Update at 6:25 p.m. — All lanes are back open.
A van flipped on its side at the exit from westbound I-66 to Route 267 (Dulles Toll Road). All lines of westbound I-66 are blocked, and traffic is being diverted onto Route 267.
Traffic on I-66 is currently backed up all the way to Glebe Road in Arlington.
Local realtor Laura Rubinchuk first alerted us to the wreck just after 5:00 p.m. via Twitter.