Three children and an adult were lucky to escape with minor to no injuries after their car rolled twice on the Hume Highway at Bookham on Thursday.
It's understood the 40-year-old female driver had a medical episode at the wheel.
She was being treated by paramedics for generalised bruising, while a 13-year-old girl was being treated for shock and a 15-year-old boy for grazes to his arms and legs.
The car with a Victorian registration was travelling at 110 kilometres per hour when it rolled.
One of the two northbound lanes is closed near Jugiong Creek.
Traffic was moving in the other lane.
Police and Bookham Rural Fire Brigade were on scene.