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Plug-in hybrid cars release almost 5x greater planet-heating pollution than official data indicate, according to a new report.

Widening Discrepancy Between Official and Real-World Emissions

Statistics shows that PHEVs release only 19% lower CO₂ than traditional gas and diesel vehicles, based on research carried out by a advocacy group. That contrasts significantly with laboratory estimates, which assumed a three-quarters decrease in emissions.

Researchers examined information from onboard energy use monitors of 800,000 cars sold in Europe from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, increased from three and a half times in 2021.

“Real-world emissions are increasing, while official figures are falling,” stated a senior analyst participating in the report. “This gap is growing and poses a significant issue. Consequently, PHEVs pollute nearly as much as petrol cars.”

Primary Reasons Driving the Emissions Gap

Researchers linked most of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in battery power relative to overall distance. They found that only 27% of travel was completed in EV mode, while official estimates suggested over four-fifths.

Even, when operating in electric mode, pollution levels were well above lab estimates. That happened because electric motors were not strong sufficient to function independently, resulting to engines using gasoline for nearly one-third of the distance completed in electric mode.

Regulatory and Financial Consequences

According to estimates, the lowballing of PHEV emissions allowed four major carmaker groups to avoid more than €5bn in fines between 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 extra per year in running expenses than is assumed under laboratory conditions.

“The strong statements that automakers like to make about their PHEV vehicles are obviously far from the mark,” commented a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and cutting costs. In reality, PHEVs are only slightly improved than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Discussion and Automotive Lobbying

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

Several high-level politicians have proposed plug-in hybrids as a potential “compromise” option to include in the legislation.

One external energy economics expert, who was not involved with the research, called the analysis a “very useful addition” after years in which parts of the automotive industry argued there was too little data to accurately assess real-world emissions.

“These findings demonstrate, beyond any doubt, that the difference between lab and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or diesel cars,” the expert said. “Any policy adjustments regarding PHEVs should be made with utmost care and considering this data.”