Sarah Outen, 29, began her self-propelled round-the-world voyage in 2011 in London. The final leg would make history.
The Washington State Patrol chief says the Interstate 5 bridge collapse into the Skagit River at Mount Vernon was caused by an oversize truck that hit the overhead span.
The trucking company says it received a state-issued permit to carry its oversized load across the bridge.
The truck made it off the bridge and the driver remained at the scene and cooperated with investigators.
Two other vehicles went into the water Thursday evening as the bridge collapsed. Three people were rescued and are recovering.
Officials said drivers should expect delays at the break in the major north-south highway about 60 miles north of Seattle. Detours have been set up to try to ease the congestion.
In a statement Friday, Washington state Congressman Rick Larsen said emergency funds have been made available to repair the bridge:
I spoke this morning with Transportation Secretary Ray LaHood. Secretary LaHood confirmed that the Department of Transportation has emergency funds available to aid repairs. The Department of Transportation has established an interagency task force to expedite the permitting process for the bridge repair.
The Associated Press contributed reporting to this article.