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Plug-in hybrid electric vehicles release almost five times more global warming emissions than lab-reported data show, according to a new report.

Growing Gap In Lab and Actual Emissions

Statistics shows that PHEVs release only one-fifth lower CO₂ than conventional petrol and diesel vehicles, according to research conducted by a advocacy organization. That differs sharply with laboratory estimates, which suggested a 75% reduction in emissions.

Researchers examined information from onboard fuel consumption meters of 800,000 vehicles registered in the EU between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported figures are falling,” said a lead analyst participating in the report. “That gap is widening and poses a serious problem. As a result, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Factors Behind the Emissions Gap

Analysts linked the majority of the gap to overestimates of the “utility factor” – the percentage of miles travelled in battery mode relative to overall distance. The team found that just 27% of travel was completed in EV mode, while official estimates suggested over four-fifths.

Additionally, when operating in electric mode, pollution levels were well above official projections. This occurred because EV motors were not strong enough to operate independently, leading to combustion motors using gasoline for nearly a third of the distance completed in electric mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV CO2 output enabled four large carmaker groups to avoid over €5bn in penalties from 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra per year in operating expenses than would be assumed under lab conditions.

“The strong statements that automakers often promote about their PHEV cars are clearly far from the mark,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are little better than regular petrol and diesel vehicles in terms of energy use, CO₂ emissions, and operating costs.”

Policy Debate and Industry Pressure

Plug-in hybrid cars have lately been drawn again into political discussions as carmakers have lobbied the European Union to relax CO₂ targets. A planned prohibition on new internal combustion vehicles in 2035 has faced intense lobbying from the car industry and opposition from EU countries with significant automotive industries.

Several senior politicians have proposed plug-in hybrids as a potential “flexibility” solution to include in the legislation.

One independent energy policy specialist, who was not involved with the research, described the analysis a “highly valuable addition” after years in which parts of the car industry claimed there was too little data to accurately evaluate real-world CO2 output.

“The results show, beyond any doubt, that the difference between lab and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or conventional cars,” the expert said. “All regulatory adjustments concerning PHEVs should be implemented with utmost caution and considering this data.”