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Plug-in hybrid electric vehicles emit almost 5x more global warming pollution than lab-reported data show, according to a new analysis.

Widening Gap Between Lab and Real-World Emissions

Statistics shows that PHEVs release just 19% less CO₂ than traditional petrol and diesel vehicles, based on research conducted by a non-profit group. That differs sharply with lab estimates, which suggested a 75% reduction in pollution.

Analysts studied data from in-vehicle energy use meters of eight hundred thousand vehicles sold in Europe between 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, up from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported emissions are falling,” stated a lead researcher involved in the report. “That discrepancy is widening and poses a significant problem. Consequently, PHEVs pollute almost as heavily as gasoline vehicles.”

Primary Factors Behind the Discrepancy

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the ratio of kilometers travelled in electric power relative to overall distance. They found that just 27% of travel was completed in electric mode, while official estimates assumed over four-fifths.

Additionally, when running in electric mode, emission levels were well above official projections. That happened because EV motors were insufficiently powerful enough to function alone, leading to engines burning fossil fuels for almost a third of the distance covered in EV mode.

Policy and Economic Consequences

According to calculations, the lowballing of PHEV emissions enabled four large carmaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs would spend about €500 extra per year in operating expenses than is assumed under laboratory conditions.

“The strong claims that automakers often promote about their PHEV vehicles are obviously far from the mark,” stated a automotive analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating costs.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have lately been drawn again into policy debates as carmakers have pressed the European Union to relax CO₂ targets. A proposed prohibition on new internal combustion cars in 2035 has faced heavy pressure from the automotive industry and opposition from member states with significant car manufacturing.

Some high-level officials have suggested plug-in hybrids as a potential “compromise” option to introduce in the legislation.

An independent energy economics specialist, who was not involved with the research, called the report a “very useful addition” after years in which parts of the automotive industry argued there was insufficient information to properly evaluate real-world emissions.

“The results demonstrate, without question, that the difference between official and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or diesel cars,” they stated. “All regulatory changes concerning PHEVs should be implemented with utmost caution and considering this data.”