Why does motorway driving use more fuel?

At higher speeds, aerodynamic drag increases exponentially (drag is proportional to speed squared). At 70 mph, your engine works much harder against air resistance than at 50 mph. This means MPG drops significantly on motorways compared to mixed driving, despite the constant speed and fewer stops.

How much does speed affect fuel consumption?

Reducing speed from 70 to 60 mph can improve fuel economy by 10-15%. The difference between 60 and 80 mph can be 25-30% more fuel. The Department for Transport estimates that driving at 80 mph uses around 25% more fuel than driving at 70 mph.

What is the most fuel-efficient motorway speed?

For most cars, the most fuel-efficient speed is between 45-55 mph. This balances engine efficiency with aerodynamic drag. However, on a motorway, driving this slowly may not be safe or practical. Cruise control at 60-65 mph offers a good balance of efficiency and journey time.

Does cruise control save fuel on motorways?

Yes, cruise control typically saves 5-10% fuel on motorways by maintaining a constant speed. Without it, drivers tend to vary speed, which wastes fuel through unnecessary acceleration. Adaptive cruise control can save even more by smoothing out speed changes in traffic.

Why is motorway fuel more expensive?

Motorway service stations typically charge 10-20p per litre more than supermarket forecourts. Planning ahead and filling up before joining the motorway, or leaving at a junction to find cheaper fuel, can save significant money on long journeys.

CarCalcs

Motorway Fuel Calculator — Higher Speed Fuel Usage

Calculate fuel consumption for motorway journeys accounting for higher speeds and reduced efficiency.

Motorway Distance

Normal MPG (mixed driving)

Fuel Price

Cruising Speed

Fuel Type

How We Calculate This

How It Works

Motorway fuel consumption is calculated by adjusting your normal (mixed driving) MPG for the higher sustained speeds:

60 mph: MPG drops by ~5% vs mixed driving
65 mph: MPG drops by ~10%
70 mph: MPG drops by ~15%
75 mph: MPG drops by ~22%
80 mph: MPG drops by ~30%

The Formula

Motorway MPG = Normal MPG x Speed Factor

Fuel (litres) = (Distance / Motorway MPG) x 4.546

Cost = Fuel (litres) x Price per litre

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Actual figures may vary based on driving conditions, vehicle specifications, and other factors.