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Plug-in hybrid cars produce nearly 5x more global warming pollution than lab-reported data indicate, according to a new analysis.

Growing Gap Between Lab and Actual Emissions

Data shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel cars, according to research conducted by a non-profit group. This differs significantly with lab estimates, which assumed a three-quarters reduction in pollution.

Analysts studied information from in-vehicle energy use meters of 800,000 vehicles sold in the EU between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Actual emissions are rising, while official emissions are falling,” said a senior researcher participating in the study. “That discrepancy is widening and poses a serious issue. As a result, PHEVs emit almost as heavily as gasoline vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in electric mode relative to overall mileage. They found that only 27% of travel was done in EV mode, whereas lab estimates suggested 84%.

Additionally, when running in electric mode, emission amounts were significantly higher than official projections. This occurred because EV motors were insufficiently powerful sufficient to operate independently, resulting to combustion motors using gasoline for nearly a third of the travel completed in electric mode.

Policy and Financial Implications

According to calculations, the underestimation of PHEV emissions enabled four major automaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 more annually in running expenses than would be assumed under lab tests.

“The bold claims that manufacturers often promote about their plug-in hybrid cars are obviously way off the mark,” stated a transport expert. “Consumers are being misled into thinking that by purchasing a PHEV, they are helping the environment and saving costs. Actually, PHEVs are only slightly better than standard petrol and diesel cars in terms of fuel use, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Pressure

Hybrid vehicles have lately been drawn back into policy debates as automakers have pressed the European Union to weaken CO₂ targets. A proposed ban on new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and resistance from member states with large car manufacturing.

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

One independent energy policy expert, who was not involved with the research, called the report a “highly valuable contribution” after a long period in which segments of the automotive sector argued there was too little information to properly evaluate actual CO2 output.

“These findings show, without question, that the difference in official and actual PHEV fuel consumption and CO₂ output is much, much larger than for gasoline or conventional vehicles,” they stated. “Any regulatory adjustments concerning PHEVs should be made with extreme caution and in the light of that data.”