THE B478 at Playhatch is now completely closed in both directions due to flooding and erosion under the road.
Engineers from the county council have been keeping the road under scrutiny since the first floods hit in January, and managed to keep the road open using temporary traffic lights.
However the latest flooding means that the road is impassable and engineers are concerned that the large volume of moving water has washed away some of the supporting earth beneath the road surface.
County Councillor David Nimmo Smith, Cabinet member for transport, said: “Our team took swift action to close the road for safety reasons when the water levels rose and they are to be commended for this.
“It may be some time before the road is accessible to undertake the necessary inspections to fully understand the extent of the damage to the road. It is vital that the structural integrity of the carriageway is understood before it is opened up to traffic. For time being we have put barriers in place across the whole road to ensure that no one is put at risk.
“It looks as though the edge of carriageway in places may have been lost as some signs and markers have moved significantly.
“County council staff from our highways team, fire and rescue, social care and many other services are working very hard to protect public safety and keep Oxfordshire moving. I would like to take this opportunity to thank them for everything they are doing in these difficult conditions.”