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Plug-in hybrid electric vehicles emit almost five times more planet-heating pollution than official figures show, according to a new analysis.

Growing Gap Between Lab and Actual Emissions

Statistics shows that PHEVs emit just 19% less CO₂ than traditional gas and diesel cars, based on research carried out by a non-profit group. That contrasts sharply with laboratory estimates, which suggested a 75% reduction in emissions.

Researchers studied information from onboard fuel consumption monitors of 800,000 cars registered in the EU from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” said a senior researcher involved in the study. “This gap is growing and creates a serious problem. Consequently, PHEVs pollute nearly as heavily as petrol vehicles.”

Primary Reasons Driving the Discrepancy

Researchers attributed the majority of the gap to overestimates of the “utility factor” – the ratio of kilometers driven in battery power relative to overall distance. The team determined that just a quarter of driving was completed in EV mode, whereas official estimates suggested 84%.

Additionally, when operating in electric mode, emission levels were significantly higher than official estimates. That occurred because EV motors were not strong sufficient to operate independently, leading to combustion motors burning fossil fuels for almost one-third of the distance completed in electric mode.

Regulatory and Financial Implications

Based on calculations, the lowballing of PHEV CO2 output allowed several large carmaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs could pay about €500 extra annually in running costs than is assumed under lab conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are clearly far from the mark,” commented a automotive expert. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little improved than regular gas and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have lately been brought back into policy discussions as automakers have pressed the European Union to weaken CO₂ standards. A proposed ban on sales of new combustion engine cars in 2035 has faced intense pressure from the automotive industry and resistance from EU countries with large car industries.

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

One external energy policy specialist, who was unaffiliated with the research, called the analysis a “very useful contribution” after years in which segments of the automotive industry argued there was too little data to accurately assess real-world emissions.

“The results show, without question, that the difference in official and real-world PHEV energy use and CO₂ emissions is much, much larger than for gasoline or diesel cars,” they stated. “Any policy adjustments regarding PHEVs should be made with utmost caution and in the light of that data.”