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Plug-in hybrid cars emit almost five times more planet-heating pollution than lab-reported data indicate, according to a new analysis.

Growing Gap In Official and Actual Emissions

Data shows that PHEVs release just one-fifth lower CO₂ than traditional gas and diesel vehicles, based on research conducted by a advocacy organization. That contrasts sharply with laboratory tests, which assumed a three-quarters decrease in pollution.

Researchers studied information from in-vehicle fuel consumption monitors of 800,000 cars registered in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Real-world emissions are rising, while lab-reported emissions are decreasing,” said a lead researcher involved in the report. “That discrepancy is growing and creates a serious problem. Consequently, PHEVs pollute nearly as much as gasoline cars.”

Primary Reasons Driving the Discrepancy

Analysts linked the majority of the gap to overestimates of the “electric driving share” – the ratio of miles travelled in battery mode compared to total mileage. The team determined that just a quarter of driving was completed in electric mode, whereas lab assumptions assumed over four-fifths.

Even, when running in electric mode, pollution amounts were significantly higher than official projections. This occurred because electric motors were not strong enough to function independently, resulting to engines burning gasoline for nearly a third of the travel completed in electric mode.

Regulatory and Economic Implications

According to estimates, the lowballing of PHEV emissions allowed several large carmaker groups to avoid over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend about €500 more annually in operating expenses than is assumed under lab conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the truth,” stated a transport analyst. “Consumers are being duped into believing that by buying a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are only slightly improved than regular petrol and diesel cars in terms of energy consumption, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Lobbying

Plug-in hybrid cars have lately been brought again into policy discussions as carmakers have pressed the EU to relax CO₂ standards. A planned prohibition on new internal combustion cars in 2035 has faced intense pressure from the car sector and opposition from member states with large automotive industries.

Several high-level officials have suggested PHEVs as a possible “compromise” option to introduce in the regulation.

One external energy economics expert, who was not involved with the study, described the report a “highly valuable contribution” after a long period in which segments of the automotive industry argued there was insufficient data to properly assess real-world emissions.

“The results show, without question, that the gap in official and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or conventional cars,” they said. “Any regulatory changes concerning PHEVs should be made with utmost care and considering this evidence.”