It occurred at 12.35pm on Monday 12 August 2013, on an unclassified road near Nunwick, involving a pedal cycle and a tractor, which was trimming the hedge at the side of the road.
Officers are trying to trace a woman driving a white car, which passed the tractor at the time of the collision.
Traffic Constable Martin Recchia, of North Yorkshire Police’s Roads Policing Group, said:
if you are the woman who drove past the tractor, please contact the police straight away as you may have vital information that could help my enquiry.
Anyone who can help with this investigation is asked to contact North Yorkshire Police on 101, select option 2 and ask for Martin Recchia. Alternatively information can be emailed to firstname.lastname@example.org