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Plug-in hybrid cars release nearly five times more planet-heating emissions than lab-reported data show, according to a new analysis.

Growing Gap In Lab and Actual Emissions

Statistics shows that PHEVs emit only one-fifth lower CO₂ than traditional gas and diesel cars, based on research carried out by a advocacy organization. This contrasts sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers studied data from onboard energy use meters of eight hundred thousand cars registered in Europe between 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while official emissions are falling,” stated a lead researcher participating in the study. “That discrepancy is widening and creates a significant problem. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles travelled in battery mode relative to total mileage. The team determined that only 27% of travel was done in electric mode, while lab assumptions suggested 84%.

Additionally, when operating in electric mode, emission levels were well above official estimates. That happened because EV motors were insufficiently powerful sufficient to operate independently, leading to combustion motors using gasoline for nearly one-third of the travel completed in EV mode.

Regulatory and Economic Consequences

Based on calculations, the lowballing of PHEV emissions allowed four major carmaker companies to escape more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 more annually in running expenses than is estimated under lab conditions.

“The bold statements that automakers often promote about their plug-in hybrid cars are obviously far from the mark,” stated a transport analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Discussion and Industry Pressure

Hybrid vehicles have lately been brought back into political discussions as carmakers have pressed the EU to weaken CO₂ standards. A planned ban on sales of new combustion engine cars in 2035 has faced heavy pressure from the car industry and resistance from EU countries with significant car industries.

Some high-level officials have proposed plug-in hybrids as a potential “compromise” solution to introduce in the regulation.

An independent energy economics expert, who was unaffiliated with the study, called the analysis a “highly valuable contribution” after a long period in which segments of the car industry claimed there was insufficient information to properly assess actual CO2 output.

“The results show, without question, that the difference between lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel vehicles,” they stated. “All regulatory changes concerning PHEVs should be made with extreme caution and in the light of this data.”