Motorists are being urged to ignore their sat navs to avoid causing traffic jams during this weekend’s “unprecedented” closure of the M25.
National Highways has issued a warning as it prepares to close a five-mile stretch of the motorway in Surrey from 9pm on Friday to 6am on Monday.
The company estimates that motorists who follow detour route signs on A Road will have an hour added to their normal travel time between junctions 10 and 11, which is closed in both directions.
There are concerns that some people will try to find alternative routes via the main road.
National Highways Project Leader Jonathan Wade said how well the region coped with the M25 closure would partly depend on whether motorists adhered to official detours.
He told the PA news agency: “How many people will take the initiative to use a sat nav?”
“If people think they can just do their thing and ignore the signs and find a shorter or faster route, then there is probably a greater risk of congestion.
“This may cause further congestion at some key junctions and should be avoided where possible.”
M25 closed detour route map
(PA wire)
Daniel Kittredge, senior project manager for National Highways, said: “As people move away from the detours we have put in place, it creates further problems on different parts of the road network.
“Most of the time it will be local roads, so it will have a big impact on residents in certain areas.
“That’s why we’re trying to encourage people not to follow Nav.
“Please stick to the prescribed detour route. It will be more suitable for your journey.”
Motorists have been warned to avoid the area if possible during the closure, marking the first planned daytime closure of all lanes of the M25 since it opened in 1986.
Highway officials said the move was necessary to demolish the bridge and install a new gantry.
Modeling conducted during the plan’s development estimated that without mitigation measures, such as encouraging drivers to leave their cars or creating detours, drivers could face delays of up to five hours.
National Highways believes the measures, based on a 50% reduction in traffic, will only increase journey times by around an hour.
But Wade said, “It’s so unprecedented that we don’t have anything to benchmark against.”
He added: “We’ve never had a shutdown of this nature before. We really don’t know how many people will listen to the message we give.
“At the moment it is very difficult to determine how effective all traffic management is.
“If possible, don’t travel.”
The M25 typically carries between 4,000 and 6,000 vehicles per hour in each direction between junctions 9 and 11 between 10am and 9pm on weekends.
Daytime highway closures will be implemented four more times through September.
The project, due to be completed in summer 2025, will increase the number of lanes and ease access at Junction 10 of the M25, one of the UK’s busiest and most dangerous motorway junctions.
