Journey times over the Christmas period will be 14% longer than last year as almost 20 million trips are made by motorists this week.

Predictions from the RAC and INRIX suggest 40% of all journeys will take place between December 23-24 as a largescale walkout from rail workers leads to more traffic on the roads.

The AA has also issued a traffic warning for the two days and is predicting traffic to build between 10.00 and 18.00 on Friday, while the main congestion on Saturday could be felt between 10.00 and 16.00.

Interchanges connecting the M25 with the M3, M4, M1, M11, M20 and A1(M) are forecast to experience delays over the two-day period.

In the north, delays are expected to be felt in Cumbria on the M6 interchange with the A69, M62/M60 junctions around Manchester, the A64 between Leeds and York and the M8 surrounding Edinburgh.

The M4/M5 interchange at Bristol is likely to experience heavy congestion throughout the period as well as the M5 at Exeter, while delays are predicted to take place on the M6 Birmingham area and the M11/A14 junction north of Cambridge.

Christmas Day itself is also expected to see a lot of people on the move, with an estimated 3.6m leisure journeys by car taken, with a further 3.3m on Boxing Day and an extra 1.4m trips across both days – but with no commuter traffic on the roads, overall traffic volumes should be lower, meaning serious delays are less likely.

Transport analytics specialists INRIX expects travel times to be around 14% longer compared to the same period last year with stretches of the M25, M60 near Manchester, M6 in the north-west and M40 in Oxfordshire seeing some of the longest jams.

RAC Breakdown spokesman Rod Dennis said: “Our research suggests getaway traffic will build steadily all week, culminating in two frantic days of travelling just before Christmas itself. By Friday, we fear it will be a case of ‘jams today and jams tomorrow’ on the roads as millions of people jump behind the wheel to see family and friends – with last-minute Christmas shoppers as well as the impact of another rail strike also leading to an increase in traffic. If possible, drivers should try to make their trips on a quieter day earlier this week if they possibly can.”

Jack Cousens, head of roads policy for the AA, added: “During the recent snow and icy weather, we attended numerous breakdowns which could have been avoided completely had their car been checked before leaving. While tyres and oil levels are common items to tick off the list, ensuring screen wash isn’t frozen and wiper blades are in good condition are just as vital, especially with more grit and dirt being kicked up off the road.

“Breakdowns add to traffic jams, so if everyone spent 10 minutes checking their car before leaving it could save everyone hours on their journey.”