The last bank holiday weekend of the summer is expected to bring an extra 14 million cars on the road – and rain is forecast to hit many parts of the country.
From Friday to Sunday, rain in the north and west of the UK is expected to bring traffic lanes to a crawl en route to and from popular holiday destinations.
Road and train networks will also face disruption from engineering improvements as well as the weather and extra drivers, with 85 separate sections affected including the M25, M5 and M1.
Train delays are expected on the West Coast mainline, and Network Rail has warned of long journey times between Glasgow and London - meaning two million Britons have opted to fly out of Heathrow for their break instead.
Poor weather in the north and west of the country, including grey cloud, rain and a chilly breeze, will be in contrast to sunnier weather in the south and east on Saturday.
But showers and heavy rain are then expected on Sunday in the south as well, with the one million visitors to Notting Hill in London scheduled a downpour on Sunday before drier weather on Monday.
For those choosing to drive to other destinations, the consumer watchdog Which? has said that at least half face travelling delays.
This is part owing to 55% more cars being on the road than this time last year, as falling oil prices have knocked an average of £9 off the cost of filling up a petrol tank.
RAC spokesman Pete Williams said the group was expecting breakdowns.
"We tend to see an increase in engine related breakdowns at this time of year due to congestion and extended journey times," he told the Daily Mirror.
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