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Why is my car's fuel consumption so much higher than the official numbers?

Recent literature shows that there is a considerable difference between a car's official CO2 emissions, obtained upon homologation under the NEDC test cycle (more information on the NEDC cycle is found in the first paragraph of this page), and CO2 emissions in real traffic. This difference has grown over the past few years and currently stands at an average of 20 to 25%. For fuel-efficient vehicles, the difference is even larger. About half of the difference is due to the test cycle itself which is not fully representative, e.g. by the low average speed and driving dynamics of the test cycle and by not taking into account the effect of using the air conditioning. The remainder of the difference is due to licit intervention by the manufacturers during the test procedure itself, e.g. by removing unnecessary weight or by greatly increasing the tire pressure. A new test cycle (WLTP) is currently being developed and will be more in line with reality and will be used by countries/regions all over the world. This test procedure is expected to come into force at the earliest in 2017.

Both consumers and policy should must be aware that cars are less energy-efficient than the official homologation data suggest. Nevertheless, the current official data remain useful as a base of comparison. Although the real-life emission levels of the various vehicles differ less from each other than the official values suggest, a fuel-efficient car according to the test cycle remains more economical in practice as well.

last database update: 12/05/2022 - next database update planned for: 15/07/2022
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