An amber traffic warning has been issued for this weekend, when there are an estimated 15 million holiday leisure trips.
The AA issued the alert, which is only the second such warning issued by the motoring association, because it expects 45% of UK drivers to embark on at least one non-travel journey between Friday and Monday
Families returning from summer holidays before the start of the new school year will be jostling for space on the road alongside festival-goers and day-trippers.
Events taking place this weekend include the Reading and Leeds festivals, CarFest South in Hampshire, the closing weekend of the Edinburgh festival, a full schedule of football matches and an England v South cricket match Africa in Manchester.
The AA predicts that leisure traffic will peak on Saturday between 10am and 4pm.
Planned transit points include the M4/M5 interchange near Bristol; the M1 between the M25 and Newport Pagnell, Buckinghamshire; the M6/M42 interchange in Birmingham; and the M62 between Liverpool and Manchester.
Monday is a bank holiday throughout the UK, except Scotland, and is the last bank holiday of the summer.
Sean Sidley, who was named AA Patrolman of the Year, said: “This year we expect up to 15 million journeys will be made over the August Bank Holiday as families make the most of the warm weather and they have one last chorus before the new school year.
“With events and festivals returning to normal, localized congestion will peak at closing time in major locations, but the rest of the UK could see a peak in travel on Saturday.
“Traffic is likely to pick up again from Monday afternoon and into Tuesday, so allow plenty of time if you’re traveling then.
“Routes there from coastal resorts and beauty spots will be the busiest, so drivers should plan their journey in advance and check their car before setting off.”
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Train service on some routes will be disrupted this weekend due to engineering work.
Network Rail said £90m worth of upgrades would be carried out, but stressed that 95% of the lines would remain open.
There will be a reduced timetable between Northampton/Milton Keynes and London Euston due to HS2 work between Saturday and Monday.
Projects to rebuild the junctions mean there will be no trains to London Charing Cross or Cannon Street stations on Saturday or Sunday, with a limited service from Hastings/Tonbridge to London Bridge on both days.
London Bridge and Cannon Street will be fully reopened on Monday, while Charing Cross will remain closed until the following day.
Services between London Waterloo and Reading will be altered and diverted over the three-day weekend due to the resignation work.
There will be no Great Northern or Thameslink trains between Finsbury Park and Stevenage via Welwyn Garden City on Sunday, and trains from Grand Central will be diverted with longer journey times.
The disruption will come as a further blow to commuters who have been hit repeatedly by rail strikes in recent weeks.
Andrew Haines, chief executive of Network Rail, said: “I’m pleased to say that the vast majority of rail will be open for business as usual this bank holiday, so passengers can trust us to get them where they need to go .as they make the most of their summers.
“Our crews will be carrying out some upgrade works to improve future journeys for passengers, so we would ask people to check this before they travel and make sure their route is not affected.”