An 84-year-old man died when his car crossed all three lanes of the M40 in Buckinghamshire and came off the road.
The crash at Denham at about 1430 GMT on Sunday did not involve any other vehicles, police said.
The black Bentley Arnage saloon was heading towards London when the driver appeared to lose control just before junction 1a, police said.
It travelled down an embankment next to the hard shoulder. The driver was pronounced dead at the scene.
Witnesses are asked to contact Thames Valley Police.