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Plug-in hybrid cars release nearly five times more planet-heating emissions than lab-reported data show, according to a recent report.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs emit just 19% lower CO₂ than traditional gas and diesel cars, according to analysis conducted by a advocacy group. This differs significantly with laboratory tests, which assumed a three-quarters reduction in emissions.

Analysts examined data from in-vehicle fuel consumption monitors of 800,000 cars registered in Europe from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are decreasing,” said a senior researcher participating in the study. “This gap is widening and creates a significant problem. As a result, PHEVs emit nearly as heavily as petrol vehicles.”

Key Reasons Driving the Emissions Gap

Analysts linked the majority of the difference to overestimates of the “electric driving share” – the ratio of miles travelled in battery mode compared to total distance. They found that only 27% of travel was done in EV mode, while lab assumptions suggested over four-fifths.

Even, when operating in EV mode, emission levels were well above official estimates. This happened because EV motors were insufficiently powerful sufficient to function independently, resulting to engines using fossil fuels for almost one-third of the travel completed in electric mode.

Regulatory and Economic Implications

According to estimates, the underestimation of PHEV emissions allowed several large carmaker companies to avoid over €5bn in penalties from 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ standards.

Furthermore, drivers of PHEVs would spend approximately €500 extra annually in running costs than is estimated under lab tests.

“The strong statements that automakers often promote about their plug-in hybrid vehicles are obviously far from the mark,” commented a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are little improved than regular gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Discussion and Industry Pressure

Plug-in hybrid cars have lately been drawn back into policy discussions as automakers have pressed the EU to relax CO₂ targets. A proposed prohibition on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant automotive manufacturing.

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

One independent energy economics specialist, who was not involved with the study, called the report a “highly valuable addition” after years in which parts of the automotive industry argued there was too little data to properly assess actual emissions.

“The results show, beyond any doubt, that the difference between official and actual PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional cars,” the expert said. “Any policy changes concerning PHEVs should be implemented with extreme caution and considering this evidence.”