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Plug-in hybrid electric vehicles emit nearly 5x greater planet-heating pollution than official data indicate, according to a recent report.

Widening Discrepancy In Official and Actual CO2 Output

Data reveals that PHEVs release only one-fifth lower CO₂ than conventional gas and diesel vehicles, according to research conducted by a advocacy organization. That contrasts sharply with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers examined data from in-vehicle energy use monitors of 800,000 vehicles sold in Europe between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than official figures, up from three and a half times in 2021.

“Actual CO2 output are increasing, while lab-reported figures are decreasing,” said a senior researcher participating in the report. “This discrepancy is widening and creates a significant issue. Consequently, PHEVs pollute nearly as much as petrol cars.”

Primary Factors Driving the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in battery mode relative to overall distance. They determined that only 27% of travel was done in EV mode, whereas official estimates assumed over four-fifths.

Additionally, when running in EV mode, emission levels were well above official projections. That occurred because EV motors were insufficiently powerful enough to operate independently, leading to engines burning gasoline for nearly one-third of the distance completed in EV mode.

Policy and Economic Implications

According to calculations, the underestimation of PHEV emissions allowed several large carmaker groups to escape more than €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ standards.

Furthermore, drivers of PHEVs would pay about €500 more annually in running costs than is estimated under lab conditions.

“The bold claims that automakers like to make about their PHEV cars are clearly way off the mark,” stated a transport expert. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are little better than regular petrol and diesel cars in terms of energy use, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Pressure

Hybrid cars have recently been brought again into policy debates as automakers have lobbied the EU to weaken CO₂ targets. A proposed prohibition on new combustion engine cars in 2035 has faced heavy lobbying from the automotive sector and resistance from EU countries with large automotive industries.

Some senior officials have proposed PHEVs as a possible “compromise” solution to include in the legislation.

One external energy economics expert, who was not involved with the research, described the report a “very useful contribution” after years in which segments of the automotive industry argued there was too little information to accurately assess actual CO2 output.

“The results show, without question, that the gap between lab and actual PHEV energy use and CO₂ emissions is much, much larger than for gasoline or conventional cars,” the expert stated. “All policy adjustments concerning PHEVs should be made with utmost care and considering this data.”