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Plug-in hybrid cars produce nearly 5x greater planet-heating emissions than lab-reported data show, as per a new analysis.

Widening Gap In Lab and Actual Emissions

Data shows that PHEVs emit just one-fifth less CO₂ than conventional gas and diesel cars, based on analysis carried out by a advocacy group. This differs sharply with lab tests, which suggested a three-quarters decrease in pollution.

Researchers examined data from in-vehicle energy use monitors of 800,000 vehicles registered in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are falling,” said a senior researcher participating in the report. “That gap is widening and creates a serious issue. As a result, PHEVs pollute nearly as much as gasoline cars.”

Primary Factors Behind the Discrepancy

Researchers attributed most of the gap to overestimates of the “utility factor” – the ratio of miles driven in electric mode compared to total distance. The team found that just 27% of travel was done in EV mode, while official estimates assumed 84%.

Additionally, when running in EV mode, pollution amounts were significantly higher than lab projections. This occurred because EV motors were insufficiently powerful enough to operate independently, leading to combustion motors burning gasoline for almost one-third of the travel completed in electric mode.

Policy and Financial Consequences

According to estimates, the lowballing of PHEV CO2 output allowed several major carmaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay approximately €500 more per year in operating expenses than is estimated under laboratory tests.

“The bold claims that manufacturers often promote about their PHEV cars are obviously far from the truth,” stated a transport expert. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly better than standard petrol and diesel cars in terms of energy use, CO₂ production, and running costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have lately been brought again into policy discussions as carmakers have lobbied the European Union to weaken CO₂ targets. A proposed ban on new combustion engine cars in 2035 has faced intense pressure from the automotive sector and resistance from member states with significant car manufacturing.

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

An independent energy economics expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after years in which parts of the automotive industry claimed there was insufficient data to properly evaluate actual CO2 output.

“The results show, without question, that the difference between official and actual PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or diesel cars,” they stated. “All policy adjustments concerning PHEVs should be implemented with utmost caution and considering that data.”