The speed limit on a section of the M2o between Hythe and Ashford will be reduced to 50mph while a new junction is installed.
Highways England warns that the limit will be in force until 2020 during which time cameras will monitor vehicle speeds.
It is creating a new 10a junction south of Ashford to relieve pressure on junction 1o.
The 50mph limit came into force yesterday (Monday) between junction 11 for Hythe and junction 9 for north Ashford.
Building work will involve lane closures and diversions.
A Highways England spokesman said: “The M20 is an international route and is used by large volumes of heavy goods and holiday traffic. Long distance traffic from the M20, A20 and A2070 south of Ashford conflicts with local traffic from Hythe Road and Kennington Road.
“We predict that the existing M20 junction 10 will suffer from congestion and long delays in the future if additional capacity is not created.
“We have identified the scheme as essential to the future development of south Ashford. The recent improvements at junction 10, to increase the capacity and improve safety, will allow some development to go ahead but will not be sufficient for all of the proposed developments.”
A new roundabout will be built over the motorway some 800 yards away from the junction 10.
Highways England is also creating new safer pedestrian and cycles crossings over the motorway.
It added that the long term aims of the scheme are to provide improved infrastructure, to support development in the Ashford area, to help separate long distance traffic from local traffic, to reduce congestion and improve journey time reliability and improve road safety.
The work is expected to last until May 2020. Drivers using the road are advised to pay attention to signposted diversion routes during road closures.