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

Growing Discrepancy In Lab and Actual Emissions

Data shows that PHEVs release only 19% lower CO₂ than conventional gas and diesel vehicles, according to analysis conducted by a advocacy group. That contrasts sharply with lab estimates, which assumed a 75% decrease in pollution.

Researchers studied information from in-vehicle energy use meters of eight hundred thousand vehicles registered in the EU from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported emissions are falling,” said a senior researcher involved in the report. “This discrepancy is widening and creates a serious problem. Consequently, PHEVs pollute almost as heavily as petrol vehicles.”

Key Reasons Behind the Emissions Gap

Analysts linked most of the gap to inflated estimates of the “electric driving share” – the ratio of miles driven in battery mode relative to overall mileage. They determined that only a quarter of travel was completed in EV mode, while official estimates suggested 84%.

Even, when operating in EV mode, emission amounts were significantly higher than lab projections. This happened because EV motors were not strong enough to function independently, resulting to engines using fossil fuels for almost one-third of the travel covered in EV mode.

Regulatory and Financial Consequences

According to estimates, the underestimation of PHEV CO2 output allowed four large carmaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ targets.

Additionally, drivers of PHEVs would spend approximately €500 more per year in operating expenses than is estimated under laboratory tests.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the truth,” stated a automotive expert. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of energy consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Industry Lobbying

Hybrid vehicles have lately been brought back into policy debates as automakers have lobbied the EU to weaken CO₂ targets. A proposed prohibition on sales of new internal combustion cars in 2035 has faced heavy lobbying from the automotive industry and opposition from EU countries with significant automotive industries.

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

An external energy policy specialist, who was unaffiliated with the research, described the report a “very useful addition” after a long period in which parts of the automotive sector claimed there was insufficient data to accurately evaluate real-world CO2 output.

“The results show, without question, that the gap in lab and real-world PHEV fuel consumption and CO₂ output is significantly greater than for petrol or conventional cars,” the expert said. “All regulatory changes regarding PHEVs should be implemented with utmost caution and in the light of this data.”