The Interstate 5 bridge over the Skagit River collapses in Mount Vernon, Washington.
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. Three people in two different vehicles fell into the river below and were rescued by boat, escaping serious injury. 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.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. It consists of four consecutive spans that are structurally independent. Only the northernmost span collapsed into the river; the adjacent span also sustained impact damage from the same vehicle, but not severe enough to result in a collapse. The overhead support structure was known to have been struck by a truck as recently as October 2012.
Not long before the accident, the bridge had been evaluated as safe. Although not structurally deficient, it was considered "functionally obsolete", meaning it did not meet current design standards. The bridge's design was "fracture-critical," meaning that 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.
Within a month of the collapse, two temporary bridges were erected and placed on the failed span's support columns while the permanent bridge was built. In September 2013, the permanent bridges were installed and work began to prevent similar failures of the remaining three spans.
Interstate 5 (I-5) is the main north–south Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific coast of the contiguous U.S. from Mexico to Canada. It travels through the states of California, Oregon, and Washington, serving several large cities on the U.S. West Coast, including San Diego, Los Angeles, Sacramento, Portland, and Seattle. It is the only continuous Interstate highway to touch both the Mexican and the Canadian borders. Upon crossing the Mexican border at its southern terminus, I-5 continues to Tijuana, Baja California, as Mexico Federal Highway 1 (Fed. 1). Upon crossing the Canadian border at its northern terminus, it continues to Vancouver as British Columbia Highway 99 (BC 99).
I-5 was originally created in 1956 as part of the Interstate Highway System, but it was predated by several auto trails and highways built in the early 20th century. The Pacific Highway auto trail was built in the 1910s and 1920s by the states of California, Oregon, and Washington, and was later incorporated into U.S. Route 99 (US 99) in 1926. I-5 largely follows the route of US 99, with the exception of portions south of Los Angeles and in the Central Valley of California. The freeway was built in segments between 1956 and 1978, including expressway sections of US 99 that were built earlier to bypass various towns along the route. US 99 was removed in 1972.