UK drivers are expected to make 21 million leisure trips between Monday and Christmas Eve, leading to warnings of daily delays.
Getaway traffic will climb slowly at the start of the week before jumping from 2.2 million trips on Thursday to 3.2 million on Friday, the last working day before Christmas Day, the RAC said.
Some 13.5 million leisure journeys by car are expected between Friday and Christmas Eve, up 20% on the equivalent period last year.
Congestion is likely to peak on Friday as drivers embarking on getaway trips compete for road space with commuters and business traffic.
Transport analysis company Inrix warned there are likely to be “daily delays of around 40 minutes” between Friday and Christmas Eve on the M25 clockwise west of London.
It predicted the worst queues on the motorway network will be on the M25 clockwise between junction 7 (for the M23/Gatwick airport) and junction 16 (for the M40/Birmingham) on Friday.
Drivers heading anti-clockwise between junction 17 (Rickmansworth) and junction 12 (for the M3) on the same day are also being warned to prepare for hold-ups.
Other motorway stretches identified as potential hotspots include the M1 north from Woburn, Bedfordshire to Daventry, Northamptonshire and the M6 south from Wigan, Greater Manchester to Stafford, Staffordshire.
During the weekend before Christmas, between 12pm and 2pm is expected to be the busiest time to travel on the roads.
Drivers are advised to set out before 11am or after 6pm to reduce the chance of being stuck in long queues.
National Highways said it will remove more than 1,000 miles of roadworks on England’s motorways and major A roads by 6am on Tuesday.
That means more than 98% of its network will be free of roadworks until January 2.
RAC spokeswoman Alice Simpson said: “Since Christmas falls on a Monday this year, there’s no need for drivers to use annual leave for getaway trips as they can travel over the weekend before.
“For that very reason, our research suggests these days will be the busiest times to drive, so we urge people to set off as early as possible on Saturday and Sunday.”
She advised drivers to carry out vehicle checks before setting off, such as on tyres, fuel, oil, coolant and screenwash.
Inrix transportation analyst Bob Pishue said: “Our recommendation is to avoid peak commuting hours and use traffic apps to minimise holiday travel traffic frustrations.”
People hoping to embark on festive getaways by train also face disruption due to Network Rail carrying out engineering work.
London Paddington will be closed between Christmas Eve and December 27, meaning no mainline trains will serve Heathrow Airport during that period.
London King’s Cross will also be closed on Christmas Eve.
Outside of the capital, an engineering project near Southampton will cause some disruption to services, as will work to build the new Cambridge South station.
No trains will operate on Christmas Day, with a very limited service running on Boxing Day.
Network Rail said 96% of the rail network will remain open as normal but it is carrying out “some significant projects”.
It added that engineering work is planned to “target the quietest times” to minimise disruption.
Airports will be busy with many people heading overseas for festive holidays or arriving in the UK to spend Christmas with loved ones.
Heathrow Airport expects 6.5 million passengers will travel through its terminals this month, with tens of thousands departing on Christmas Day.
– The RAC’s traffic estimates are based on a survey of 2,100 UK adults who were asked about their travel plans by research company FindOutNow in the week commencing December 4.