The M1 southbound was closed for several hours last night after a man fell from a moving van suffering serious injuries.
He was airlifted to Addenbrooke’s Hospital just before 7pm.
The southbound carriageway was closed between J9 for the A5 exit and J8 for Hemel Hempstead while police attempted to piece together exactly what had happened.
A Herts Police spokesman said: “At 6.40pm we received a call about concerns for the welfare of a man on the southbound carriageway of the M1.
“We attended and it appears, for reasons we don’t know, a passenger in a white van has fallen or left the moving vehicle and suffered serious injuries as a result.”
The northbound carriageway was also closed briefly to allow the air ambulance to land.
Police investigations are ongoing and anyone with information is asked to contact officers via the non-emergency number 101.