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Plug-in hybrid electric vehicles release nearly 5x more planet-heating pollution than official data indicate, according to a new analysis.

Growing Gap Between Lab and Real-World Emissions

Statistics reveals that PHEVs emit only 19% less CO₂ than conventional petrol and diesel cars, according to research carried out by a non-profit group. That differs significantly with lab estimates, which suggested a three-quarters decrease in pollution.

Researchers studied data from in-vehicle energy use monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab estimates, up from 3.5 times in 2021.

“Actual emissions are rising, while lab-reported emissions are decreasing,” said a lead analyst involved in the study. “That gap is growing and creates a significant problem. Consequently, PHEVs pollute almost as much as gasoline vehicles.”

Primary Factors Driving the Discrepancy

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery mode relative to total distance. They determined that only 27% of driving was done in electric mode, while official assumptions assumed over four-fifths.

Even, when running in electric mode, pollution amounts were well above lab estimates. That happened because EV motors were not strong enough to operate alone, resulting to combustion motors using gasoline for almost one-third of the travel covered in electric mode.

Policy and Financial Implications

Based on estimates, the lowballing of PHEV emissions enabled four major automaker companies to avoid over €5bn in penalties between 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ standards.

Furthermore, drivers of PHEVs could pay approximately €500 extra annually in running costs than would be estimated under lab tests.

“The bold statements that automakers often promote about their plug-in hybrid cars are clearly far from the truth,” commented a automotive analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are only slightly better than standard gas and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have lately been drawn again into policy discussions as carmakers have pressed the EU to weaken CO₂ standards. A planned ban on new internal combustion cars in 2035 has faced intense lobbying from the automotive industry and resistance from member states with large car industries.

Several senior officials have proposed plug-in hybrids as a possible “compromise” solution to include in the regulation.

One external energy policy expert, who was not involved with the study, called the report a “very useful contribution” after a long period in which segments of the car sector argued there was too little data to accurately evaluate real-world emissions.

“These findings demonstrate, beyond any doubt, that the gap in official and actual PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or conventional cars,” the expert stated. “Any regulatory changes regarding PHEVs should be implemented with utmost caution and in the light of this evidence.”