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Plug-in hybrid electric vehicles produce almost five times greater planet-heating pollution than official figures indicate, according to a new analysis.

Growing Gap In Lab and Real-World CO2 Output

Data reveals that PHEVs release just one-fifth lower CO₂ than traditional petrol and diesel cars, based on research carried out by a advocacy group. That contrasts significantly with lab tests, which suggested a three-quarters reduction in emissions.

Researchers studied data from in-vehicle fuel consumption monitors of 800,000 vehicles sold in Europe from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, increased from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” stated a senior researcher involved in the study. “That gap is growing and creates a significant problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers attributed the majority of the gap to overestimates of the “utility factor” – the percentage of miles travelled in electric power compared to overall distance. The team determined that only 27% of travel was completed in electric mode, whereas lab assumptions assumed 84%.

Additionally, when operating in EV mode, emission levels were significantly higher than lab estimates. This occurred because EV motors were not strong enough to function independently, leading to engines burning gasoline for nearly a third of the travel covered in EV mode.

Regulatory and Financial Implications

Based on calculations, the lowballing of PHEV CO2 output allowed several major carmaker groups to avoid more than €5bn in fines from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ targets.

Additionally, owners of PHEVs would spend about €500 more per year in operating expenses than is assumed under laboratory conditions.

“The bold claims that manufacturers like to make about their PHEV vehicles are obviously far from the truth,” stated a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are little better than regular petrol and diesel cars in terms of energy consumption, CO₂ production, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have lately been brought again into political discussions as carmakers have lobbied the European Union to relax CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and opposition from EU countries with significant automotive industries.

Several senior politicians have suggested plug-in hybrids as a potential “compromise” solution to include in the legislation.

One independent energy economics specialist, who was unaffiliated with the study, described the report a “highly valuable contribution” after years in which segments of the car sector claimed there was insufficient data to properly evaluate real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in lab and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or conventional vehicles,” the expert stated. “All regulatory adjustments concerning PHEVs should be implemented with extreme care and in the light of that data.”