Drivers are being warned to expect severe congestion, with the AA issuing its first “amber traffic warning” for Friday and Saturday.
Congestion is expected to peak between 11am and 3pm on both days.
This is due to a combination of the first switchover days for holiday lets during the school summer holidays in England and Wales, a rail strike, the Commonwealth Games in Birmingham, and the start of the Football League season in England.
Roads approaching Dover and the Eurotunnel terminal at Folkestone are expected to be busy, as well as those serving Devon and Cornwall, such as the M5, A303 and A30.
The south-west and western sections of the M25, the Bristol M4/M5 junction, and the M6, M42, M1 and M62 are also vulnerable to jams this weekend.
Jack Cousens, head of roads policy for the AA, said: “With holiday let switchover day starting on Friday mixed with train strikes and a huge weekend of sport, we are concerned that drivers will experience delays across the network, with the south of England particularly vulnerable.
“All eyes will be on Dover and Folkestone, but we believe changes have been made throughout the week and we will keep our fingers crossed for a smoother trip across the Channel.
“Breakdowns can make jams worse and last weekend we saw a rise in breakdowns where vehicle checks had not been carried out before setting off.
“Spending 10 minutes checking tyres and fluid levels before setting off can make a big difference in helping people getting to their destination.”
RAC traffic spokesman Rod Dennis said: “Analysis of Inrix traffic data shows that long delays are expected on Friday, Saturday and Sunday on the M25 between Bromley and the Dartford Crossing, as well as on the A303 westbound towards Devon.
“Over the weekend, the M5 southbound near Bristol and M25 clockwise between the junctions for the M23 and M40 motorways are also likely to see some lengthy queues.
“Drivers using these routes, as well as those through Kent that may be affected by traffic destined for the port at Dover, should prepare for a longer trip and not rely on the first estimated time of arrival given by their sat-navs.
“Setting off early in the morning is the best way of avoiding the traffic.”
Tens of thousands of families saw the start of their cross-Channel journeys ruined last weekend as the roads approaching Dover were gridlocked, leading to delays of several hours.
This was blamed on a shortage of French border officers and a serious crash on the M20.
The operation was much smoother on Friday morning, with P&O Ferries saying there were “no queues at border controls and traffic is free-flowing through the port”.
Port of Dover chief executive Doug Bannister said on Thursday that French border controls will be “fully resourced”, which will make a “fundamental difference”.
The port expects to welcome around 140,000 passengers, 45,000 cars and 18,000 freight vehicles between Thursday and Sunday.
National Highways, which manages England’s motorways and major A roads, said: “Drivers travelling in and around Kent are advised to plan ahead as this weekend is likely to be extremely busy.
“Operation Brock contraflow remains in place on the M20 and is part of a series of measures to improve Kent’s resilience and ensure the smooth flow of traffic through the region in the event of disruption to services across the English Channel.”