CO2 claims under fire

Manufacturers could be grossly underestimating their cars' CO2 output - casting doubt over the UK's road tax system

Auto Express Car Reviews

Ford Focus 1.6
Official CO2 figures 161g/km
Our CO2 figures 193g/km

By Chris Thorp

22nd February 2007

Auto Express's own fuel efficiency investigations suggest makers' quoted combined economy figures are unrealistic. "We found their claims to be 17-20 per cent above what motorists will achieve in everyday driving," said road test editor Oliver Marriage.

CO2 emissions - the Government's car taxation measure - are directly proportionate to fuel efficiency. There is little research readily available, but the US environmental protection agency said: "Each one per cent rise in consumption results in a one per cent rise in emissions." So, official CO2 figures could be up to 20 per cent too low.

Our investigation came as European Commissioners announced plans to force makers to cut CO2 emissions and encourage more environmentally conscious driving.

Auto Express's findings mean top-selling cars could be contributing more to global warming than first thought. Ford's Focus 1.6, for example, officially puts out 161g/km of CO2. But it's more likely to emit 193g/km. That would move the car from Band D to Band F, increasing road tax by £65 a year.

Government agencies appear to have little faith in the current set-up. The Vehicle Certification Agency (VCA) states on its website: "Emissions tests cannot fully represent real-life driving conditions."