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Plug-in hybrid cars release nearly 5x more planet-heating pollution than official data indicate, according to a new analysis.

Widening Gap Between Official and Real-World Emissions

Data shows that PHEVs emit just one-fifth less CO₂ than conventional petrol and diesel cars, according to analysis carried out by a advocacy organization. That differs sharply with lab tests, which suggested a three-quarters reduction in pollution.

Analysts examined information from onboard energy use meters of eight hundred thousand vehicles sold in Europe from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” said a senior analyst participating in the report. “This gap is growing and creates a serious problem. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Key Factors Behind the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery power relative to overall mileage. They found that just a quarter of driving was completed in EV mode, whereas lab estimates suggested over four-fifths.

Even, when operating in electric mode, pollution amounts were significantly higher than lab estimates. This happened because EV motors were not strong sufficient to function independently, leading to engines using gasoline for nearly one-third of the distance covered in electric mode.

Regulatory and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output enabled several major automaker companies to escape over €5bn in fines between 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs could pay about €500 extra annually in running costs than would be estimated under lab conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are obviously way off the mark,” stated a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are only slightly improved than standard gas and diesel vehicles in terms of energy consumption, CO₂ production, and operating expenses.”

Policy Discussion and Automotive Pressure

Hybrid cars have lately been brought back into policy debates as carmakers have lobbied the EU to weaken CO₂ standards. A planned prohibition on new internal combustion vehicles in 2035 has faced heavy lobbying from the car industry and resistance from member states with large car manufacturing.

Some senior politicians have suggested PHEVs as a possible “compromise” solution to introduce in the legislation.

An external energy economics expert, who was unaffiliated with the study, described the report a “highly valuable contribution” after a long period in which parts of the automotive industry argued there was insufficient data to accurately evaluate real-world CO2 output.

“The results demonstrate, without question, that the gap between lab and real-world PHEV fuel consumption and CO₂ output is much, much greater than for petrol or diesel cars,” they said. “Any regulatory changes regarding PHEVs should be made with utmost caution and in the light of that evidence.”