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Plug-in hybrid cars produce almost five times more planet-heating emissions than official figures show, according to a recent analysis.

Widening Discrepancy Between Official and Real-World CO2 Output

Data reveals that PHEVs release only 19% lower CO₂ than traditional petrol and diesel cars, based on analysis carried out by a non-profit group. This contrasts sharply with lab tests, which suggested a three-quarters reduction in emissions.

Analysts studied information from in-vehicle fuel consumption monitors of 800,000 vehicles registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, up from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” said a senior researcher involved in the study. “This gap is widening and poses a serious problem. As a result, PHEVs pollute nearly as heavily as gasoline cars.”

Key Reasons Driving the Discrepancy

Researchers linked most of the difference to overestimates of the “electric driving share” – the ratio of miles travelled in battery mode compared to total mileage. They determined that only 27% of driving was completed in EV mode, whereas lab assumptions assumed 84%.

Additionally, when running in electric mode, pollution amounts were well above official projections. That happened because electric motors were insufficiently powerful enough to operate independently, resulting to engines burning fossil fuels for nearly a third of the travel completed in electric mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV CO2 output enabled four major automaker companies to escape more than €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra annually in operating expenses than is assumed under laboratory conditions.

“The strong statements that automakers like to make about their PHEV cars are obviously way off the mark,” commented a transport expert. “Buyers are being duped into thinking that by buying a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Political Discussion and Automotive Pressure

Plug-in hybrid vehicles have lately been brought again into policy discussions as automakers have pressed the EU to weaken CO₂ targets. A planned prohibition on new internal combustion cars in 2035 has faced intense pressure from the car industry and resistance from EU countries with significant automotive manufacturing.

Several high-level politicians have proposed PHEVs as a potential “compromise” solution to include in the legislation.

An external energy economics expert, who was unaffiliated with the research, called the report a “very useful contribution” after years in which segments of the car sector argued there was insufficient data to accurately evaluate real-world emissions.

“These findings demonstrate, without question, that the gap between lab and real-world PHEV energy use and CO₂ output is significantly greater than for petrol or conventional vehicles,” they stated. “All policy adjustments concerning PHEVs should be implemented with utmost caution and in the light of this data.”