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Plug-in hybrid cars produce almost 5x greater global warming pollution than lab-reported figures show, as per a new report.

Widening Gap Between Lab and Actual Emissions

Data shows that PHEVs release just one-fifth lower CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a advocacy group. This differs significantly with laboratory tests, which assumed a 75% decrease in emissions.

Researchers examined data from onboard fuel consumption monitors of eight hundred thousand vehicles registered in Europe from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are decreasing,” said a lead researcher participating in the report. “That discrepancy is widening and creates a serious problem. As a result, PHEVs emit almost as heavily as petrol cars.”

Key Factors Behind the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in battery mode relative to overall mileage. The team found that only a quarter of driving was done in EV mode, whereas lab estimates assumed 84%.

Additionally, when operating in EV mode, pollution amounts were significantly higher than lab projections. That occurred because EV motors were insufficiently powerful enough to operate independently, resulting to engines burning gasoline for nearly one-third of the travel covered in electric mode.

Regulatory and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output enabled several major automaker groups to escape over €5bn in fines from 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs would pay approximately €500 more annually in running costs than would be assumed under laboratory tests.

“The strong statements that automakers often promote about their PHEV cars are obviously way off the mark,” stated a automotive expert. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little better than standard gas and diesel cars in terms of energy consumption, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Lobbying

Hybrid vehicles have recently been drawn back into political discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned ban on new internal combustion vehicles in 2035 has faced intense pressure from the car industry and resistance from member states with large automotive manufacturing.

Several senior officials have suggested plug-in hybrids as a potential “compromise” solution to introduce in the legislation.

One independent energy economics specialist, who was unaffiliated with the research, described the report a “highly valuable addition” after a long period in which parts of the car industry argued there was too little data to accurately assess actual CO2 output.

“These findings demonstrate, beyond any doubt, that the gap in lab and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or diesel vehicles,” the expert stated. “All regulatory adjustments concerning PHEVs should be implemented with utmost caution and considering that data.”