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Plug-in hybrid cars produce almost five times greater planet-heating emissions than lab-reported figures show, according to a new analysis.

Widening Gap Between Lab and Actual Emissions

Data shows that PHEVs emit just one-fifth lower CO₂ than traditional gas and diesel vehicles, according to research conducted by a advocacy group. This differs significantly with laboratory estimates, which assumed a 75% decrease in pollution.

Analysts examined information from in-vehicle fuel consumption monitors of 800,000 vehicles sold in Europe from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab estimates, increased from 3.5 times in 2021.

“Actual emissions are increasing, while lab-reported emissions are decreasing,” stated a senior researcher involved in the report. “This discrepancy is widening and creates a significant problem. As a result, PHEVs emit nearly as much as petrol cars.”

Primary Reasons Driving the Emissions Gap

Researchers attributed most of the difference to overestimates of the “utility factor” – the ratio of miles driven in electric power relative to overall mileage. They determined that only a quarter of travel was done in electric mode, while lab assumptions assumed over four-fifths.

Additionally, when operating in electric mode, emission amounts were significantly higher than lab estimates. This occurred because electric motors were insufficiently powerful sufficient to function alone, resulting to engines using fossil fuels for nearly one-third of the distance completed in EV mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV CO2 output enabled several large automaker companies to escape over €5bn in penalties from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ standards.

Furthermore, drivers of PHEVs could pay about €500 extra annually in operating costs than would be estimated under laboratory tests.

“The bold statements that automakers like to make about their plug-in hybrid cars are clearly far from the truth,” stated a transport analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the planet and saving money. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of energy use, CO₂ production, and operating expenses.”

Political Debate and Automotive Lobbying

Plug-in hybrid vehicles have recently been brought again into political debates as automakers have lobbied the European Union to weaken CO₂ targets. A planned ban on new combustion engine cars in 2035 has faced intense lobbying from the car industry and opposition from EU countries with large automotive manufacturing.

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

An independent energy policy expert, who was not involved with the research, called the analysis a “highly valuable addition” after a long period in which segments of the automotive sector claimed there was insufficient information to accurately evaluate actual CO2 output.

“These findings demonstrate, beyond any doubt, that the difference between official and real-world PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or conventional cars,” they said. “All regulatory changes concerning PHEVs should be implemented with utmost care and considering this data.”