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Plug-in hybrid cars emit nearly 5x greater planet-heating emissions than lab-reported data show, as per a new analysis.

Growing Discrepancy Between Official and Real-World Emissions

Data shows that PHEVs emit just one-fifth less CO₂ than traditional gas and diesel vehicles, according to research carried out by a non-profit group. That contrasts sharply with lab tests, which assumed a 75% decrease in pollution.

Researchers studied information from in-vehicle fuel consumption meters of eight hundred thousand cars registered in the EU between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, up from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are falling,” said a senior researcher involved in the study. “That gap is growing and poses a serious issue. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric mode compared to overall mileage. They determined that just a quarter of driving was completed in EV mode, while official assumptions assumed 84%.

Additionally, when operating in EV mode, emission levels were well above lab estimates. That occurred because EV motors were insufficiently powerful sufficient to operate alone, leading to engines using gasoline for nearly a third of the travel covered in electric mode.

Policy and Financial Consequences

According to calculations, the underestimation of PHEV CO2 output allowed several major automaker companies to avoid over €5bn in penalties between 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs could spend approximately €500 extra annually in running costs than would be assumed under lab conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid cars are obviously far from the truth,” commented a automotive expert. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy use, CO₂ emissions, and operating costs.”

Policy Debate and Industry Lobbying

Plug-in hybrid vehicles have lately been drawn again into policy debates as carmakers have lobbied the European Union to relax CO₂ targets. A planned prohibition on sales of new combustion engine cars in 2035 has faced intense pressure from the car industry and opposition from member states with large car industries.

Some senior officials have suggested plug-in hybrids as a possible “compromise” option to include in the regulation.

One external energy policy specialist, who was not involved with the research, described the analysis a “very useful addition” after a long period in which segments of the car industry claimed there was too little information to accurately evaluate real-world CO2 output.

“These findings demonstrate, without question, that the difference in lab and actual PHEV fuel consumption and CO₂ emissions is significantly larger than for gasoline or conventional cars,” the expert said. “All regulatory adjustments regarding PHEVs should be made with utmost caution and in the light of this evidence.”