The M25 will be closed all weekend with an urgent warning for drivers facing a 10-mile diversion.
It is the third of five such closures to allow for the construction of a new bridge near the junction 10 roundabout.
The busy motorway, which rings London, will be closed between junctions 10 and 11 from 9pm on Friday until 6am next Monday, National Highways said.
Those heading along the Goodwood Festival of Speed ​​route will be diverted onto the A roads.
The festival organizer warned drivers to check the route before leaving.
“Perhaps it would be wise to allow a little more time than planned,” he told Autocar.
Many travelers to, from and between the UK’s two busiest airports, Heathrow and Gatwick, will also be affected.
National Highways project manager Jonathan Wade urged drivers to follow the temporary signs, saying: “Please ignore your sat navs and follow our detour route instead.”
National Highways has also advised drivers that it may also be quicker to avoid the closure by heading in the opposite direction around the M25 via the Dartford Crossing.
The bridge will be installed as part of ongoing works to make roads safer and reduce pollution.
It consists of 68 beams, each weighing 16 tons, and another four beams weighing 40 tons.
It is part of a £317m project to improve Junction 10.
The closure in March was the first scheduled daily shutdown of the M25 since it opened in 1986.
Due to be completed in the summer of 2025, the project will increase the number of lanes at junction 10, which is one of the busiest and most dangerous motorway junctions in the UK.
Full details of diversion route
Full details of all diversion routes are provided below.
Link 10 – Link 11: exit the M25 at J10 and take the 3rd exit north of the A3 onto the A245 Painshill Junction, the A245 towards Woking and Byfleet.
Then at the Six Crossroads roundabout take the 5th exit onto the A320 and continue to the M25 Junction 11 where the diversion will end.
Connection 11 – Connection 10: exit the M25 at J11 and take the 3rd exit onto the A320 south towards Woking, then at the Six Crossroads roundabout take the A245 towards Byfleet.
Continue on the A245 to the A3 Painshill junction, then take the 3rd exit onto the A3 southbound to junction 10 where the junction will end.
Avoiding the closure by taking the M25 via the Dartford Crossing may also be quicker, the National Highways said.
Between 4,000 and 6,000 vehicles in each direction normally use the M25 between junctions 9 and 11 every hour from 10:00 to 21:00 at weekends.
The last two weekend closures under the project will take place later this year.
It comes as there is also a 15-mile diversion on the M1 this weekend, with motorists facing delays of up to 40 minutes.
Planned closure of the M25 in 2024 and beyond
The first closures of 2024 took place on March 15 between junctions 10 and 11 in Surrey on Britain’s biggest motorway.
They held out over the weekend, with the road not reopening until Monday, March 17.
The second series of closures took place over the weekend in mid-May, with junctions 9 and 10 closed in both directions.
Now the M25 is set to close for the third time this year as National Highways said it will close the motorway between junctions 10 and 11 in Surrey from 9pm on Friday 12 July until 6am on Monday 15 July.
It will be the third of five weekend closures of the motorway – which circles London – as part of a £317 million project to improve Junction 10.