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Plug-in hybrid cars release almost 5x greater planet-heating pollution than lab-reported data show, as per a new analysis.

Growing Gap In Lab and Actual CO2 Output

Statistics reveals that PHEVs release just one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to analysis conducted by a advocacy group. This differs sharply with lab tests, which assumed a three-quarters reduction in emissions.

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 estimates, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” said a lead analyst participating in the study. “This discrepancy is growing and creates a serious problem. Consequently, PHEVs pollute almost as heavily as petrol cars.”

Primary Factors Driving the Emissions Gap

Researchers attributed most of the gap to overestimates of the “electric driving share” – the ratio of miles travelled in battery power compared to total distance. The team determined that just 27% of travel was done in electric mode, while official assumptions suggested 84%.

Even, when operating in EV mode, emission levels were significantly higher than lab projections. This occurred because electric motors were not strong enough to operate alone, resulting to combustion motors burning fossil fuels for almost one-third of the distance completed in electric mode.

Policy and Economic Implications

Based on calculations, the underestimation of PHEV CO2 output allowed four major carmaker companies to avoid more than €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could pay about €500 more per year in operating costs than would be estimated under laboratory conditions.

“The strong statements that automakers often promote about their plug-in hybrid cars are obviously way off the truth,” commented a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are only slightly improved than regular gas and diesel cars in terms of fuel consumption, CO₂ production, and operating costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have recently been drawn back into policy discussions as automakers have lobbied the EU to weaken CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the car industry and resistance from EU countries with significant car industries.

Some high-level officials have proposed plug-in hybrids as a possible “flexibility” option to include in the legislation.

An external energy policy expert, who was unaffiliated with the research, called the report a “highly valuable addition” after years in which segments of the automotive sector argued there was insufficient information to accurately evaluate real-world CO2 output.

“The results show, without question, that the gap between official and real-world PHEV energy use and CO₂ output is much, much greater than for gasoline or conventional cars,” they said. “Any regulatory changes regarding PHEVs should be made with utmost caution and considering this data.”