A 62-year-old man is recovering after having his throat slashed in a road rage attack, police said.
The victim from Billericay, Essex, was attacked shortly after stopping on the A1 at Alwalton, Cambridgeshire.
Police said he stopped when he was flashed by the driver of a following car who then attacked him with a knife.
"It was a very serious incident and the victim needed hospital treatment. It could have been a fatal attack," a police spokeswoman said.
Police said they had "operational reasons" for not releasing details of the attack earlier.
The incident took place on the southbound carriageway of the A1 on the afternoon of 3 April.
The spokeswoman said the attacker, who drove off, was driving a blue Fiat and was white, stocky, about 50 and had short, fair hair and a moustache.