If you’re planning to head north of Seattle over the holiday weekend, you’ll need to budget some extra time to deal with the traffic issues caused by last night’s collapse of the I-5 bridge over the Skagit River near Mount Vernon. The Washington Department of Transportation says that the investigation into the collapse is continuing, but it appears that all four lanes of the freeway dropped into the water after a commercial truck with an oversized load hit a portion of the bridge superstructure. A number of cars went into the river, but it appears that all of the occupants were rescued, with only three people needing hospitalization for hypothermia. WashDOT says that they expect to have a signed detour in place by early this morning, but with more than 67,000 vehicles using that bridge each day, the backups are expected to be extensive. To avoid a lengthy delay, you’re advised to use some other alternate route. Inspectors from the National Traffic Safety Board are expected to be on the scene before noon today; removal of debris and repair of the bridge will begin after the NTSB completes its investigation.