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Plug-in hybrid electric vehicles release almost five times greater planet-heating pollution than lab-reported data show, according to a new report.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data reveals that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, based on research carried out by a advocacy group. This differs sharply with lab estimates, which suggested a 75% decrease in pollution.

Analysts studied data from in-vehicle fuel consumption meters of eight hundred thousand cars registered in Europe between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab estimates, increased from 3.5 times in 2021.

“Real-world emissions are rising, while lab-reported emissions are decreasing,” said a lead researcher participating in the study. “That gap is growing and poses a significant problem. As a result, PHEVs emit almost as much as petrol cars.”

Primary Reasons Behind the Emissions Gap

Analysts attributed the majority of the difference to overestimates of the “utility factor” – the ratio of miles driven in battery power relative to overall mileage. The team found that just 27% of driving was completed in EV mode, whereas lab assumptions assumed 84%.

Additionally, when operating in EV mode, emission levels were well above lab projections. That occurred because EV motors were not strong sufficient to operate independently, leading to engines using fossil fuels for almost one-third of the distance covered in electric mode.

Regulatory and Economic Implications

Based on estimates, the lowballing of PHEV CO2 output allowed several major carmaker groups to escape over €5bn in fines between 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 extra per year in running expenses than is assumed under lab conditions.

“The bold statements that automakers like to make about their plug-in hybrid vehicles are clearly way off the truth,” commented a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are little better than regular petrol and diesel cars in terms of fuel use, CO₂ emissions, and operating expenses.”

Political Debate and Industry Pressure

Hybrid vehicles have lately been drawn again into political debates as carmakers have pressed the European Union to weaken CO₂ targets. A planned prohibition on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant automotive manufacturing.

Some senior officials have proposed PHEVs as a possible “compromise” solution to introduce in the regulation.

One independent energy policy expert, who was unaffiliated with the study, called the analysis a “very useful addition” after a long period in which segments of the automotive industry claimed there was too little data to properly evaluate real-world emissions.

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