Green cars and the cost of motoring

Driving a green car is not just about helping the environment. ‘Greener’ cars can deliver lower running costs, lower tax, less fuel consumption and even exemption from congestion charges in some areas.

As car makers focus more and more on efficient technology in their cars, it is increasingly easier to find greener, more frugal cars without having to sacrifice practicality, performance or design.

Green doesn’t have to mean an electric or even a hybrid car. Several petrol and diesel engines can deliver excellent fuel economy now, and more are set to be released this year.

All manufacturers now boast an eco signature, but what exactly should you be looking for if you want to buy a greener car?

Below we’ve listed some of the criteria that makes a car a green car, and why choosing it can save you money on running costs.

What is a green car?

Green is a blanket term, and its use has caused plenty of controversy in the car industry. For example, road tax, European engine legislation and the London congestion charge all use CO2 emissions as the criteria for a greener car.

If you want to know how road tax is calculated and how much road tax you will pay, take a look at our road tax guide.

CO2 emissions

This means the lower the CO2 tailpipe emissions (measured in grams per kilometre driven, or g/km), the greener the car.

Therefore all electric cars deliver zero tailpipe emissions (the emissions used to create the electricity is not counted) and diesels generally perform better than petrols and are therefore cheaper to tax.

However, diesels also emit particulates – or soot – as well as higher amounts of another pollutant, nitrate oxides (NOx). Therefore, buying a diesel doesn’t automatically make the car ‘greener’ just because it has lower CO2 emissions.

CO2 emissions are important for a buyer in monetary terms, however. If cutting costs is your aim, lower CO2 emissions will mean lower road tax. It could even mean free road tax if CO2 emissions are below 100g/km.

Alternatively, road tax can be extremely high for cars with 200g/km-plus CO2 emissions. The official CO2 emissions figure varies with each model, engine and technology used on each car, so it is important to check before buying the car.

As a rough guide, smaller engines will emit less CO2 than larger ones. Obviously, this means smaller cars are more likely to save you money on road tax.

Examples include the Fiat 500, which is the first car to boast road tax free petrol and diesel versions, the Citroen C1, Vauxhall Corsa and Ford Fiesta – all of which come with zero road tax in their most efficient models.

Similarly, diesels will generally emit less CO2 than similar-sized petrol engines. However, diesel models will be more expensive and fuel will cost more. You will need to work out if the potential savings outweigh the initial outlay.

It may be with a small car the potential savings are small between a petrol and a diesel compared to a price difference of several thousand pounds.

Fuel consumption

Fuel consumption is exactly what it sounds like; the amount of fuel you car uses when it is being driven.

Fuel consumption is measured by the amount of miles driven per gallon of fuel (mpg). The higher the official mpg figure, the better. The official figure should be the ‘combined cycle’ fuel consumption, which is an average of a number of readings taken for every new car on the market.

For more on the official fuel consumption figure, take a look here.

Once again, smaller, lighter cars will generally boast the best fuel consumption figures and mean less trips to the pumps for the driver.

However, extras such as low running resistance tyres, a more aerodynamic body and simple efficient driving can lead to fuel economy above the official figures. For more on ways you can improve fuel economy, take a look at our guide to eco driving.


The type of powertrain you choose will have a huge effect on costs. As already explained, diesel delivers lower CO2 emissions than petrol, but is more expensive and emits other harmful emissions.

Hybrid cars, most often include an electric motor matched to a petrol engine. These help to reduce the amount of petrol used. Plug-in hybrid cars can be charged via an electrical socket and are capable of travelling using just electric power for short distances to further save on fuel costs.

Alternatively, electric cars use energy from the national grid to charge a (usually) lithium ion battery pack, which in turn powers an electric motor. Examples of electric cars include the Peugeot iOn and Citroen C-Zero, both of which are available to buy in the UK now.

For a full guide on petrol, diesel, hybrid and electric engines, click here.

What else should I look out for?

The CO2 emissions and fuel consumption figures are two of the most important for motorists. Both of these figures will be affected by a number of innovations introduced on some of the newer cars in the industry.

The following have all been introduced by car makers to create ‘greener’ cars and lower costs for motorists.

StartStop – StartStop technology is known as several variations of the ‘Stop and Start’ name. It simply means the engine has a system which cuts power when the car is stationary. The engine switches itself back on instantly when the brake is released. This will cut fuel consumption in busy traffic.

e-booster – Some manufacturers, for example Peugeot in the new 508 saloon, have included an electric ‘boost’ button to the StartStop system. An e-booster starts the engine a fraction quicker than a normal StartStop system.

Low rolling resistance tyres – More efficient tyres mean less drag and allow the car to use less fuel to generate the power to punch it through the air.

DPF – DPF stands for diesel particulate filter. This is included on some diesel cars and collects particulates – a type of pollutant exclusive to diesels – before they are emitted from the exhaust.

How to choose a green car?

The best thing to do is to base your criteria on the cost to you, the motorist. Luckily, this doesn’t mean you will need to do any complicated sums with a calculator.

Perrys’ green car section has all the tools you’ll need to find out if your green car can save you money.

These include a running costs calculator giving an estimated price per week of any car, a road tax calculator for all new cars sold at Perrys dealerships and even a Benefit in Kind calculator for business and fleet operators.

You can calculate the cost of your car in our green car section.