Driving at 70mph Instead of 60 Costs Every Driver 9 Percent More in Fuel

• Department for Transport data shows driving at 70mph instead of 60mph uses up to 9 percent more fuel, and pushing on to 80mph burns a further 25 percent on top of that.
• The Energy Saving Trust puts the cheapest cruising speed for most cars at between 50 and 60mph, the point where air resistance starts to outweigh every other saving.
• Simple changes, changing up to top gear by 50mph and keeping a steady throttle, can claw back much of that lost mileage without a single change to the car itself.

The speed that is quietly draining your fuel tank

Most drivers choose a cruising speed based on the limit, the traffic and how late they are running. Almost nobody chooses it based on fuel consumption, yet speed is one of the biggest single factors in how far a tank of fuel actually takes you, bigger than tyre pressure, bigger than a dirty air filter, and bigger than most of the tips that get repeated every winter.

The answer to the question “what speed saves the most fuel” is specific, and it is lower than most people assume.

Where the official numbers land

According to official Department for Transport figures, driving at 70mph uses up to 9 percent more fuel than driving the same distance at 60mph. Push on to 80mph and the penalty compounds further, with the RAC calculating that a car can burn up to 25 percent more fuel at 80mph than it does at 70mph. Stack those two increases together and a driver doing 80mph on a motorway run can be burning noticeably more than a third more fuel than the same journey done at 60mph.

The Energy Saving Trust’s research points to 50 to 60mph as the cheapest band for most cars on the road today. Below that range, an engine is often running at lower revs than it is designed for and fuel consumption rises again. Above it, aerodynamic drag increases sharply with every extra mph, as drag rises with the square of speed rather than in a straight line. That is the physics reason a seemingly small jump from 70mph to 80mph costs so much more than the jump from 60mph to 70mph.

Why air resistance does the damage, not the engine

Below around 50mph, a car’s fuel consumption is mostly a function of its weight and the rolling resistance of its tyres. Past that point, pushing air out of the way becomes the dominant cost, and it scales badly. Doubling your speed does not double the air resistance, it roughly quadruples it, which is why a flat-out motorway cruise at 80mph can feel barely faster than 70mph in traffic terms but costs so much more at the pump.

This is true whether the car is petrol, diesel or a hybrid, and it is one of the few fuel-saving facts that does not depend on the make or age of the vehicle. A roof box, an open window at speed, or towing a trailer all make the same aerodynamic penalty worse again, on top of the speed effect.

What this actually costs over a year

For a driver doing 10,000 motorway miles a year in a car averaging 45mpg at 60mph, consistently driving at 70mph instead could add roughly a tank of fuel’s worth of extra cost across those miles, and driving at 80mph instead of 70mph adds a similar penalty again on top. For anyone doing a daily motorway commute, the gap between a 60mph cruise and an 80mph one can run into several hundred pounds a year at current pump prices, without the destination ever being reached meaningfully faster once traffic, roadworks and speed cameras are factored in.

How to actually hold the cheaper speed

Knowing the number is only half the job. A few practical habits make it realistic to drive closer to that range without turning every journey into a frustration for other road users.

Use cruise control on flat, open roads. Holding a steady 55 to 60mph avoids the fuel spikes caused by constantly speeding up and slowing down, which can do more damage to your mpg than the top speed itself.

Change up to top gear by around 50mph in a manual car, and keep revs as low as the road allows without labouring the engine. Most modern engines are tuned to use least fuel in their higher gears at modest revs, not held in a lower gear at speed.

Pick your lane and your speed together on faster roads. Sitting in the middle lane at 68 to 70mph on a three-lane motorway, rather than drifting to 80mph in the outer lane, is usually both safer and measurably cheaper, and rarely adds more than a few minutes to a typical journey once the maths is done honestly.

Take off roof boxes and bike racks when they are not in use. The aerodynamic penalty from a roof box at 70mph can rival the saving from driving 10mph slower, which makes it one of the easiest wins available to anyone who only needs the extra carrying capacity for a few trips a year.

None of this means crawling along under the limit. The data simply shows that the fastest legal speed on a given road is very rarely the cheapest one, and for most cars, the cheapest cruising speed sits closer to 55 or 60mph than to the 70mph limit most motorway driving defaults to.

Does this apply to electric cars too

Aerodynamic drag affects every vehicle on the road regardless of what powers it, so the same speed penalty applies to an electric car’s range as it does to a petrol or diesel car’s fuel economy. An EV cruising at 80mph can see its range drop by well over a quarter compared with the same car at 60 to 65mph, which counts for more with electric drivers as a shorter range directly affects how often, and how long, they need to stop and charge on a long journey. Cold weather compounds the same effect, and there the deciding factor is equipment rather than driving style, as what a heat pump is actually worth in winter runs to 15 percentage points of range at zero degrees. Several range tests by independent reviewers have shown family electric cars losing well over 20 percent of their claimed range simply by holding 80mph on a motorway for an extended stretch, compared with cruising nearer 65mph.

What actually changes if you slow down

It helps to put the time cost in perspective. On a 200 mile motorway trip, the difference between averaging 70mph and averaging 60mph is roughly 29 minutes, assuming no stops, no traffic and no speed variation at all in either scenario, which is unrealistic in practice as traffic, roadworks and junctions already slow most journeys well below the speed limit for a meaningful part of the route. In other words, the time saved by driving faster is usually smaller in the real world than the fuel cost suggests, as congestion erases much of the advantage before it ever shows up on the clock.

For a household running two cars and doing a combined 20,000 miles of motorway driving a year, trimming an average cruising speed from 75mph to 62mph can be worth several hundred pounds over twelve months at current fuel prices, money that is otherwise spent for no real gain in arrival time once ordinary traffic conditions are factored in.

The habit that undoes all of this

Even a driver who picks the right cruising speed can lose most of the saving through heavy acceleration and late braking. Pulling away hard from every junction and braking late for every roundabout can cost as much in fuel as driving 10 to 15mph faster than necessary, as an engine working hard under acceleration consumes disproportionately more fuel than one maintaining a steady speed. Looking further ahead, easing off the accelerator earlier, and treating the brake pedal as a last resort rather than a first response, does more for fuel economy over a typical commute than obsessing over the exact number on the speedometer.

Sources:

• RAC fuel economy advice