Is it illegal to leave your car running?

Last updated February 04, 2022

When you leave your engine running idle, you are not just wasting fuel, you are breaking the law and you may face a fine. Engine idling is legislated against in the UK and it’s important that you know the rules before getting behind the wheel.

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What is engine idling?

Idling is the act of leaving the engine of a vehicle running unnecessarily. For example, if you’re picking someone up from school and you wait outside with the engine on the whole time, this would be classified as idling.

Is it illegal to idle your car in the UK?

The short answer, is yes: engine idling is against the law.

Also known as stationary idling, Section 42 of the Road Traffic Act 1988 prohibits leaving your engine on when it is not needed. This act enforces Rule 123 of the Highway Code, which states “you must not leave a vehicle’s engine running unnecessarily while that vehicle is stationary on a public road”.

If you do leave your engine idle, you could face a fine upwards of £20, or £80 in areas of London – as per the Road Traffic (Vehicle Emissions) Regulations of 2002.

Why is engine idling prohibited?

An idling engine can contribute massively to air pollution, potentially producing up to twice the emissions of a car in motion. Idling engines can churn out nitrogen oxide, sulphur dioxide and particulate matter. These chemicals can have a negative effect on people and the environment by contributing to poor air quality. Therefore, to reduce the impact of these pollutants, idling has been prohibited to limit emissions.

Are there any exceptions?

There aren’t many exceptions to engine idling. If you are stuck in a traffic jam, it would be expected that you would turn your engine off as you aren’t going anywhere.

It’s a common misconception that stopping and starting the engine uses up more fuel than leaving the car running. So, by switching off, you’re also cutting down on fuel costs.

On a warm day, keeping the air conditioning on by leaving the engine running may seem like a valid reason, but unfortunately, it is not.

One of the few valid reasons to leave your engine idling while you aren’t driving is if you need to defrost your windscreen on a cold morning. However, you shouldn’t leave the car unattended while you do so.

How to avoid engine idling

If you think you’re likely to be waiting for more than a minute, it’s best to just turn the engine straight off. If you’re loading or unloading goods, waiting at car parks, laybys or pick-up points, turn the engine off too.

A small moment of your time could make a massive difference in emissions. If in doubt, just switch the engine off.