The collision happened at 10.05am yesterday when a car drove into the back of a lorry on the southbound carriageway of the A167(M) Central Motorway in Newcastle.
The car driver, a 53-year-old woman, was taken to the city's Royal Victoria Infirmary, where she remains in a life-threatening critical condition.
At this stage it is believed her injuries were caused by a medical episode.
The driver of the HGV, who stopped at the scene but left before police arrived, has now been in contact with officers.
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Police continue to carry out inquiries into the crash, and are appealing for any witnesses to the collision to come forward.
Anyone who could help is asked to call Northumbria Police on 101, quoting reference 255 121216.