A man died after a crash involving five vehicles and a lorry.
Thames Valley Police were called to reports of a collision on the A404 southbound – between the Handy Cross Roundabout and the Marlow exit slip road in High Wycombe, Buckinghamshire – between 06:10 and 06:25 BST on Friday.
A man, aged in his 50s, died at the scene, police said.
Officers are appealing for anyone with information or footage of the crash to contact them.
A woman, aged in her 30s, suffered minor injuries and was taken to hospital but has since been discharged, the force added.
Det Sgt Lyndsey Blackaby said: “First and foremost, our thoughts are with the family of the man who has tragically died in this collision.
“They are being supported by a specially trained family liaison officer.
“We are in the early stages of our investigation and are still trying to establish the full circumstances.”
He appealed for anyone who was driving in the area, who might have information about the crash or dash-cam footage, to contact the force.