Millions of people are set to head out of London in the coming days as the capital empties out for Christmas.
The annual getaway began on Thursday as an estimated 1.3 million drivers were expected to take to the roads to avoid traffic on ‘Frantic Friday’.
But motorists were warned they could face long delays at blackspots including the M3 in Surrey.
Journeys are set to be even slower on Friday as the last of the year's commuter traffic clashes with the Christmas getaway, amid a rail strike.
The RAC expects traffic to peak between 4pm and 8pm on Friday.
Inrix data shows that the worst non-accident traffic blackspot on the Friday before Christmas 2016 was the A303 at Stonehenge.
There were tailbacks for seven miles when congestion at the notorious bottleneck peaked shortly after 6pm on December 23 last year.
Empty London like a 'ghost town' on Christmas Day 2016
RAC traffic spokesman Rod Dennis added: "Things tend to get worse on the last working day before Christmas, with 'Frantic Friday' this year falling on the 22 December.
"We strongly urge drivers planning long journeys to avoid this day if they possibly can."
The RAC estimates that 11.5 million leisure trips will be made by car between December 17 and Christmas Eve, but this will be eclipsed by the 17.5 million taking place between Christmas Day and New Year's Day as people take advantage of post-Christmas sales at shops.
Almost 400 miles of roadworks will be lifted by Highways England to ease journeys.
The "roadworks embargo" will be in place on motorways and major A roads from 6am on Friday until 12.01am on January 2.
A strike by rail workers on Virgin Trains on Friday will see a reduced timetable in operation, which could force more people to travel on already congested roads.
Some 260 engineering projects on the railway will also disrupt journeys.
Many of Britain's mainline routes will be partially shut as Network Rail carries out its biggest ever Christmas investment programme.
Great Western Railway is urging passengers to complete journeys by Saturday "at the latest" as London Paddington will be closed between Christmas Eve and December 27.
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The West Coast main line will be halted between Preston and Lancaster from Christmas Eve to December 27, with buses replacing trains.
Passengers travelling between London and Glasgow during this time are advised to go via Edinburgh, adding around an hour to journeys.
Southeastern, which serves London, Kent and East Sussex, will not be able to run trains to London Bridge, Charing Cross and Cannon Street between Saturday and January 1.
Network Rail chief executive Mark Carne said: "We know that our railway is up to 50% quieter than usual during the festive period so taking on and delivering these huge transformational schemes at this time of year minimises our impact on passengers."
