England fans are racing to get home for the World Cup semi-final, making for an earlier rush hour than usual.
The RAC said motorways are busy and traffic will peak at 18:00 BST before the roads become "dead" by kick-off.
Rail travellers say early evening services are "packed", especially as some operators have lifted ticket restrictions on peak-time journeys.
England play Croatia at Moscow's Luzhniki Stadium at 19:00 BST - their first World Cup semi-final in 28 years.
"It's not so much a rush hour as a 'coming home hour'," said Simon Williams of the RAC, who said the heaviest traffic will be between 16:00 and 18:00.
The AA predicted that millions of people will be going home early and, by 19:00, roads will be "much quieter than on Christmas Day".
Edmund King, president of the AA, said: "Historically, the biggest TV events and quietest roads in the UK were during the World Cup final in 1966 followed by the funeral of Diana, Apollo 13, royal weddings and Muhammad Ali's 'Rumble in the Jungle'. This game will join the list.
"Rail commuters may also take earlier trains, perhaps worried about delays or staff shortages due to the match."
Highways England said traffic dropped by about a third when England played Colombia earlier in the tournament, with people travelling home earlier or choosing not to travel at all by working from home or watching the match near work.
The Rail Delivery Group said there was a 25% increase in timetable searches on National Rail for trains between 15:00 and 16:00, compared with a usual Wednesday.
Tube, Waterloo, train all packed - guess all of London has been sent home early for #ENGCRO!— Nicole Wilkins (@FSN_Nicole) July 11, 2018
National Express West Midlands tweeted that congestion "is pretty bad at the moment as many are leaving work early to get home for the football".
Meanwhile, the union for shopworkers, Usdaw, urged employers to be "as flexible as possible" with staff wanting to support England and watch tonight's game.
About 1,000 workers at BMW Mini in Oxford will finish three hours early today, with the firm's press officer Steve Wrelton saying it "felt like the right thing to do".
And Rolls-Royce in Goodwood will suspend all production early to give its employees a chance to watch the game.
And the Asian Catering Federation, which represents the Asian takeaway and restaurant industry, urged any fans wanting a curry to "order your takeaway early".
The British Beer and Pub Association predicts that the number of pints bought will soar by 10 million during tonight's semi-final, and it could bring a boost to the economy of up to £30m.
Chief executive Brigid Simmonds said it was "fantastic news" for the "great British pub".
Many people - including staff at Nunnery Wood High School in Worcester - are embracing so-called "waistcoat Wednesday" in honour of England manager Gareth Southgate.
Others noticed the difference on their morning commute.
British Airways gave free waistcoats to some passengers travelling from London Heathrow to Moscow, along with boarding passes showing a traveller named "football" and the destination "home".
Anticipation is reaching fever pitch, with the possibility that England could reach their first World Cup final since 1966 if they defeat Croatia.
Nearly 20 million television viewers watched England beat Sweden in the quarter-finals on Saturday.
The winners of tonight's game will face France in the final at 16:00 on Sunday.
Hundreds of England supporters have been arranging last-minute trips to Russia after the side booked their semi-final place with a 2-0 win over Sweden on Saturday.
England catches World Cup fever
- Supermarket chains Aldi and Lidl promised to close stores early on Sunday should England make the World Cup final so staff can watch the match
- Wiltshire landmark the White Horse was briefly made into an England flag when fans rolled out red plastic
- According to parenting website ChannelMum.com, two-thirds of parents say the name Gareth could make a comeback for babies
- Confident fans have been getting England football-themed tattoos, with one Doncaster man getting a tattoo of Harry Maguire's face on his chest
- Concerts and comedy gigs have been axed or altered because of the clash with Wednesday's semi-final. Justin Timberlake will screen the game before his concert while All Saints will wait for the game to finish before beginning theirs
- The Duke of Sussex, Prince Harry, has shown his support for the England squad, professing that football is "most definitely" coming home, when asked by a reporter during the royal visit to Dublin. His brother, Prince William said: "A new generation is enjoying the magic of this World Cup run. Come on England - it's coming home"
- The song "Three Lions" looks set to go to number one after a massive spike in streams and downloads
- A Three Lions video celebrating children with Down's syndrome has moved David Baddiel to tears
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