The A36 is expected to remain closed in both directions from Heytesbury to Deptford, until Sunday.
A man, aged in his 40s, was seriously injured on the A36 near Codford in Wiltshire.
The pedestrian, in his 40s, is in hospital with life-threatening injuries after the collision.
Six fire crews were called to the village of Heytesbury in Wiltshire on Wednesday morning.
