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Plug-in hybrid cars produce nearly five times more global warming emissions than lab-reported data show, according to a recent report.

Growing Discrepancy Between Lab and Real-World Emissions

Statistics shows that PHEVs release only one-fifth lower CO₂ than traditional petrol and diesel cars, based on analysis conducted by a advocacy group. This contrasts significantly with laboratory tests, which suggested a three-quarters reduction in emissions.

Researchers examined data from onboard fuel consumption monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are falling,” stated a lead researcher participating in the report. “That gap is growing and creates a significant problem. As a result, PHEVs emit nearly as much as gasoline vehicles.”

Key Factors Driving the Emissions Gap

Analysts linked most of the gap to overestimates of the “electric driving share” – the ratio of miles driven in electric power compared to overall distance. The team determined that only 27% of driving was completed in electric mode, whereas lab estimates suggested over four-fifths.

Additionally, when running in electric mode, pollution levels were significantly higher than lab projections. This occurred because EV motors were not strong sufficient to function alone, leading to engines using gasoline for almost a third of the travel covered in electric mode.

Regulatory and Financial Consequences

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

Furthermore, drivers of PHEVs would pay about €500 extra per year in operating expenses than would be estimated under laboratory tests.

“The strong statements that automakers often promote about their plug-in hybrid cars are clearly way off the truth,” stated a automotive analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little better than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running costs.”

Policy Debate and Industry Lobbying

Hybrid cars have recently been drawn again into political debates as automakers have pressed the EU to weaken CO₂ targets. A planned prohibition on sales of new internal combustion cars in 2035 has faced intense lobbying from the automotive sector and resistance from member states with significant automotive manufacturing.

Some senior politicians have proposed plug-in hybrids as a potential “compromise” solution to introduce in the regulation.

One external energy policy expert, who was not involved with the study, described the report a “highly valuable addition” after years in which parts of the automotive sector argued there was too little data to properly assess actual CO2 output.

“The results show, beyond any doubt, that the gap in official and real-world PHEV energy use and CO₂ output is significantly larger than for petrol or diesel vehicles,” the expert said. “All policy adjustments regarding PHEVs should be implemented with utmost caution and in the light of that evidence.”