Drivers are being warned to expect "bumper-to-bumper" traffic as millions of people travel in the run-up to Christmas.
The RAC and AA motoring groups expect sections of the M1, M5, M6 and M25 to see the worst delays.
Highways England has promised 98% of roadworks on motorways and major A-roads would be lifted or completed by 06:00 GMT on Friday.
Rail passengers have been advised to plan ahead due to engineering works and strikes.
The RAC and traffic data company Inrix estimated about 31 million "leisure" journeys would be made by car between Tuesday and Sunday, with Wednesday and Thursday set to be the worst for delays as Christmas traffic mixes with commuters.
Ben Aldous from the RAC said "bumper-to-bumper traffic on some motorways and major A-roads" was "near-guaranteed".
Inrix has also predicted places likely to have some of the longest delays, based on analysis of traffic flows during previous Christmas getaways, as well as things like planned roadworks and events.
Where will traffic be worst?
The M1 between Bedfordshire and Northamptonshire is expected to be heavily congested on Saturday and Sunday, along with the northern and western sections of the M25 around London.
Delays of up to an hour are also possible from Friday morning on the M6 between Birmingham and Wolverhampton, Inrix warned.
The AA said it expected traffic to reach a peak on Friday after 16:00, with the M5 between Bristol and Weston-Super-Mare likely to see hold-ups.
Where are the roadworks?
Highways England said it would remove 98% of its roadworks by Friday morning, freeing up more than 800 miles of motorways and major roads, but that the rest would have to stay in place for safety reasons.
The longest stretch of roadworks to remain in place is 43 miles on the M4 between junction six, near Slough, and junction 12 near Reading. The work is part of the £848 million smart motorways project to open the hard shoulder to traffic.
Other smart motorway roadworks staying in place include 20 miles of the M62 near Manchester and 19 miles of the M6 near Stafford.
There is more information on the Highways England website and also at Traffic Scotland , Traffic Wales and Trafficwatch Northern Ireland .
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Will my train run?
No trains run on Christmas Day, 25 December, and it is normal for only a few to run on 26 December.
Network Rail is working on 386 engineering projects between Friday and 2 January.
Most lines will remain open as normal but London Paddington station will be closed from Tuesday, Christmas Eve, until Friday 27 December, with no trains running.
Changes to services include:
- Paddington: No trains between 24-27 December and a reduced timetable will be in effect from 28-31 December
- King's Cross: Reduced timetable on Friday 27 December
- Liverpool Street: Services to Stansted Airport to start and terminate at Tottenham Hale on 26 December
- Ashford International to Canterbury West: Replacement buses from 27-29 December and Southeastern high-speed and Eurostar trains will not stop at Ashford from 26-29 December.
- Southend Victoria and Southminster: Replacement buses to and from London Liverpool Street from 27 December to 1 January
- Replacement buses between Bristol Parkway, Chepstow, Cwmbran, Ebbw Vale Town and Cardiff Central from 27 December to 2 January
- Edinburgh Haymarket: Replacement buses to and from Edinburgh Waverley from 27-28 December
What about strike action?
Services on South Western Railway (SWR) are affected by strike action until 20 December.
The operator is running a reduced timetable , warning peak services are likely to be busier than normal and replacement buses on some routes.
A spokesman for SWR said an alternative timetable would be in place for the week starting 23 December.
The strikes may mean Great Western Railway services are busier than normal as SWR passengers use them as an alternative.
The dispute between SWR and the RMT union is over the role of guards on trains.
Planned strike action on West Midlands Trains on Saturdays in December was called off .
How are you getting home for Christmas? Do you have any plans to avoid the rush? Share your stories by emailing haveyoursay@bbc.co.uk .
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