UK drivers are embarking on an estimated 20million car journeys to see friends and family as Christmas Day approaches.
The RAC said leisure traffic would increase steadily from Monday before peaking on Friday and Saturday, which is Christmas Eve.
Pressure on the roads will be increased due to a strike by thousands of Railway, Maritime and Transport (RMT) union members at Network Rail from 6pm on Christmas Eve.
Train passengers are advised to travel from lunchtime on this day, meaning many people will opt to travel by car or coach instead.
The RAC has predicted that 7.9 million getaway trips will be made in the two days immediately preceding Christmas Day.
The worst traffic on these days is expected to be between 10 a.m. and 7 p.m. on Friday, and between noon and 1 p.m. on Saturday.
Total traffic volumes will be much higher ahead of the weekend as drivers heading away for the holiday season compete for road space with commuters and everyday motorists.
This is likely to cause traffic jams in cities and on major roads.
Transport analytics firm Inrix expects journey times to be around 14% longer compared to the same period last year.
Roads likely to be hit by congestion this week include the M25, the M60 near Manchester, the M6 in the North West of England and the M40 in Oxfordshire.
National Highways said it will ensure nearly 98% of England’s motorways and major A roads are fully open from 6am on Tuesday until the end of January 2 by completing or lifting roadworks.
RAC spokesman Rod Dennis said: “Our research suggests that getaway traffic will increase steadily throughout the week, culminating in two frantic days of travel just before Christmas itself.
“By Friday, we fear it will be a case of traffic jams today and traffic jams tomorrow on the roads as millions of people jump behind the wheel to see family and friends – with the purchases of Last minute Christmas as well as the impact of another rail strike also resulting in increased traffic.
“If possible, drivers should try to take their journeys on a calmer day earlier this week if they can.”
The RAC traffic estimates are based on a survey of 1,886 UK adults last week.
The AA, which issued an ‘orange traffic warning’ for Friday and Saturday, urged motorists to carry out car checks such as fuel, oil, coolant and screen wash levels , and make sure the tires are properly inflated.
Company traffic policy manager Jack Cousens said: ‘Breakdowns make traffic jams worse, so if everyone spent 10 minutes checking their car before leaving, it could save everyone hours on their way.”