Drivers are being warned to expect long delays as millions of Britons set off on Easter getaway trips.
Transport analysis company Inrix predicted Thursday afternoon will see the worst congestion.
Meanwhile, airports and airlines expect numbers over the bank holiday weekend and school holidays to return to pre-pandemic levels.
And rail passengers are advised to plan ahead because of engineering works.
Meanwhile, while everywhere in the UK will see spells of dry and fairly sunny weather, low pressure is expected to mean clouds and downpours, with snow already falling in Devon.
Sunshine or showers for Easter?
Motoring company RAC warned journeys on popular routes could take twice as long as the bank holiday weekend coincides with the start of the Easter holidays.
A survey by RAC and Inrix suggested 14 million Easter getaway trips are expected to be
made.
"With Easter falling earlier than usual at the start of the school holidays, it could be carmageddon for holidaymakers," an RAC breakdown spokesperson said.
In particular, journeys on the M25, between the M23 for Gatwick the M1 in Hertfordshire, are expected to take over two hours - twice the usual time.
The M5 southbound between Bristol and Taunton is also likely to be congested.
Meanwhile, tourist board Visit England said 11 million people in the UK are planning an overnight trip this Easter.
Airports and airlines are expecting big numbers, in some cases above 2019 levels.
Manchester Airport said it was preparing for about 320,000 passengers this weekend, 8% more than the equivalent last year.
Glasgow Airport said it would have extra staff in place during "three exceptionally busy weekends ahead".
Low-cost airline Easyjet is predicting its busiest ever Easter weekend.
What about train travel?
Network Rail is urging people to check their journey details before they travel.
There will be disruption on some rail routes over the bank holiday as some major routes close due to engineering work.
London Euston, one of the UK's busiest railway stations, will be closed between Good Friday and Easter Monday - except for London Overground trains.
It is because Network Rail engineering works between London and Milton Keynes will close part of the West Coast Main Line.
There will be replacement buses on this stretch. Avanti West Coast will operate a revised service on its network.
There is more information about other changes to train services around the country on the National Rail website.
Tighter checks at Dover
French authorities at Dover have stepped up border monitoring following the Moscow concert hall attack. Drivers are being advised to plan ahead and leave extra time.
Around 20,000 cars are expected to travel through the port between Thursday and Easter Sunday.
People heading to the Channel Tunnel at the Port of Dover will find the traffic management system Operation Brock in place on the M20.
At peak times over the next few days, Dover has told coach operators that even with the right resources in place at the border, wait times could be up to 2.5 hours.
Eurotunnel told the BBC it was putting on extra shuttles and staff to cope with expected high numbers.
How is the weather looking?
The Easter break is likely to begin with some less-than-preferable weather before calming down through the weekend, says BBC Weather presenter Chris Fawkes.
Overnight rain turned to snow in parts of southwest England and Wales, giving a wintry start to Thursday.
By Good Friday, he says, the UK is set to see a mix of sunshine and showers with the potential for some heavy rain and hail, though temperatures will remain close to average.
Throughout Saturday and Sunday, some showers are expected, though these are unlikely to be as widespread, and slightly warmer temperatures will mean pockets of sunshine will feel quite pleasant.
By Monday, he says wet and windy weather is likely to lash England and Wales, but Scotland and Northern Ireland look to remain pleasant with sunny spells.