Drivers are being warned to prepare for long queues as millions of people embark on journeys to spend Christmas with friends and family.
The AA said Friday will be the busiest day on the roads this week, with an estimated 16.9 million journeys being made across the UK.
A further 16.6 million journeys are expected to be made on Christmas Eve.
Congestion will be increased due to a strike by thousands of members of the Rail, Maritime and Transport union (RMT) at Network Rail causing train services to finish at around 3pm on Saturday.
The RAC said roads will be busiest on Friday – the last working day before Christmas – between 10am and 7pm.
Transport analytics company Inrix expects journey times to be around 14% longer compared with the same period last year.
Roads likely to be hit by congestion include the M25, the M60 near Manchester, the M6 in north-west England and the M40 in Oxfordshire.
National Highways said almost 98% of England’s motorways and major A-roads will be fully open until the end of January 2 due to it completing and lifting roadworks.
AA head of roads policy Jack Cousens said: “We are advising those heading out in their cars to be prepared for some congestion, especially on popular routes heading out of London.
“The rail strikes have convinced more people to travel by car this year, and while hundreds of miles of roadworks have been removed to ease the pain, it might not be enough to keep the queues away.”
RAC spokesman Rod Dennis said there will be “two frantic days of travelling just before Christmas”.
Inrix transportation analyst Bob Pishue said: “With pre-pandemic levels of travellers hitting the road this holiday, drivers must be prepared for delays – especially in and around major cities.”