Drivers are being warned to expect "significant congestion on major roads" when the Christmas getaway starts this week.
An estimated 20 million leisure journeys will be made in the UK in the run-up to Christmas Day, according to traffic experts.
The anticipated jams will be compounded by extensive disruption to the rail network, with planned engineering work and strikes forcing more people on to the roads.
Strikes are likely to affect routes run by Northern Rail and South Western Railway, while Network Rail is planning engineering work on lines running into major stations such as London Paddington and London Victoria.
Research by the RAC and traffic information firm Inrix suggests road traffic will be staggered over the coming days, reaching a peak towards the weekend.
Thursday and Friday are expected to be the worst days for congestion, with 2.5 million and 2.8 million vehicles respectively making leisure trips while battling for road space with regular commuters.
On Thursday, delays of up to three hours are expected on one section of the northbound M6, while on Friday part of the southbound M40 could see drivers queuing for over 90 minutes.
Drivers are being advised to use alternative routes or wait until 8pm before setting off to avoid the worst queues.
Inrix data scientist Joshua Kidd said: "Our data shows that compared to a normal day, Thursday 20th December will see the biggest increase in cars on the road.
"With most drivers setting out mid-morning, traffic will become heavier over the course of the afternoon and stay congested into the evening.
"But it's not just those off to see family and friends – commuters, last-ditch shoppers and online deliveries will contribute to clogging the roads.
"Drivers are advised to seek out alternative routes to their destinations and use the latest technology for real-time updates."
Highways England will lift more than 200 miles of roadworks on the country's motorways and major A-roads by 6am on Friday to ensure more than 97% of the network is open for the getaway.
Where will the worst queues be during the getaway?
:: Wednesday 19 December (2.8 million leisure trips)
Worst time to travel: 3pm to 6.30pm
Best time to travel: After 7.30pm
Worst road for delays: M25 clockwise from J20 to J28 from 3.30pm. Up to 80-minute delay
:: Thursday 20 December (2.5 million trips)
Worst time to travel: 11.30am to 6.30pm
Best time to travel: After 8pm
Worst road for delays: M6 north J15 to J25 from 12.30pm. Up to 181-minute delay
:: Friday 21 December (2.8 million trips)
Worst time to travel: 11.30am to 6.30pm
Best time to travel: After 7.30pm
Worst road for delays: M40 south from M42 (Warwickshire) to J8A (Oxford). Up to 110-minute delay
:: Saturday 22 December (2.2 million trips)
Worst time to travel: 10.30am to 4pm
Best time to travel: Before 9.30am or after 7.30pm
Worst road for delays: M40 north from J8A (Oxford) to M42 (Warwickshire). Up to 61-minute delay.
More from UK
:: Sunday 23 December (1.9 million trips)
Worst time to travel: 4pm to 6.30pm
Best time to travel: Before 11am or after 8pm
Worst road for delays: N/A
:: Monday 24 December (2.5 million trips)
Worst time to travel: 11am to 1pm
Best time to travel: At other times
Worst road for delays: M1 north J21 (Coventry/Leicester) to J26 (Nottingham/Ripley). Up to 22-minute delay.
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