Are used cars environmentally friendly?

Want to change your car but not sure whether buying new or used is better for the environment? Let us give you a steer

James Wilson
Sep 20, 2021

With increasing concerns over climate change and the resulting ever-stricter emissions regulations, a car’s environmental credentials are a more important consideration than ever.

A car’s ‘green’ credentials also have a significant financial impact on drivers, as the UK government uses a car’s emissions and fuel type (petrol, diesel, hybrid or electric) to determine the cost of things such as vehicle excise duty - more commonly known as road tax - and benefit-in-kind tax.

Some may believe that the answer to running an environmentally friendly car is to buy something brand new, as the latest cars are fitted with the most up-to-date technology to reduce emissions. However, the truth is far less clear-cut.

Although a new car may emit few, if any, emissions from its exhaust, when being assembled, it will still require parts to be sourced and shipped around the world, potentially with a great environmental impact - and some of the latest 'low-emission' cars may not be as economical in reality as you'd hope.

In addition, buying a new car is simply too expensive for many drivers. If you're looking to minimise the environmental impact of your car but are on a budget, a used car could actually make more sense. That's because while the car may have slightly higher official emissions figures, you're not causing a whole lot more pollution elsewhere in requiring materials to be sourced and shipped around for your brand new car to be built.

So, going for a second-hand car should mean your initial impact on the environment is reduced. But what about the other factors involved in running a car? Keep reading to get a better feel for whether it's better to buy new or go used.

The types of car emissions

Carbon dioxide (CO2) is the most commonly known gas to be emitted by cars. Of all the greenhouse gases cars emit, CO2 makes up a significant majority, posing one of the biggest threats to the planet.

Cars also emit methane (CH4), which, although produced in significantly smaller quantities than CO2, is believed to be about 25 times more harmful to the environment over a 100-year period. Therefore, if you want to limit your contribution towards global warming, you also need to take your methane emissions into account.

Some gasses emitted from cars are less of a concern for the environment in terms of climate change, but more of an active concern for human health. The big hitters here are carbon monoxide (CO) and nitrogen oxides (NOx).

The latter is not to be confused with nitrous oxides (NxO) which are about 300 times worse as a greenhouse gas than carbon dioxide and are predominantly released during agricultural processes.

Take away points

• Carbon dioxide and methane are the two most significant greenhouse gases emitted by petrol and diesel cars
• Other pollutants, such as nitrogen oxides and particulate matter are a particular threat to human health

Emissions and economy

Fiat 500 front three quarters view

When it comes to being environmentally friendly, cars with lower emissions figures and higher fuel economy are better. Provided a car is properly looked after, its emissions and economy figures shouldn't get worse as they get older. In fact, in the past, it took cars several thousand miles before they were producing maximum power and running with the greatest efficiency.

Saying that, due to official tests being largely conducted in laboratories, the actual economy and emission figures cars are sold with tend to be more optimistic than what you can expect to achieve in the real world. Be aware that over recent years two different types of economy and emissions tests have been used. Nevertheless, these figures provide a great starting point for comparison.

For cars registered before September 2018, the 'NEDC' economy test was used. This test format didn't reflect real traffic and driving styles and so claimed fuel economy figures are typically much higher than most drivers are likely to achieve in everyday driving. As a result, from September 2018 onwards, a new more realistic 'WLTP' test was phased in for new cars.

This should be much more representative of real roads and traffic, and so you should be able to get closer to this figure with normal driving. All new cars registered from September 2019 onwards should have fuel economy and emissions figures calculated using the more realistic WLTP test. Bearing this in mind a car that achieves 50mpg on the newer WLTP test is likely to be more economical in everyday driving than one that has a 50mpg figure recorded on the old NEDC test.

Lately, there has been an increased focus on reducing the emissions detrimental to human health rather than just CO2. A knock-on effect of the technology designed to reduce CO and NOx emissions is that more fuel can be burnt, which means more CO2 is produced. It's a bit of a Catch 22 scenario right now, although carmakers are working on improving the balance.

