Traffic was backed up about four miles on northbound Interstate 5 near Boeing Field after a multi-vehicle collision shortly after 9:30 a.m. today.
Reports from the scene indicate up to six vehicles may have been involved. There were no immediate reports of injuries.
The accident initially blocked four lanes, but by 10 a.m., three lanes were open.
Traffic was heavy on Highway 99 and on Interstate 405 as drivers sought alternative routes.