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Plug-in hybrid cars release almost 5x greater planet-heating pollution than lab-reported figures indicate, according to a new analysis.

Growing Discrepancy Between Official and Actual Emissions

Data shows that PHEVs emit only 19% less CO₂ than conventional petrol and diesel cars, based on analysis conducted by a advocacy organization. That differs sharply with lab tests, which suggested a three-quarters decrease in pollution.

Researchers studied data from onboard fuel consumption meters of 800,000 vehicles registered in the EU from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” said a senior researcher participating in the report. “That gap is widening and creates a significant problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Key Reasons Behind the Discrepancy

Researchers linked the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in electric power relative to total mileage. The team found that just 27% of travel was completed in electric mode, while official assumptions suggested 84%.

Even, when operating in EV mode, emission levels were well above official estimates. This occurred because EV motors were insufficiently powerful enough to function independently, resulting to engines burning fossil fuels for nearly a third of the travel covered in electric mode.

Regulatory and Financial Consequences

Based on estimates, the underestimation of PHEV emissions allowed several major automaker groups to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ targets.

Additionally, drivers of PHEVs would spend approximately €500 more annually in operating expenses than is assumed under lab tests.

“The strong claims that automakers like to make about their plug-in hybrid vehicles are obviously far from the truth,” commented a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and operating costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been brought back into policy debates as automakers have pressed the EU to weaken CO₂ standards. A planned prohibition on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the car industry and opposition from EU countries with large car industries.

Some senior politicians have suggested plug-in hybrids as a possible “compromise” solution to introduce in the legislation.

An external energy policy specialist, who was not involved with the research, called the report a “highly valuable addition” after years in which parts of the automotive sector argued there was insufficient data to accurately evaluate real-world CO2 output.

“These findings show, beyond any doubt, that the difference between official and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or diesel cars,” they stated. “All regulatory changes regarding PHEVs should be implemented with utmost caution and in the light of this data.”