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Plug-in hybrid cars produce almost five times more planet-heating emissions than official figures show, according to a new analysis.

Widening Discrepancy Between Official and Real-World CO2 Output

Statistics reveals that PHEVs emit just 19% less CO₂ than traditional gas and diesel cars, based on research carried out by a advocacy group. This contrasts significantly with lab estimates, which assumed a three-quarters reduction in pollution.

Analysts studied information from onboard fuel consumption monitors of 800,000 vehicles registered in the EU between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are falling,” said a senior researcher participating in the study. “This discrepancy is widening and creates a serious problem. Consequently, PHEVs pollute nearly as much as gasoline cars.”

Primary Reasons Behind the Discrepancy

Researchers linked the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in electric power compared to total distance. The team found that only a quarter of driving was completed in EV mode, whereas official assumptions suggested over four-fifths.

Even, when running in EV mode, emission levels were well above official estimates. This happened because electric motors were not strong enough to operate alone, leading to engines burning gasoline for nearly a third of the travel covered in electric mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output enabled several large carmaker companies to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ standards.

Furthermore, owners of PHEVs would spend about €500 extra annually in running costs than would be assumed under lab conditions.

“The strong claims that automakers like to make about their PHEV cars are clearly far from the truth,” commented a transport expert. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Debate and Industry Lobbying

Plug-in hybrid vehicles have lately been drawn again into policy discussions as automakers have lobbied the EU to relax CO₂ targets. A planned ban on new internal combustion cars in 2035 has faced heavy lobbying from the car industry and opposition from EU countries with significant automotive manufacturing.

Some high-level politicians have proposed PHEVs as a possible “compromise” option to include in the regulation.

An independent energy economics expert, who was not involved with the research, called the report a “highly valuable contribution” after a long period in which parts of the automotive industry argued there was insufficient information to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the gap between lab and actual PHEV energy use and CO₂ emissions is significantly greater than for gasoline or conventional cars,” they stated. “Any regulatory adjustments regarding PHEVs should be implemented with utmost care and considering that data.”