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Plug-in hybrid electric vehicles release almost five times greater planet-heating pollution than lab-reported figures indicate, according to a recent analysis.

Growing Gap Between Lab and Real-World Emissions

Statistics shows that PHEVs emit only one-fifth lower CO₂ than conventional petrol and diesel cars, based on analysis conducted by a non-profit group. That differs sharply with lab tests, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard fuel consumption monitors of eight hundred thousand vehicles sold in Europe from 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” stated a lead analyst involved in the study. “That gap is widening and poses a significant issue. Consequently, PHEVs emit almost as heavily as gasoline vehicles.”

Primary Reasons Driving the Discrepancy

Researchers linked the majority of the difference to overestimates of the “utility factor” – the percentage of miles travelled in battery mode relative to overall distance. They found that only a quarter of driving was done in electric mode, while lab estimates suggested over four-fifths.

Even, when running in EV mode, pollution amounts were significantly higher than official estimates. That occurred because EV motors were not strong sufficient to operate independently, leading to combustion motors burning fossil fuels for nearly one-third of the distance covered in EV mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV emissions enabled several large automaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would spend about €500 more annually in running expenses than is assumed under laboratory tests.

“The bold claims that automakers often promote about their plug-in hybrid vehicles are obviously far from the mark,” stated a transport expert. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the environment and cutting money. Actually, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have recently been brought back into policy debates as carmakers have pressed the EU to weaken CO₂ standards. A planned prohibition on new internal combustion vehicles in 2035 has faced heavy pressure from the automotive industry and opposition from EU countries with large automotive manufacturing.

Some senior politicians have proposed plug-in hybrids as a potential “flexibility” solution to include in the legislation.

One independent energy economics expert, who was unaffiliated with the study, described the report a “very useful addition” after a long period in which parts of the car sector argued there was too little information to properly assess actual emissions.

“These findings show, beyond any doubt, that the difference between official and actual PHEV energy use and CO₂ emissions is significantly larger than for petrol or conventional vehicles,” the expert said. “Any policy changes concerning PHEVs should be made with extreme care and in the light of this evidence.”