The M1 northbound between junction 5 and junction 6 has been reopened after a serious accident this morning.
Two cars and a lorry crashed shortly after 9.30am and three casualties taken to hospital.
A woman in her 20s and a man in his 50s suffered serious head injuries and were taken to St Mary's Hospital in London. Another patient with minor injuries was taken to Watford General Hospital.
Two lanes of the motorway reopened just after 3pm.
All lanes are now open and the vehicles recovered.
Police are escorting traffic through with a rolling road block.
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