Drivers are warned to expect delays as work begins to repair a road damaged by a spell of dry weather.
The A40 westbound Oxford ring road suffered subsidence after a drought that caused it to shrink in places.
The resurfacing project will close one lane between Headington and Cutteslowe in both directions for 18 weeks, according to the county council.
Meanwhile, the A4095 Church Street in Faringdon, Oxfordshire, is also closed both ways for resurfacing work.