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Plug-in hybrid cars produce nearly 5x more planet-heating pollution than official data show, according to a new analysis.

Widening Discrepancy Between Lab and Real-World Emissions

Statistics shows that PHEVs release just 19% lower CO₂ than conventional gas and diesel vehicles, based on analysis conducted by a non-profit organization. This differs significantly with lab tests, which suggested a three-quarters decrease in emissions.

Researchers examined information from in-vehicle fuel consumption monitors of eight hundred thousand vehicles sold in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official figures, up from 3.5 times in 2021.

“Actual emissions are rising, while official figures are falling,” said a senior analyst participating in the study. “This discrepancy is growing and poses a significant issue. As a result, PHEVs emit nearly as much as gasoline cars.”

Primary Factors Behind the Discrepancy

Analysts linked most of the difference to overestimates of the “utility factor” – the percentage of miles driven in electric power compared to overall mileage. They found that just a quarter of travel was completed in EV mode, while official assumptions suggested over four-fifths.

Even, when running in electric mode, pollution amounts were well above lab estimates. That happened because electric motors were not strong enough to operate independently, resulting to engines burning gasoline for almost a third of the travel covered in EV mode.

Regulatory and Financial Consequences

Based on estimates, the underestimation of PHEV emissions enabled several large automaker companies to avoid over €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ standards.

Additionally, owners of PHEVs would spend about €500 extra annually in running expenses than would be assumed under lab tests.

“The bold statements that automakers often promote about their PHEV vehicles are clearly far from the truth,” commented a automotive analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Political Discussion and Automotive Pressure

Plug-in hybrid cars have lately been drawn again into policy discussions as automakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive industry and opposition from member states with significant car manufacturing.

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

An external energy policy expert, who was unaffiliated with the study, called the analysis a “highly valuable addition” after years in which segments of the car sector argued there was insufficient data to properly assess actual CO2 output.

“These findings show, beyond any doubt, that the difference between lab and actual PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or conventional vehicles,” the expert said. “All policy changes regarding PHEVs should be implemented with utmost care and in the light of this data.”