A car was forced into a ditch after a lorry the driver was trying to overtake veered to the right.
The driver of the Ford Orion car, a man in his 30s, was left badly shaken but uninjured.
He had been driving in rush hour traffic on the A4260 Oxford to Kidlington Road at 8.15am on Tuesday, when the lorry pulled out in front of him at Tackley, north of Kidlington.
Police said they did not think the lorry driver realised what had happened in his wake.
The car driver was about to try to overtake the lorry when it suddenly pulled out.
Oxford Mail reporter Alison Bartlett witnessed the incident.
She said: "It was quite frightening. The car looked like a piece of Lego being thrown off the road.
"Three of us pulled over and someone ran to see if the driver was okay. He climbed out himself. I was very surprised he was not badly hurt."
A police spokesman said: "The lorry driver might not have realised anything had happened and may have veered right to avoid something in the road."
Police are trying to trace the driver and are appealing for witnesses to the incident.
Anyone with information is asked to call 01865 846000 or Crimestoppers on 0800 555111.
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