On the way to ‘real-world’ CO2 values? The European passenger car market after 5 years of WLTP

This paper investigates how the gap, or divergence, between official and real-world data on CO₂ emissions from passenger cars in the EU has developed since introducing a new type-approval test procedure, the Worldwide harmonized Light vehicles Test Procedure (WLTP). The results indicate that there is a growing divergence between real-world and WLTP CO₂ emissions data for internal combustion engine cars and hybrid cars, as observed for New European Driving Cycle (NEDC) type-approved vehicles in the past.

Figure 1 shows that the official WLTP type-approval CO₂ emission values are more representative of real-world values than the ones from the previous NEDC test procedure. Our analysis shows a divergence of 7.7% for WLTP in 2018 compared to 32.7% for NEDC. However, the gap between real-world and official CO₂ emissions increased by over 80% in the 5 years since the introduction of the WLTP, reaching 14.1% in 2022.

Figure 1. Divergence between real-world and type-approval CO₂ emission values for internal combustion engine and hybrid passenger cars registered in Germany. Data sources: European Environmental Agency (EEA) and spritmonitor.de

This growing gap diminishes the effectiveness of the European Union’s CO₂ standards in reducing tailpipe CO₂ emissions from cars and vans. This is because CO₂ reduction goals are implemented by setting lower targets for official CO₂ emissions. The growing gap between official and real-world emission values, however, leads to a lower reduction in real-world CO₂ emissions than intended by the regulators.

Figure 2 compares the reduction in official versus real-world CO₂ emissions between 2009 and 2022. While official CO2 emission values decreased by 19.5%,real-world emissions decreased by only 5.8% over the same period due to the growing gap.

Figure 2. Reduction of internal combustion engine and hybrid car type-approval and real-world CO₂ emissions since the adoption of CO₂ standards in the EU in 2009 and 2022. WLTP CO₂ emissions in 2022 were converted to NEDC-equivalent values using a conversion factor of 1.21.

The analysis is based on official CO₂ emission data 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 platform.

The European Commission has been tasked through the CO₂ standards regulation with developing a mechanism or process that prevents this gap from growing. For this purpose, real-world fuel consumption data recorded by on-board fuel and energy consumption monitoring (OBFCM) devices should be used. However, while the availability of OBFCM data will allow the implementation of such a mechanism by 2027, regulators foresee this measure starting in 2030.

Based on the analysis, the authors offer the following recommendations to prevent the gap from growing and mitigate excess CO₂ emissions caused by a growing gap, using reliable and transparent data:

• The European Commission could develop a mechanism that prevents further growth of the gap, and a proposal for such a mechanism is provided in this paper. The described mechanism intends to both mitigate the growing gap and compensate for the excess real-world CO2 emissions released prior to the introduction of a correction mechanism.
• The availability of OBFCM real-world consumption data would support applying the correction mechanism starting in 2027.
• Real-world fuel consumption estimates could be displayed on vehicle efficiency labels for consumers.
• Anonymized OBFCM data could be made publicly available.
• OBFCM could be made mandatory for electric vehicles to ensure the availability of real-world energy consumption data.

Read more in our press release in German and English.

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