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Plug-in hybrid electric vehicles release nearly 5x greater planet-heating pollution than lab-reported data show, according to a new report.

Growing Discrepancy Between Lab and Real-World Emissions

Statistics shows that PHEVs emit only 19% lower CO₂ than traditional gas and diesel cars, based on research carried out by a advocacy group. That differs significantly with laboratory estimates, which suggested a three-quarters reduction in emissions.

Researchers examined data from in-vehicle fuel consumption meters of 800,000 cars sold in Europe from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are decreasing,” stated a senior analyst involved in the report. “This gap is growing and creates a serious issue. As a result, PHEVs pollute nearly as heavily as gasoline vehicles.”

Key Reasons Behind the Emissions Gap

Analysts attributed the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in electric power relative to overall mileage. They determined that only a quarter of driving was done in EV mode, while official assumptions assumed 84%.

Additionally, when running in EV mode, pollution amounts were significantly higher than lab estimates. That occurred because electric motors were not strong sufficient to function independently, resulting to engines burning fossil fuels for nearly a third of the travel covered in electric mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV emissions enabled four large carmaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 extra per year in operating expenses than would be estimated under laboratory tests.

“The bold claims that automakers often promote about their PHEV vehicles are obviously far from the truth,” stated a automotive expert. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and cutting money. Actually, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Political Debate and Automotive Lobbying

Plug-in hybrid vehicles have lately been brought again into political discussions as carmakers have pressed the European Union to weaken CO₂ targets. A planned ban on new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive sector and resistance from member states with significant car manufacturing.

Several senior politicians have proposed plug-in hybrids as a possible “flexibility” solution to include in the legislation.

One external energy policy specialist, who was not involved with the research, called the analysis a “highly valuable addition” after years in which segments of the car industry argued there was insufficient information to accurately evaluate real-world emissions.

“The results show, beyond any doubt, that the difference between lab and real-world PHEV fuel consumption and CO₂ emissions is significantly larger than for petrol or conventional vehicles,” they stated. “Any policy changes regarding PHEVs should be implemented with extreme caution and in the light of this evidence.”