Congestion is predicted to reach a peak towards the end of this week as those embarking on an early Christmas getaway fight for road space with commuters.
Research by the RAC and traffic information supplier Inrix suggests the worst jams will be on the M1, M25, M5 and M6.
A survey of 1,600 motorists indicated that 4.7 million leisure trips will take place on Thursday alone.
Motorists are advised to delay journeys on major roads until after 8pm to avoid the worst of the traffic.
Some 31.2 million leisure trips are expected between Tuesday and Christmas Eve.
This is the most since the RAC first asked drivers about their festive travel plans in 2013.
The breakdown rescue firm is urging motorists to carry out basic checks before long journeys, such as tyres, oil and coolant.
Three stretches of motorway identified as having the longest expected delays on Thursday:
- M25 clockwise J23 Hatfield to J28 Chelmsford (delays of 56 minutes)
- M25 anticlockwise J17 Maple Cross to J12 for M3 (delays of 48 minutes)
- M5 north J11 Cheltenham to J1 West Bromwich (delays of 33 minutes)
RAC patrol of the year Ben Aldous said: "Our figures suggest many more drivers are planning leisure trips by car in the run-up to Christmas this year, so bumper-to-bumper traffic on some motorways and major A-roads is near-guaranteed.
"While Christmas Day is still a little way off, it looks as though millions of drivers are planning to complete their getaway trips this week.
"Unfortunately, when you add in the prospect of unsettled weather, with heavy rain and strong winds in some parts, these are likely to be pretty unpleasant drives for many of us."
Inrix transportation analyst Trevor Reed said: "It does look as though this week is going to see a marked rise in traffic volumes on major roads in the UK, with Thursday expected to see the largest increase in vehicles compared to a normal December day.
"Drivers desperate to get away for Christmas are going to find themselves competing with commuters and shoppers for road space, so we recommend keeping tuned in to the changing traffic conditions on local radio and via in-car apps."
Highways England said 98% of England's motorways and major A-roads will be clear of roadworks between Friday and January 2.
Some train journeys will be disrupted over the festive period as Network Rail carries out 386 engineering projects.
Services in the South East will be worst hit by the closure of rail lines, with services to and from King's Cross, Paddington and Liverpool Street among the worst affected.
Network Rail chief executive Andrew Haines said: "Our passengers expect and deserve a more reliable railway. That's why this Christmas we are working on the railway across the country to improve services for our passengers.
"While significantly fewer people travel over Christmas, we know that some of our passengers will have important plans to visit friends and family, so please do check before you travel."