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

Growing Gap In Official and Real-World Emissions

Data shows that PHEVs emit only 19% less CO₂ than conventional gas and diesel cars, based on research carried out by a non-profit group. This contrasts significantly with laboratory tests, which assumed a three-quarters reduction in emissions.

Analysts studied data from in-vehicle energy use meters of 800,000 vehicles registered in the EU from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official figures, up from 3.5 times in 2021.

“Real-world emissions are increasing, while official emissions are decreasing,” stated a lead analyst participating in the report. “That gap is widening and creates a significant issue. As a result, PHEVs emit almost as much as gasoline cars.”

Key Reasons Driving the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the percentage of miles travelled in battery mode relative to overall distance. They found that only a quarter of travel was completed in electric mode, whereas official assumptions assumed over four-fifths.

Additionally, when operating in electric mode, emission amounts were well above official projections. This occurred because EV motors were insufficiently powerful enough to operate independently, leading to engines burning fossil fuels for nearly a third of the distance covered in electric mode.

Policy and Economic Implications

According to calculations, the underestimation of PHEV emissions allowed four major automaker companies to escape over €5bn in penalties from 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ targets.

Additionally, owners of PHEVs could pay approximately €500 more per year in running costs than would be estimated under laboratory conditions.

“The strong claims that manufacturers often promote about their PHEV cars are clearly way off the truth,” stated a transport analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are only slightly better than standard petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Debate and Industry Pressure

Hybrid vehicles have lately been brought again into political debates as automakers have pressed the EU to relax CO₂ standards. A planned prohibition on new combustion engine cars in 2035 has faced heavy lobbying from the automotive sector and opposition from member states with significant automotive manufacturing.

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

One independent energy economics specialist, who was unaffiliated with the study, called the analysis a “very useful contribution” after a long period in which parts of the automotive industry claimed there was too little information to properly evaluate real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the difference between official and real-world PHEV energy use and CO₂ output is significantly greater than for petrol or conventional vehicles,” they stated. “All regulatory changes concerning PHEVs should be implemented with extreme care and in the light of that evidence.”