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.

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A European Environment Agency (EEA) report, Explaining road transport emission: a non-technical guide, provides a simplified explanation of the often complex information available on road transport emissions as well as the technologies to reduce them.
The report outlines three main reasons for these discrepancies:

  1. an outdated test procedure used in Europe that does not reflect real-world driving conditions;
  2. permitted “flexibilities” in the current testing procedures that allow manufacturers to optimise certain testing conditions, and thereby achieve lower fuel consumption and CO2 emission values (see infographic);
  3. and several in-use factors which are driver dependent (such as driving style) or independent (for example, environmental conditions).

Meanwhile, the European Commission has tabled legislative proposals to ensure car manufacturers comply strictly with all EU safety, environmental and production requirements.

Under current rules, national authorities are solely responsible for certifying that a vehicle meets all requirements to be placed on the market and for policing manufacturers’ compliance with EU law.

The proposals (see factsheet) will make vehicle testing more independent and increase surveillance of cars already in circulation.