Motorists are being warned to expect delays on the roads this festive season despite hundreds of miles of roadworks being removed by 6am Wednesday to ease congestion.
The warning follows what unions labelled a "pre-Christmas fortnight from hell" on the railway networks.
The Rail, Maritime and Transport (RMT) union said Britain's "over-stretched" railways had suffered from signal failures, staff shortages and overcrowding in recent weeks.
Airports were also expected to be busy with an estimated four million people travelling abroad during the Christmas and new year period.
The Association of British Travel Agents said Wednesday and December 30 would be the most popular travel dates.
Meanwhile, an AA poll of more than 29,000 motorists found that 40% would drive at least 20 miles on Wednesday and 36% would cover that distance on Thursday.
The RAC predicted that Christmas Eve would be the busiest day for traffic at 4.1 million journeys as people head to their Christmas destinations with just hours to spare.
Nearly 400 miles of roadworks were removed Wednesday ahead of the rush, but 184 schemes will remain in place during the festive period. There was 219 during the same period last year.
Transport Secretary Patrick McLoughlin said officials were "determined to apply common sense" in a bid to minimise disruption.
Some of the worst routes for congestion are likely to include the Merstham Interchange on the M25 in Surrey, the A4 westbound from Earl's Court to Reading and the M5 southbound from Stroud to Gordano, according to traffic information supplier Inrix.
National Express also said Wednesday would be the most popular day for coach travel.
The operator said it has added an extra 77,000 seats to its capacity over Christmas because of high demand.
Fresh problems on the railway on Wednesday included a fault with the signalling system near Chippenham which caused disruption to Great Western journeys between Bristol Temple Meads and Swindon.
A temporary shortage of train crew again caused disruption to Southern services, with some trains altered or cancelled, which is expected to continue all day.
South West Trains said a tree that fell on to the London-Portsmouth line on Tuesday, causing delays and disruption to its services, was on private land.
RMT general secretary Mick Cash claimed recent problems on the network should fuel demands for the system to be taken back into public ownership.
He added: "The scandal of Britain's privatised, rip-off railways has seen a further round of problems this morning wrap up another blast of chaos for passengers."
Network Rail said 20,000 of its workers would carry out almost 500 improvement projects across Britain over the festive season.
This would see rail links to Britain's two busiest airports severed.
At Heathrow, the normal one-day closure on Christmas Day will be extended by three days due to Crossrail works.
The disruption at Gatwick will last even longer, with the main line serving the airport blocked for 10 days due to engineering works.
On Boxing Day, passengers from central London can travel by train to East Grinstead and then catch a rail replacement bus to the airport, while from Sunday a train will operate direct to the airport via Horsham.
The work to replace a major railway junction at Purley will also cut off direct services from Brighton to the capital.
Passengers travelling to the South West and South Wales will endure extended journey times because of the line closure between Paddington and Slough.
The West Coast main line will be closed between Crewe and Stafford between Friday and Tuesday, while there is also a shutdown on lines from London Liverpool Street to Colchester, Ipswich and Norwich.
NR chief executive, Mark Carne, has said he is ''acutely conscious'' that people want to use the railway over Christmas to see their friends and families.
He added: ''Passengers have shown themselves to be incredibly understanding of planned improvement work and I'd like to thank them in advance for their support and understanding as we deliver the big improvements that the travelling public want to see.''
There was severe disruption last year when engineering work on the lines from King's Cross and Paddington overran, delaying travellers on the first Saturday after Christmas.
Passengers wanting to use the East Coast main line were advised to go to Finsbury Park in north London, which led to serious overcrowding.Suggest a correction