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Plug-in hybrid electric vehicles release nearly five times more global warming pollution than lab-reported data indicate, according to a new analysis.

Growing Discrepancy In Official and Actual Emissions

Statistics shows that PHEVs release only one-fifth lower CO₂ than conventional petrol and diesel vehicles, based on research conducted by a non-profit organization. This differs significantly with laboratory tests, which assumed a three-quarters reduction in pollution.

Analysts examined information from in-vehicle fuel consumption monitors of 800,000 vehicles registered in the EU from 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Real-world emissions are increasing, while official emissions are decreasing,” said a senior researcher participating in the study. “That discrepancy is growing and creates a serious problem. As a result, PHEVs emit nearly as much as gasoline cars.”

Primary Factors Driving the Emissions Gap

Researchers linked the majority of the gap to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power relative to total mileage. They found that just a quarter of driving was done in EV mode, whereas lab estimates assumed over four-fifths.

Additionally, when running in electric mode, emission levels were well above lab estimates. That occurred because EV motors were insufficiently powerful enough to function independently, resulting to combustion motors burning fossil fuels for nearly a third of the distance covered in EV mode.

Regulatory and Financial Implications

According to calculations, the lowballing of PHEV emissions allowed four large carmaker companies to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs could spend approximately €500 extra per year in operating costs than would be estimated under laboratory conditions.

“The strong statements that manufacturers like to make about their PHEV cars are clearly far from the mark,” stated a transport expert. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid cars have recently been brought again into political discussions as automakers have pressed the European Union to relax CO₂ standards. A proposed prohibition on new combustion engine cars in 2035 has faced intense pressure from the automotive sector and resistance from EU countries with significant automotive manufacturing.

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

An external energy economics specialist, who was unaffiliated with the research, called the report a “highly valuable addition” after a long period in which parts of the automotive sector claimed there was insufficient information to properly assess real-world CO2 output.

“The results demonstrate, without question, that the difference in official and real-world PHEV energy use and CO₂ output is much, much larger than for gasoline or diesel cars,” they stated. “All policy changes concerning PHEVs should be made with utmost care and considering this evidence.”