Plug-in Hybrid electric Vehicles Emit Almost as Much as Gasoline Vehicles, Study Finds

Plug-in hybrid cars emit almost 5x more planet-heating pollution than lab-reported figures indicate, according to a new analysis.

Growing Discrepancy Between Lab and Actual Emissions

Data shows that PHEVs release only one-fifth less CO₂ than conventional gas and diesel vehicles, according to research carried out by a non-profit organization. That contrasts sharply with laboratory tests, which assumed a three-quarters decrease in emissions.

Researchers studied data from onboard fuel consumption meters of eight hundred thousand cars sold in Europe from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than lab estimates, up from 3.5 times in 2021.

“Real-world emissions are rising, while official figures are falling,” said a senior researcher involved in the study. “This gap is widening and poses a serious issue. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Key Factors Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “electric driving share” – the ratio of kilometers travelled in battery power relative to overall mileage. The team found that only 27% of travel was completed in EV mode, whereas lab estimates assumed over four-fifths.

Even, when operating in EV mode, emission amounts were well above official projections. That occurred because EV motors were not strong enough to function independently, resulting to combustion motors using fossil fuels for almost a third of the travel covered in EV mode.

Regulatory and Financial Implications

Based on calculations, the underestimation of PHEV emissions enabled four major automaker groups to escape over €5bn in penalties from 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ standards.

Furthermore, drivers of PHEVs would spend approximately €500 more per year in operating expenses than is estimated under lab conditions.

“The strong claims that manufacturers like to make about their PHEV vehicles are obviously way off the truth,” commented a transport analyst. “Buyers are being duped into thinking that by buying a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Policy Debate and Industry Pressure

Plug-in hybrid vehicles have lately been drawn back into political debates as carmakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on sales of new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and opposition from member states with significant automotive manufacturing.

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

An external energy policy expert, who was not involved with the study, described the analysis a “highly valuable contribution” after a long period in which parts of the car industry claimed there was too little information to properly evaluate real-world CO2 output.

“These findings demonstrate, without question, that the gap in official and actual PHEV fuel consumption and CO₂ emissions is significantly larger than for gasoline or diesel vehicles,” they said. “All regulatory changes regarding PHEVs should be implemented with extreme caution and in the light of this data.”