The Washington State Department of Transportation first posted about the crash on X at 2:35 a.m., stating that the motorway is blocked just south of Highway 531 and 172nd Street Northeast, around milepost 206.
Trooper Kelsey Harding of the Washington State Patrol reports that the accident involved many cars, including a motorcycle.
Harding stated that as troopers investigate the collision, drivers are encouraged to take detours and allow extra time if they travel south.
On Tuesday, at 5:45 a.m., the Washington State Department of Transportation reported that the backlog had extended to Arlington. An update at 6:15 a.m. stated that 4 miles of backup had been reached.