A couple died when their car went out of control and crashed head-on with another on the A1 in Northumberland on Christmas Eve.
Plant driver Peter Mitcheson, 64, and his wife Valerie, 47, a sales assistant, suffered multiple injuries when their Honda Accord drifted into the wrong lane on a single-carriageway stretch near Morpeth.
An inquest was told yesterday that the reason why Mr Mitcheson veered into the northbound lane would never be known.
A witness said the car came out of a junction onto the main A1 at high speed, travelled south for a short distance then crossed into the wrong lane, where it crashed with a Vauxhall Astra going in the opposite direction.
Astra driver Lisa Kirkbride was travelling at about 58mph and had no time to brake or avoid the accident, the Morpeth hearing was told.
Mrs and Mrs Mitcheson, from Cragdale Gardens, Peatcarr, Hetton-le-Hole, were trapped in the wreckage and died but Miss Kirkbride and her child passenger survived.
The accident happened at about 2.30pm last Christmas Eve near the Highlaws and Hebron junctions just north of Morpeth.
Witness Sarah Hall of Queen's Road, Alnwick, said she was driving north behind the Astra when she saw a silver car come out onto the A1 from the Hebron junction "at high speed" and then turn into the path of the Astra.
"I was very surprised that he came out and didn't look or stop. It was a really dangerous move and within a split second he turned right into the path of the car in front.
"It looked to me as though it came round the corner on two wheels, it was going so fast."
Miss Kirkbride told police: "I saw a car coming close to the white lines in the middle of the road and the next thing he was right in front of me, side on."
Northumbria Police accident investigation expert PC Raymond Aitman said Mr Mitcheson had lost control of his car and crossed into the opposite lane. "Sadly, we may never know the reason for this."
North Northumberland coroner Ian McCreath said: "This leaves a feeling of uncertainty because of the lack of an explanation for why this happened."