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Plug-in hybrid electric vehicles release almost 5x greater planet-heating emissions than lab-reported data show, according to a recent analysis.

Growing Gap In Lab and Real-World Emissions

Data shows that PHEVs emit just one-fifth lower CO₂ than traditional petrol and diesel vehicles, based on analysis conducted by a advocacy organization. That contrasts significantly with lab tests, which assumed a three-quarters decrease in emissions.

Analysts examined information from onboard energy use monitors of eight hundred thousand cars sold in the EU between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are falling,” said a lead researcher involved in the study. “That discrepancy is widening and poses a serious issue. As a result, PHEVs pollute nearly as much as petrol cars.”

Primary Factors Driving the Discrepancy

Analysts linked the majority of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in electric power compared to total mileage. They determined that just a quarter of travel was completed in EV mode, while lab assumptions assumed over four-fifths.

Even, when operating in EV mode, pollution levels were well above lab projections. That occurred because EV motors were not strong sufficient to function alone, leading to engines burning fossil fuels for almost one-third of the travel covered in electric mode.

Regulatory and Economic Implications

Based on estimates, the underestimation of PHEV CO2 output allowed four large carmaker groups to avoid more than €5bn in fines between 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs would spend approximately €500 more annually in running costs than is assumed under lab tests.

“The bold claims that automakers often promote about their PHEV vehicles are clearly way off the truth,” commented a automotive expert. “Buyers are being misled into believing that by buying a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are little improved than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have lately been brought again into policy debates as automakers have pressed the European Union to relax CO₂ targets. A proposed ban on sales of new internal combustion cars in 2035 has faced heavy lobbying from the automotive industry and resistance from EU countries with large car industries.

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

One external energy policy specialist, who was not involved with the research, described the analysis a “highly valuable contribution” after a long period in which segments of the car sector argued there was insufficient data to accurately assess actual CO2 output.

“These findings show, without question, that the gap between official and real-world PHEV energy use and CO₂ emissions is much, much larger than for gasoline or diesel cars,” the expert said. “All regulatory adjustments regarding PHEVs should be implemented with utmost caution and in the light of that data.”