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Plug-in hybrid cars release nearly five times greater planet-heating emissions than official figures indicate, as per a new report.

Growing Discrepancy Between Lab and Actual Emissions

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

Researchers studied data from in-vehicle energy use meters of eight hundred thousand vehicles sold in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, up from 3.5 times in 2021.

“Actual emissions are increasing, while lab-reported emissions are falling,” said a senior researcher involved in the study. “That gap is growing and creates a serious issue. Consequently, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Reasons Driving the Emissions Gap

Analysts attributed the majority of the gap to inflated estimates of the “electric driving share” – the ratio of miles travelled in electric power compared to total distance. The team found that only 27% of driving was completed in EV mode, while official estimates assumed 84%.

Additionally, when operating in electric mode, pollution levels were well above lab estimates. That occurred because electric motors were insufficiently powerful enough to function alone, resulting to engines burning fossil fuels for nearly one-third of the distance completed in EV mode.

Policy and Financial Implications

According to estimates, the underestimation of PHEV emissions allowed several major carmaker groups to escape over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ standards.

Furthermore, drivers of PHEVs could pay approximately €500 extra annually in running expenses than would be estimated under lab conditions.

“The bold statements that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the truth,” stated a transport expert. “Consumers are being misled into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Political Debate and Automotive Pressure

Hybrid cars have lately been drawn again into policy debates as automakers have pressed the European Union to relax CO₂ targets. A planned ban on new internal combustion vehicles in 2035 has faced intense pressure from the automotive sector and opposition from member states with significant automotive manufacturing.

Several high-level officials have suggested plug-in hybrids as a possible “compromise” solution to introduce in the legislation.

One external energy policy specialist, who was not involved with the study, described the analysis a “very useful addition” after a long period in which parts of the automotive sector argued there was insufficient data to properly assess real-world CO2 output.

“These findings show, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ output is significantly greater than for gasoline or conventional cars,” they said. “Any regulatory adjustments regarding PHEVs should be implemented with utmost caution and considering that data.”