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Plug-in hybrid electric vehicles produce almost five times greater planet-heating emissions than official data show, according to a new analysis.

Widening Gap Between Lab and Actual Emissions

Data shows that PHEVs release only one-fifth lower CO₂ than conventional petrol and diesel vehicles, according to analysis conducted by a non-profit organization. That differs significantly with laboratory estimates, which assumed a 75% reduction in pollution.

Researchers studied data from onboard energy use meters of 800,000 cars registered in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are falling,” said a senior researcher participating in the report. “That discrepancy is growing and poses a serious issue. Consequently, PHEVs pollute nearly as heavily as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers linked the majority of the gap to overestimates of the “utility factor” – the ratio of miles driven in electric power relative to total distance. They found that just 27% of travel was done in EV mode, whereas lab assumptions suggested 84%.

Additionally, when running in electric mode, emission levels were significantly higher than official estimates. This happened because electric motors were insufficiently powerful enough to operate alone, resulting to engines using fossil fuels for almost one-third of the distance covered in electric mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV emissions enabled four major carmaker companies to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra annually in running expenses than would be estimated under laboratory conditions.

“The bold claims that automakers like to make about their PHEV cars are clearly way off the truth,” stated a transport expert. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are little better than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ production, and operating expenses.”

Policy Debate and Automotive Lobbying

Plug-in hybrid vehicles have lately been brought again into policy debates as automakers have pressed the European Union to relax CO₂ targets. A planned prohibition on sales of new combustion engine cars in 2035 has faced intense lobbying from the automotive industry and resistance from member states with significant automotive manufacturing.

Several senior officials have proposed plug-in hybrids as a potential “flexibility” option to include in the legislation.

One external energy policy expert, who was unaffiliated with the study, described the analysis a “highly valuable addition” after years in which parts of the car industry argued there was insufficient information to properly evaluate real-world CO2 output.

“The results show, beyond any doubt, that the gap in lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel cars,” they said. “All policy changes regarding PHEVs should be implemented with utmost caution and in the light of that evidence.”