The AA has warned that 70% of drivers fail to make basic checks on their cars before a journey, as the Easter Bank Holiday exodus continues.
EASTER TRAVEL HOTSPOTS
Heavy holiday traffic
M1: J21-J26 northbound
M4: Westbound from London
M5: Southbound from Bristol; northbound through Midlands
M6: West Midlands, Liverpool and Manchester
M25: J15 and J16 near Heathrow; J20 and 21
M1: Contraflow J81J10
M6: Southbound onto M5; contraflow J12-J13
M25: Holmesdale Tunnel
The motoring organisation says drivers lack the knowledge to perform simple tasks like oil and water checks.
About 18m cars are expected to travel over Easter and many will breakdown needlessly, the AA said.
Airports will also be busy, with a record 2.5m Britons planning to spend the long weekend abroad.
Heathrow dealt with 212,000 passengers on Thursday, making it the airport's busiest day of the holiday period.
The airport operator BAA said it was also expecting 600,000 people to travel from Gatwick between Thursday and Tuesday.
BAA warned that passengers would need to be aware of the continuing baggage restrictions.
Air travellers are still banned from carrying liquids in containers larger than 100ml in their hand luggage.
AA Roadwatch said the worst traffic congestion was on Thursday afternoon, with jams easing into the evening.
Drivers on the M1 northbound out of London, the M60 in Greater Manchester and the M42 east of Birmingham all faced long delays.
Two people died in a crash on the M6 near Alsager in Cheshire which also caused huge tailbacks for northbound vehicles on Thursday morning.
On Friday, traffic was less heavy, although roads heading to the coast and tourists attractions were slow, AA Roadwatch said.
"It is a lot better than yesterday, but people are heading to the coast and attractions because of the weather as well as to shopping centres, which is causing heavy traffic," a spokesman added.
Dave McIntyre, the AA's patrolman of the year, said motorists should not set out without drinking water, a charged mobile phone and full tank of petrol.
On the railways, there is engineering work planned for sections of lines on a number of routes during the Easter holiday period.
Rail travellers in Scotland will face major disruption on Saturday and Sunday with the suspension of some services to and from Glasgow Central Station due to the upgrading of signals and engineering points.
Virgin Trains and GNER services will be affected and replaced by buses for all or part of the route.
The BBC's Weather Centre said in London and the southern counties temperatures were expected to hit highs of 20C (68F) - hotter than usual for this time of year.
Although there will be variations in the amount of sun, most of the country is expected to remain dry and fine well into next week with temperature in the early to late teens.