As the truck was entering the bridge, its load -- which Rudeen described as an equipment casing form for a drill rig -- hit a support girder, causing the bridge to collapse.

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The bridge has a maximum clearance of about 17 feet, but there is no signage to indicate how to safely navigate the bridge with a tall load.

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An initial investigation shows the 1, 111-foot-long bridge collapsed when a tractor-trailer hauling an oversized load hit one of the bridge's overhead tresses, according to Deborah Hersman, chairwoman of the National Transportation Safety Board, which is investigating the incident.

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The trucking company said it received a state permit to carry its oversized load across the bridge.

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In Washington state this past week, a bridge collapsed when a truck driver's load bumped against the steel framework.

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Every engineer will tell you that the bridge should not be wider than its capacity to support people or load.

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Travis Phelps, spokesman for the Washington State Department of Transportation, said a flatbed truck with an oversize load hit the upper part of the steel-lattice bridge.

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The tractor-trailer was hauling a housing for drilling equipment southbound when the top right front corner of the load struck several trusses on the north end of the bridge, the patrol said.

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Sligh told KOMO he was traveling south on the interstate behind the tractor trailer when he realized the load appeared to be about four feet too wide to fit through the bridge's superstructure.

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"The size of the load that he was carrying appeared to create a problem, causing him to strike the bridge, " he said.

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