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

Growing Gap Between Lab and Real-World Emissions

Data reveals that PHEVs release just 19% less CO₂ than traditional gas and diesel cars, according to analysis conducted by a non-profit organization. That contrasts significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official figures are falling,” said a senior researcher involved in the study. “That gap is growing and creates a significant problem. As a result, PHEVs emit nearly as heavily as petrol vehicles.”

Key Factors Behind the Emissions Gap

Researchers attributed most of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in battery mode compared to total mileage. The team found that just 27% of travel was done in EV mode, whereas lab assumptions assumed over four-fifths.

Even, when operating in electric mode, emission levels were well above lab estimates. That happened because EV motors were insufficiently powerful enough to operate independently, leading to engines using gasoline for nearly a third of the travel covered in EV mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV emissions allowed four major automaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially easing adherence with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could spend approximately €500 extra annually in running costs than would be assumed under lab conditions.

“The bold statements that manufacturers often promote about their PHEV cars are obviously far from the truth,” stated a automotive expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and saving costs. In reality, PHEVs are little better than standard petrol and diesel cars in terms of energy use, CO₂ production, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid cars have recently been drawn again into political debates as automakers have pressed the EU to relax CO₂ targets. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the car industry and resistance from EU countries with large car industries.

Several high-level officials have proposed plug-in hybrids as a potential “flexibility” solution to introduce in the legislation.

One external energy policy expert, who was unaffiliated with the research, called the analysis a “very useful addition” after a long period in which parts of the car sector claimed there was too little data to properly evaluate actual CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in official and actual PHEV energy use and CO₂ output is much, much greater than for petrol or diesel cars,” the expert stated. “All regulatory changes concerning PHEVs should be implemented with extreme caution and in the light of that evidence.”