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Plug-in hybrid electric vehicles produce nearly five times greater global warming emissions than lab-reported figures indicate, as per a new analysis.

Growing Discrepancy Between Lab and Real-World Emissions

Data reveals that PHEVs emit just 19% lower CO₂ than conventional gas and diesel cars, based on research conducted by a non-profit group. That differs sharply with laboratory tests, which suggested a three-quarters reduction in emissions.

Analysts examined information from onboard fuel consumption monitors of 800,000 vehicles sold in Europe from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than lab estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” stated a lead researcher involved in the study. “That discrepancy is widening and poses a serious problem. Consequently, PHEVs emit almost as much as gasoline vehicles.”

Primary Reasons Driving the Discrepancy

Analysts linked the majority of the difference to inflated estimates of the “utility factor” – the ratio of miles driven in battery power compared to overall mileage. They found that just 27% of driving was completed in EV mode, whereas official estimates assumed over four-fifths.

Even, when operating in EV mode, pollution levels were well above official estimates. That happened because electric motors were not strong sufficient to operate independently, resulting to engines burning gasoline for almost a third of the distance completed in EV mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV CO2 output allowed several large automaker groups to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ standards.

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

“The strong claims that automakers often promote about their PHEV cars are clearly way off the truth,” commented a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are little better than standard gas and diesel cars in terms of fuel use, CO₂ emissions, and running costs.”

Political Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been brought again into policy discussions as carmakers have pressed the EU to relax CO₂ standards. A planned ban on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from member states with significant car industries.

Several high-level officials have proposed plug-in hybrids as a potential “compromise” option to include in the legislation.

An independent energy policy specialist, who was unaffiliated with the research, described the report a “very useful contribution” after a long period in which segments of the automotive industry claimed there was insufficient information to accurately evaluate real-world emissions.

“The results demonstrate, beyond any doubt, that the gap between lab and real-world PHEV energy use and CO₂ output is significantly greater than for petrol or conventional cars,” the expert stated. “Any policy changes regarding PHEVs should be made with utmost caution and considering that data.”