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Plug-in hybrid cars emit almost five times more planet-heating emissions than lab-reported data indicate, as per a new report.

Widening Gap Between Lab and Actual Emissions

Data shows that PHEVs emit only 19% lower CO₂ than conventional petrol and diesel vehicles, based on analysis carried out by a non-profit group. This contrasts sharply with lab estimates, which assumed a 75% reduction in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of eight hundred thousand vehicles registered in Europe between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official figures are decreasing,” stated a senior analyst participating in the report. “This discrepancy is growing and poses a significant problem. Consequently, PHEVs pollute almost as much as gasoline cars.”

Primary Reasons Driving the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the ratio of miles travelled in battery power relative to overall mileage. The team found that just a quarter of driving was done in electric mode, while official assumptions suggested over four-fifths.

Additionally, when running in electric mode, pollution amounts were significantly higher than lab projections. This occurred because electric motors were not strong sufficient to function alone, resulting to combustion motors burning gasoline for almost one-third of the distance completed in EV mode.

Policy and Financial Implications

Based on estimates, the lowballing of PHEV emissions allowed four major automaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend about €500 more per year in operating costs than is estimated under lab conditions.

“The bold claims that automakers like to make about their plug-in hybrid cars are clearly far from the mark,” stated a transport expert. “Buyers are being misled into believing that by buying a PHEV, they are helping the planet and cutting money. In reality, PHEVs are little better than regular petrol and diesel cars in terms of fuel consumption, CO₂ production, and operating costs.”

Policy Debate and Automotive Pressure

Hybrid cars have recently been brought again into policy discussions as carmakers have lobbied the European Union to relax CO₂ standards. A proposed ban on sales of new combustion engine cars in 2035 has faced intense lobbying from the car sector and resistance from EU countries with large car manufacturing.

Several high-level officials have proposed PHEVs as a possible “flexibility” option to include in the legislation.

One external energy economics expert, who was not involved with the study, called the analysis a “highly valuable contribution” after a long period in which parts of the automotive industry argued there was insufficient information to properly assess actual emissions.

“The results show, without question, that the difference between lab and actual PHEV energy use and CO₂ emissions is significantly greater than for petrol or conventional vehicles,” they stated. “All policy adjustments concerning PHEVs should be made with extreme caution and in the light of that evidence.”