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Plug-in hybrid electric vehicles emit nearly five times more planet-heating pollution than official data indicate, according to a new report.

Widening Discrepancy In Lab and Real-World CO2 Output

Data shows that PHEVs release just one-fifth lower CO₂ than traditional gas and diesel cars, based on research carried out by a non-profit group. This contrasts significantly with laboratory tests, which suggested a 75% decrease in emissions.

Researchers examined information from in-vehicle energy use meters of eight hundred thousand cars registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than lab estimates, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are decreasing,” said a senior analyst participating in the report. “That discrepancy is growing and creates a serious problem. As a result, PHEVs pollute nearly as much as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Analysts linked most of the difference to overestimates of the “electric driving share” – the ratio of miles travelled in electric power relative to total mileage. The team determined that only 27% of driving was completed in EV mode, while lab assumptions suggested 84%.

Even, when running in EV mode, emission levels were well above official estimates. That occurred because electric motors were not strong sufficient to operate independently, leading to combustion motors burning gasoline for nearly a third of the distance covered in electric mode.

Regulatory and Economic Implications

Based on estimates, the underestimation of PHEV CO2 output allowed several major carmaker groups to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could spend approximately €500 extra per year in running costs than would be estimated under lab conditions.

“The strong statements that automakers like to make about their plug-in hybrid vehicles are clearly way off the mark,” stated a transport expert. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are little improved than regular gas and diesel cars in terms of fuel consumption, CO₂ production, and running expenses.”

Political Debate and Automotive Lobbying

Hybrid cars have lately been drawn again into policy debates as automakers have lobbied the EU to weaken CO₂ targets. A planned ban on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the car industry and resistance from EU countries with large car manufacturing.

Some high-level officials have proposed PHEVs as a potential “flexibility” solution to include in the regulation.

An external energy economics specialist, who was not involved with the study, described the analysis a “very useful addition” after years in which parts of the car sector claimed there was insufficient information to accurately evaluate actual CO2 output.

“The results demonstrate, without question, that the gap between official and actual PHEV energy use and CO₂ output is much, much greater than for petrol or conventional vehicles,” the expert stated. “Any regulatory adjustments regarding PHEVs should be implemented with utmost caution and considering this evidence.”