Real-world emissions from plug in hybrids are five times higher than official tests

A new analysis of European plug-in hybrid electric vehicles (PHEVs) has revealed that their real-world emissions are five times higher than official tests would suggest, warping consumers’ understanding of the actual emissions and fuel efficiency of the cars they drive.

The findings are important because PHEVs currently account for 8.6 per cent of all new car sales in the European Union so far this year, and European carmakers are desperate to keep selling PHEVs beyond the 2035 deadline for zero-emission cars.

However, according to a Transport & Environment (T&E) analysis, PHEVs are emitting on average 139g of CO₂ per kilometre – as compared to the 28g per km recorded in official tests and touted by the carmakers.

“Plug-in hybrids are still worse for the climate than carmakers claim and the gap with reality has only gotten worse,” said Lucien Mathieu, cars director at T&E.

“The car industry is demanding that the EU turn a blind eye so it can delay investing in fully electric cars. The EU Commission must stand its ground and stick to the already agreed utility factors for 2025 and 2027.”

The European Environment Agency (EEA) has since 2021 collected data from fuel monitors known as on-board fuel consumption meters (OBFCM), part of a legislated requirement to evaluate how well the standard Worldwide Harmonised Light Vehicles Test Procedure (WLTP) valued real-world driving.

Concerns were raised due to fixed assumptions in how the WLTP predicted driving behaviours, with research published by Fraunhofer ISI in 2022 showing that the WLTP was overly optimistic in assuming how often a driver would drive in electric-only mode.

At the time, Fraunhofer ISI warned that “real-world fuel consumption of PHEVs in Europe is on average three to five times higher than WLTP type-approval values.”

The analysis published by (T&E) confirms this original result. In their analysis of the three years’ worth of data currently available, T&E revealed that the gap between the official tests and real-world data continues to grow, despite carmakers’ claims that their hybrid technology is becoming cleaner.

Specifically, the EEA’s OBFCM dataset currently covers over 800,000 PHEVs that were registered between 2021 and 2023, including 127,000 registered in 2023. Over the three years covered by the data, the gap between standardised WLTP test cycles and real-world OBFCM emissions has steadily grown each year.

As can be seen in the graph below, real-world CO2 emissions were 3.5-times higher than official tests in 2021, and have only increased in the years following, to nearly 5-times higher in 2023.

In an effort to better account for the real-world emissions of PHEVs, the EU is changing how the WLTP measures PHEVs over the next two years, with the utility factor (UF) – the standardised assumption reflecting the share of total driving powered solely by electricity – set to be reduced.

The currently used UF assumes that a PHEV with a 60-kilometre range will drive over 80 per cent of that distance using only its battery.

However, new UF thresholds are being introduced to better reflect historically real-world driving – down to 54 per cent in 2025/26, and 34 per cent in 2027/28.

EU Commission president Ursula von der Leyen confirmed last Friday, in a “strategic dialogue” with the car industry, that the Commission would accelerate a review of its target of ending the sale of internal combustion engine (ICE) vehicles by 2035, and present a proposal to carmakers in December.

However, all indications appear to suggest that von der Leyen will maintain the 2035 ICE exit, despite loud calls by some in the European car industry for the target to be relaxed.

And with T&E’s latest analysis highlighting the EEA’s own data on the real-world emissions of hybrids, it would seem unlikely that business-as-usual will be able to continue for long.