Motorists are being warned of heavy traffic as about nine million vehicles take to the roads over the weekend ahead of a summer getaway.
The RAC predicts 36.5 million "leisure" journeys in the first fortnight of the English and Welsh school holidays.
It said drivers would experience "customary chaos" and warned of traffic hotspots on motorways to popular destinations.
The busiest period is likely to be Saturday between 11:00 and 16:00 BST.
RAC traffic spokesman Rod Dennis said: "This weekend will bring unwelcome customary chaos to Britain's major roads as people flock to take advantage of the first week or two of the summer holidays on home soil.
"While not as busy as Easter, which is typically the pinnacle of leisure traffic due to it being the first break for several months, 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.
"Sadly, for many 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."
A new stretch of dual carriageway on the A30 west of Temple should provide some relief for drivers heading to Cornwall, he said.
Predicted traffic hotspots
• 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 M6 and the coast
• M53 between Liverpool and Chester
Source: RAC Traffic Watch
There are hundreds of roadworks planned for the weekend on motorway and major trunk roads where the delay to journeys is expected to be more than 30 minutes, with many of them taking place overnight.
Highways England will not be lifting roadworks for the weekend. It only does so when a getaway coincides with a bank holiday, such as at Christmas or Easter.
Work with warnings of "severe" disruption include:
- The M6 at J6 (Spaghetti Junction), Birmingham - exit slip roads are closed for repair over the weekend
- The M3 westbound entry slip at junction 2 will be closed from 22:30 on Sunday until 05:30 on Monday. It has its hard shoulder and third lane closed as well as work on the junction 4 slip road
- The M5 northbound entry slip at J3, near Frankley - lanes one and two will be closed overnight during the weekend
- The M62 eastbound exit slip road at J20, near Castleton - closed from 20:00 on Saturday until 05:00 on Monday
Highways England chief executive Jim O'Sullivan 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."
Figures from the organisation revealed 22 drivers a day broke down last July and August because they had run out of fuel.
The RAC's figures are based on the travel plans of 3,100 motorists, with 36.5 million leisure journeys expected between Friday 21 July and Sunday 6 August.