Stay in gear when you slow down to save fuel

It sounds like free fuel. The car is rolling anyway, so shift to neutral and the engine stops holding it back. A UK government agency’s blog says that for most vehicles it works the other way round.

To save fuel when you slow down, take your foot off the accelerator early and keep the car in gear for as long as you can; do not coast in neutral or with the clutch pressed down. In an automatic, that means leaving the lever in Drive.

This page is for petrol (gasoline in the US) and diesel cars. If yours is electric or a hybrid, check its owner’s manual; this page does not cover them.

What the official sources say

The Highway Code, which applies to England, Scotland and Wales, describes coasting in rule 122 as “a vehicle travelling in neutral or with the clutch pressed down”. The safety note at the top of this page lists the ways the Code says coasting can reduce driver control.

On fuel, the UK Vehicle Certification Agency, a government agency, says to slow down or go downhill by taking your foot off the accelerator as early as you can and staying in gear. It says that in most situations and for most vehicles this activates the fuel cut-off switch, which reduces fuel flow to virtually zero. A 2019 article on the Driver and Vehicle Standards Agency’s blog gives the reason: in neutral the engine is still burning fuel to keep itself idling.

The same article names an exception. At low revs, such as in stop-start traffic, it says the fuel cut-off does not operate, most engines add enough fuel to avoid stalling, and neutral or clutch down is then more efficient. So in a crawling queue the article’s fuel advice and the Highway Code’s control warning pull in different directions. At normal road speeds, staying in gear is the advice on both. This page cannot say at what speed your car’s fuel cut-off stops working; your owner’s manual or the maker can.

Some people argue the opposite: that a gas engine keeps injecting fuel even in gear, and one person says that holding a gear can take slightly more fuel than idling in neutral, though the difference is small. This page found no US government source that says whether coasting in neutral saves or wastes fuel. The US fuel economy site page on driving habits, which this page read, does not mention neutral, and no source this page read says how much fuel coasting in gear saves.

For automatic cars, one vehicle maker’s owner’s manual supplement, for one model, says that except in an emergency you should not shift to N (neutral) while driving, and that coasting in neutral may cause serious damage to the transmission.

What does save fuel

Many people say that easing off early and keeping a steady speed saves fuel and wears brakes and tyres (tires in the US) less. The US fuel economy site says aggressive driving, meaning speeding, rapid acceleration and braking, can lower gas mileage by roughly 15% to 30% at highway speeds and 10% to 40% in stop-and-go traffic. The UK Vehicle Certification Agency says harsh acceleration is particularly bad for fuel consumption, and that watching the traffic as far ahead as you can helps you avoid unnecessary acceleration and braking. One person says a bad habit is speeding up towards a light that is already red.

Some people say keeping tyres inflated is a cheap way to save fuel. The US site says that keeping them at the proper pressure can improve gas mileage by 0.6% on average, up to 3% in some cases, that the proper pressure is usually on a sticker in the driver’s door jamb or the glove box and in the owner’s manual, and that you should not use the maximum pressure printed on the tyre’s sidewall. There is a page here called Check the spare, and fill to the door sticker.

The UK agency says the best way to reduce fuel use is to use the car only when it is necessary, for example by walking, cycling or taking public transport instead of short journeys, and to combine trips. Some people say a bicycle for very short trips removes the fuel cost, and some say that driving a long way to buy slightly cheaper fuel is not worth the extra fuel and time. How much any of this adds up to depends on your car, how far you drive and what fuel costs where you live.

Savings that are not worth the risk

Following close behind a truck to cut wind risks tailgating. One person says it can save fuel, and adds that it is stressful and hides the view. The Highway Code, in rule 126, says tailgating is where the gap to the vehicle in front is too small for you to stop safely if it suddenly brakes, and that tailgating is dangerous, intimidating and can cause collisions.

One person warns that slowing without touching the brake means no brake lights, and that the drivers behind rely on those lights as a cue; the same person says coasting in neutral makes it slower to react in an emergency. The point about brake lights applies to easing off in gear as well. Highway Code rule 161 says to use your mirrors in good time before you change speed.

Who this page is not for

If you drive an electric car or a hybrid, or a very old car with a carburettor (carburetor in the US), your owner’s manual comes first. Not everyone can drive less to cut the fuel bill: one person points out that advice to drive less ignores medical conditions and legal limits on driving.