ICCT: ‘Gap between official and real-world consumption of cars widens again’

A new study by the International Council on Clean Transportation (ICCT) indicates that the gap between real-world and official CO2 emission and fuel consumption values of new combustion engine cars increased from 8% to 14% between 2018 and 2022.

The average gap, or divergence, between the official and real-world fuel consumption and CO2 emission values of passenger cars in Europe, has grown again despite introducing a new vehicle test procedure. The gap reached a level of 14% in 2022, i.e., real-world emission levels were 14% higher than advertised by manufacturers.

“The gap has grown 80% in five years, going up from a level of 8% in 2018. If not addressed, this trend will compromise the effectiveness of the EU’s CO2 reduction targets. It will also lead to false consumer expectations about real-world fuel consumption and the associated costs and environmental impact,” ICCT fears.

Gap grows again

The results are based on an investigation by ICCT. The study analyzes official CO2 emission data, a proxy for fuel consumption, reported by the European Environment Agency (EEA), combined with real-world fuel consumption information from more than 160 000 combustion engine and conventional hybrid cars reported by consumers on the spritmonitor.de website. Plug-in hybrid cars were analyzed separately in a previous report.

Official CO2 emission values are determined through measurements in a controlled laboratory environment. In 2017, a new test procedure, the Worldwide harmonized Light vehicles Test Procedure (WLTP), replaced the former New European Drive Cycle (NEDC).

While the new WLTP values are more representative of real-world values than their predecessor—consequently lowering the gap from 33% in 2018 to 8% in the same year—the gap is now growing again. While official fuel consumption and CO2 emission values dropped by about 7.3% between 2018 and 2022, the reduction achieved on the road was less than one-third, with only 2.3%.

Jan Dornoff, Research Lead at the ICCT and co-author of the report, emphasizes: “Our analysis shows that the real-world gap is growing again after the introduction of WLTP. Without counteraction, official CO2 emission values will become increasingly unrepresentative of real-world values, and mandatory reductions for official values will not be reflected in the actual CO2 emissions. This will undermine the EU’s efforts to reduce transport-related CO2 emissions and result in consumers paying more for fuel than anticipated.”

Correction mechanism

To prevent the gap from growing, the European Commission is mandated by the CO2 standards regulation to assess the development of a mechanism or process. This mechanism would adjust the manufacturers’ CO2 emission performance based on real-world data recorded by onboard fuel and energy consumption monitoring (OBFCM) devices. The ICCT study proposes a correction mechanism to compensate for excess CO2 emissions from a growing gap.

“The ICCT has been monitoring these disparities since the early 2010s, and fortunately, EU regulators now have appropriate tools to correct these divergences with transparent and reliable data. Using these tools, a correction mechanism can ensure that the CO2 emissions reduction targets that manufacturers must meet in the coming years are proportionally updated in accordance with the intended original stringency written into the law,” recommends Dr. Peter Mock, ICCT Europe’s Managing Director.

Additionally, onboard fuel consumption data could benefit consumers by providing real-world estimates of emissions and fuel consumption on vehicle efficiency labels. Furthermore, the authors suggest making anonymized OBFCM data, merged with relevant vehicle characteristics, publicly available to facilitate independent research using representative real-world fuel and energy consumption data.


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