Transport & Environment’s analysis of the 2023 European Environment Agency (EEA) data – covering 806,000 PHEVs – reveals that real-world CO₂ emissions are nearly five times higher than official test figures.
This gap is driven by overly optimistic Utility Factors (UFs)—the assumed share of electric driving for plug-in hybrids—in official computations.
The gap is widening
Since 2021, the EEA has collected data from fuel monitors to inform decisions about which utility factors (UFs) to set. T&E has analysed the EEA data from 2023 and has discovered that the gap between real-world and official emissions is widening, from 3.5 in 2021 to 4.9 in 2023. These figures are based on official data from on-board fuel consumption meters (OBFCM).
The gap is mainly caused by flawed assumptions on the share of electric driving mode (the ‘utility factor’, UF), which leads to a drastic underestimate of official PHEV emissions.
Correction
This has misled consumers about the actual emissions and fuel efficiency of PHEVs, and carmakers exploit this loophole to meet EU CO₂ targets with ‘low-emission’ PHEVs that, in reality, emit far more.
To correct this, the EU has updated the assumption about the share of electric driving (utility factors, or UF) to better align the official CO2 ratings with the emissions that vehicles actually produce in real-world conditions. The EU has begun implementing UF corrections for 2025–2028.
It is welcome that the UF values are being corrected. But even with the planned 2027/28 UF correction, PHEV real-world emissions would be 18% higher than the official figures.
The first correction will take effect in 2025 for newly registered PHEVs and in 2026 for existing models. A second correction is scheduled for 2027/28. This is an essential correction as it aims to better align official figures with the actual use of PHEVs on the road.
A word of explanation about PHEVs
PHEVs are equipped with two distinct powertrains: an electric motor (e-motor) powered by a rechargeable battery and an internal combustion engine (ICE). These systems generally operate independently, enabling vehicles to switch between electric and combustion-based propulsion depending on driving conditions and battery charge status.
Because of this multi-mode functionality, the actual fuel consumption and resulting CO2 emissions of PHEVs can vary significantly in real-world use.
This variability is related to multiple factors, including how frequently the vehicle is charged and driving behaviour, particularly the share of kilometres driven in a particular driving mode (for instance, running on electricity from the battery or using exclusively the combustion engine).
As a result of these real-world variabilities, estimating PHEV emissions using standardized test cycles, such as the WLTP, is often inaccurate.
T&E has long flagged the PHEV loophole, and wants to reinforce the urgency of accelerating these changes and to ensure they are sufficiently ambitious. The new data strengthen the case for faster, more accurate regulation—and T&E’s briefing arrives just as real-world implications are intensifying.
PHEVs are also expected to be on the agenda when the EU Commission President Ursula von der Leyen has her ‘strategic dialogue’ with the car industry, NGOs, and other stakeholders next Friday.
