Britain is being told to expect the busiest time of the festive period on the roads.
Some 18m cars are expected on the roads during Friday, with 16m likely on what are set to be the second busiest days, 27 and 28 December.
Rail travellers are facing severe problems because the West Coast Mainline is closing for five days.
UK airport workers have voted for industrial action, which will be taking place on 7, 14 and 17 January.
The dispute with BAA, which operates seven UK airports including Heathrow and Gatwick, is over the closure of final salary pensions to new employees.
A record 3.5m Britons will head abroad for Christmas.
Christmas Day should be much quieter on UK roads, with only 4m cars being driven.
The Highways Agency is suspending roadworks on several motorways and major A-roads in England over the holiday period, but roadworks remain on some key routes, including the M1 and M25.
Adam Cracknell of the RAC said there would be a high volume of traffic on the roads on the 27 and 28 December because of the post-Christmas sales.
"On those days people will be going back to work but they'll also be going sale shopping, so before noon there will be a lot of congestion on the nation's roads, but that shouldn't be as bad in the afternoon and evening.
"People tend to spend more time with the family on Boxing Day, but after that the bargain mist comes down."
Rail disruption
Kevin Groves, of Network Rail, said rail travellers on the West Coast Mainline will experience disruption because the company had "made a mistake" and under-estimated the amount of work being planned over the Christmas break.
As a result, engineering work beginning on 27 December will now last until New Year's Eve, a day later than originally planned.
The work will mean the closure of the West Coast Mainline, which affects any services that would have passed through Rugby, disrupting travel between London and Scotland, Manchester and Birmingham.
This is always a peak time for travel as people make the most of the bank holidays, and once again there are a record number travelling
Justin Fleming, Abta
Airport workers to strike
These are mostly Virgin Train's services, but the closure also affects some London Midland and First ScotRail Sleeper services.
Alternative services will be provided either by other train operating companies or replacement coaches.
"It's completely our fault. We under-estimated the amount of time we needed," said Mr Groves.
"There are alternative routes from Scotland, from Manchester, from Birmingham that go into different stations in London, that are completely unaffected by engineering works."
Mr Groves also said the busiest remaining times for rail travel would be Friday and Saturday.
The Association of Train Operating Companies (Atoc) said up to 4m passengers, about one million more than a typical weekday, are expected to take the train on Friday, and Saturday is also predicted to be busy.
George Muir, its director general, said: "Christmas Day falls this year on a Tuesday and with more and more people taking two weeks off, we are expecting many passengers to travel on the Friday and Saturday before Christmas.
"We strongly advise people to book ahead and reserve seats wherever possible."
A spokeswoman for the Met Office said conditions on the roads would be "tricky" on Saturday morning.
"We can expect a frost on Friday night in southern England and quite a sharp frost over south-east England and East Anglia by Saturday morning.
"Northern England and Scotland has the biggest potential for travel problems. There is a risk of ice, mostly over Scotland, with snow over mountains in Grampian.
"That risk continues through the higher ground in northern England, places such as Lancashire, North Yorkshire, Cumbria, Northumberland and Durham.
"Those icy conditions will last during Saturday morning and could cause problems for Scottish airports in Glasgow, Aberdeen and Edinburgh."
Steve Crosthwaite, head of the National Traffic Control Centre, said patchy fog was possible in many areas on Saturday morning, as well as freezing rain in the West from Birmingham to the Scottish Borders.
Foreign destinations
Temperatures are expected to rise on Sunday, with only a light frost in England and Wales and rain and wind in Scotland.
For those heading abroad, top city-break destinations include Paris, Amsterdam, Dublin and New York, according to the Association of British Travel Agents (Abta).
The Canary Islands, Egypt, Goa and Dubai are also proving popular among travellers this year. Abta also said the busiest day for overseas travel will be Saturday, followed by 30 December when people head for New Year's Eve celebrations abroad.
A total of 1.2m passengers are expected to leave from London's Heathrow airport between Friday and 2 January.
Abta president Justin Fleming said: "This is always a peak time for travel as people make the most of the bank holidays, and once again there are a record number travelling." (BBC NEWS)
