Families embarking on summer getaways are being hit by traffic jams and delays.
National Highways closed part of the Dartford Crossing because of a crash on Friday, causing long tailbacks.
The location is where the M25 – the UK’s busiest motorway – crosses the River Thames east of London between Dartford and Thurrock.
The smash forced the closure of one of the crossing’s two tunnels, which are used for northbound traffic, shortly before 7am.
The tunnel was later reopened but National Highways said the incident caused five miles of congestion, with traffic stretching back to Junction 3 for Swanley.
An estimated 12.6 million car journeys will be made for a day trip or holiday between Friday and Monday as the majority of schools in England and Wales finish for the summer, the RAC said.
National Highways said traffic was held on the northbound carriageway of the M6 from Junction 16 (Crewe) and Junction 17 (Sandbach) due to a crash involving a lorry.
All lanes had reopened by 11.30am, but shortly before 10.30am there were about four miles of congestion and delays to journeys of about half an hour.
Other traffic hotspots included the M5 south from near Bristol (junction 15) to Bridgwater (junction 23), which is a popular route for holidaymakers travelling to the South West.
Another was the M25 clockwise between junction 10 for the A3 to Kingston and junction 6 for the A22 to East Grinstead.
Travel trade organisation Abta said more than two million UK holidaymakers will head overseas this weekend.
The Port of Dover said shortly after 6am it was taking about 90 minutes for departing passengers to pass through border checks.
It said it was “an extremely popular travel day” and traffic was “moving according to plan”.
Processing times were cut to just 20 minutes by 9.45am but rose to 45-50 minutes at 10.50am.
Waiting times rose again in the evening and were up to 90 minutes by 7.30pm.
By 8.23pm some 26,784 passengers had sailed from the Kent port to France.
Enhanced post-Brexit passport checks by French border officials Police Aux Frontieres have significantly increased processing times at the port.
Ferry operator DFDS said it is operating additional sailings to meet demand this weekend.
Hundreds of thousands of passengers are travelling through Heathrow and Gatwick airports over the coming days.
Abta said about 200,000 people will depart from Manchester airport and 71,000 from Bristol.
Schools in Scotland are already well into their summer holidays but many people will still be flying from Scottish airports this weekend, with more than 100,000 from Glasgow alone.
We’re encouraging people to have a fun and safe holiday by taking sensible precautions if you’re heading to an area with exceptionally high temperatures and taking particular care when in the water and on balconies— Mark Tanzer, Abta chief executive
Spain remains the top destination for families, in particular the Costa del Sol and the Balearic and Canary Islands, but Abta members are also reporting strong demand for Bulgaria, Portugal, Turkey, Morocco and Greece, the travel association added.
Airline Jet2.com and sister company Jet2holidays said this weekend would be the busiest in their history, with more than 800 flights taking hundreds of thousands of customers to and from holidays.
The Met Office has warned of disruption as downpours begin on Saturday, with a risk of thunderstorms on Sunday.
Meanwhile, much of Europe will continue to see temperatures in the high 30s and low 40s.
Mark Tanzer, Abta chief executive, said: “Thousands of families will be jetting off this weekend as the majority of schools in the UK start their summer break.
“Many of these will be taking their first overseas summer holiday since the pandemic, returning to much-loved destinations, and will have a fantastic experience in store.
“We’re encouraging people to have a fun and safe holiday by taking sensible precautions if you’re heading to an area with exceptionally high temperatures and taking particular care when in the water and on balconies.”
Rail passengers will be disrupted by strikes on Saturday as members of the Rail, Maritime and Transport union (RMT), including station staff and train managers, strike again in a long-running dispute over pay, jobs and conditions.
