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Plug-in hybrid cars produce almost five times more planet-heating pollution than lab-reported data indicate, according to a recent report.

Widening Gap In Lab and Actual CO2 Output

Data shows that PHEVs emit only 19% less CO₂ than conventional petrol and diesel cars, based on analysis conducted by a advocacy organization. That contrasts sharply with laboratory tests, which suggested a 75% decrease in pollution.

Researchers studied data from in-vehicle fuel consumption monitors of 800,000 vehicles registered in Europe from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official figures, up from three and a half times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are decreasing,” stated a senior analyst involved in the study. “This gap is growing and poses a serious issue. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts attributed the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers travelled in battery power compared to total distance. They found that just a quarter of travel was done in EV mode, whereas lab assumptions suggested 84%.

Even, when operating in EV mode, pollution amounts were significantly higher than lab estimates. This happened because EV motors were insufficiently powerful sufficient to function alone, leading to combustion motors burning fossil fuels for almost one-third of the distance completed in EV mode.

Regulatory and Economic Implications

According to estimates, the underestimation of PHEV CO2 output enabled several major automaker groups to avoid over €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs could pay about €500 more annually in operating expenses than is assumed under laboratory tests.

“The bold statements that manufacturers often promote about their plug-in hybrid cars are clearly far from the mark,” commented a transport expert. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are only slightly improved than regular petrol and diesel cars in terms of fuel use, CO₂ emissions, and operating costs.”

Political Discussion and Automotive Pressure

Plug-in hybrid vehicles have recently been drawn again into political discussions as carmakers have pressed the European Union to relax CO₂ targets. A planned prohibition on sales of new internal combustion cars in 2035 has faced heavy lobbying from the automotive sector and resistance from member states with significant automotive industries.

Some high-level politicians have proposed plug-in hybrids as a possible “flexibility” solution to include in the legislation.

An external energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable contribution” after years in which parts of the car industry claimed there was too little data to properly assess actual emissions.

“These findings demonstrate, beyond any doubt, that the difference between lab and real-world PHEV fuel consumption and CO₂ output is significantly greater than for petrol or diesel cars,” the expert stated. “All policy adjustments regarding PHEVs should be made with utmost caution and in the light of that evidence.”