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Plug-in hybrid electric vehicles emit nearly 5x more planet-heating pollution than lab-reported data indicate, according to a recent report.

Widening Discrepancy Between Official and Real-World CO2 Output

Statistics shows that PHEVs release just one-fifth less CO₂ than conventional gas and diesel cars, according to analysis conducted by a advocacy organization. That contrasts sharply with lab estimates, which assumed a 75% reduction in emissions.

Researchers studied data from in-vehicle energy use monitors of 800,000 vehicles sold in Europe between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, increased from three and a half times in 2021.

“Real-world CO2 output are rising, while official figures are decreasing,” said a senior researcher participating in the study. “This gap is growing and poses a significant problem. As a result, PHEVs emit almost as heavily as gasoline vehicles.”

Primary Factors Driving the Discrepancy

Researchers attributed the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles driven in electric power compared to overall mileage. The team found that just 27% of driving was completed in electric mode, whereas lab estimates assumed over four-fifths.

Even, when running in EV mode, pollution levels were significantly higher than official estimates. This happened because electric motors were not strong sufficient to function alone, leading to engines burning gasoline for almost a third of the distance covered in EV mode.

Regulatory and Financial Implications

Based on estimates, the lowballing of PHEV CO2 output allowed four large automaker companies to escape more than €5bn in penalties from 2021 and 2023, by artificially easing adherence with EU fleet-average CO₂ standards.

Furthermore, owners of PHEVs would pay approximately €500 more per year in running expenses than is assumed under laboratory tests.

“The bold statements that manufacturers like to make about their plug-in hybrid vehicles are clearly way off the mark,” commented a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are only slightly better than regular gas and diesel cars in terms of energy consumption, CO₂ production, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have lately been drawn back into policy discussions as carmakers have pressed the EU to weaken CO₂ standards. A proposed ban on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the car industry and resistance from EU countries with large car industries.

Several senior officials have proposed plug-in hybrids as a potential “flexibility” solution to introduce in the regulation.

One external energy economics specialist, who was unaffiliated with the study, called the analysis a “very useful addition” after years in which parts of the car sector argued there was too little data to accurately assess actual emissions.

“The results demonstrate, without question, that the difference in official and actual PHEV energy use and CO₂ output is much, much greater than for petrol or conventional cars,” they stated. “Any policy adjustments regarding PHEVs should be implemented with extreme care and considering this data.”