Drivers were facing the worst of the Easter traffic on Thursday evening as people getting away for the holiday break competed with regular commuters.
According to transport data supplier Inrix, traffic would be 28% above typical Thursday afternoon levels but could be normal by the evening.
Earlier a crash involving a car and lorry on the M25 forced traffic to be held, leading to lengthy jams.
About 20 million car journeys will be made between Thursday and Monday.
A further two million Britons are planning to head overseas over Easter, says travel trade organisation Abta, which says Good Friday will be the busiest day for travel.
Tourism body Visit England, meanwhile, says 6.6 million Britons are planning a trip involving an overnight stay over the weekend, up from six million last year.
Highways England is advising drivers to allow extra time for their journeys or consider alternative routes.
Will it be sunny?
If you're lucky. BBC Weather is forecasting cloud and outbreaks of rain in the west of the UK on Good Friday. That will slowly spread south-eastwards. Brighter, cooler, windier weather with showers is forecast for Scotland, and it may even feel wintry on the highest ground.
The sun should make an appearance between Saturday and Monday, alongside showers and perhaps longer spells of rain in the north and east of England, where it will be breezy and cool. The south and west of England should be dry with sunshine and feel warm, according to BBC Weather.
On the roads
Don't expect to get anywhere fast. Journeys on major motorways could take three times as long as normal, Inrix says.
Drivers between junctions 9 and 21 on the M25 should expect delays of up to 90 minutes - meaning a typical 40-minute journey could take more than two hours, it says.
Motorists heading in both directions on the M6 and southbound on the M5 towards the West Country should also prepare for hold-ups of almost an hour, according to the data supplier's report.
Easter Sunday is expected to be the quietest day on the roads with 25% fewer vehicles than an average Sunday.
On the trains
The Bank Holidays mean it's Network Rail's favourite time to crack on with engineering projects so don't expect a straightforward journey.
Trains to London, Manchester, Bath, Edinburgh and Glasgow are among those affected.
Network Rail said it is carrying out more than 200 engineering projects over the four-day weekend because fewer passengers use the railways then.
The cross-Channel rail operator, Eurostar, is expecting its busiest ever Easter weekend with 163,000 passengers, up 12% on last year.
In the skies
Airports are busy, with 425,000 passengers jetting off from Heathrow, 250,000 from Gatwick, 153,000 from Stansted and 150,000 from Manchester.
Disgruntled passengers took to social media earlier to complain about long queues at passport control.
Grant Lipton at Heathrow wrote on Twitter earlier: "Huge queues at passport control. Over 45 minutes so far with no end in site (sic)."
But it is not all bad news as Sarah Kelly described. She tweeted from Gatwick Airport on Thursday night: "With the most passengers I've ever seen it's been the quickest queue time."
Spain is the UK's favourite foreign holiday destination for the weekend, with temperatures set to reach 27C (81F) on the Costa del Sol.
A Heathrow spokeswoman said the most popular destinations were New York, Dubai and Dublin.
Are you travelling over the Easter weekend? How are you planning to avoid disruption? Let us know how your journey goes by emailing email@example.com.
Please include a contact number if you are willing to speak to a BBC journalist. You can also contact us in the following ways: