Jacqui Hori-Hoult, Northland manager for the NZ Transport Agency, said contractors had now completed drainage work to take care of ground water, reshaping the road shoulders and dug out and replaced soft and fatigued materials in the road underlay.
Work had now begun to rebuild the road surface before applying a final chip seal.
The Bulls Gorge rehabilitation was due to be completed before Christmas but some night work could be required to achieve that.
Stop/go operators tried to minimise delays, ''but once we start something it is hard to stop part way through'', she said.
The agency apologised for any inconvenience to motorists as it worked to get the essential repairs done before the peak holiday season.