As a guide, any non-hybrid petrol or diesel car with a CO2 emission figure of under 100 grams per kilometre of driving (typically presented as 100 g/km) should be considered pretty green. Plug-in hybrids should be able to achieve less than half that figure with 'self-charging' hybrids sitting somewhere in between. There is a big but with plug-in hybrids, however...

Plug-in hybrids only emit far lower emissions than conventional petrol or diesel models if you regularly charge them (most have a claimed electric range of around 30 miles, potentially less on real roads). If you fail to charge regularly, plug-in hybrids can actually prove bad for the environment, as once the battery charge is depleted they rely on their petrol or diesel engine and also have to carry the weight of the electric motor and batteries around - with extra weight typically resulting in worse fuel consumption and greater emissions.

Yes, you can expect a small boost from the electric motor in a plug-in hybrid if you're driving around town and the batteries are flat, as braking adds back a little charge, but driving like this in a plug-in hybrid is likely to be pretty inefficient.

Furthermore, plug-in hybrids require more materials to be mined in the first place - as not only do they have a petrol or diesel engine, they also have an electric motor and batteries. As a result, there are big question marks over the environmental credentials of plug-in hybrids. The logic behind these models is that they can run with zero emissions around town for short distances - if you charge them regularly - but are also capable of a long trip without the need to regularly stop and recharge.

As many electric cars now offer a claimed range of more than 200 miles, though, these make sense even for drivers who need to do the occasional long journey. If all your driving is motorway trips of more than 200 miles, then you're likely to be better off going for a petrol or diesel car than a plug-in hybrid, as you wouldn't be getting any real benefit from a plug-in hybrid at higher speeds.

Take away points

• More recent 'WLTP' fuel economy figures are more realistic than older 'NEDC' ones for comparing emissions and economy figures
• Plug-in hybrids only make environmental sense if you charge regularly. Fail to do so and they are particularly bad for the environment
• Emissions of less than 100g/km of carbon dioxide is very good for non-hybrid petrol or diesel cars

Maintenance and longevity

Maintenance has a huge bearing on whether or not a used car is as environmentally friendly as a new one. For starters a car’s emissions are directly related to how much fuel is burned, so an engine that isn’t running properly may emit more pollution than one that is.

Exhaust systems are vital in reducing vehicle emissions and in older cars with lower values they can be neglected by drivers as replacement parts can be pricey. Items such as catalytic converters, particulate filters and exhaust gas recirculation valves all have limited lifespans and will need to be replaced at set mileages to ensure a used car is keeping its emissions under control.

This typically affects cars that are over 10 years old, so in most cases, there's no need to worry unduly if you are buying anything below around seven years old, but it's something to bear in mind, especially if you plan to keep the car for many years.

When a car is neglected this shortens its useful lifespan. Keep a car well fed and watered and it will last significantly longer than one which isn’t, and since building new cars requires an awful lot of energy, it's good for the environment to keep older cars running, rather than simply building more and more new ones. Scrapping cars takes its toll on the environment as well, especially if they are not disposed of properly.

While a well-maintained car should (in theory) produce the same emissions no matter how old it is, that is not to say it will be better for the environment than a new model in this regard. New cars on paper emit less CO2 than older ones due to technological advances, but you have to balance this with the extra energy used up and pollution caused by sourcing the materials for a brand new car, shipping them around the world and then building said new car. Keep reading for more on this point.

Take away points

• When buying used, look for well-maintained vehicles as these should emit less than poorly maintained cars
• A well-maintained car should last longer, which in turn should help reduce its overall environmental impact
• Disposing of a car has environmental impacts as well - choosing a used car is another example of recycling

Manufacturing and materials

All cars typically require a lot of steel and aluminium for components such as the body, suspension and braking systems. Then there is copper for all the electronic wiring and a whole bunch of plastic for things such as bumpers, switches, dashboards and seats.

Unless these materials come from recycled or sustainable sources - and the car is constructed using renewable energy - the construction of a new car will have a substantial detrimental impact on the environment. The negative impacts of plastic are well documented today - since so much plastic is binned or discarded, with much of this not being biodegradable it can take centuries to rot down, it consequently ends up polluting the environment and potentially harming animals, too.

