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Plug-in hybrid electric vehicles release nearly five times greater planet-heating emissions than lab-reported data indicate, according to a new report.

Widening Gap In Lab and Actual CO2 Output

Data reveals that PHEVs emit only one-fifth lower CO₂ than conventional gas and diesel vehicles, according to research carried out by a non-profit organization. That differs significantly with laboratory tests, which assumed a 75% reduction in emissions.

Researchers studied information from in-vehicle energy use meters of 800,000 cars sold in the EU from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while official emissions are falling,” stated a lead analyst participating in the report. “That gap is widening and creates a serious issue. As a result, PHEVs emit nearly as much as petrol cars.”

Key Factors Behind the Emissions Gap

Analysts attributed most of the difference to overestimates of the “utility factor” – the ratio of miles driven in electric power compared to overall mileage. The team found that only 27% of travel was done in electric mode, whereas official assumptions suggested 84%.

Even, when operating in EV mode, pollution amounts were well above official projections. That occurred because electric motors were insufficiently powerful enough to operate alone, leading to combustion motors using gasoline for almost a third of the travel covered in EV mode.

Policy and Financial Consequences

Based on calculations, the lowballing of PHEV emissions enabled several major carmaker companies to escape over €5bn in penalties from 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could pay approximately €500 extra per year in running costs than would be assumed under laboratory conditions.

“The strong claims that manufacturers like to make about their plug-in hybrid vehicles are obviously way off the mark,” stated a automotive analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and cutting money. Actually, PHEVs are only slightly better than regular gas and diesel cars in terms of energy consumption, CO₂ emissions, and running expenses.”

Political Discussion and Industry Pressure

Plug-in hybrid vehicles have lately been drawn back into policy debates as carmakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced intense lobbying from the automotive industry and resistance from EU countries with large car manufacturing.

Several high-level officials have suggested plug-in hybrids as a potential “compromise” solution to include in the regulation.

One independent energy economics expert, who was unaffiliated with the research, described the analysis a “very useful contribution” after years in which segments of the car sector argued there was insufficient information to accurately assess actual CO2 output.

“These findings show, without question, that the gap between lab and actual PHEV fuel consumption and CO₂ output is much, much greater than for petrol or diesel vehicles,” the expert said. “All policy adjustments regarding PHEVs should be implemented with extreme caution and considering that data.”