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PHEVs produce almost five times greater global warming pollution than lab-reported data show, according to a new analysis.

Widening Discrepancy Between Lab and Actual CO2 Output

Data shows that PHEVs emit only one-fifth less CO₂ than traditional petrol and diesel vehicles, based on analysis conducted by a non-profit organization. This differs significantly with lab estimates, which suggested a three-quarters reduction in pollution.

Analysts studied data from onboard fuel consumption monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are falling,” said a lead researcher involved in the study. “That gap is growing and creates a significant issue. Consequently, PHEVs emit almost as heavily as gasoline vehicles.”

Primary Reasons Driving the Discrepancy

Analysts attributed the majority of the difference to inflated estimates of the “utility factor” – the percentage of kilometers driven in battery mode compared to total distance. The team found that just 27% of driving was done in EV mode, whereas lab estimates assumed 84%.

Additionally, when running in electric mode, pollution amounts were well above official projections. This happened because EV motors were not strong enough to operate independently, leading to engines burning gasoline for nearly one-third of the distance completed in EV mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV emissions allowed several major automaker companies to escape over €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with European Union average fleet CO₂ standards.

Additionally, owners of PHEVs could pay approximately €500 more annually in running costs than is assumed under lab tests.

“The bold statements that automakers often promote about their plug-in hybrid vehicles are obviously way off the mark,” stated a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have lately been brought back into policy debates as carmakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive industry and resistance from EU countries with significant automotive manufacturing.

Several high-level politicians have proposed PHEVs as a possible “compromise” option to include in the legislation.

An external energy economics specialist, who was unaffiliated with the research, described the analysis a “highly valuable contribution” after years in which segments of the car industry argued there was insufficient information to properly evaluate actual CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in official and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or conventional vehicles,” they stated. “Any regulatory adjustments regarding PHEVs should be implemented with utmost care and considering that data.”