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Plug-in hybrid cars produce nearly 5x more planet-heating pollution than official data show, according to a new report.

Growing Discrepancy In Official and Actual Emissions

Statistics reveals that PHEVs emit just one-fifth less CO₂ than traditional petrol and diesel cars, according to analysis carried out by a advocacy group. This differs sharply with lab tests, which suggested a 75% reduction in pollution.

Researchers studied information from in-vehicle fuel consumption monitors of eight hundred thousand cars sold in the EU between 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, up from 3.5 times in 2021.

“Actual emissions are rising, while lab-reported emissions are falling,” stated a senior researcher participating in the report. “That discrepancy is growing and poses a serious issue. As a result, PHEVs pollute nearly as heavily as gasoline cars.”

Key Factors Driving the Discrepancy

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of miles travelled in electric mode relative to overall mileage. They found that just 27% of driving was completed in EV mode, whereas lab estimates suggested over four-fifths.

Additionally, when running in electric mode, emission levels were significantly higher than lab estimates. This happened because electric motors were insufficiently powerful sufficient to function independently, leading to engines burning fossil fuels for almost a third of the distance covered in electric mode.

Regulatory and Economic Implications

According to calculations, the underestimation of PHEV emissions allowed four large carmaker companies to avoid over €5bn in fines between 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra per year in operating expenses than is estimated under laboratory tests.

“The strong claims that manufacturers like to make about their plug-in hybrid cars are obviously way off the truth,” stated a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are helping the environment and saving money. In reality, PHEVs are little better than regular petrol and diesel cars in terms of energy consumption, CO₂ emissions, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been brought back into policy debates as carmakers have lobbied the EU to weaken CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced heavy lobbying from the car industry and resistance from EU countries with large car manufacturing.

Several high-level officials have proposed PHEVs as a potential “compromise” option to introduce in the legislation.

One external energy economics specialist, who was not involved with the study, called the report a “very useful addition” after a long period in which parts of the automotive sector argued there was insufficient information to accurately assess real-world CO2 output.

“These findings demonstrate, without question, that the difference between lab and real-world PHEV energy use and CO₂ output is significantly larger than for gasoline or diesel vehicles,” they said. “Any policy adjustments concerning PHEVs should be made with extreme care and considering that data.”