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Plug-in hybrid electric vehicles produce almost five times more global warming emissions than lab-reported data indicate, according to a new report.

Widening Discrepancy In Lab and Actual Emissions

Data shows that PHEVs release just 19% less CO₂ than conventional petrol and diesel vehicles, according to analysis conducted by a advocacy group. This contrasts sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Analysts studied information from in-vehicle energy use monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than official figures, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while official emissions are decreasing,” said a lead researcher involved in the report. “This discrepancy is growing and poses a serious problem. As a result, PHEVs pollute almost as much as gasoline cars.”

Key Reasons Driving the Emissions Gap

Researchers linked most of the gap to overestimates of the “electric driving share” – the ratio of miles travelled in electric mode relative to overall distance. They found that just 27% of driving was completed in EV mode, while lab estimates assumed 84%.

Additionally, when operating in EV mode, pollution levels were significantly higher than official estimates. This happened because electric motors were insufficiently powerful enough to operate independently, resulting to engines using gasoline for nearly one-third of the travel covered in EV mode.

Policy and Financial Consequences

Based on estimates, the underestimation of PHEV emissions enabled several major carmaker companies to escape over €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs would pay about €500 more annually in operating costs than would be assumed under lab conditions.

“The strong claims that automakers like to make about their PHEV vehicles are clearly far from the truth,” stated a transport expert. “Consumers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly improved than standard gas and diesel vehicles in terms of fuel use, CO₂ emissions, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been brought back into political discussions as automakers have lobbied the EU to weaken CO₂ targets. A planned prohibition on new internal combustion cars in 2035 has faced intense lobbying from the automotive industry and resistance from member states with significant automotive manufacturing.

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

One independent energy policy specialist, who was not involved with the research, called the report a “highly valuable contribution” after years in which parts of the automotive industry argued there was insufficient information to accurately assess actual emissions.

“These findings demonstrate, beyond any doubt, that the gap between lab and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or conventional vehicles,” they said. “All policy adjustments concerning PHEVs should be made with extreme care and considering this evidence.”