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Plug-in hybrid cars emit nearly 5x greater planet-heating pollution than lab-reported figures indicate, according to a new report.

Widening Discrepancy Between Lab and Actual Emissions

Data reveals that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, based on research conducted by a non-profit organization. This differs significantly with laboratory tests, which suggested a 75% decrease in emissions.

Analysts examined information from in-vehicle energy use monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, increased from three and a half times in 2021.

“Actual CO2 output are rising, while official figures are decreasing,” stated a lead researcher participating in the study. “That gap is widening and creates a serious problem. As a result, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Reasons Behind the Emissions Gap

Researchers linked most of the difference to overestimates of the “utility factor” – the ratio of kilometers travelled in electric power relative to overall distance. The team determined that only a quarter of travel was done in EV mode, whereas official assumptions assumed 84%.

Even, when running in EV mode, emission amounts were well above official projections. This occurred because electric motors were insufficiently powerful sufficient to operate independently, resulting to combustion motors using fossil fuels for almost one-third of the distance covered in EV mode.

Policy and Economic Consequences

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

Furthermore, drivers of PHEVs could spend about €500 more annually in operating costs than is estimated under laboratory tests.

“The strong statements that manufacturers like to make about their PHEV vehicles are obviously way off the mark,” commented a transport analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and saving money. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have lately been brought again into political discussions as carmakers have lobbied the European Union to weaken CO₂ targets. A planned prohibition on new combustion engine cars in 2035 has faced heavy lobbying from the automotive industry and opposition from member states with significant automotive industries.

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

One independent energy economics expert, who was unaffiliated with the study, called the analysis a “very useful addition” after years in which parts of the automotive industry claimed there was too little data to properly assess real-world emissions.

“These findings demonstrate, without question, that the gap between lab and real-world PHEV energy use and CO₂ emissions is much, much greater than for petrol or diesel vehicles,” they said. “All regulatory changes regarding PHEVs should be made with extreme care and considering that data.”