The road was shut for about 12 hours while investigations took place after emergency services were called shortly before 11:00 BST.
Police are appealing for witnesses and dash cam footage from the westbound carriageway.
Det Insp Andy Heath said: “Our thoughts are with those who have been affected by this incident.
“Specialists from the Roads Policing Team and Serious Collisions Investigation Team have continued enquiries through the weekend, and the investigation team will be pursuing several lines of enquiry over the coming weeks.
“It is not possible to provide detail of the cause of the collision, and I would ask the public not to speculate.”
He added further information would be made available “in due course”.
“Our priority at this time is to support those that have been directly affected by this tragic incident and to secure the evidence required for a thorough investigation.”