A two-car collision in the southbound lanes of the Interstate 5 Bridge has traffic backed up to 39th Street in Vancouver. The cause of the wreck and the extent of any injuries is unclear. What is clear: A trip across the bridge is likely to be slow.Traffic appears to be moving somewhat smoothly in the northbound lanes, according to traffic cameras on the Oregon Department of Transportation website. At least one southbound lane was temporarily closed while emergency crews tended to the wreck. All lanes reopened shortly after 3 p.m.