An average car used in the UK emits 17.6 per cent more carbon dioxide emissions than officially claimed, resulting in an extra 10 million tonnes of the greenhouse gas being released into the atmosphere per year.
The analysis, carried out by consumer website HonestJohn, looked at the fuel economy submissions of 100,000 British motorists and compared the data with official figures.
It concluded that the gap between official claims and reality seems to be widening.
According to Honest John, the Lexus NX is the worst offender, emitting 53.8 per cent more CO2 than officially claimed. The Lexus is followed by Land Rover Discovery Sport with 53.6 per cent and Mercedes-Benz SLK with 48.8 per cent.
The study found that older cars tend to perform much better, with Jaguar XK, Toyota MR2, Jaguar XJ and Honda S200 being most accurate in meeting their claims in real driving conditions.
“Car emissions made the headlines for all the wrong reasons in 2015, but the Volkswagen scandal is only half the story,” said Dan Powell, Managing Editor at HonestJohn.co.uk. “Real MPG highlights the disparities between the information motorists are given when they buy a new car and the reality of everyday driving.”
As a result of the disparity between the claimed and real fuel consumption, an average car driven on UK roads emits 330kg of CO2 per year more than its maker says. Instead of producing 1,900kg of CO2 per year, the average car produces 2,200kg. With 31 million cars on British roads, that makes a total of an extra 10 million tonnes of CO2 being emitted into the atmosphere.
The study also found that although officially claimed values have been decreasing, the real emissions levels have barely moved.
This study also highlighted that the gap between advertised miles per gallon and Real MPG has been growing since 2011. The UK’s average shortfall now accounts for 2,404 million litres of unleaded and 1,751 million litres of diesel sold annually.
HonestJohn says the reason for these discrepancies lies in the fact that since 2015, car makers have been fined by the European Commission for not meeting limits in laboratory tests. That means that instead of optimising cars for real driving conditions, car manufacturers focus solely on making them perform well in unreliable laboratory tests.
“Unlike official [laboratory tested] fuel consumption figures, Real MPG gives real-life comparative data and allows car owners and buyers to see how much on-the-road fuel a vehicle really uses,” Powell said.