Part of the C92 between Linton on Ouse and Newton on Ouse collapsed when the Ouse burst its banks and poured into a culvert, taking some of the road with it.
North Yorkshire County Council has begun a repair operation and is aiming to complete the work before Christmas.
County Councillor Gareth Dadd, executive member for highways, said: “The flood caused very extensive damage to this road, and the repair is a major operation.
“We have made the site safe and taken preventative measures to ensure that there is no further collapse of the road.
“Topographical surveys have been completed and debris is being cleared to facilitate the repair work