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Plug-in hybrid cars release almost five times greater planet-heating emissions than official data indicate, according to a recent report.

Growing Gap Between Lab and Real-World CO2 Output

Statistics shows that PHEVs emit just one-fifth lower CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a non-profit organization. That contrasts significantly with lab tests, which assumed a three-quarters decrease in pollution.

Analysts studied information from in-vehicle energy use meters of 800,000 vehicles sold in the EU between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” said a lead analyst participating in the report. “This gap is growing and poses a significant problem. Consequently, PHEVs pollute almost as heavily as petrol cars.”

Primary Factors Behind the Discrepancy

Analysts attributed most of the gap to inflated estimates of the “utility factor” – the percentage of kilometers travelled in battery power relative to overall mileage. The team determined that just 27% of driving was completed in electric mode, while official assumptions assumed over four-fifths.

Additionally, when operating in EV mode, pollution amounts were well above lab estimates. This occurred because electric motors were not strong enough to operate independently, resulting to combustion motors using gasoline for almost one-third of the distance covered in electric mode.

Policy and Economic Implications

According to estimates, the underestimation of PHEV CO2 output allowed several major automaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially easing adherence with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs would pay approximately €500 extra annually in running costs than is assumed under laboratory conditions.

“The bold claims that automakers often promote about their PHEV cars are clearly far from the truth,” stated a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are only slightly better than standard petrol and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Policy Discussion and Industry Pressure

Hybrid vehicles have lately been drawn back into political discussions as automakers have lobbied the European Union to relax CO₂ standards. A proposed ban on new combustion engine cars in 2035 has faced intense lobbying from the car industry and opposition from EU countries with significant automotive manufacturing.

Several senior politicians have proposed PHEVs as a possible “compromise” option to introduce in the legislation.

One external energy economics specialist, who was not involved with the study, called the analysis a “highly valuable addition” after years in which segments of the car sector claimed there was insufficient information to accurately assess real-world emissions.

“These findings demonstrate, beyond any doubt, that the gap in official and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel vehicles,” they said. “All regulatory adjustments regarding PHEVs should be made with extreme caution and in the light of this evidence.”