Skagit River Bridge

I-5 Skagit River Bridge
Boats in the water and a helicopter overhead about an hour and a half after the bridge collapse.
Coordinates	48°26′43.8″N 122°20′28.1″W / 48.445500°N 122.341139°W / 48.445500; -122.341139Coordinates: 48°26′43.8″N 122°20′28.1″W / 48.445500°N 122.341139°W / 48.445500; -122.341139
Carries	I‑5
Crosses	Skagit River
Locale	Mount Vernon, Washington
Maintained by	Washington State Department of Transportation
ID number	0004794A0000000
Characteristics
Design	Through-truss bridge
Material	Steel
Total length	1,112 feet (339 m)
Width	72 feet (22 m)
No. of spans	4
History
Opened	1955
Collapsed	May 23, 2013
Statistics
Daily traffic	70925
References

The I-5 Skagit River Bridge collapse occurred on May 23, 2013, in the state of Washington, in the northwestern United States. At approximately 7:00 pm PDT, one bridge span carrying Interstate 5 over the Skagit River collapsed into the river below. Three people in two different vehicles fell with the span; they were rescued by boat and did not sustain serious injury. The cause of the collapse was determined to be an oversize load striking several overhead support beams on the bridge, which led to an immediate collapse of the northernmost span.

The through-truss bridge was built in 1955 and connects the Skagit County cities of Mount Vernon and Burlington. It had recently been evaluated as safe and though not structurally deficient, it was considered "functionally obsolete", meaning it did not meet current design standards. The bridge's design was "fracture-critical"; i.e., it did not have redundant structural members to protect its structural integrity in the event of a failure of one of the bridge's support members. The overhead support structure was known to have been struck by a truck as recently as October 2012. From an engineering standpoint, the bridge actually consists of four consecutive spans which are structurally independent. Only the deck and overhead superstructure of the northernmost span collapsed into the river; the span south of the collapsed span also sustained damage from being struck by the same truck, though not severe enough to result in a collapse. Also, the piers below the deck were not damaged.

Because the bridge collapse severed a vital transportation link between Vancouver, British Columbia and Seattle, replacing the collapsed span became a high priority for the Washington state government. In June 2013, two temporary bridges were erected and placed on the collapsed span's support columns while the permanent bridge was built. In September 2013, the permanent bridges were installed and work began to prevent similar failure of the remaining three spans.