Car idling: is it OK and what are the rules?

You’re waiting to pick up a friend or member of your family in your car. It’s busy so you’ve had to pull over in an awkward spot. You’ll only be there a few minutes, so you keep your engine running.

Sound familiar? Lots of drivers leave their car running while stationary. But they may not realise how much harm they’re doing, or that they could even fined by the police.

The problem with idling

Idling is when you leave your car engine running while parked, stationary, or when waiting at junctions or traffic lights.

What drivers may not realise or perhaps forget, is that idling is adding to high levels of air pollution, contributing to a greater chance of developing lung cancer and heart disease, as well as increases in asthma, coughs and bronchitis.

Running engines emit fumes. And in some cases, cars can pump out almost twice the emissions while stationary as they do while in motion.

Emissions such as nitrogen oxide, sulphur dioxide and fine particulate matter are major contributors to poor air quality.

And exposure to these emissions can have serious negative effects on health. It’s estimated that man-made air pollution causes between 28,000 and 36,000 deaths in the UK every year, contributing to asthma, lung cancer and heart disease.

Although it’s difficult to separate different types of pollutants for the purposes of these figures, traffic emissions are doubtless a huge factor. According to Transport for London, over half of the capital’s air pollution is caused by polluting vehicles.

The law on idling

If you leave your car idling, then you could also get in trouble with the law.

Leaving your car idling is looked upon dimly by the law. The Highway Code clearly states: "You must not leave a vehicle’s engine running unnecessarily while that vehicle is stationary on a public road."

Drivers can face a fine of upwards of £20 for leaving the engine on while in a stationary car; this can go up to £80 in some areas of London.

In fact, some councils have been pushing for tougher rules regarding idling, including instant on-the-spot fines. This was echoed by the government in June 2019, when the Transport Secretary at the time, Chris Grayling, announced a consultation regarding tightening up the law in this area.

Notably, idling could be banned outside schools and hospitals, and other areas where people are especially sensitive to air pollution.

Idling in cold weather

What about leaving your car idling on a freezing morning, to let it warm up?

On a chilly winter morning, when your windscreen is covered in a thick layer of ice, it can be tempting to start your car, and then head back into the warmth of your house for a few minutes while it defrosts*. 

But the same rules apply – you could face a fine. You also put your car at risk of getting stolen by thieves who are searching for easy pickings. There is an even a name for this common winter crime - frost jacking [1].

However, the law only applies on public roads, meaning you can legally leave the engine on if you’re on a private driveway.

*The car will not be covered if it's stolen when left unattended with the keys in.

[1] https://www.tracker.co.uk/tracker-hub/news/winter-months-see-return-frost-jacking-car-thieves