The woman was in the passenger seat of a car that rear-ended a white van at the Kings Meadows connector about 4pm on Thursday. 

The occupant of the van said he was forced to slow down when a vehicle in front of him reduced its speed.

The man, who did not wish to be named, said the car ahead of him slowed down to avoid hitting the open door of a test-drive car parked on the side of the highway.

''I've come up and just touched (the vehicle ahead), but with the power of this car hitting my back end I've hit her a bit harder,'' he said.

''They've hit me up the bum, but I'm worried about the girl.

''I've got a couple of kids ... the way their car's hit, there's no airbags, you've got to worry.''

Police closed one of the highway's southbound lanes at the scene for about an hour while emergency crews tended to the crash.

Tasmania Police acting sergeant Josh Hayes said inattention was believed to be the cause of the crash.

''We'd like people to be attentive while driving on the roads, don't be distracted,'' acting sergeant Hayes said.

''Traffic can slow and stop at any stage, be prepared to respond to conditions.''