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Emissions explained

  • We explain CO2 emissions and how they're tested
  • How manufacturers effectively produce desired results
  • What you need to know about how results are affected

By 2015 the average car will emit just 130g/km of CO2. Well, that’s the EU’s plan anyway. In the UK at least it looks as though we’re on track.

Since 2000 there’s been a 23% reduction in average CO2 emissions, with the UK’s average now 138g/km. But what does all this mean? In this article we explain all about CO2 emissions.

When choosing a new car, you’re shown the CO2 emissions information and it would be entirely reasonable to expect these figures are accurate and honest. However, that’s not strictly true. Measuring carbon dioxide emissions is something carried out by manufacturers, and there’s so much riding on the outcome of these tests that car companies leave absolutely nothing to chance.

The tests, for both emissions and fuel economy rating, are carried out on rolling roads. A firm supplies a driver who follows a set of instructions about when he should go up and down the gears and which speeds he should reach. The results are then used as a base for the rest of the range.

However, such tests don’t even have to be carried out in the country the car is to be sold in, and the tests can be resubmitted if the firm doesn’t like the outcome. This is how many cars slip just under certain CO2 thresholds – such as all those 99g/km you can buy now – meaning vast reductions in running costs for the driver. With respect to road tax, or VED, just 1g/km can mean a difference of up to £60 per year.

For company car drivers there are also Benefit-in-Kind implications. If your car emits say 116g/km you’ll be paying 13% for a diesel car this year, but that could shoot up to 17% from April 1, as the bandings shift.  

It’s also worth noting that CO2 emissions vary wildly from one model to another. Factors such as a big set of alloy wheels and fuel-saving technology such as stop/start can make a huge difference to CO2 emissions, and choosing an automatic gearbox can also have implications. For this reason it’s vital you check the CO2 rating for your particular derivative rather than for the range as a whole.

As a general rule, the lowest CO2 emissions come from diesel cars. However you have to weigh the savings up against the premium a diesel car costs to buy and also the 3% levy placed on diesel cars with regards to company car tax.