On May 23, 2013, at approximately 7:00 pm PDT, a span of the bridge carrying Interstate 5 over the Skagit River in the U.S. state of Washington collapsed.

The cause of the catastrophic failure was determined to be an oversize load striking several of the bridge's overhead support beams, leading to an immediate collapse of the northernmost span.

[2] The through-truss bridge was built in 1955 and connects the Skagit County cities of Mount Vernon and Burlington, providing a vital link between Vancouver, British Columbia and Seattle.

In September 2013, the permanent bridges were installed and work began to prevent similar failures of the remaining three spans.

The bridge carries a section of Interstate 5 (I-5) over the Skagit River between Mount Vernon and Burlington, in Washington state, about 60 miles (97 km) north of Seattle.

[3] The bridge was built in 1955, as part of the state government's upgrades to the U.S. Route 99 corridor and a year before the Interstate Highway System was begun.

This steel through-truss bridge had a "fracture-critical" design with non-redundant load-bearing beams and joints that were each essential to the whole structure staying intact.

In 2007 the I-35W Mississippi River bridge in Minneapolis collapsed suddenly from slow cracking of a single undersized and over-stressed gusset plate.

Following the Minneapolis incident, such age-related disasters in fracture-critical bridges are now avoided by finding and repairing cracks in a required thorough inspection every two years.

The chords are normally kept aligned and held in place by vertical posts, diagonals, and sideways sway struts.

There was a known strike on this bridge that occurred on October 22, 2012, and investigators found evidence of several other impacts in years past.

The collapse was caused by a southbound semi-trailer truck from Canada hauling an oversize load to Vancouver, Washington, directly damaging sway struts and, indirectly, the compression chords in the overhead steel frame (trusswork) on the northernmost span of the bridge.

[23] The company's vice-president, Ed Sherbinski, said permits had been issued from Washington State that included clearance for all bridge crossings on the route.

It attributes the bridge collapse to the collision taking out multiple sway braces, which destabilized the critical load-bearing (upper-chord) members.

[citation needed] The right lane of the bridge was closed for about two hours while crews welded the joint back into place and spread new asphalt.

[citation needed] A $6.87 million contract was awarded to contractor Max J. Kuney Construction of Spokane to design and build a permanent replacement span.

[34] Shortly afterward, changes were made to the three remaining spans to raise the bridge's maximum allowable height, which included replacing the curved overhead sway braces with straight ones.

[40] Prior to the bridge collapse the Seattle Section of the American Society of Civil Engineers (ASCE) issued the 2013 Report Card for the State of Washington's infrastructure.

[41] The advocacy group Transportation for America reports that 5.1% of Washington's bridges are structurally deficient, which is the sixth best in the country.