The M1 is now open after being closed for most of the morning following a crash that killed two men and injured for others.
Police reopened Junctions 4 and 5 going southbound at midday.
They had closed the road following a collision between two BMWs at 2.40 this morning.
Two men, the driver and front seat passenger of one of the cars, died at the scene.
Two other vehicle passengers, both men, suffered serious injuries and have been taken to a London hospital.
The two men in the second car were also injured and taken to Watford General Hospital.
Hertfordshire Highways has said that the southbound carriageway will remain closed until at least mid-morning whilst investigations at the scene continue.
Drivers are being advised to use either the A1 or M40/A40 as alternative routes and to leave plenty of time for their journeys.
The northbound carriageway had been closed but has since been reopened