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Plug-in hybrid electric vehicles produce almost 5x greater planet-heating pollution than lab-reported data indicate, according to a new report.

Growing Discrepancy In Official and Actual Emissions

Statistics shows that PHEVs emit only 19% less CO₂ than conventional gas and diesel cars, based on analysis conducted by a advocacy organization. That differs sharply with lab estimates, which assumed a 75% reduction in pollution.

Researchers examined data from in-vehicle energy use monitors of 800,000 vehicles registered in Europe between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, up from 3.5 times in 2021.

“Actual emissions are increasing, while official figures are decreasing,” stated a senior researcher participating in the study. “That gap is widening and creates a serious problem. As a result, PHEVs emit almost as heavily as petrol cars.”

Key Factors Driving the Discrepancy

Analysts attributed most of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to total distance. The team found that just 27% of travel was done in EV mode, while lab estimates assumed 84%.

Additionally, when operating in EV mode, pollution amounts were well above official estimates. That happened because electric motors were not strong sufficient to function independently, resulting to engines using fossil fuels for nearly a third of the distance completed in electric mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output enabled several major automaker companies to avoid over €5bn in fines from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ targets.

Additionally, owners of PHEVs could pay approximately €500 extra annually in running costs than is estimated under lab conditions.

“The strong claims that automakers like to make about their PHEV vehicles are clearly far from the truth,” stated a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than regular gas and diesel vehicles in terms of fuel consumption, CO₂ production, and running costs.”

Policy Debate and Industry Lobbying

Hybrid cars have recently been drawn again into policy debates as automakers have pressed the EU to relax CO₂ targets. A proposed prohibition on new internal combustion vehicles in 2035 has faced heavy pressure from the car sector and opposition from member states with large automotive manufacturing.

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

An independent energy policy specialist, who was not involved with the research, called the analysis a “highly valuable contribution” after years in which parts of the car industry argued there was too little information to properly evaluate real-world CO2 output.

“The results demonstrate, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or diesel cars,” the expert said. “Any regulatory changes concerning PHEVs should be implemented with utmost caution and in the light of that evidence.”