Gwyn Williams was over taken by the ambulance shortly before the crash in the New Forest and told ITV Meridian what he saw.
He had been driving along the A336 between Brockenhurst and Lyndhurst in the New Forrest.
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Tuesday's weather for the west of the region
Tuesday's weather for the east of the region
A GP surgery in Caversham which has been placed in special measures, is to be taken over by Berkshire Healthcare NHS Foundation Trust.