Plug-in Hybrid Cars Pollute Nearly as Heavily as Gasoline Vehicles, Study Finds

PHEVs produce nearly five times more planet-heating pollution than official data show, according to a recent report.

Widening Gap Between Official and Actual Emissions

Data reveals that PHEVs emit just 19% lower CO₂ than conventional gas and diesel cars, according to research conducted by a non-profit organization. This differs significantly with lab estimates, which assumed a three-quarters reduction in pollution.

Researchers studied information from onboard fuel consumption monitors of 800,000 vehicles sold in the EU from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” stated a lead researcher participating in the report. “This discrepancy is growing and creates a significant problem. As a result, PHEVs emit nearly as much as gasoline cars.”

Primary Reasons Behind the Emissions Gap

Researchers linked most of the gap to overestimates of the “utility factor” – the percentage of kilometers driven in battery mode relative to overall mileage. The team found that only a quarter of driving was completed in electric mode, whereas official estimates suggested over four-fifths.

Additionally, when operating in electric mode, emission amounts were well above lab projections. That happened because electric motors were insufficiently powerful sufficient to operate independently, resulting to combustion motors burning fossil fuels for almost one-third of the travel completed in electric mode.

Regulatory and Financial Consequences

Based on calculations, the underestimation of PHEV emissions enabled several large automaker groups to avoid over €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs would pay about €500 more annually in operating costs than is assumed under laboratory tests.

“The strong statements that manufacturers like to make about their PHEV vehicles are clearly way off the truth,” stated a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ production, and running costs.”

Policy Debate and Industry Pressure

Plug-in hybrid vehicles have lately been brought again into political discussions as automakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on new internal combustion vehicles in 2035 has faced intense lobbying from the automotive sector and opposition from member states with significant car industries.

Some high-level officials have suggested plug-in hybrids as a possible “flexibility” option to include in the legislation.

One external energy policy expert, who was unaffiliated with the research, called the analysis a “very useful contribution” after a long period in which segments of the automotive sector argued there was insufficient information to properly evaluate real-world emissions.

“The results show, beyond any doubt, that the difference in lab and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or conventional vehicles,” they said. “Any regulatory changes concerning PHEVs should be made with utmost caution and in the light of that data.”