Engine idling: the impact on the environment and laws you may not be aware of

We know our cars have an impact on the environment, but it’s how we use them that can really affect how detrimental driving is to the world around us. Engine idling is one of the behaviours we can easily change. People may run their engine without moving to warm up the car on a cold day or while they are stopped in traffic or waiting for someone.

However, idling your engine does more harm than good. And not just for the environment. There are rules around when you shouldn’t leave your car running – in this guide, we cover the details.

What is engine idling?

Engine idling is leaving a vehicle’s engine running while it isn’t moving. Sometimes engine idling is unavoidable, for example, if you’re in nose-to-tail traffic that stops and starts. At other times, it’s unnecessary, for example if you’re waiting for someone or traffic isn’t moving any time soon.

Why is engine idling harmful?

Engine idling releases more exhaust fumes into the air than when the car is moving, which is bad for the environment and our health.

Environmental concerns

Exhaust fumes contain carbon dioxide, which traps heat in the atmosphere and contributes towards global warming. This rise in average temperatures causes more severe weather, such as heatwaves, storms, and floods; destroys habitats and ecosystems; and could lead to people having to leave places due to them becoming uninhabitable.

Government statistics published in 2022 show that in 2020:

79% of the UK’s greenhouse gas emissions were made up of carbon dioxide
Emissions from transport were down 19.2% compared to 2019, due to the pandemic
However, transport was still the sector responsible for the highest amount of emissions – 24% of all greenhouse gas emissions in the UK

Provisional figures have been released for 2021, and although they’ve yet to be confirmed, these estimates can give us an indicator of how getting back to a more normal way of life post pandemic has affected the UK’s emissions:

Carbon dioxide emissions increased by 6.3% in 2021 compared to 2020
Carbon dioxide emissions from the transport sector rose 10% in 2021 compared to 2020

While the UK’s greenhouse gas emissions have generally been decreasing since 1990, average global temperatures are still rising quickly.

Health concerns

Exhaust fumes contain carbon monoxide, nitrogen dioxide, and hydrocarbons. These gases are linked to cardiovascular and respiratory conditions, including asthma and lung cancer. In fact, poor air quality is ‘the largest environmental risk to public health in the UK’.

The World Health Organization (WHO) has found that almost the entire global population (99% of people) breathes air that exceeds WHO air quality guidelines. These guidelines, which aren’t legally binding but give governments targets to consider, recommend levels for common air pollutants.

Data from Public Health England estimates that long-term exposure to man-made air pollution has an effect that’s equivalent to between 28,000 and 36,000 deaths per year. Their research also suggests that reducing air pollution could prevent:

50,900 cases of coronary heart disease
16,500 strokes
9,300 cases of asthma
4,200 lung cancers

Is engine idling illegal?

Yes. Under Section 42 of the Road Traffic Act 1988, engine idling is an offence.

The Highway Code also has a rule against engine idling. Rule 123 states:

“You MUST NOT leave a parked vehicle unattended with the engine running or leave a vehicle engine running unnecessarily while that vehicle is stationary on a public road. Generally, if the vehicle is stationary and is likely to remain so for more than a couple of minutes, you should apply the parking brake and switch off the engine to reduce emissions and noise pollution. However, it is permissible to leave the engine running if the vehicle is stationary in traffic or for diagnosing faults.”

In the Highway Code, the words ‘must’ and ‘must not’ indicate legal requirements. Other parts of the Code use ‘should’, ‘should not’, ‘do’, and ‘do not’ and while violating these rules isn’t a criminal offence, it can still be used against you in court.

This law only applies to public roads, so it’s not illegal to leave your engine running while your car’s on private property (for example, on your drive). However, it’s best practice to switch the engine off if you’re going to be waiting for a while. Not only is this better for health and the environment, it’s also better for your vehicle.

It’s also good not to get into the habit of leaving your car’s engine running while you’re not in it. In addition to the reasons above, it offers opportunist criminals the chance to steal or cause some kind of damage to your vehicle.

