when Aggregate Industries of Leicestershire, UK, a company that delivered construction materials by barge, cut production in the area.

[150] The Minnesota Twins played their home game as scheduled, against the Kansas City Royals at the Hubert H. Humphrey Metrodome just west of I-35W, on the evening of the accident.

[151] The Twins and Minnesota Vikings honored the victims of the collapse by placing a decal of a simulated I-35W shield sign with the date "8-1-07" on the backstop wall within the Metrodome, which was always visible in the typical behind-the-pitcher viewpoint on televised games.

National TV networks sent CBS anchor Katie Couric, NBC's Brian Williams and Matt Lauer, MSNBC's Contessa Brewer, ABC's Charles Gibson, CNN's Soledad O'Brien and Anderson Cooper, and Fox News Channel's Greta Van Susteren and Shepard Smith to broadcast from the Twin Cities.

Among the presenters were representatives of the Christian, Islamic, Jewish, Hindu, Native American and Hispanic communities, police, fire and emergency responders, the governor, the mayor, a choir and several musicians.

[100][non-primary source needed] Gold Medal Park near the Guthrie Theater was a gathering place for those who wished to leave flowers or remembrances for those who died.

[citation needed] Local record label Electro-Voice released a three-disc benefit CD, Musicians for Minneapolis, which raised money for the victims of the bridge collapse.

Musicians included Deke Dickerson, Los Lobos, Steve Vai, Dick Dale, Les Claypool, Calexico, DJ Spooky, and M. Ward, as well as local bands such as the Vibro Champs.