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Plug-in hybrid electric vehicles emit almost 5x greater planet-heating pollution than lab-reported data show, as per a recent report.

Growing Discrepancy Between Official and Real-World Emissions

Data reveals that PHEVs release just one-fifth lower CO₂ than traditional petrol and diesel vehicles, based on analysis carried out by a non-profit organization. That contrasts sharply with laboratory tests, which assumed a 75% reduction in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Real-world emissions are rising, while official emissions are falling,” said a senior researcher participating in the report. “This discrepancy is growing and creates a significant problem. Consequently, PHEVs emit almost as much as petrol cars.”

Primary Factors Driving the Emissions Gap

Analysts linked the majority of the difference to inflated estimates of the “electric driving share” – the ratio of miles travelled in battery power relative to total mileage. They determined that only a quarter of driving was done in EV mode, while official assumptions assumed 84%.

Additionally, when running in electric mode, emission amounts were significantly higher than official estimates. That occurred because EV motors were insufficiently powerful sufficient to operate alone, leading to combustion motors burning gasoline for nearly one-third of the travel covered in EV mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV emissions allowed several major automaker groups to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 more per year in running costs than would be assumed under laboratory tests.

“The strong statements that automakers like to make about their plug-in hybrid cars 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 cutting costs. Actually, PHEVs are only slightly improved than regular gas and diesel cars in terms of energy consumption, CO₂ emissions, and operating expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have lately been drawn back into political discussions as carmakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on new combustion engine cars in 2035 has faced intense lobbying from the automotive industry and resistance from EU countries with large automotive manufacturing.

Several high-level officials have suggested PHEVs as a possible “flexibility” solution to include in the legislation.

An external energy policy specialist, who was unaffiliated with the study, called the analysis a “highly valuable addition” after a long period in which parts of the car industry argued there was insufficient information to properly evaluate actual CO2 output.

“The results demonstrate, without question, that the difference between lab and actual PHEV fuel consumption and CO₂ emissions is significantly larger than for gasoline or diesel vehicles,” they said. “Any policy changes concerning PHEVs should be made with utmost caution and considering this data.”