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Plug-in hybrid electric vehicles emit almost 5x more planet-heating pollution than official data show, according to a new analysis.

Growing Gap Between Lab and Actual Emissions

Statistics shows that PHEVs emit just one-fifth lower CO₂ than conventional petrol and diesel cars, based on research carried out by a advocacy group. This differs significantly with lab tests, which assumed a three-quarters reduction in pollution.

Analysts examined information from in-vehicle fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab estimates, increased from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are decreasing,” said a lead researcher involved in the study. “That gap is growing and poses a serious problem. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Primary Factors Driving the Discrepancy

Analysts attributed the majority of the difference to overestimates of the “electric driving share” – the ratio of miles driven in battery mode relative to overall mileage. The team found that only 27% of driving was done in electric mode, while official assumptions assumed 84%.

Additionally, when operating in EV mode, emission levels were significantly higher than official projections. That occurred because electric motors were insufficiently powerful sufficient to operate independently, resulting to engines burning gasoline for nearly one-third of the travel completed in EV mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV CO2 output enabled several major automaker companies to escape over €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend approximately €500 more annually in running costs than is estimated under lab tests.

“The bold claims that automakers like to make about their plug-in hybrid vehicles are clearly far from the truth,” stated a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of energy use, CO₂ production, and running expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been brought back into policy debates as carmakers have pressed the European Union to weaken CO₂ targets. A proposed ban on sales of new internal combustion cars in 2035 has faced intense lobbying from the automotive industry and resistance from member states with large automotive industries.

Some high-level politicians have proposed PHEVs as a potential “compromise” solution to introduce in the legislation.

One independent energy policy expert, who was unaffiliated with the study, described the report a “highly valuable addition” after a long period in which parts of the car industry claimed there was insufficient information to properly evaluate real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the difference in official and actual PHEV energy use and CO₂ output is much, much larger than for petrol or diesel vehicles,” the expert stated. “All policy adjustments regarding PHEVs should be made with extreme caution and in the light of that data.”