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Plug-in hybrid cars emit almost five times more planet-heating emissions than official data show, according to a new analysis.

Widening Gap Between Lab and Actual Emissions

Statistics shows that PHEVs release only 19% lower CO₂ than conventional petrol and diesel vehicles, according to analysis carried out by a non-profit organization. This contrasts sharply with laboratory estimates, which assumed a three-quarters reduction in pollution.

Researchers studied data from onboard fuel consumption monitors of eight hundred thousand vehicles sold in the EU from 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, up from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” said a lead researcher involved in the report. “That discrepancy is growing and poses a serious issue. Consequently, PHEVs emit nearly as heavily as gasoline vehicles.”

Key Reasons Driving the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the percentage of miles driven in electric mode relative to overall distance. They determined that just 27% of travel was done in EV mode, while official assumptions assumed 84%.

Additionally, when operating in EV mode, pollution amounts were significantly higher than lab projections. That occurred because electric motors were insufficiently powerful enough to operate independently, resulting to engines burning fossil fuels for almost one-third of the distance completed in electric mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV CO2 output allowed four major automaker groups to escape over €5bn in fines from 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 extra annually in running expenses than would be assumed under laboratory conditions.

“The bold statements that automakers like to make about their plug-in hybrid vehicles are obviously far from the truth,” commented a automotive analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving money. In reality, PHEVs are little better than standard gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Pressure

Hybrid cars have recently been drawn again into policy debates as automakers have pressed the EU to relax CO₂ targets. A planned ban on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from EU countries with significant car manufacturing.

Several high-level politicians have suggested plug-in hybrids as a possible “flexibility” option to introduce in the regulation.

One independent energy policy specialist, who was not involved with the study, called the analysis a “very useful contribution” after a long period in which parts of the car sector argued there was insufficient data to accurately assess real-world CO2 output.

“The results demonstrate, beyond any doubt, that the difference between official and real-world PHEV energy use and CO₂ output is significantly larger than for petrol or conventional cars,” they stated. “Any regulatory changes regarding PHEVs should be implemented with extreme care and considering that data.”