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Plug-in hybrid cars emit almost five times greater planet-heating emissions than lab-reported figures show, according to a new analysis.

Widening Gap In Official and Actual Emissions

Statistics shows that PHEVs release only 19% lower CO₂ than conventional petrol and diesel cars, according to research carried out by a non-profit group. That differs significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers examined information from in-vehicle energy use monitors of 800,000 cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than official estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while official figures are falling,” said a senior researcher participating in the report. “That discrepancy is widening and creates a significant issue. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Reasons Behind the Emissions Gap

Researchers attributed the majority of the difference to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric power compared to overall mileage. The team determined that just 27% of travel was completed in electric mode, whereas lab estimates assumed over four-fifths.

Additionally, when running in electric mode, pollution amounts were significantly higher than official projections. This happened because electric motors were insufficiently powerful enough to operate independently, leading to combustion motors using fossil fuels for almost one-third of the distance covered in EV mode.

Policy and Economic Consequences

According to estimates, the underestimation of PHEV emissions allowed four major carmaker groups to avoid over €5bn in fines from 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ standards.

Furthermore, drivers of PHEVs would pay about €500 more per year in running costs than is assumed under laboratory tests.

“The bold claims that automakers like to make about their plug-in hybrid cars are clearly way off the mark,” stated a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the planet and cutting costs. In reality, PHEVs are little improved than regular petrol and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Policy Discussion and Industry Lobbying

Plug-in hybrid cars have recently been brought back into policy debates as carmakers have pressed the EU to relax CO₂ targets. A proposed prohibition on new combustion engine vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with large car industries.

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

One independent energy policy expert, who was not involved with the study, called the analysis a “very useful contribution” after years in which parts of the automotive sector claimed there was insufficient information to accurately assess real-world CO2 output.

“The results demonstrate, beyond any doubt, that the difference between official and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for gasoline or diesel vehicles,” the expert stated. “All regulatory adjustments concerning PHEVs should be implemented with utmost caution and in the light of that data.”