Operation Brock – a no-deal Brexit plan that sees one side of a motorway closed – begun on Monday.
One side of the M20 is now reserved for queuing lorries heading to the port of Dover.
All other traffic will be restricted to a contraflow system on the opposite side of the motorway.
The system between junctions 8 and 9 is supposed to ease congestion in Kent if traffic grinds to a standstill in the event of a no-deal Brexit.
Highways England said Operation Brock will offer “a safe, scalable response to disruption”.
Highways England project director John Kerner said: “Operation Brock strengthens this resilience even further and offers a safe, scalable response to disruption that can be used to queue up to 11,000 lorries heading for mainland Europe, while keeping other traffic flowing for people living, working and travelling in and around Kent.”
The UK was expected to leave the European Union on Friday but the deadline has since been extended to April 12 at the earliest.
From Monday, the M20 contraflow will be in effect from north of Junction 8 (for Maidstone) to Junction 9 at Ashford.
Lorries heading to Dover will have a 30mph speed limit in place, while all other traffic will be restricted to 50mph – with two lanes in each direction.