A low-loader was carrying two new tracked excavators down the A194 in South Tyneside on Sunday morning.
One of the excavators or the lorry is suspected to have collided with a railway bridge as it passed below knocking the machines into the path of the car at Fellgate, near Leam Lane, Jarrow.
Firefighters had to cut the woman free from the wreckage. She was then flown to the Royal Victoria Infirmary in Newcastle by the Great North Air Ambulance suffering from serious head injuries.
Two other people were taken to South Tyneside General Hospital in Shields with minor injuries.
The new excavators were part of a delivery from HM Plant, by a third party haulage company, to a civils contractor operating in the south.