A passenger fell from a van as it travelled southbound between junction 9 for Redbourn and junction 8 for Hemel Hempstead on the M1 in an unexplained incident last night.
Herts Police are appealing for witnesses and information following the accident when a man fell from a white Volkswagen panel van before 6.40pm yesterday evening.
The driver, a 43-year-old man from Hayes, stopped the vehicle and the man, a 44-year-old from Harrow, was taken by air ambulance to Addenbrookes hospital with serious head injuries.
He remains in a serious but stable condition.
Anyone with information is asked to contact Herts Police on non-emergency number 101.
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