Work has begun in earnest on a £70 million project to dual a section of the A21.
The Highways Agency says the scheme, between Tonbridge and Pembury, should reduce delays and accidents.
Heavy plant machinery is due to move in after weeks of preparing the site.
Currently there is a narrow stretch of single carriageway between the two sections of dual carriageway at Pembury and Southborough which can result in congestion and long delays.
Work is expected to be completed by December 2016.
A Public Inquiry for the scheme was held between 14 May and 9 July 2013 and the Secretary of State’s decision confirming that the scheme will go ahead was announced on May 1 2014.
The new dual carriageway will broadly follow the line of the existing A21 with a new grade separated junctions at Fairthorne (by the petrol station) and at Longfield Road, replacing the existing roundabout at the southern end of the scheme. At the northern end, there will be a minor change to the line of the slip road from the Vauxhall Lane roundabout where it joins the A21.
Parts of the existing A21 will be retained to provide access to houses, businesses, fields and woodland. A new bridleway for pedestrians, cyclists and horse riders will be provided along the whole length of the scheme. A new footbridge will be provided across the Pembury Bypass at Blackhurst Lane, replacing the existing crossing.
The A21 will remain open during the building phase. Site manager Alastair Smith, of contractors Balfour Beatty, said: “We are coming to the building phase but the A21 will run all the time.
“We can build the road without being on the road. There will be a space between the traffic and where we work, so we can build in sections.”
The scheme entails the unavoidable loss of 9 hectares of Ancient Woodland for which 18 hectares of translocated and planted woodland will be provided in mitigation. These areas will be managed for 25 years. In addition, 27 hectares of existing woodland will be managed for 10 years while the new planting becomes established.
Highways Agency Project manager Graham Link said: “One of the reasons we are doing the scheme is because there is access for houses and woodland, which can cause accidents. It is also used by walkers and cyclists.
“One of the big problems at the moment is that you have got three lanes coming into one, which causes most congestion at Southborough.
“We will keep people updated as we go on phase by phase.”