Motoring organisers expect that today will be the busiest day for travel, with numbers expected to peak again at around lunchtime on Christmas Eve.
The festive getaway will bring an estimated extra 2.2 million cars on to the road, and drivers are warned that traffic is likely to be heavy on popular routes such as the M6, M40, M42 and M25.
The traffic is predicted to peak between 10.30am and 4pm today, with drivers advised to travel earlier or later.
Traffic is expected to be relatively quiet on Sunday, before another peak around lunchtime on Christmas Eve.
The AA estimates that a total of 19 millions drivers were on Britain's roads yesterday and as many people began their Christmas travel early.