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Plug-in hybrid electric vehicles release almost 5x more planet-heating emissions than lab-reported data indicate, according to a new analysis.

Growing Gap In Lab and Actual Emissions

Statistics shows that PHEVs emit only 19% lower CO₂ than traditional gas and diesel vehicles, based on analysis conducted by a non-profit group. That contrasts sharply with lab estimates, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard energy use monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, up from 3.5 times in 2021.

“Actual emissions are rising, while official figures are falling,” stated a lead researcher participating in the report. “That discrepancy is growing and poses a significant issue. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Primary Factors Behind the Emissions Gap

Analysts attributed most of the gap to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric power compared to overall distance. The team determined that just 27% of travel was completed in EV mode, while official assumptions assumed over four-fifths.

Additionally, when operating in electric mode, pollution amounts were well above lab estimates. This happened because electric motors were insufficiently powerful sufficient to operate independently, leading to combustion motors using gasoline for nearly a third of the travel covered in EV mode.

Regulatory and Financial Implications

According to estimates, the underestimation of PHEV CO2 output enabled several major carmaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend about €500 extra annually in running costs than would be assumed under lab tests.

“The bold statements that automakers like to make about their PHEV cars are clearly way off the mark,” commented a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are little improved than regular petrol and diesel cars in terms of fuel use, CO₂ production, and operating costs.”

Political Discussion and Automotive Pressure

Hybrid vehicles have recently been drawn again into political debates as carmakers have lobbied the EU to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine cars in 2035 has faced intense lobbying from the car sector and opposition from EU countries with significant automotive industries.

Several senior officials have proposed PHEVs as a possible “flexibility” solution to introduce in the legislation.

One external energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable contribution” after a long period in which segments of the car industry claimed there was too little data to accurately evaluate actual CO2 output.

“The results show, beyond any doubt, that the difference in lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for gasoline or conventional vehicles,” the expert stated. “Any policy adjustments regarding PHEVs should be implemented with extreme caution and considering this data.”