Baltimore-Washington Parkway is partially closed Tuesday night after a road worker using a lawn tractor was hit by a car ahead of the evening rush hour, officials say.

Northbound lanes are closed starting at Riverdale Road (MD-410), about 5 miles south of the Capital Beltway, U.S. Park Police said. Traffic is delayed for miles, video shot from Chopper4 shows.

The worker hit about 3:45 p.m. was rushed to a hospital with life-threatening injuries.

Northbound traffic is deing diverted onto Riverdale Road.

The closure is expected to last for hours, a National Park Service spokeswoman said.

Investigators have not determined whether the car that hit the worker left the roadway, the park service said in an update.

U.S. Park Police are investigating.

Stay with News4 for more details on this developing story.