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Plug-in hybrid electric vehicles emit nearly five times more planet-heating pollution than official data indicate, according to a new report.

Growing Gap Between Lab and Real-World Emissions

Statistics shows that PHEVs release just 19% lower CO₂ than conventional petrol and diesel cars, according to analysis carried out by a advocacy group. This differs sharply with lab estimates, which suggested a three-quarters reduction in pollution.

Analysts examined information from in-vehicle energy use meters of eight hundred thousand vehicles sold in Europe between 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported figures are falling,” stated a senior analyst involved in the report. “This discrepancy is widening and poses a serious issue. Consequently, PHEVs pollute almost as much as gasoline vehicles.”

Primary Factors Driving the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in battery mode relative to total mileage. They determined that only 27% of driving was completed in electric mode, while official assumptions assumed over four-fifths.

Additionally, when operating in electric mode, emission levels were well above official projections. This happened because electric motors were not strong sufficient to operate alone, leading to combustion motors using gasoline for almost one-third of the travel completed in electric mode.

Policy and Economic Consequences

Based on calculations, the lowballing of PHEV CO2 output enabled four major carmaker groups to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 more per year in running expenses than would be estimated under lab conditions.

“The strong statements that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the mark,” stated a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are only slightly better than regular petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been drawn back into political debates as automakers have pressed the EU to weaken CO₂ standards. A proposed prohibition on new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive sector and resistance from member states with significant automotive industries.

Several high-level politicians have proposed plug-in hybrids as a possible “compromise” solution to introduce in the legislation.

An external energy economics specialist, who was unaffiliated with the research, called the analysis a “highly valuable addition” after years in which parts of the automotive industry argued there was too little information to accurately assess real-world emissions.

“These findings show, without question, that the gap between official and real-world PHEV energy use and CO₂ emissions is significantly larger than for petrol or conventional cars,” they stated. “Any policy adjustments regarding PHEVs should be implemented with utmost care and in the light of this data.”