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Plug-in hybrid electric vehicles release almost 5x greater planet-heating emissions than official data indicate, according to a new report.

Growing Discrepancy In Lab and Actual Emissions

Data shows that PHEVs emit only 19% less CO₂ than traditional gas and diesel vehicles, based on analysis carried out by a advocacy organization. This differs significantly with lab estimates, which suggested a 75% decrease in pollution.

Analysts studied data from onboard fuel consumption monitors of 800,000 vehicles sold in the EU from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, up from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are decreasing,” stated a senior researcher participating in the report. “That gap is growing and poses a significant problem. As a result, PHEVs emit almost as heavily as petrol vehicles.”

Key Factors Driving the Emissions Gap

Researchers linked most of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric power relative to overall distance. The team determined that only a quarter of driving was done in electric mode, whereas official assumptions suggested 84%.

Even, when running in EV mode, pollution levels were significantly higher than lab projections. This happened because EV motors were not strong enough to function alone, leading to engines using gasoline for nearly one-third of the travel covered in electric mode.

Regulatory and Economic Implications

Based on estimates, the underestimation of PHEV emissions allowed four major carmaker companies to avoid over €5bn in penalties between 2021 and 2023, by falsely easing compliance with European Union average fleet CO₂ standards.

Additionally, owners of PHEVs would spend approximately €500 more annually in operating expenses than is estimated under lab conditions.

“The bold claims that manufacturers often promote about their PHEV vehicles are obviously way off the mark,” commented a automotive analyst. “Buyers are being misled into believing that by buying a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are little improved than standard gas and diesel cars in terms of fuel use, CO₂ emissions, and running costs.”

Policy Debate and Automotive Lobbying

Plug-in hybrid cars have lately been drawn again into policy debates as carmakers have pressed the EU to relax CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the car sector and opposition from member states with significant automotive industries.

Several senior officials have suggested plug-in hybrids as a potential “flexibility” solution to introduce in the regulation.

One external energy economics specialist, who was unaffiliated with the research, described the analysis a “highly valuable contribution” after years in which parts of the automotive industry argued there was insufficient data to properly evaluate real-world CO2 output.

“These findings show, without question, that the difference in lab and actual PHEV energy use and CO₂ emissions is much, much greater than for petrol or conventional cars,” the expert said. “All policy adjustments regarding PHEVs should be implemented with utmost care and in the light of this evidence.”