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Plug-in hybrid electric vehicles produce almost five times more planet-heating pollution than lab-reported data show, according to a recent analysis.

Growing Discrepancy Between Official and Real-World Emissions

Data shows that PHEVs emit just 19% lower CO₂ than conventional petrol and diesel vehicles, based on research carried out by a non-profit group. That contrasts significantly with laboratory estimates, which assumed a 75% decrease in emissions.

Analysts examined information from onboard energy use monitors of 800,000 cars registered in Europe between 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are falling,” stated a lead researcher involved in the report. “That gap is growing and poses a serious problem. Consequently, PHEVs pollute almost as heavily as petrol vehicles.”

Key Reasons Behind the Emissions Gap

Researchers attributed most of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in electric power compared to total mileage. They found that just 27% of travel was completed in electric mode, whereas official assumptions suggested 84%.

Even, when running in electric mode, pollution amounts were significantly higher than official projections. This happened because EV motors were insufficiently powerful enough to operate alone, leading to engines burning gasoline for nearly a third of the distance completed in EV mode.

Regulatory and Economic Consequences

Based on estimates, the lowballing of PHEV CO2 output enabled several major carmaker companies 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 would spend approximately €500 more annually in operating costs than is assumed under laboratory conditions.

“The bold statements that manufacturers like to make about their PHEV cars are clearly far from the truth,” stated a transport expert. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Political Discussion and Industry Pressure

Hybrid vehicles have recently been drawn back into policy discussions as automakers have pressed the EU to weaken CO₂ standards. A proposed ban on sales of new internal combustion vehicles in 2035 has faced intense pressure from the automotive industry and opposition from EU countries with significant automotive industries.

Some high-level officials have proposed plug-in hybrids as a possible “flexibility” solution to include in the regulation.

An external energy policy expert, who was not involved with the research, described the report a “very useful contribution” after a long period in which segments of the car sector claimed there was too little data to properly assess actual CO2 output.

“These findings demonstrate, without question, that the difference in official and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for petrol or conventional vehicles,” they said. “Any regulatory adjustments regarding PHEVs should be made with extreme caution and in the light of this evidence.”