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Plug-in hybrid electric vehicles release almost 5x greater planet-heating pollution than lab-reported data show, as per a new analysis.

Widening Gap Between Lab and Actual Emissions

Data shows that PHEVs emit only one-fifth less CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a advocacy group. That differs sharply with laboratory tests, which suggested a three-quarters decrease in emissions.

Researchers studied data from in-vehicle fuel consumption meters of eight hundred thousand vehicles registered in Europe from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, increased from three and a half times in 2021.

“Actual CO2 output are increasing, while official emissions are falling,” said a lead researcher participating in the study. “This discrepancy is widening and poses a significant issue. Consequently, PHEVs emit nearly as much as petrol cars.”

Primary Reasons Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “electric driving share” – the ratio of miles driven in battery power compared to overall mileage. The team determined that just a quarter of driving was done in electric mode, while official assumptions suggested 84%.

Even, when running in electric mode, emission amounts were significantly higher than lab estimates. That happened because electric motors were not strong enough to function independently, leading to engines burning fossil fuels for almost a third of the distance completed in EV mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV emissions enabled four large carmaker groups to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with European Union average fleet CO₂ standards.

Furthermore, drivers of PHEVs would pay about €500 more annually in running expenses than would be assumed under lab conditions.

“The bold statements that automakers often promote about their PHEV vehicles are clearly far from the truth,” commented a automotive analyst. “Buyers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving costs. In reality, PHEVs are little better than standard gas and diesel vehicles in terms of fuel use, CO₂ emissions, and running expenses.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have recently been drawn again into policy discussions as carmakers have pressed the EU to weaken CO₂ standards. A planned ban on new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and resistance from EU countries with large automotive manufacturing.

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

An external energy policy expert, who was not involved with the research, described the report a “very useful addition” after a long period in which segments of the car sector claimed there was insufficient data to properly assess actual CO2 output.

“These findings demonstrate, beyond any doubt, that the difference in lab and real-world PHEV fuel consumption and CO₂ emissions is significantly larger than for gasoline or conventional cars,” the expert stated. “All regulatory adjustments concerning PHEVs should be made with extreme care and in the light of that evidence.”