Drivers will face congested roads while rail passengers will have to contend with disruption on some routes as millions move off on a bank holiday weekend promising to be a mixture of sunshine and showers.
The Highways Agency has completed a number of roadworks and suspended others over the holiday, but works remain on some key routes.
The AA and traffic information company Trafficmaster have predicted that as many as 17 million cars could take to the roads over the weekend, with numbers swelled by a series of sporting events, music festivals and air shows.
Gatwick is expecting 270,000 passengers to fly off from the West Sussex airport over the weekend. The top five destinations are Barcelona and Malaga in Spain, Palma in Majorca, Nice on the French Riviera and Faro in Portugal.
Those staying at home are likely to experience cooler and wetter weather than of late.
Buses will replace trains on a number of rail routes. Work on the West Coast main line will mean reduced services between London and Birmingham New Street/Manchester Piccadilly from 8pm on Saturday to noon on Monday.
Engineering work is also taking place between Liverpool South Parkway and Edge Hill with all lines closed over the weekend..
Routes where buses replace trains include between Twyford in Berkshire and Henley in Oxfordshire, Slough to Reading in Berkshire, Dover Priory to Ramsgate in Kent, between Glasgow Central and Whifflet in Scotland, between Knottingley and Goole in Yorkshire, and between Oxford and Bicester in Oxfordshire.
Among routes with amended services at some times over the weekend are Newport to Cardiff Central, Cardiff Central to Fishguard Harbour, Sheffield to Mexborough/Moorthorpe in Yorkshire, and Falkirk Grahamston to Stirling in Scotland.
Rail industry organisation the Rail Delivery Group said there were 7.7% fewer buses being used compared with the late May bank holiday last year, while 5.4% more services were operating this year.
A spokesman said: "Britain has a fast-growing and increasingly popular railway and work goes on every day of the year to maintain our record as the safest major network in Europe.
"Larger improvement projects are carried out when the network is quieter and this work to deliver faster, more reliable journeys is planned carefully to ensure that the vast majority of passengers will not be disrupted."
Members of the RMT union at Heathrow Express will walk out for 24 hours from 3am tomorrow, and again from the same time on Monday in protest at plans to make £6 million of savings, which the RMT said threatened more than 200 jobs.
Heathrow Express said it planned to run a normal service despite the strikes.
Also, talks were resuming today at conciliation service Acas in a bid to avert a three-day strike from Saturday by RMT power control staff on London Underground.
The Highways Agency said 180 miles of roadworks on England's motorway and major A-road network would be completed by tomorrow, with a further 145 miles of works being suspended until Tuesday.
For safety reasons a number of works will have to remain in place. These include a section of the M1 in Northamptonshire, part of the M40 in Bicester in Oxfordshire, a northern section of the M25 in Hertfordshire and part of the M5 near Gloucester.
The AA and Tr afficmaster said there would be a busier-than-usual evening rush-hour tomorrow and more jams on Saturday.
Areas expected to be particularly busy include:
:: All sections of the M25, especially both ways between junctions 12 and 17 west of London near Heathrow Airport
:: The M1 in Hertfordshire, Bedfordshire and Buckinghamshire
:: The M6 in the Midlands, the M5 in south-west England and the A303 heading west
:: The M4 westbound from west London to Newbury in Berkshire and the section going into Wales
Another traffic information company, Inrix, said journeys that would normally take 60 minutes on a Friday are likely to take 90 minutes tomorrow.
A survey by the RAC showed that Saturday is likely to be the busiest day of the holiday period, with around 3.5 million motorists on the move.
National Express is laying on 10,000 extra seats on coaches over the weekend, with tomorrow expected to be the company's busiest day over the holiday.
London is its most-popular destination, followed by Birmingham, Bristol, Leeds, Manchester and Bournemouth.