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Plug-in hybrid electric vehicles release nearly five times greater planet-heating pollution than official figures show, according to a new analysis.

Widening Gap In Lab and Real-World CO2 Output

Data shows that PHEVs release only 19% less CO₂ than traditional gas and diesel cars, according to research conducted by a non-profit organization. This differs significantly with laboratory tests, which assumed a three-quarters reduction in emissions.

Analysts examined information from in-vehicle fuel consumption meters of eight hundred thousand cars sold in the EU between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, up from three and a half times in 2021.

“Real-world emissions are rising, while lab-reported figures are falling,” said a lead researcher participating in the report. “That discrepancy is widening and poses a significant issue. Consequently, PHEVs emit almost as much as gasoline vehicles.”

Key Factors Behind the Discrepancy

Researchers attributed the majority of the gap to inflated estimates of the “utility factor” – the ratio of kilometers driven in battery mode relative to total mileage. They determined that just a quarter of travel was done in electric mode, while lab assumptions suggested over four-fifths.

Additionally, when operating in electric mode, pollution levels were significantly higher than lab estimates. That happened because EV motors were insufficiently powerful enough to operate alone, resulting to combustion motors burning gasoline for nearly a third of the distance covered in electric mode.

Policy and Financial Implications

Based on calculations, the lowballing of PHEV CO2 output enabled four major carmaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ targets.

Furthermore, drivers of PHEVs would spend approximately €500 extra annually in operating expenses than is estimated under laboratory tests.

“The strong statements that automakers like to make about their PHEV cars are obviously far from the mark,” stated a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are little improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ production, and running costs.”

Political Debate and Industry Pressure

Plug-in hybrid cars have recently been drawn back into policy debates as carmakers have lobbied the European Union to relax CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with large car manufacturing.

Several high-level politicians have suggested PHEVs as a potential “flexibility” option to include in the legislation.

One independent energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable addition” after a long period in which segments of the automotive sector argued there was insufficient data to properly evaluate actual CO2 output.

“The results demonstrate, without question, that the difference between official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for petrol or diesel cars,” they said. “Any policy adjustments concerning PHEVs should be made with extreme care and in the light of this data.”