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Plug-in hybrid electric vehicles release nearly five times more planet-heating pollution than lab-reported data show, as per a new analysis.

Growing Gap In Official and Real-World Emissions

Data shows that PHEVs emit just 19% lower CO₂ than conventional gas and diesel vehicles, based on research carried out by a non-profit organization. That contrasts sharply with laboratory estimates, which suggested a 75% decrease in emissions.

Analysts examined data from onboard fuel consumption meters of eight hundred thousand vehicles sold in Europe from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are decreasing,” said a lead analyst participating in the report. “This gap is widening and poses a significant issue. As a result, PHEVs emit nearly as much as petrol cars.”

Key Factors Driving the Discrepancy

Researchers attributed most of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in electric power compared to overall mileage. They determined that just 27% of travel was completed in EV mode, while official assumptions assumed 84%.

Additionally, when operating in EV mode, pollution levels were significantly higher than lab projections. That happened because EV motors were insufficiently powerful sufficient to function alone, leading to combustion motors using fossil fuels for nearly a third of the travel completed in EV mode.

Policy and Financial Consequences

Based on estimates, the lowballing of PHEV emissions allowed several major carmaker groups to escape over €5bn in fines between 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ standards.

Additionally, owners of PHEVs would pay approximately €500 extra annually in running expenses than would be assumed under laboratory tests.

“The strong claims that manufacturers like to make about their plug-in hybrid vehicles are obviously way off the truth,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are little improved than regular petrol and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy Discussion and Industry Pressure

Hybrid vehicles have recently been drawn back into policy debates as carmakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the car sector and opposition from EU countries with large automotive manufacturing.

Several high-level politicians have proposed plug-in hybrids as a possible “compromise” solution to introduce in the legislation.

An independent energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable contribution” after years in which segments of the automotive sector argued there was insufficient data to accurately evaluate actual CO2 output.

“The results show, without question, that the gap in official and actual PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or diesel cars,” they said. “All policy changes regarding PHEVs should be made with utmost caution and in the light of this evidence.”