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Plug-in hybrid cars produce almost 5x greater planet-heating pollution than lab-reported data show, according to a recent analysis.

Widening Gap Between Official and Real-World CO2 Output

Statistics shows that PHEVs release only one-fifth lower CO₂ than traditional gas and diesel vehicles, based on analysis conducted by a non-profit organization. That differs sharply with laboratory estimates, which assumed a three-quarters decrease in emissions.

Researchers examined information from in-vehicle fuel consumption monitors of eight hundred thousand vehicles sold in Europe from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab figures, increased from 3.5 times in 2021.

“Actual emissions are rising, while official figures are decreasing,” said a senior researcher involved in the report. “That gap is growing and poses a serious issue. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Key Factors Driving the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery mode relative to total mileage. The team determined that just a quarter of travel was completed in electric mode, whereas official assumptions assumed 84%.

Even, when running in electric mode, emission levels were well above lab projections. That happened because electric motors were not strong enough to operate alone, resulting to engines burning fossil fuels for almost a third of the travel completed in EV mode.

Regulatory and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output allowed four large carmaker companies to escape more than €5bn in fines between 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ standards.

Additionally, owners of PHEVs could spend approximately €500 extra annually in operating expenses than would be estimated under laboratory tests.

“The bold statements that manufacturers like to make about their PHEV vehicles are clearly way off the truth,” commented a transport expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and cutting costs. In reality, PHEVs are little improved than regular gas and diesel cars in terms of energy consumption, CO₂ emissions, and running costs.”

Policy Discussion and Industry Lobbying

Hybrid vehicles have lately been brought back into political debates as automakers have lobbied the European Union to relax CO₂ standards. A proposed prohibition on sales of new internal combustion cars in 2035 has faced heavy pressure from the car industry and opposition from EU countries with large car industries.

Some high-level politicians have suggested plug-in hybrids as a potential “compromise” solution to introduce in the legislation.

An independent energy economics expert, who was not involved with the study, called the analysis a “very useful contribution” after years in which parts of the car industry argued there was insufficient data to properly assess real-world CO2 output.

“The results 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 vehicles,” they stated. “All policy adjustments regarding PHEVs should be made with extreme caution and in the light of this evidence.”