Workmen began preliminary works at Peppermint junction in Holbeach on Monday before contractors break ground in May.
Initial work completed on Tuesday included tree removal, which was being carried out ahead of bird nesting season.
From April 3 to 7, work will begin to alter fence lines south of the A17 and clear shrubs from the ditches to the north of the A17 and a small section of New River Drain.
The works will not require any road closures or traffic management measures. As part of the highway scheme, new vegetation and trees will be introduced to the site.
Coun Richard Davies, executive member for highways and transport, said: “On-site work for the Peppermint Junction improvement scheme has begun ahead of construction officially starting in May, which is great news for Holbeach and people travelling in and around it.
“Things are really progressing with the scheme at the moment. Over the next couple of weeks, we hope to identify and announce the contractor who will carry out the improvement and infrastructure works.
“When complete, the new roundabout layout will make the junction much safer for road users.”