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Plug-in hybrid electric vehicles release nearly 5x greater global warming pollution than lab-reported figures indicate, according to a recent report.

Growing Discrepancy Between Lab and Real-World Emissions

Data shows that PHEVs release only 19% less CO₂ than conventional gas and diesel vehicles, according to research conducted by a advocacy group. This differs sharply with lab estimates, which suggested a three-quarters decrease in emissions.

Researchers studied information from in-vehicle fuel consumption monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, increased from 3.5 times in 2021.

“Actual emissions are increasing, while lab-reported figures are falling,” stated a lead researcher participating in the report. “That gap is growing and creates a significant issue. Consequently, PHEVs emit almost as heavily as gasoline cars.”

Key Factors Driving the Discrepancy

Analysts attributed most of the gap to inflated estimates of the “electric driving share” – the ratio of miles travelled in electric mode compared to overall distance. They determined that only a quarter of travel was done in electric mode, whereas lab estimates suggested 84%.

Even, when running in electric mode, pollution levels were well above lab projections. This occurred because electric motors were not strong sufficient to function independently, leading to engines burning fossil fuels for nearly one-third of the distance covered in EV mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV emissions allowed four large automaker companies to escape over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs could pay approximately €500 extra annually in operating expenses than would be estimated under lab tests.

“The strong claims that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the mark,” commented a transport expert. “Consumers are being misled into thinking that by buying a PHEV, they are helping the planet and saving money. In reality, PHEVs are little better than regular petrol and diesel cars in terms of energy consumption, CO₂ emissions, and running expenses.”

Policy Debate and Industry Pressure

Hybrid cars have recently been drawn back into policy discussions as carmakers have lobbied the European Union to weaken CO₂ standards. A proposed prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the automotive sector and resistance from EU countries with large automotive manufacturing.

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

One independent energy policy expert, who was unaffiliated with the study, called the report a “very useful addition” after years in which segments of the car industry claimed there was insufficient data to accurately assess actual CO2 output.

“The results demonstrate, beyond any doubt, that the gap between official and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert said. “All policy changes concerning PHEVs should be made with utmost care and considering this data.”