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PHEVs release almost 5x greater planet-heating pollution than lab-reported data show, according to a new analysis.

Growing Gap Between Lab and Actual CO2 Output

Data shows that PHEVs emit only 19% less CO₂ than conventional gas and diesel cars, according to analysis conducted by a non-profit organization. That contrasts significantly with lab tests, which assumed a 75% decrease in emissions.

Researchers examined information from in-vehicle fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Actual emissions are rising, while official figures are falling,” said a lead analyst participating in the report. “That discrepancy is widening and poses a significant issue. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Key Reasons Driving the Discrepancy

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the ratio of miles driven in electric mode relative to overall mileage. They determined that only 27% of driving was completed in EV mode, whereas official assumptions assumed 84%.

Additionally, when running in electric mode, emission amounts were significantly higher than lab estimates. This occurred because electric motors were not strong enough to function independently, leading to engines using gasoline for nearly a third of the travel completed in electric mode.

Regulatory and Economic Implications

According to calculations, the lowballing of PHEV emissions enabled four major carmaker groups to escape more than €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ standards.

Additionally, owners of PHEVs could spend about €500 extra annually in operating costs than is assumed under laboratory conditions.

“The strong claims that manufacturers like to make about their PHEV cars are obviously far from the mark,” stated a transport expert. “Consumers are being misled into believing that by buying a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are little better than regular gas and diesel cars in terms of fuel use, CO₂ emissions, and running expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been brought back into policy debates as automakers have lobbied the European Union to weaken CO₂ standards. A planned ban on sales of new combustion engine cars in 2035 has faced heavy lobbying from the car industry and resistance from EU countries with large car manufacturing.

Several high-level politicians have proposed plug-in hybrids as a possible “flexibility” option to include in the legislation.

An external energy economics expert, who was not involved with the study, called the report a “highly valuable addition” after a long period in which segments of the car industry argued there was too little information to properly evaluate actual CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in official and actual PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or conventional vehicles,” the expert said. “Any regulatory changes concerning PHEVs should be implemented with utmost care and in the light of that data.”