Transport analytics company Inrix warned the worst times for traffic jams are likely to be between 10am and 6pm on Friday, and between 10am and 1pm on Saturday.
Network Rail will carry out a number of major engineering projects, which will affect three intercity lines serving London.
Airports will see one of their busiest weekends of the year, with the industry hoping for no repeat of the outage by air traffic control company Nats, which grounded flights on last year’s August bank holiday Monday.
The RAC estimated that 19.2 million leisure trips by car will be made across the UK between Friday and Monday.
The figure, based on a survey of 2,128 UK adults, is the highest since the motoring services company began recording data for the summer bank holiday in 2015.
Friday is likely to be the busiest day on the roads, the AA said, due to the combination of getaway journeys and regular commutes.
National Highways, which manages motorways and major A roads in England, said it will lift more than 500 miles of roadworks by 6am on Friday until Tuesday to “keep people moving”.
It issued an alert for the M56 and M6 in north-west England as up to 70,000 dance music fans head to the four-day Creamfields festival in Cheshire, which starts on Thursday.
Thousands of drivers were stuck for several hours in queues during the event last year.
Motorists are being urged to follow dedicated signs to the site and not rely on sat navs, which could put vehicles on “unsuitable, narrow roads”, National Highways said.
Extra police and traffic officers will be deployed around junction 11 of the M56 at Daresbury to deter festival-goers from walking on the motorway, which has happened during previous years, particularly following the end of the event.
Roads in Kent will also be busy as many people head to Europe via the ports.
The Port of Dover expects to be used by more than 20,000 cars over the bank holiday period.
Network Rail engineering work means no long-distance services on the East Coast Main Line will run to or from London King’s Cross from early evening on Saturday until early morning on Monday.
This will affect people travelling south returning from the Edinburgh Fringe Festival.
A reduced timetable will be in place between London Euston and Milton Keynes on Saturday and Sunday due to track renewals at Primrose Hill.
Journeys between London Paddington and south Wales will be diverted – taking longer than normal – as engineering work will close the line between Bristol Parkway and Severn Tunnel Junction.
Services will also be disrupted in the Stoke area from Saturday until Tuesday.
Travel trade organisation Abta estimated that more than two million people will be heading overseas between Friday and Monday, with Friday expected to be the busiest day for departures.
Popular destinations include beach resorts in Spain, Portugal, Greece and Turkey, with many people heading on city breaks to Dublin, Amsterdam, Paris, Barcelona and Milan.
Regulator the Civil Aviation Authority (CAA) will issue new videos on its social media channels outlining passengers’ rights when flights are delayed or cancelled.
This includes food and drink, overnight accommodation, refunds and rebooking options.
CAA data shows 160,000 flights were delayed and 8,000 were cancelled across UK airports in July and August last year.
