A truck crashed on the George Washington Parkway, closing the northbound lanes in Virginia at the beginning of the evening rush hour.
The truck jackknifed and hit a tree just before the CIA overpass in Langley. It's unclear why it left the road.
U.S. Park Police flew the driver to a hospital with serious injuries.
Trucks usually aren't allowed on the parkway, but this mail carrier truck was authorized to be there. Previous reports said the truck did not have permission.
All northbound traffic was diverted on to Route 123. The cleanup was extensive and stretched into the evening commute.
The northbound lanes reopened just after 8 p.m., hours after the crash.
No other vehicles were involved.