By Peter Woodman
Drivers at the beginning of the summer holiday getaway are being warned of weeks of delays on the roads.
The first major jams will be on Friday July 25, and the five Saturdays that follow, starting July 26 and ending August 23, are expected to be the most-congested days of the summer.
From traffic information company Inrix, the warnings included forecasts that hour-long journeys on Friday could take up to 90 minutes.
Summer traffic worse than rush hour
The company added that drivers could expect every subsequent Saturday up to and including August 23 to be 25% busier, with the busiest Saturday likely to be August 9.
South east and north west England are expected to see the worst of the hold-ups.
"With more cars on the UK's roads, the unwary traveller could face many hours stuck in queues with the potential for missed flights or ferries" said Chris Lambert of Inrix.
He went on: "Summer Saturday traffic can be far busier than even the very worst weekday rush hour, which shows the scale of the problem facing drivers this summer.
"Drivers should plan their journeys carefully and make them at the quietest times of day. "
RAC spokesman Simon Williams said:
"With the length of the summer holidays, we would expect to see motorists hitting the road over a longer period of time, rather than a big rush to get away.
"However the unpredictable British summer weather is likely to be a big influence, and if the sunshine decides to come out, thousands will head to coastal areas to make the most of it."
Holidaymakers drive 1,082 miles on average
Meanwhile, research from Kwik Fit shows that British families will rack up a total of 15.7 billion miles in their own cars during holidays this year.
Motorists using their car for trips will drive an average of 1,082 miles each. The majority of these trips will be within the UK, with 13.2 million cars being used for domestic holidays.
Also, 2.2 million cars will head to France, 550,000 to Germany, 520,000 to Spain and 390,000 to Italy.
For those holidaying in Britain, the most popular places to visit are the south west of England (28%), the south coast (21%), Wales (20%) and Scotland (19%).
The Lake District (16%), Yorkshire Dales (14%) and Midlands (13%) also scored highly.
Motorists in the West Midlands plan to travel the greatest distance in their own cars, with expected average mileage of 1,322 miles.
Welsh drivers plan to stay closer to home with the lowest average distance at 722 miles.