A 44 year old man who fell from a moving van on the M1 remains in hospital with serious head injuries.
Police are attempting to piece together how and why the man, from Harrow, left the white Volkswagen panel van just before 6.40pm on Thursday.
It happened as the vehicle travelled southbound between J9 and J8 and the carriageway was closed for several hours while officers investigated.
The driver of the van - a 43 year old man from Hayes - stopped at the scene.
Police are appealing for anyone with information and witnesses to get in touch by calling PC Jackie Lister via the Herts Police non-emergency number 101, quoting Operation Den.