Green Heroes: California Subscribe to RSS feed. Follow us on Twitter. Sign up for our newsletter

Awards won by

The Green Apple Awards 2011 GreenFleet Award



How are CO2 emissions measured?

The amount of carbon dioxide (CO2) emitted from a cars exhaust pipe is calculated in grams per kilometre (g/km). Tests on the new cars are conducted in a laboratory on a "rolling road" and the output is based on a "combined cycle" in which a variety of driving conditions are replicated. The CO2 output is then printed on the V5 registration document of all cars registered after February 2001.

As a rule of thumb, the larger the cars engine, the higher the emissions. This is due to the need to draw in more oxygen and burn more fuel in order to develop more power.

The CO2 emissions of each model of car allows consumers to buy cars that have reduced impact on the environment and also allow the UK Government to tax cars at different rates.

Recent figures have shown that driving a low CO2 emission car can save an individual up to £400 a year.

On this site we have brought together all the green cars (CO2 emissions under 150 g/km) in the UK and this will help you to choose a car that will not only reduce your impact on the environment but also save you hundreds of pounds every year.

Share this article

Lee Sibbald

Filed under: Latest News


simon price

Are the CO2 emissions calculated from the comsumption figures or are the levels actually measured? If they are simply calculated then there is no point having them. Even if actually measured they should corrospond to the consumption figures anyway. Rolling road numbers may be reproducible but are hardly realistic. Areodynamics and weight are not taken into account and hydrids have an unfair advantage that does not translate into real world figures. Time to scrap these useless numbers and use real road tests.


CO2 emissions are actually measured. The offical fuel consumption figures are then calculated from the CO2.

Vehicle aerodynamics and weight are used to calibrate the rolling road for the CO2 tests.

It's difficult to measure CO2 accurately and repeatably on the road so the manufacturers are required by law to do the measurements under laboratory conditions.

Leave a comment

Popular posts

Image: Biofuels: the pros and cons
Image: Hybrid cars: a guide
Image: LPG conversion: a helpful guide
The Green Piece
Available UK charge points for electric vehicles