Traffic lights are being installed at the Corringham Road/Thorndike Way junction in a move which was expected to take 12 weeks when the scheme began in September.
Now it is anticipated that the work will be completed by the end of January.
Until then, temporary traffic signals will remain at the junction during the works and there will be lane closures on the A631 Thorndike Way dual carriageway.
Cllr Clio Perraton-Williams, county councillor for Scotter Rural and executive support councillor for highways, said: "Over the past couple months, we've seen higher than average amounts of rainfall, including ten wet days in December alone.
"Combined with the contractor experiencing some supply chain issues due to coronavirus and unexpected ground conditions throughout the project, we haven't been able to finish these improvements in December as originally planned.
"Despite Balfour Beatty working tirelessly to tackle these challenges throughout the project, we now expect to have the new signals switched on and the project completed at the end of January.
"I know this is less than ideal, but rest assured that the junction will continue operating as efficiently as it is now throughout January and that we will be doing everything we can to finish these works up as soon as possible in the new year."
Residents have campaigned for years to improve safety at the junction where people have died and others been hurt in accidents.
The junction is one of the most dangerous in Nottinghamshire.
When the news about the improvement work was announced, Coun Perraton-Williams said: "This is great news for Gainsborough and the surrounding area since it means we're one step closer to increasing safety even further here by installing traffic signals at this busy junction.”
“Not only that, but these works will also ensure the junction can cope with the extra traffic generated by any new housing in the surrounding area over the coming years.”