Drivers hoping to get to the continent via the port of Dover in Kent are facing delays of up to three hours as the bank holiday getaway begins.
In a post on X, port officials, who have warned of delays as they deal with 18,000 travellers between Friday and Sunday, said there is currently "a 150-180 minute processing time for tourist traffic in the Buffer Zone".
While check-in was described as "free-flowing", it warned of "significant congestion" on approach roads.
Heavy traffic is expected on roads to popular tourist destinations, with the AA forecasting 23.4 million car journeys will take place on Friday.
Routes heading towards east coast destinations such as Skegness, the M4 from London towards Wales, and the M6 towards the northwest coast are among the likely blackspots.
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The RAC expects leisure traffic to peak on Friday and Saturday.
In addition, strike action and engineering works will cause disruption on a number of railway routes.
Walkouts by members of the Transport Salaried Staffs' Association on Friday and Saturday in a pay dispute will affect West Midlands Railway (WMR) and London Northwestern Railway services, with timetables on both networks slashed on both days.
Key intercity lines will be shut because of Network Rail engineering works and the East Coast Main Line will be closed between York and Darlington from Saturday through to Monday.
Buses will replace trains between Newport and Bristol Parkway from Saturday for two weeks.
There will be no Thameslink services through central London between Saturday and Monday, affecting services to Gatwick and Luton airports.
Families will be heading off on holiday this weekend as it marks the start of half-term breaks for many schools, Abta, the travel trade organisation, said.
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Mainland Spain, Italy, the Balearic and Canary Islands, and Portugal are among the most sought-after destinations, as well as city breaks in Milan, Nice and Barcelona.
Saturday is likely to be the busiest day of the long weekend at coastal towns and cities such as Bournemouth, Hastings and Torquay, parking app company RingGo said, based on recent bank holiday periods.
It said seaside towns are "consistently outperforming inland locations" during bank holidays in terms of the number of parking sessions recorded.
The Met Office has forecast a heatwave in some parts this weekend.
Temperatures are set to peak on Monday when 33C could be recorded in southern England and the Midlands.
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