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Plug-in hybrid electric vehicles produce almost 5x greater global warming emissions than lab-reported data indicate, according to a new analysis.

Widening Gap In Lab and Actual Emissions

Data reveals that PHEVs release only 19% lower CO₂ than traditional petrol and diesel vehicles, based on research conducted by a advocacy group. This contrasts sharply with lab tests, which assumed a three-quarters reduction in emissions.

Researchers studied information from onboard fuel consumption monitors of eight hundred thousand vehicles registered in Europe between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are decreasing,” said a lead analyst involved in the report. “That gap is growing and poses a serious issue. As a result, PHEVs emit nearly as heavily as petrol cars.”

Primary Reasons Driving the Discrepancy

Researchers linked most of the difference to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric mode relative to total mileage. They found that only a quarter of driving was completed in electric mode, while lab estimates assumed over four-fifths.

Additionally, when running in EV mode, emission levels were significantly higher than lab estimates. This happened because electric motors were insufficiently powerful enough to function alone, leading to combustion motors using gasoline for almost one-third of the distance completed in electric mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV CO2 output enabled several large automaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ standards.

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

“The bold statements that manufacturers like to make about their plug-in hybrid cars are obviously way off the truth,” commented a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving money. In reality, PHEVs are little improved than regular gas and diesel cars in terms of energy consumption, CO₂ production, and running costs.”

Political Discussion and Automotive Lobbying

Plug-in hybrid cars have recently been brought back into policy discussions as carmakers have pressed the European Union to weaken CO₂ targets. A planned prohibition on new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive sector and resistance from member states with large car industries.

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

An independent energy economics expert, who was unaffiliated with the study, described the report a “highly valuable addition” after a long period in which parts of the automotive sector claimed there was insufficient information to properly assess actual emissions.

“These findings show, beyond any doubt, that the gap between official and real-world PHEV fuel consumption and CO₂ output is much, much larger than for gasoline or conventional vehicles,” the expert stated. “Any policy adjustments regarding PHEVs should be made with extreme care and considering this data.”