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Part of the A2 was closed for more than six hours following a serious crash.
Both carriageways near Ebbsfleet were closed to allow an air ambulance to land at the scene, where a man in his 60s was treated before being taken to King's College Hospital in London.
He remains there in a serious condition following the crash between Bean and Ebbsfleet on the coastbound carriageway at 4.25pm.
The London-bound side was reopened just before 6.30pm once the air ambulance had left the scene.
The coastbound section remained closed until about 10pm, although traffic which had been trapped on the carriageway was released past the scene at around 7.30pm.
At its worst, traffic stretched back eight miles.
Drivers heading towards Kent from London had more than an hour added to their journey times.
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