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Plug-in hybrid electric vehicles produce almost five times more planet-heating emissions than official figures show, according to a new analysis.

Widening Discrepancy Between Official and Actual Emissions

Data reveals that PHEVs emit just one-fifth less CO₂ than traditional gas and diesel vehicles, based on analysis conducted by a non-profit organization. This contrasts sharply with lab tests, which assumed a three-quarters decrease in emissions.

Analysts studied data from in-vehicle fuel consumption monitors of 800,000 vehicles registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” said a senior researcher involved in the study. “That discrepancy is growing and poses a serious issue. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Key Reasons Behind the Discrepancy

Analysts linked the majority of the difference to overestimates of the “utility factor” – the percentage of miles driven in battery mode compared to total mileage. They found that only 27% of travel was done in EV mode, whereas official estimates suggested 84%.

Even, when running in electric mode, pollution amounts were well above official estimates. This occurred because electric motors were insufficiently powerful enough to function alone, leading to combustion motors burning gasoline for almost a third of the distance covered in electric mode.

Regulatory and Economic Consequences

According to calculations, the lowballing of PHEV CO2 output allowed several major automaker groups to escape more than €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs could pay approximately €500 extra annually in running costs than would be estimated under laboratory conditions.

“The strong statements that manufacturers often promote about their PHEV vehicles are obviously way off the truth,” stated a automotive analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly better than regular gas and diesel vehicles in terms of fuel use, CO₂ emissions, and running costs.”

Political Discussion and Industry Lobbying

Plug-in hybrid cars have recently been brought again into political debates as carmakers have pressed the EU to weaken CO₂ standards. A proposed ban on new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from member states with significant automotive manufacturing.

Some senior politicians have proposed plug-in hybrids as a possible “flexibility” option to introduce in the regulation.

One independent energy policy specialist, who was unaffiliated with the research, described the analysis a “very useful contribution” after years in which segments of the automotive industry argued there was insufficient data to properly evaluate actual emissions.

“These findings demonstrate, without question, that the gap between official and real-world PHEV energy use and CO₂ emissions is significantly greater than for gasoline or diesel vehicles,” they said. “All regulatory changes regarding PHEVs should be implemented with extreme care and in the light of this data.”