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Plug-in hybrid electric vehicles produce almost 5x more planet-heating pollution than lab-reported data show, as per a new analysis.

Growing Gap Between Lab and Actual CO2 Output

Data shows that PHEVs emit only one-fifth less CO₂ than traditional gas and diesel vehicles, based on research carried out by a non-profit organization. That differs sharply with laboratory tests, which assumed a three-quarters reduction in pollution.

Researchers studied data from in-vehicle energy use monitors of 800,000 cars registered in Europe between 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official figures, increased from three and a half times in 2021.

“Real-world emissions are rising, while lab-reported emissions are falling,” said a senior researcher involved in the report. “This gap is widening and poses a serious problem. As a result, PHEVs pollute nearly as heavily as petrol cars.”

Key Factors Driving the Discrepancy

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in battery mode relative to overall mileage. The team determined that only a quarter of travel was completed in electric mode, whereas lab assumptions suggested 84%.

Even, when running in EV mode, pollution amounts were well above official estimates. That happened because EV motors were not strong enough to operate alone, leading to engines burning fossil fuels for almost one-third of the travel completed in electric mode.

Regulatory and Financial Consequences

According to estimates, the lowballing of PHEV emissions allowed four major automaker groups to escape more than €5bn in penalties between 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs could spend approximately €500 extra per year in running expenses than is assumed under laboratory conditions.

“The strong statements that manufacturers often promote about their PHEV cars are clearly far from the truth,” stated a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are only slightly improved than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Policy Debate and Industry Pressure

Hybrid cars have recently been brought back into political debates as carmakers have lobbied the European Union to relax CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and opposition from EU countries with significant automotive industries.

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

One external energy policy expert, who was unaffiliated with the study, called the report a “highly valuable contribution” after a long period in which segments of the automotive sector claimed there was too little data to accurately assess real-world emissions.

“The results demonstrate, without question, that the difference between lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel cars,” they stated. “Any policy adjustments concerning PHEVs should be made with extreme caution and considering that data.”