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Plug-in hybrid electric vehicles emit almost 5x more planet-heating pollution than lab-reported figures indicate, according to a new analysis.

Growing Gap Between Official and Real-World CO2 Output

Data reveals that PHEVs emit only one-fifth lower CO₂ than traditional gas and diesel cars, according to research carried out by a non-profit group. That differs sharply with laboratory tests, which assumed a 75% decrease in emissions.

Researchers studied data from in-vehicle fuel consumption monitors of 800,000 cars registered in the EU from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, increased from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a senior analyst participating in the study. “This discrepancy is growing and creates a significant issue. Consequently, PHEVs emit nearly as much as petrol cars.”

Key Reasons Driving the Emissions Gap

Analysts attributed most of the difference to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric mode compared to overall mileage. They found that just 27% of driving was done in electric mode, while official estimates assumed over four-fifths.

Additionally, when operating in electric mode, emission amounts were well above official projections. This occurred because electric motors were not strong enough to function alone, resulting to combustion motors burning fossil fuels for almost one-third of the travel covered in EV mode.

Policy and Economic Implications

According to estimates, the underestimation of PHEV emissions enabled four major automaker groups to avoid over €5bn in fines between 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay about €500 extra annually in running costs than is estimated under lab tests.

“The bold statements that automakers often promote about their PHEV cars are clearly far from the mark,” stated a automotive expert. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are little better than regular gas and diesel cars in terms of energy use, CO₂ production, and operating expenses.”

Political Discussion and Industry Lobbying

Plug-in hybrid cars have recently been drawn back into policy debates as carmakers have pressed the EU to relax CO₂ targets. A proposed ban on new internal combustion vehicles in 2035 has faced heavy lobbying from the automotive industry and resistance from EU countries with large car manufacturing.

Several senior politicians have proposed PHEVs as a possible “flexibility” solution to introduce in the regulation.

One external energy policy specialist, who was not involved with the research, called the analysis a “very useful contribution” after a long period in which parts of the car industry argued there was too little information to accurately assess real-world emissions.

“These findings show, beyond any doubt, that the gap in official and actual PHEV fuel consumption and CO₂ output is much, much greater than for petrol or diesel vehicles,” the expert said. “All policy adjustments concerning PHEVs should be implemented with extreme caution and in the light of that evidence.”