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Plug-in hybrid cars emit almost five times more planet-heating emissions than lab-reported data show, according to a new report.

Growing Gap Between Lab and Actual Emissions

Statistics shows that PHEVs release just 19% lower CO₂ than traditional gas and diesel vehicles, based on research carried out by a non-profit organization. That differs sharply with laboratory estimates, which suggested a three-quarters reduction in pollution.

Analysts studied information from in-vehicle fuel consumption monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab estimates, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while official figures are falling,” stated a senior researcher involved in the report. “That gap is growing and creates a significant problem. Consequently, PHEVs pollute nearly as heavily as petrol cars.”

Primary Factors Driving the Emissions Gap

Researchers linked most of the gap to overestimates of the “electric driving share” – the ratio of miles driven in battery mode compared to total mileage. They found that only a quarter of travel was completed in EV mode, while lab estimates assumed 84%.

Additionally, when operating in EV mode, pollution amounts were significantly higher than lab projections. This happened because EV motors were insufficiently powerful sufficient to function alone, leading to engines burning gasoline for almost a third of the travel completed in EV mode.

Policy and Economic Implications

Based on estimates, the underestimation of PHEV CO2 output enabled several major carmaker companies to avoid more than €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs would pay approximately €500 extra per year in running expenses than would be estimated under lab tests.

“The bold statements that manufacturers often promote about their PHEV vehicles are obviously far from the mark,” stated a automotive analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Political Discussion and Industry Pressure

Plug-in hybrid vehicles have lately been drawn back into political debates as automakers have pressed the European Union to relax CO₂ standards. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from member states with large automotive industries.

Several senior politicians have proposed PHEVs as a possible “compromise” solution to introduce in the regulation.

An independent energy policy expert, who was unaffiliated with the research, described the report a “highly valuable addition” after years in which segments of the automotive industry argued there was insufficient data to accurately assess actual emissions.

“The results demonstrate, beyond any doubt, that the gap between lab and real-world PHEV energy use and CO₂ emissions is significantly greater than for gasoline or conventional vehicles,” they said. “Any policy changes regarding PHEVs should be implemented with utmost caution and in the light of that evidence.”