The arrival of school summer holidays and tropical weather will be marked by 6,000,000 extra leisure car journeys will be taken between Friday and Sunday, according to RAC.
The RAC suggests Friday will be the busiest day with journey times severely impacted.
Analytics experts predict a 29% increase in delays on Friday, compared to typical July travel times.
RAC stressed that checking tyres, oil, coolant and screenwash levels could make the difference between drivers getting safely to their holiday destinations or being broken down at the side of a busy road.
RAC Breakdown spokesman Simon Williams said: “With the current heatwave, the scene is really set for an incredibly busy few weeks on the country’s roads.
“It’s never been more important to plan ahead to avoid the busiest times.”