What will happen if I get caught with the engine running while my car is stationary?

Drivers caught engine idling will be issued a fixed penalty notice if they refuse to switch their engine off by authorised personnel. This fine is:

£20 initially
£40 if you don’t pay the initial fine within 28 days
£80 if you don’t pay the £40 within 14 days

(source)

How does engine idling affect my car?

Leaving a vehicle running while it remains still isn’t efficient, because the fuel may not combust the way it’s supposed to. It can also leave behind a residue that causes damage, and after a longer period of time the battery may drain.

It’s true that in the past some vehicles did need time to warm up – especially those fitted with carburettors. However, modern vehicles have what is known as a fuel-injection engine, which are ready to go in a matter of seconds.

How can I avoid engine idling?

Think about how long you’re going to be in stationary traffic. If it’s likely to be more than a couple of minutes, switch your engine off.
Next time you need to replace your car, look for a model with stop-start technology, and keep this option turned on so you don’t need to think about it.
Switch your engine off if you’re doing any of the following:
- Waiting in a car park
- Waiting at a pick-up point
- Waiting in a lay-by
- Waiting outside someone’s house
- Loading or unloading your vehicle
Switch your engine off but leave on the ignition, so you can still use systems like air conditioning.

Do I need to worry about engine idling if I can have a car with a stop-start system?

If your vehicle has stop-start technology, you don’t need to worry about engine idling. The engine will stop when the vehicle does, then switch back on when you apply the clutch.

Not only does this reduce emissions, but it also reduces the amount of fuel you use, saving you money. It won’t reduce the vehicle’s battery life either.

What is being done to tackle air pollution in the UK?

Legislation

The UK Government introduced the Environment Bill in 2021. The bill requires the government to set targets on air quality. One of these targets is to reduce the annual average of fine particulate matter in ambient air, which is the most harmful for human health.

The government also introduced the Clean Air Strategy 2019, which explains how they’ll:

Research, measure and monitor air quality
Protect public health
Protect the environment
Develop technology to tackle air pollution
Reduce transport emissions
Reduce home emissions
Reduce farming emissions
Reduce industry emissions

Clean Air Zones

In terms of transport and driving, Clean Air Zones (CAZs) are steadily being implemented across the country. CAZs are areas that charge or penalise highly polluting vehicles. The pollution level of a vehicle is based on its Euro emission standard, which is a number from one to six. Each type of vehicle must meet a minimum Euro emission standard to avoid being charged.

Vehicle type	Clean Air Zone minimum standard
Bus, coach, heavy goods vehicle	Euro six
Van, minibus, taxi, private hire vehicle, car (petrol)	Euro four
Van, minibus, taxi, private hire vehicle, car (diesel)	Euro six
Motorcycle	Euro three

(source: Gov.uk)

There are four types of Clean Air Zones:

A. Buses, coaches, taxis, private hire vehicles

B. Buses, coaches, taxis, private hire vehicles, heavy goods vehicles

C. Buses, coaches, taxis, private hire vehicles, heavy goods vehicles, vans, minibuses

D. Buses, coaches, taxis, private hire vehicles, heavy goods vehicles, vans, minibuses, cars (the local authority may also choose to add motorcycles to this list)

The government has an online tool which you can use to check whether or not you need to pay the charge.

Low and Ultra Low Emissions Zones

The rules are slightly different in London, where there is the Low Emission Zone (LEZ) and Ultra Low Emissions Zone (ULEZ). Vehicles which do not meet the LEZ or ULEZ standards must pay a charge to drive inside the zone.

The Low Emission Zone covers most of Greater London and is in constant operation. It doesn’t apply to vehicles parked in the zone. All roads in Greater London, including those at Heathrow and parts of the M1 and M4 are included. The M25 is not included.
The Ultra-Low Emission Zone operates every day of the year, 24 hours a day, except 25 December. It covers all areas within the North and South Circular Roads. The North Circular (A406) and South Circular (A205) roads are not in the zone.