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Explaining vehicle emissions – why do laboratory and road measurements differ?

The road transport sector is a major contributor to Europe’s emissions of greenhouse gases and air pollution. For certain pollutants, vehicles can emit substantially higher emissions on the road than official emissions tested in laboratories. A report released yesterday by the European Environment Agency (EEA) provides a non-technical guide that describes the reasons for these often significant discrepancies.

 

Measuring exhaust emissions from vehicles is a complex issue, and it’s a topic that has been extensively discussed in the media over the past months. This report explains in simple terms how vehicle emissions occur and how they are tested, and the reasons for the gap between tested and real-world driving emissions.

EEA Executive Director Hans Bruyninckx

Despite improvements in vehicle efficiencies over past decades, EEA reports show that the road transport sector is responsible for almost one fifth of Europe’s greenhouse gas emissions. It also contributes to high concentrations of air pollutants above EU standards in many of Europe’s cities.

‘Measuring exhaust emissions from vehicles is a complex issue, and it’s a topic that has been extensively discussed in the media over the past months,’ said EEA Executive Director Hans Bruyninckx. ‘This report explains in simple terms how vehicle emissions occur and how they are tested, and the reasons for the gap between tested and real-world driving emissions.’

The new report, ‘Explaining road transport emissions: a non-technical guide’, gives a simplified explanation of the often complex information available on road transport emissions as well as the technologies to reduce them.

Standardised measurements are made in laboratories to check that vehicles meet the official requirements for exhaust emissions. However, the official procedures currently used in Europe are not representative of real driving conditions. For certain pollutants, there is a significant difference between official emission measurements and vehicle performance on the road. Nitrogen oxides (NOx), a major air pollutant which harms health and the environment, can be more than seven times higher under real world driving conditions for new vehicles than in official tests. New vehicles similarly can emit up to 40 % more carbon dioxide (CO2) than official measurements would indicate.

The report outlines three main reasons for these discrepancies:

  • An outdated test procedure used in Europe that does not reflect real-world driving conditions;
  • Permitted ‘flexibilities’ in the current testing procedures that allow manufacturers to optimise certain testing conditions, and thereby achieve lower fuel consumption and CO2emission values;
  • Several in-use factors which are driver dependent (e.g. driving style) or independent (e.g. environmental conditions)

Click here for full press release

 

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