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Plug-in hybrid cars release almost five times greater planet-heating emissions than lab-reported figures show, according to a new report.

Widening Discrepancy In Lab and Real-World Emissions

Data reveals that PHEVs release only one-fifth less CO₂ than conventional petrol and diesel vehicles, according to research carried out by a non-profit group. That contrasts sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Analysts examined information from onboard fuel consumption monitors of eight hundred thousand vehicles registered in the EU from 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than official estimates, up from three and a half times in 2021.

“Actual emissions are rising, while official figures are falling,” stated a lead researcher participating in the study. “This discrepancy is growing and creates a significant problem. As a result, PHEVs emit nearly as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Researchers linked most of the difference to inflated estimates of the “electric driving share” – the ratio of miles driven in electric power compared to overall distance. They found that just 27% of driving was done in EV mode, whereas lab assumptions suggested 84%.

Additionally, when running in electric mode, emission amounts were well above lab estimates. That occurred because electric motors were not strong sufficient to function alone, leading to combustion motors using gasoline for nearly one-third of the travel covered in electric mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output allowed several large carmaker groups to avoid over €5bn in fines from 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs could pay about €500 extra per year in running costs than would be estimated under lab tests.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are clearly way off the mark,” stated a automotive analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and saving money. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been drawn again into policy discussions as automakers have pressed the European Union to relax CO₂ targets. A planned ban on new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from member states with large automotive industries.

Several senior officials have proposed plug-in hybrids as a possible “flexibility” option to include in the legislation.

One independent energy policy specialist, who was not involved with the study, called the analysis a “highly valuable contribution” after years in which parts of the car sector claimed there was insufficient data to accurately evaluate actual emissions.

“These findings show, without question, that the difference in official and real-world PHEV energy use and CO₂ output is much, much larger than for gasoline or conventional vehicles,” they stated. “Any policy adjustments regarding PHEVs should be implemented with extreme caution and considering this data.”