Motorists are being warned to expect delays this weekend as almost nine million vehicles embark on the start of the summer getaway.
The RAC predicted that a total of 37 million leisure trips will be made over the first two weeks of the school holidays.
Saturday will be the busiest day of the weekend for UK getaway traffic with 3.4 million journeys being made.
But congestion could reach a peak on Friday as 2.5 million cars making an early dash for a break vie for space with regular commuters.
On Sunday 2.8 million vehicles are expected to be en route to their holiday destinations or making a day trip.
The worst times to travel are anticipated to be:
:: Friday between 1pm and 8pm
:: Saturday between 11am and 4pm
:: Sunday between 11am and 4pm
The figures are based on analysis of the travel plans of 3,176 motorists.
RAC traffic spokesman Rod Dennis warned that drivers will face "customary chaos" this weekend.
"The very much-needed family summer holiday might begin stressfully as long tailbacks are inevitable, particularly in the South West on the M5 which is the main conduit to the beaches of Devon and Cornwall," he said.
"The Great British summer holiday getaway begins with an initial rush for the roads this weekend as that's when the majority of schools break up.
"But unlike any other time of year, the country's major tourist routes will remain steadily busy through the rest of the six weeks."
Mr Dennis advised drivers to travel very early in the morning or late in the evening, but accepted this will not be possible for many people.
"If you are one vehicle in the 3.4 million making a leisure journey on Saturday, a healthy dose of patience is going to be required," he added.
The RAC predicted that congestion hotspots will include:
:: M5 Almondsbury Interchange and from Bristol to Taunton
:: A30 and A38 Exeter to Cornwall
:: A303 Andover to Ilminster
:: M4 between Cardiff and Swansea
:: M25 between Gatwick and M1
:: A23/M23 to Brighton
:: A34 and M3 south and south-west to the south coast
:: A47 Swaffham to Great Yarmouth
:: A11 Thetford to Norwich
:: M55 between Preston and Blackpool
:: A14 between the Midlands and the east coast
:: A590/A591 between the M6 and the Lake District
:: A66 between the M6 and the coast
:: M53 between Liverpool and Chester
More than 200 sets of roadworks expected to cause delays of at least half an hour are planned by Highways England on motorways and major A-roads. Much of the work will take place overnight to minimise disruption.
The organisation's chief executive Jim O'Sullivan advised drivers to check their vehicles to avoid basic mechanical problems.
He said: "I want all drivers to arrive at their destinations safely during the summer holidays. We are urging motorists to make sure they are ready to go on their journeys by checking their fuel, tyres and oil. With a few simple checks everyone will be safer."