The crash followed two earlier incidents in the same area
A four-week-old baby boy who was on board an ambulance which overturned on a motorway remains in a critical condition in hospital.
The "seriously ill" child was being moved from Preston to Leeds for treatment when the crash happened on Sunday morning.
The ambulance is thought to have hit a patch of ice at the junction of the M62 and M621 at Gildersome.
Police said two other crashes were reported in the same area.
A doctor and nurse were travelling in the ambulance along with a paramedic crew when the vehicle turned onto its side and skidded along the motorway.
The crew were said to be shocked but there were no other injuries.
The parents of the child, who was described as being in a serious condition prior to the accident, were travelling separately.
Another ambulance took the baby to Leeds General Infirmary where police described his condition as "critical but stable".
A West Yorkshire Police spokesman added: "It is believed ice on the roadway was a primary contributory factor."
He confirmed that when the ambulance crashed police were already driving to the scene to attend other accidents which had occurred around the same stretch of road.
A Toyota Corrolla and VW Passat collided nearby and shortly afterwards a Nissan Micra hit the central barrier.