The collapse of a key Interstate highway bridge in the state of Washington should serve as a wake up call for the whole of the US says the chairperson of the country's National Transportation Safety Board.

Debbie Hersman made the remarks over the weekend while inspecting the wreckage of the bridge which spanned the Skagit River and played a vital role in connecting the western United States with Canada.

“This is a really significant event and we need to learn from it, not just in Washington but around the country,” Hersman said.

The bridge collapse has triggered renewed calls from lawmakers throughout the US for greater investment in the maintenance and upgrade of the nation’s aging infrastructure, much of which is in a dilapidated condition.

The four lane Skagit River bridge, situated halfway between Seattle and Vancouver on the Interstate 5 highway which connects the US and Canada, collapsed last Thursday at around 7 pm local time, sending several vehicles and individuals into the waters below.

While the collapse did not result in any fatalities, officials say three people needed to be rescued and were subsequently sent to hospital for medical treatment.

Debbie Hersman

Debbie Hersman, Chairperson Of NTSB.

Authorities believe the cause of the collapse was a truck colliding with at least one girder on the bridge, fatally compromising its structural integrity. The truck itself traversed the bridge safely before a portion of the structure collapsed into the river below.

“We had a collision between a very heavy vehicle traveling at probably not a small amount of speed crashing into not just one but probably multiple girders, and it failed,” Washington Governor Jay Inslee said.

The Skagit River bridge was built in 1955 and possessed a steel truss design. The Federal Highway Administration classified the bridge as “fracture critical” due to its lack of redundant support elements, which mean that when one part of the structure is damaged the risk of collapse increases.

Fracture critical bridges were frequently built in the 1960s and 1970s as part of the Interstate highway system due to their shorter construction time and lower cost.

Officials say the bridge was not on the list of structures classified as “structurally deficient,” which can refer to inability to bear designated traffic loads. The privately run National Bridge Inventory Database had listed the bridge as “functionally obsolete,” however, a designation reserved for bridge which possess outdated features or fail to meet current standards.

According to the American Society of Civil Engineers, around a quarter of Washington’s 7,840 bridges are categorized as structurally deficient or functionally obsolete, garnering the state a C- for its bridges in the society’s 2013 infrastructure report card.