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Plug-in hybrid electric vehicles produce almost 5x greater planet-heating emissions than official figures show, according to a new report.

Widening Gap Between Official and Real-World CO2 Output

Data reveals that PHEVs release only one-fifth less CO₂ than traditional petrol and diesel vehicles, based on research conducted by a advocacy group. This differs significantly with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers studied data from in-vehicle energy use meters of eight hundred thousand vehicles registered in the EU from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, up from 3.5 times in 2021.

“Actual CO2 output are rising, while official emissions are decreasing,” said a lead researcher participating in the study. “That discrepancy is widening and poses a serious problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Key Reasons Driving the Emissions Gap

Researchers attributed the majority of the gap to overestimates of the “electric driving share” – the percentage of miles driven in electric mode compared to total distance. The team found that just a quarter of driving was completed in electric mode, while official estimates suggested 84%.

Even, when running in electric mode, pollution levels were well above lab projections. This happened because EV motors were not strong sufficient to operate independently, leading to engines using gasoline for almost one-third of the travel covered in EV mode.

Regulatory and Financial Consequences

Based on estimates, the lowballing of PHEV emissions enabled several major carmaker groups to escape over €5bn in penalties from 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would spend approximately €500 more annually in operating costs than would be estimated under lab conditions.

“The bold claims that automakers often promote about their plug-in hybrid cars are obviously way off the truth,” commented a automotive expert. “Buyers are being duped into thinking that by buying a PHEV, they are benefiting the planet and saving costs. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ production, and operating costs.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought back into policy debates as carmakers have lobbied the EU to relax CO₂ targets. A planned prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the car sector and resistance from member states with significant automotive manufacturing.

Some high-level politicians have suggested plug-in hybrids as a potential “compromise” solution to include in the regulation.

An external energy policy specialist, who was not involved with the research, called the report a “very useful addition” after a long period in which segments of the car industry claimed there was too little data to accurately evaluate real-world emissions.

“These findings demonstrate, beyond any doubt, that the gap in lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or conventional vehicles,” they said. “Any policy adjustments concerning PHEVs should be made with extreme care and considering that data.”