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Plug-in hybrid electric vehicles emit nearly five times greater planet-heating pollution than official data indicate, as per a new report.

Growing Gap Between Lab and Actual CO2 Output

Statistics reveals that PHEVs release only one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to analysis conducted by a advocacy group. That contrasts significantly with lab estimates, which suggested a three-quarters reduction in pollution.

Researchers examined data from onboard energy use meters of 800,000 vehicles registered in the EU from 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official figures, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official emissions are falling,” said a lead analyst involved in the report. “That discrepancy is widening and creates a serious issue. As a result, PHEVs pollute almost as heavily as gasoline vehicles.”

Key Reasons Driving the Emissions Gap

Researchers linked most of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers driven in electric power relative to overall mileage. The team determined that just 27% of driving was done in electric mode, whereas official estimates assumed over four-fifths.

Additionally, when running in EV mode, emission levels were well above lab estimates. That happened because EV motors were insufficiently powerful enough to operate alone, leading to engines burning fossil fuels for nearly a third of the distance covered in EV mode.

Regulatory and Financial Implications

According to calculations, the underestimation of PHEV CO2 output enabled four large carmaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ standards.

Furthermore, drivers of PHEVs would pay approximately €500 more per year in operating costs than is assumed under lab tests.

“The bold statements that manufacturers often promote about their plug-in hybrid cars are clearly far from the truth,” commented a automotive analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the environment and cutting money. Actually, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy use, CO₂ production, and running costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have lately been drawn again into policy discussions as carmakers have pressed the EU to weaken CO₂ targets. A proposed prohibition on new internal combustion vehicles in 2035 has faced heavy lobbying from the car industry and resistance from EU countries with significant automotive manufacturing.

Some senior politicians have proposed PHEVs as a potential “flexibility” option to include in the regulation.

An independent energy policy expert, who was unaffiliated with the research, described the analysis a “very useful contribution” after a long period in which segments of the automotive industry argued there was insufficient data to accurately assess real-world emissions.

“The results 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 conventional cars,” the expert stated. “Any regulatory adjustments regarding PHEVs should be made with extreme care and in the light of that data.”