Work was originally due to start on October 19, but contractors Clugstons have announced they are able to start sooner.
Work will start after the rush hour traffic at around 9.30am Monday.
The Brigg Road entry onto the A18 roundabout will be reduced to two lanes to allow work to take place. Traffic management (cones) will be in place.
Work is expected to take around three weeks.
Councillor Neil Poole, cabinet member for Neighbourhoods at North Lincolnshire Council said: “The scheme forms the final part of the improvements to the Tata Steelworks entrances and will help improve traffic flow by providing a dedicated left turn onto Mortal Ash. I’m pleased the work will take place sooner than expected. We hope to do the majority of the work outside peak times and some of the work will be carried out at night to minimise disruption.”