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Plug-in hybrid electric vehicles emit almost 5x more planet-heating emissions than lab-reported figures indicate, according to a recent analysis.

Widening Discrepancy In Lab and Actual Emissions

Statistics shows that PHEVs emit only one-fifth less CO₂ than traditional petrol and diesel cars, based on research conducted by a non-profit group. This differs sharply with laboratory tests, which suggested a three-quarters decrease in emissions.

Researchers examined information from onboard fuel consumption meters of eight hundred thousand cars registered in the EU between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab figures, up from three and a half times in 2021.

“Real-world emissions are increasing, while official figures are falling,” said a lead researcher involved in the study. “That discrepancy is widening and creates a significant problem. As a result, PHEVs emit nearly as much as petrol cars.”

Key Reasons Driving the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “utility factor” – the ratio of miles travelled in electric mode compared to total mileage. The team determined that just 27% of travel was completed in EV mode, whereas official estimates suggested over four-fifths.

Even, when operating in electric mode, emission levels were significantly higher than lab projections. That happened because EV motors were not strong sufficient to function alone, leading to combustion motors burning fossil fuels for nearly one-third of the travel completed in EV mode.

Policy and Financial Consequences

Based on estimates, the lowballing of PHEV CO2 output enabled four large carmaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ targets.

Additionally, drivers of PHEVs would spend about €500 more annually in running costs than is assumed under lab tests.

“The strong statements that automakers often promote about their PHEV vehicles are clearly far from the mark,” commented a transport analyst. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than regular petrol and diesel cars in terms of fuel use, CO₂ production, and running expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been drawn again into policy discussions as carmakers have pressed the EU to weaken CO₂ targets. A planned prohibition on new combustion engine vehicles in 2035 has faced heavy lobbying from the car sector and opposition from member states with large car manufacturing.

Some senior politicians have proposed plug-in hybrids as a potential “compromise” option to include in the legislation.

An independent energy economics expert, who was unaffiliated with the research, called the report a “highly valuable contribution” after years in which segments of the automotive industry claimed there was too little information to properly evaluate actual emissions.

“These findings demonstrate, without question, that the gap between official and actual PHEV energy use and CO₂ emissions is significantly larger than for gasoline or diesel cars,” the expert said. “All policy adjustments concerning PHEVs should be made with extreme caution and in the light of this evidence.”