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Plug-in hybrid electric vehicles release almost five times greater planet-heating emissions than lab-reported data indicate, according to a recent report.

Growing Gap Between Lab and Real-World Emissions

Data shows that PHEVs release just one-fifth less CO₂ than traditional gas and diesel vehicles, based on analysis carried out by a non-profit organization. That contrasts significantly with laboratory tests, which assumed a 75% reduction in emissions.

Analysts examined data from in-vehicle fuel consumption meters of eight hundred thousand cars registered in the EU between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” stated a senior analyst participating in the study. “This discrepancy is widening and creates a significant problem. As a result, PHEVs pollute nearly as much as gasoline cars.”

Primary Factors Driving the Emissions Gap

Researchers attributed most of the difference to overestimates of the “electric driving share” – the ratio of miles driven in battery mode relative to total distance. They found that just 27% of driving was completed in EV mode, whereas lab assumptions suggested 84%.

Additionally, when running in EV mode, pollution amounts were well above official projections. That occurred because electric motors were not strong sufficient to function independently, resulting to engines burning gasoline for nearly one-third of the distance covered in EV mode.

Regulatory and Financial Implications

Based on estimates, the lowballing of PHEV CO2 output enabled several major automaker companies to escape over €5bn in fines between 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay approximately €500 more per year in running expenses than would be assumed under lab tests.

“The bold statements that automakers often promote about their plug-in hybrid cars are obviously way off the mark,” commented a transport analyst. “Consumers are being duped into believing that by buying a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are only slightly better than standard gas and diesel vehicles in terms of fuel use, CO₂ emissions, and running expenses.”

Political Discussion and Automotive Pressure

Hybrid vehicles have lately been drawn again into policy debates as automakers have lobbied the EU to weaken CO₂ targets. A planned prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive industry and opposition from member states with significant car manufacturing.

Several high-level politicians have proposed plug-in hybrids as a potential “flexibility” solution to include in the legislation.

An external energy economics specialist, who was unaffiliated with the study, described the analysis a “very useful contribution” after a long period in which parts of the car sector argued there was too little data to properly evaluate actual emissions.

“The results show, without question, that the gap between lab and real-world PHEV fuel consumption and CO₂ emissions is much, much greater than for gasoline or diesel cars,” the expert said. “All policy adjustments regarding PHEVs should be made with utmost caution and considering that data.”