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Plug-in hybrid cars emit nearly five times greater planet-heating pollution than official figures indicate, according to a new report.

Widening Gap Between Official and Real-World Emissions

Statistics reveals that PHEVs emit only 19% less CO₂ than conventional petrol and diesel vehicles, according to research conducted by a non-profit group. This differs sharply with lab estimates, which assumed a three-quarters reduction in pollution.

Analysts examined information from in-vehicle energy use monitors of eight hundred thousand vehicles registered in the EU from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are falling,” said a lead researcher participating in the study. “This discrepancy is growing and creates a serious problem. Consequently, PHEVs pollute almost as heavily as gasoline vehicles.”

Key Reasons Driving the Emissions Gap

Researchers attributed most of the gap to inflated estimates of the “electric driving share” – the ratio of kilometers travelled in electric mode compared to total distance. The team determined that just a quarter of driving was completed in electric mode, while lab assumptions assumed over four-fifths.

Additionally, when operating in EV mode, pollution amounts were significantly higher than official projections. This occurred because EV motors were not strong enough to operate independently, leading to engines using fossil fuels for nearly one-third of the distance completed in EV mode.

Regulatory and Financial Implications

According to estimates, the lowballing of PHEV emissions enabled several major automaker groups to avoid over €5bn in fines from 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ standards.

Furthermore, drivers of PHEVs could spend approximately €500 more per year in running expenses than is assumed under laboratory conditions.

“The bold claims that automakers often promote about their PHEV cars are clearly way off the truth,” commented a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of energy consumption, CO₂ production, and operating expenses.”

Political Debate and Automotive Pressure

Hybrid vehicles have recently been brought again into political debates as carmakers have pressed the European Union to weaken CO₂ standards. A planned prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the car industry and resistance from EU countries with significant car industries.

Some senior politicians have suggested plug-in hybrids as a potential “compromise” option to include in the regulation.

An external energy economics expert, who was not involved with the study, called the report a “highly valuable addition” after years in which parts of the automotive industry claimed there was too little information to properly assess real-world CO2 output.

“These findings show, beyond any doubt, that the gap between official and real-world PHEV fuel consumption and CO₂ output is much, much larger than for gasoline or diesel cars,” they said. “Any policy changes concerning PHEVs should be implemented with utmost care and in the light of that data.”