Why we haven't seen the end of Operation Stack in Kent after the Brexit transition period ends | Updated: 14:51, 22 December 2020 As the end of the Brexit transition period looms, many might have hoped the new year will mean the end of Operation Stack, the dreaded traffic management system which has been deployed in the county for two decades to deal with congestion heading to the Port of Dover. Involving the closure of the M20, Operation Stack allows HGVs to be âstackedâ on the motorway with other traffic diverted on to the A20. The Port of Drover remains closed Picture: Barry Goodwin