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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There is a high risk from birch pollen during any good weather. Oak pollen is also on the increase.
Wednesday's weather for the west of the region
Wednesday's weather for the east of the region