A woman in her 90s died on what is believed to have been her birthday after she drove the wrong way on the A47 and collided with another car.
The tragic head-on crash occurred on the Soke Parkway on Tuesday morning and left the driver of the other car in Peterborough City Hospital with serious injuries.
Both women are from the Peterborough area but the deceased has not yet been formally identified.
A large emergency presence including an air ambulance rushed to the scene of the collision while the road in both directions was closed from about the time that the incident occurred until around 4pm.
The emergency services were called to the parkway near the city hospital shortly after 11am.
A red Daihatsu Charade and a silver Honda Jazz had collided, killing the driver of the Charade and leaving the driver of the Jazz, a woman in her 40s, needing hospital treatment.
Aside from the police, two ambulance crews from the East of England Ambulance Service were sent to the scene, while an air ambulance was also dispatched by the East Anglian Air Ambulance service.
Cambridgeshire Fire and Rescue Service sent two crews to the scene. Using specialist cutting equipment they released the woman in her 40s from her car before she was taken to the nearby hospital by ambulance.
As of yesterday morning she was still in a serious but not life-threatening condition.
Anyone who witnessed the collision is asked to call the road policing unit on 101 or Crimestoppers, anonymously, on 0800 555 111.
They can also report it online via www.crimestoppers-uk.org.