Real world and 'official' mpg gap growing

The comparison between official and "real-world" fuel consumption and CO2 emissions for passenger cars in Europe and the US is showing that the discrepancy between them is growing.

New research by the International Council for Clean Transportation (ICCT) has revealed that the difference between has risen from less than 10% discrepancy in 2001 to 25% in 2011.

Fuel consumption and carbon dioxide emission values for new cars in Europe are determined via the so-called type-approval process, which involves testing vehicles under laboratory conditions using the new european driving cycle (NEDC).

The type-approval values are the basis for consumer information, CO2 regulation, and CO2-based vehicle taxation, and therefore ought to provide a reliable and stable indication of fuel consumption and emission levels observed under "real-world" conditions on the road. However, this is far from the case.

The analysis by ICCT, done my aggregating several large sets of on-road driving data from various European countries, shows that that expected correspondence between type-approval and real-world values is not as strong as it should be, and is getting progressively weaker.

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)

The increase in the gap was especially pronounced after 2007â€"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.

The public policy implications are significant. The growing gap between reported efficiencies and actual driving experience halves the expected benefits of Europe's passenger vehicle CO2 regulations. It creates a risk that consumers will lose faith in type-approval fuel consumption values, which in turn may undermine government efforts to encourage the purchase of fuel-efficient vehicles through labelling and tax policy.

For tax authorities, the gap between type-approval and real-world CO2 values translates into a gap between actual and potential revenues from vehicle taxes. And increasing discrepancies between type-approval and on-road CO2 emissions can result in a competitive disadvantage for some vehicle manufacturers, as it tilts the playing field.

Download the ICCT report (2.6MB)

Ben Lane

Author:Ben Lane
Date Updated:28th May 2013

Related news