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Plug-in hybrid cars produce nearly five times more planet-heating pollution than lab-reported data show, according to a recent analysis.

Growing Gap Between Official and Real-World Emissions

Data reveals that PHEVs emit only one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to research conducted by a non-profit organization. That differs sharply with lab estimates, which suggested a 75% decrease in emissions.

Researchers examined data from in-vehicle energy use monitors of 800,000 vehicles registered in the EU from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while lab-reported emissions are falling,” said a lead analyst participating in the study. “This gap is growing and creates a serious problem. Consequently, PHEVs pollute nearly as much as gasoline vehicles.”

Key Reasons Driving the Discrepancy

Researchers linked the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles travelled in electric mode relative to total distance. The team found that only a quarter of driving was done in electric mode, while official assumptions suggested 84%.

Even, when operating in EV mode, emission amounts were significantly higher than lab projections. That occurred because electric motors were not strong enough to operate alone, leading to engines using gasoline for nearly one-third of the distance covered in electric mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV CO2 output enabled four large automaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would pay approximately €500 more annually in operating expenses than would be estimated under lab conditions.

“The bold claims that automakers often promote about their plug-in hybrid vehicles are clearly way off the truth,” stated a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are little improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ production, and running costs.”

Policy Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been drawn back into policy discussions as carmakers have pressed the European Union to relax CO₂ standards. A planned ban on new internal combustion vehicles in 2035 has faced intense pressure from the car industry and opposition from member states with large automotive manufacturing.

Some high-level politicians have proposed plug-in hybrids as a possible “compromise” solution to include in the regulation.

An external energy economics expert, who was not involved with the study, described the report a “highly valuable contribution” after years in which parts of the car industry claimed there was insufficient data to properly evaluate real-world emissions.

“The results show, beyond any doubt, that the gap between official and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for petrol or conventional cars,” they stated. “All regulatory changes regarding PHEVs should be implemented with utmost caution and in the light of that evidence.”