Police in Luton want to trace the driver of a lime green Corsa, after a man was attacked.
The 54-year-old victim, who was driving a red Rover 600, says he was cut up by the Corsa's driver on the M1's northbound carriageway. Both drivers pulled off at J11, and stopped at the traffic lights.
Both men are thought to have then got out of their cars and become involved in an argument. The Corsa's driver is believed to have hit the other man over the head with an un-known object. The Rover's driver suffered a fractured skull.
Police are seeking witnesses to the attack, which took place at about 3.30pm on Wednesday (12 February).
PC Olyver Tomlinson from Bedfordshire Police said: "The offender is described as a black man, between 30 and 40 years old, with four gold teeth. [He] wore a high visibility jacket and trousers."
Anyone with information relating to this crime can contact PC Tomlinson at Luton Police Station, in confidence, on 01582 394158, or Bedfordshire Police on 101, or text information to 07786 200011.
Alternatively contact Crimestoppers, anonymously, on 0800 555 111.