Metals such as steel, aluminium and copper require mining and processing, which involves much digging - which harms affected environments - and much processing, which requires a lot of energy. Electric cars also require rarer materials such as lithium, which again need mining and processing and may only be sourced from environments with delicate ecosystems that can easily be damaged.

Then, once you have all the necessary materials to make a car, they have to be moved somewhere (most likely to another country by air, land and/or sea) and turned into something a car needs, such as a handbrake (which requires more energy).

Do this for every single component on a vehicle and the carbon footprint of even the smallest new car can be substantial. Then, of course, all those components need assembling (this again takes a lot of energy) and delivering to a customer.

This means that making a new car requires a whole heap of energy and has a substantial impact on the environment. So much so, some have suggested it is better for the environment to run a used vehicle until the environmental impact of keeping it running - should it reach an age when a significant number of parts require replacement - and potentially slightly higher emissions than a new equivalent, outweigh the environmental cost of producing a new one.

It isn’t all doom and gloom though as there are massive opportunities here. By being sensible in material choices, carmakers can limit the environmental impact of producing new cars. For example, Fiat offers mild hybrid versions of its Panda city car with a seat fabric made from plastic reclaimed from land and sea. Plastic isn’t the only material that can be recycled either: metals can be too.

Take away points

• Making a new car requires a huge amount of energy
• Materials have to be mined, transported and processed, often multiple times
• Buying a UK-built car limits shipping emissions, though many of its materials are still likely to have been shipped thousands of miles
• Buying from a maker with a transparent supply chain can help you make sure a car’s components are coming from responsible sources
• While electric cars don’t directly emit, they require scarce materials and pollution may be emitted to generate the energy needed to charge them
• Running a used car for as long as it is reliable and doesn't require many new parts can be better for the environment

Understanding emission testing and standards

Cars have been under continuous development for more than a century and part of that development is emission testing and control. Several decades ago a series of increasingly stringent 'Euro' emissions standards were introduced in Europe, to limit the tailpipe emissions allowed for new cars.

Its main focus was on reducing CO2 emissions - as CO2 is a significant contributor to global warming - with the first 'Euro 1' standard starting the move towards drastically reducing the CO2 emissions of new cars sold today. Saying that, there is no CO2 limit for individual cars currently, just an overall average limit for a car manufacturer's range of vehicles.

Currently, new cars have to meet 'Euro 6' standards, however, there are different sub-standards within these. When Euro 6 was first made mandatory for all new cars in September 2015, its main focus was cutting the amount of NOx and hydrocarbons (the family of chemicals which includes methane) emitted from diesel cars.

Since Euro 6 arrived though, things in the automotive world have changed dramatically. For starters, a new emissions and economy testing procedure was introduced. It is called the Worldwide Harmonised Light Vehicle Test Procedure, or WLTP for short and provides much more realistic figures than the test it replaced (called NEDC).

At the same time, a scandal now referred to as 'dieselgate' occurred. In short, it transpired that a number of leading car manufacturers had been cheating emissions tests, producing cars that recognised when they were having their emissions tested, and artificially limited emissions during the test. As a result, a number of models sold were significantly worse for the environment than the official numbers would lead you to believe. Volkswagen was one of the leading culprits here, but it's important to remember that they weren't alone.

As part of the authorities' attempts to get a handle on emissions, something called the real driving emissions test (or RDE/RDE2) was rolled out. RDE is an on-road test cars must undergo to make sure they meet the Euro 6 emissions standards in real-world conditions - not simply in artificial lab conditions.

To ensure the utmost clarity when understanding how environmentally friendly a car is, there are a number of sub-standards to Euro 6. The key ones are Euro 6d-Temp and Euro 6d.

Take away points

• 'Euro' emission standards dictate the permissible levels of certain pollutants a car is allowed to emit
• Look for models which at least meet the Euro 6 emission standard for the best chance of being affected by low-emission zones being introduced around the country
• Euro 6d-Temp is a more up-to-date standard and ensures cars are tested under more realistic circumstances. This became mandatory for new cars built from September 2019
• Euro 6d becomes mandatory in January 2022 and tightens emissions limits further still


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