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Plug-in hybrid electric vehicles produce nearly 5x more planet-heating pollution than official data show, according to a new report.

Growing Gap In Official and Real-World Emissions

Statistics shows that PHEVs emit just one-fifth lower CO₂ than traditional gas and diesel vehicles, according to research carried out by a non-profit organization. That differs significantly with lab estimates, which suggested a three-quarters decrease in emissions.

Researchers studied information from onboard energy use meters of 800,000 vehicles registered in the EU from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” stated a senior analyst participating in the report. “That gap is growing and creates a serious problem. As a result, PHEVs emit nearly as heavily as petrol cars.”

Key Reasons Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the ratio of miles driven in battery power compared to overall distance. The team found that just 27% of travel was done in electric mode, while lab estimates assumed 84%.

Additionally, when operating in electric mode, emission levels were significantly higher than official projections. This occurred because electric motors were insufficiently powerful sufficient to function independently, leading to engines burning gasoline for nearly a third of the travel covered in EV mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV emissions allowed four large automaker groups to escape over €5bn in penalties from 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ standards.

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

“The strong statements that automakers like to make about their plug-in hybrid cars are clearly far from the mark,” stated a automotive expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the environment and cutting money. Actually, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Political Discussion and Automotive Pressure

Plug-in hybrid cars have lately been brought again into policy debates as carmakers have lobbied the EU to relax CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and resistance from member states with large car manufacturing.

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

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

“These findings demonstrate, beyond any doubt, that the gap in lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or diesel cars,” the expert said. “Any regulatory adjustments concerning PHEVs should be implemented with extreme caution and considering this evidence.”