NTSB Releases Preliminary Report on Collapse of I-5 Bridge in Washington State

The National Transportation Safety Board continues their investigation into the I-5 bridge collapse over the Skagit River in Mount Vernon, WA. Although the collapse occurred on May 24, 2013, to date they have only released a preliminary report, covering the circumstances and causes of this collapse. The details from PRELIMINARY REPORT HIGHWAY HWY13MH012 are as follows: On Thursday, May 23, 2013, a span of the Interstate 5 Bridge (Structure 4794A) at milepost 228.25 in Mount Vernon, Skagit County, Washington, collapsed into the Skagit River.The bridge was constructed in 1955 and the collapsed span consisted of two northbound and two southbound traffic lanes divided by a concrete barrier. Leading up to the collapse, a Kenworth truck-tractor hauling an oversize load was following a pilot vehicle southbound on I-5. Witnesses reported that as these two vehicles approached the bridge, a second southbound tractor-trailor overtook and passed the vehicle with the oversize load in the left lane. The driver of the first tractor-trailor reported to NTSB investigators that he had felt “crowded” by the other vehicle trying to pass. In reaction, he moved his vehicle over towards the right hand side of the road. As the oversize load he was hauling moved onto the bridge, it collided with the overhead portal and multiple sway braces on the far right side of the truss structure. This caused major damage to load-bearing members of the bridge’s superstructure. The result was the subsequent collapse of the bridge into the river. The height of the oversize load was a major contributing factor. The driver reported the height of the load to be 15 feet 9 inches, but the lowest portion of the sway braces was later measured at only 14 feet 8 inches. Two passenger vehicles were also on the bridge span at the time of the collapse, and wound up in the river as well. Injuries but no fatalities were reported. The second part of the NTSB’s report has yet to be issued and the investigation is still listed as ongoing and active.

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