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

Widening Discrepancy Between Lab and Actual Emissions

Statistics reveals that PHEVs emit just one-fifth lower CO₂ than conventional petrol and diesel vehicles, based on research conducted by a non-profit organization. This differs sharply with laboratory tests, which assumed a 75% decrease in emissions.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 vehicles sold in Europe between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are falling,” said a lead researcher participating in the study. “This discrepancy is growing and creates a significant issue. As a result, PHEVs emit almost as heavily as petrol vehicles.”

Key Reasons Behind the Discrepancy

Researchers attributed most of the gap to inflated estimates of the “utility factor” – the ratio of kilometers travelled in electric mode compared to overall distance. The team found that just a quarter of driving was done in EV mode, whereas lab estimates suggested 84%.

Additionally, when running in EV mode, emission levels were significantly higher than official estimates. That happened because EV motors were not strong sufficient to function alone, leading to engines using fossil fuels for almost a third of the travel covered in electric mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV emissions enabled several large carmaker companies to avoid more than €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs could spend approximately €500 more per year in operating expenses than would be assumed under lab conditions.

“The strong claims that manufacturers often promote about their PHEV vehicles are obviously way off the mark,” commented a automotive analyst. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are little improved than regular petrol and diesel cars in terms of fuel use, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Lobbying

Hybrid cars have lately been brought back into political debates as automakers have pressed the EU to relax CO₂ targets. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with significant automotive industries.

Some senior officials have proposed PHEVs as a potential “compromise” option to include in the regulation.

One independent energy economics specialist, who was not involved with the study, called the analysis a “very useful contribution” after a long period in which parts of the car sector argued there was too little information to properly evaluate real-world emissions.

“The results demonstrate, beyond any doubt, that the gap in official and actual PHEV energy use and CO₂ emissions is significantly greater than for gasoline or diesel vehicles,” they said. “All regulatory adjustments regarding PHEVs should be made with utmost caution and considering that data.”