A truck will be using two lanes and travelling at 10mph on the motorways this Sunday morning (September 8).
The vehicle, carrying a large electrical transformer, will be travelling on the M25 and the northbound M1 from Tilbury Docks, in Essex, to Sundon, in Bedfordshire.
It will leave the M1 at junction 12 and continue to Sundon.
Police will escort the vehicle throughout its journey. It will be restricted to 10mph when passing junctions and crossing bridges.
Its journey will start at approximately 3am on Sunday, when it leaves Tilbury Docks; it is expected to be on the M25 between 4am and 6.30am, during which time it will pass through the major improvement scheme between junctions 25 and 23. It is expected to arrive in Sundon by 7.30am.
The Highways Agency says road users are advised to plan their journeys before they set out, and to leave extra time if they are going to be affected by this vehicle’s journey.