A pensioner was airlifted to hospital following a collision on the A120 between Braintree and Dunmow.
A man in his 80s, who was driving a red Citreon Picasso, was taken hospital with life-threatening injuries following the incident, which happened at about 4pm on Saturday.
Both lanes of the A120 were initially closed while emergrncy services worked at the scene, with a diversion towards Rayne put in place.
A spokesman for Essex Police said: "We would like to thank drivers in the area for their patience, especially given the hot weather conditions."
Anyone with information about the collision, or who may have seen a red Citreon Picasso driving in the area prior to 4pm, is asked to call 101 and quote incident number 803 of June 22.
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