Millions of families are embarking on summer holidays as schools across the UK break for the season.
Travel volumes have reached the second-highest level since tracking began in 2016, exceeded only by 2022's post-lockdown surge of 18.8 million trips.
The majority of students in England and Wales finish for the six-week break this month, while schools in Scotland and Northern Ireland have already closed.
Staycations have grown steadily in popularity, with the south-west and north-west of England expected to see the heaviest leisure traffic.
Transport analysts identified likely congestion hotspots including the M1 southbound from Northampton to Watford and both directions of the M25 between several key junctions.
RAC representatives urged drivers to plan journeys around peak times, suggesting earlier or later departures to avoid jams.
Travellers were advised to prepare for delays in hot weather by carrying water, sun cream, and umbrellas for shade.
The Port of Dover recorded approximately 7,500 outbound cars on Friday and 10,000 today, with wait times near 32 minutes in the buffer zone.
Port operators reported building queues at check-ins, though approaches remained clear and traffic flowed well.
Ferry passengers were instructed not to arrive more than two hours before departure after wait times reached an hour the previous day.
Port executives said they had prepared extensively for the influx despite concerns over delays from new EU border checks.
The port's chief executive criticised the unused Entry/Exit System facility, built under a £40m investment, because the technology had not been activated for cars.
During the May half-term, the port declared a critical incident when waits reached four and a half hours with around 8,500 outbound vehicles.
The Entry/Exit System launched in April, registering fingerprints and photographs for entry to the Schengen Area across 29 European countries.
For most UK travellers, processing occurs at foreign airports, but it is also carried out at Dover, Eurotunnel's Folkestone terminal, and London St Pancras.
The automated system is designed to strengthen border security by registering non-EU travellers each time they cross an external border.
