The collision happened at about 1.50pm on the M11 southbound at Trumpington between a silver Mercedes C260 and a black Nissan Micra. The front seat passenger of the Micra, a woman in her 20s, suffered life-threatening injuries and was taken by ambulance to Addenbrookes Hospital, in Cambridge, where she remains in a critical condition. The driver of the Micra suffered minor injuries. The driver of the Mercedes and two children travelling in the back were not injured. Anyone who witnessed the collision, or either vehicles in the lead up to it, is asked to contact our road policing unit by calling 101 and quoting incident 241 of December 16.