Pregnant mother-of-two Ami Gaston, from Carterton, saw the first vehicle crash.
She said: "A man on his own had skidded and crashed into middle barrier. My partner was driving - we had to swerve out of the right lane to avoid hitting him. His door was open and air bags were released."
She added that the heavy fog meant the situation was "really dangerous", as it was difficult to see any other car until you were "on top of it".
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