Thames Valley Police is appealing for specific witnesses to a road traffic collision in Milton Keynes, on June 2.
At around 7.50pm on the A5 northbound between Redmoor roundabout and Portway Roundabout a grey Mercedes van collided with silver Toyota IQ, which resulted in the Toyota rolling onto its side.
Officers are appealing for witnesses who stopped and helped the female driver out of the Toyota.
A woman aged 25 from Walnut Tree, Milton Keynes, was arrested on suspicion of being unfit to drive under the influence of drugs and has been bailed until September 20.
Anyone with information is urged to contact PC James Clarke from Roads Policing via the Thames Valley Police Enquiry Centre on 101 or Crimestoppers on 0800 555 111.