The quick moveable barrier is intended as a short-term solution
Work has begun on a moveable barrier which could lessen the traffic chaos caused in Kent when lorries cannot cross the Channel from Dover.
The concrete quick moveable barrier (QMB) is being installed between junctions 11 and 12 of the M20.
It will allow part of the London-bound carriageway to be used for coastbound traffic when weather or strike action affects the port or the Channel Tunnel.
The Highways Agency said the work is expected to take about 14 weeks.
The installation work will involve some lane closures and speed restrictions.
It will take place 24 hours a day, seven days a week, and at least two lanes will remain open between 0600 and 2000 BST each day.
The barrier will be deployed using a special vehicle when phase one of Operation Stack is launched.
It will create a contraflow on the London-bound carriageway, while freight traffic continues to be held on the coastbound section.
It is hoped it will improve journey times for other traffic and reduce congestion on the surrounding roads.
Roads minister, Tom Harris, said the Highways Agency would continue to work with Kent County Council, the police and other partners to help find a longer term solution.