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Plug-in hybrid cars produce nearly 5x greater planet-heating emissions than lab-reported data indicate, according to a new analysis.

Growing Gap In Official and Real-World CO2 Output

Data reveals that PHEVs release just one-fifth lower CO₂ than conventional gas and diesel vehicles, based on research conducted by a non-profit group. That contrasts sharply with laboratory estimates, which assumed a 75% reduction in pollution.

Researchers examined information from in-vehicle fuel consumption meters of eight hundred thousand vehicles registered in Europe between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Real-world emissions are rising, while lab-reported figures are decreasing,” stated a senior researcher participating in the report. “That gap is widening and poses a serious problem. Consequently, PHEVs emit nearly as much as petrol cars.”

Primary Reasons Driving the Discrepancy

Researchers linked the majority of the difference to overestimates of the “utility factor” – the percentage of kilometers travelled in battery power relative to total distance. The team found that only 27% of travel was done in EV mode, while official estimates suggested over four-fifths.

Even, when running in electric mode, pollution amounts were well above official projections. This occurred because electric motors were not strong enough to operate independently, leading to combustion motors burning gasoline for almost a third of the travel completed in EV mode.

Policy and Economic Consequences

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

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

“The bold claims that automakers like to make about their plug-in hybrid cars are obviously far from the truth,” stated a automotive analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly improved than standard gas and diesel cars in terms of energy consumption, CO₂ emissions, and running costs.”

Policy Debate and Automotive Lobbying

Plug-in hybrid vehicles have recently been brought back into policy discussions as automakers have pressed the European Union to relax CO₂ standards. A planned prohibition on new internal combustion cars in 2035 has faced intense lobbying from the car industry and resistance from member states with significant automotive manufacturing.

Several high-level politicians have suggested plug-in hybrids as a potential “compromise” option to include in the legislation.

An external energy policy expert, who was not involved with the study, called the report a “highly valuable contribution” after years in which parts of the car sector argued there was insufficient information to properly assess actual emissions.

“These findings demonstrate, without question, that the gap between lab and real-world PHEV energy use and CO₂ output is much, much greater than for petrol or conventional cars,” they stated. “Any regulatory changes regarding PHEVs should be implemented with utmost caution and in the light of this evidence.”