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Plug-in hybrid electric vehicles release almost 5x greater planet-heating pollution than lab-reported figures indicate, according to a new analysis.

Widening Discrepancy Between Official and Real-World CO2 Output

Statistics reveals that PHEVs release only one-fifth less CO₂ than traditional petrol and diesel cars, based on analysis carried out by a advocacy group. That differs significantly with laboratory tests, which suggested a three-quarters reduction in emissions.

Analysts examined data from in-vehicle fuel consumption monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, up from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported emissions are decreasing,” said a lead analyst participating in the study. “This gap is growing and creates a significant issue. Consequently, PHEVs pollute almost as heavily as gasoline cars.”

Primary Reasons Behind the Emissions Gap

Researchers linked most of the difference to inflated estimates of the “electric driving share” – the ratio of miles travelled in electric power compared to total mileage. The team determined that just a quarter of travel was completed in EV mode, while official assumptions suggested over four-fifths.

Additionally, when running in electric mode, pollution amounts were well above official estimates. That occurred because EV motors were not strong enough to operate independently, leading to combustion motors burning gasoline for almost one-third of the travel covered in EV mode.

Policy and Financial Implications

According to calculations, the underestimation of PHEV CO2 output allowed four large carmaker groups to escape more than €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would spend approximately €500 more annually in running expenses than is assumed under lab conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are obviously way off the mark,” stated a transport analyst. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and saving money. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Political Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been drawn again into policy debates as automakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on new combustion engine vehicles in 2035 has faced intense lobbying from the car sector and resistance from EU countries with large automotive industries.

Some high-level politicians have suggested PHEVs as a possible “flexibility” option to introduce in the legislation.

One independent energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable contribution” after a long period in which parts of the automotive industry argued there was too little data to accurately evaluate real-world emissions.

“The results demonstrate, beyond any doubt, that the difference between official and real-world PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional cars,” the expert stated. “Any regulatory changes regarding PHEVs should be made with utmost care and considering this evidence.”