That’s the finding of a new report published by the International Council on Clean Transport (ICCT), which shows that the average discrepancy between two figures rose from less than 10% in 2001 to 25% in 2011.

Dubbed “From Laboratory to Road”, the analysis aggregates several large sets of on-road driving data from various European countries and shows that the expected correspondence between type-approval and real-world values is not as strong as it should be, and is getting progressively weaker.

The report says the observed increase of the gap is most likely due to a combination of factors:

• Increasing application of technologies that show a higher benefit in type-approval tests than under real-world driving conditions (for example, start-stop technology)
• Increasing use of “flexibilities” (permitted variances) in the type-approval procedure (for example, during coast-down testing)
• External factors changing over time (for example, increased use of air conditioning)

It adds that the increase in the gap was especially pronounced after 2007–2008, when a number of European Union Member States switched to a CO2-based vehicle taxation system and a mandatory EU CO2 regulation for new cars was introduced.

Environmental NGO Transport & Environment has also highlighted that the study shows car manufacturers that sell the majority of gas-guzzlers in Europe manipulate fuel economy figures in tests much more than those makers that produce more fuel-efficient vehicles.

Luxury car brand BMW captures top-spot, reporting fuel efficiency figures that are on average 
30% lower than in real-life. This means that a buyer of a typical BMW car will burn on average around a third more fuel than claimed in the brochure and on labels in dealerships.

Audi ranks second with a “real v. claimed” gap as wide as 28%, followed by Opel/Vauxhall (27%) and Mercedes (26%). At the bottom of the table, Toyota’s manipulation of emissions tests produces official fuel economy figures that are just 15% lower than the real-world performance of its vehicles, while Renault’s and Peugeot Citroën’s (PSA) figures are on average 16% lower.

Transport & Environment clean vehicles manager Greg Archer said: ‘Car buyers in Europe need reliable fuel consumption figures to make informed purchase decisions. Carmakers aren’t delivering. European politicians need to end the current manipulation of fuel economy data.’

In response, T&E says that the current system of testing, the “New European Driving Cycle” is out of date and unrepresentative and contains many loopholes that carmakers are increasingly exploiting. It adds that a new global testing system, called World Light Duty Test Cycle and Procedures, which will be finalised in 2014, is more robust and representative of real-world driving. The European Parliament and European Commission propose to introduce this improved test in 2017. This decision is currently being discussed among member states of the European Union. 

‘The current test is over 30 years old and unrepresentative of real-world driving conditions. The lax testing rules allow carmakers to claim unachievable fuel economy. The European Commission and the European Parliament proposed to tackle this issue. EU member states should support them to ensure cheating of drivers stops,’ Greg Archer concluded.

The ICCT report is available by clicking here: www.theicct.org.