Extensive roadworks are expected to lead to severe traffic problems as the Easter exodus gets under way.
Roadworks are expected to cause long tailbacks
About 10% more traffic than normal is expected as hundreds of thousands head off for the long weekend.
Motoring groups warn traffic hotspots will include the M5 south of Bristol, the M4 between London and Bristol and the M1 Nottingham to Chesterfield.
Meanwhile, rail travellers face Easter closures on the West Coast, East Coast and South West main lines.
'Nightmare Maundy Thursday'
Traffic is expected to be heaviest on routes to major attractions and coastal towns.
The AA says 6.5 million cars are expected on the roads over the weekend, with Maundy Thursday and Easter Monday the busiest.
M25 Junction 1-3 nr Dartford
M27 Junction 3-4 nr Southampton and Junction 11-12 Fareham to Gosport
M1 Junction 1-3 nr London, Junction 6a-10 nr Hemel Hempstead, Junction 25-28 nr Nottingham
M4 Junction 5-7 nr Slough, Junction 13 roundabout nr Chieveley
M11 Junction 5-6 nr Theydon Bois
M42 Junction 8a -7 and M6 Junction 4a link nr Water Orton
M69 Junction 1-2 nr Hinckley
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And as many as three million passengers are expected to take the train on Thursday, according to Atoc, the Association of Train Operating Companies.
The RAC has predicted that the shorter school break in much of the UK will lead to a "nightmare Maundy Thursday" on the roads as more people head off at the same time and fewer choose to go abroad.
By 1450 GMT it said its predicted hotspots, which included the M1, M4, M5, M6 and M25, were beginning to pick up and show signs of increased traffic.
Because Easter is unusually early this year, many schools are not having their traditional two-week break until April.
Consequently, families going away for Easter only have four days, which is expected to lead to a more concentrated getaway rush than normal.
The Highways Agency has removed nearly two thirds of roadworks from England's motorways and major A roads.
A total of 38 sets of roadworks have been completed and a further 47 are suspended until midnight on Monday 24 March.
However, roadworks are still affecting the M1, M4, M5, M6, M11, M25, M42, M48, M55, M56, M57, M60, M62, M65, M69 and many A roads.
A major accident shortly after 1600 GMT involving an overturned lorry has closed the M25 clockwise between junctions 5 and 6.
The Highways Agency has closed the junction of the M26, A21 and M25 to attend to the scene and the M25 is experiencing severe delays as a result.
According to Mary Vingoe, of traffic information website Keepmoving.co.uk, the accident will take a considerable time to clear and took place "just as the Easter Thursday traffic is at its peak".
West Coast main line: Closed Good Friday-Easter Monday between Coventry, Rugby and Northampton and from London Euston Sat - Monday
East Coast main line: London King's Cross - NE England and Scotland services diverted via Leeds, 1400 Sat - 1400 Sun
Great Western main line: Didcot Parkway - Swindon and Chippenham services replaced by a bus service or diverted, Fri-Mon
South West main line: Alterations and diversions to services to and from London Waterloo due to engineering works at Clapham Junction, Fri-Mon
East Anglia/Essex coast line: Replacement bus service between Gidea Park, Billericay and Ingatestone
More than two million air passengers are expected to pass through Britain's airports over the long weekend, peaking on Good Friday.
This is fewer than last year - which travel experts say is due to Easter falling outside school holidays in many parts of the UK, combined with worries over the global credit crunch.
On the railways, more than 30 projects are to be carried out over the Easter holiday, with 6,000 people working around 300,000 man-hours, laying new track, repairing bridges and updating signalling systems.
Passenger groups have said they accept the need for the works but warn it is important that works are not allowed to over-run as they did at New Year, causing major disruption.
Train company Eurostar said it was carrying a record 160,000 travellers through the Channel Tunnel over Easter, an increase of more than 20% on the same period last year.
The RAC said an expected cold snap could add to travel problems over the weekend, with snow and icy conditions forecast for Scotland and some parts of north eastern and eastern England.
If the weather conditions are bad, motorists are advised to only make journeys that are necessary.
If they must travel, they should ensure they carry spare warm clothes, food and drink and keep mobile phones charged in case of emergency.
The rail watchdog Passenger Focus is warning rail users to plan ahead to avoid the disruption.