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PHEVs release almost five times greater planet-heating pollution than lab-reported data indicate, according to a new analysis.

Widening Gap In Lab and Real-World CO2 Output

Statistics shows that PHEVs release just 19% less CO₂ than conventional gas and diesel vehicles, based on research carried out by a non-profit organization. That contrasts significantly with laboratory tests, which suggested a three-quarters reduction in pollution.

Researchers studied information from in-vehicle fuel consumption monitors of eight hundred thousand cars registered in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official figures, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” said a lead analyst participating in the report. “That discrepancy is widening and poses a serious problem. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Key Factors Behind the Emissions Gap

Researchers attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric power compared to overall mileage. They found that only a quarter of driving was done in EV mode, while official estimates assumed 84%.

Additionally, when operating in EV mode, emission levels were significantly higher than official estimates. This occurred because EV motors were not strong enough to operate independently, resulting to combustion motors using gasoline for nearly one-third of the distance covered in EV mode.

Policy and Financial Implications

According to estimates, the lowballing of PHEV CO2 output enabled several large automaker groups to avoid more than €5bn in penalties between 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs would spend approximately €500 more per year in operating costs than is estimated under laboratory tests.

“The bold statements that automakers like to make about their plug-in hybrid vehicles are obviously far from the mark,” stated a transport expert. “Consumers 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 vehicles in terms of energy consumption, CO₂ production, and operating costs.”

Policy Debate and Industry Pressure

Plug-in hybrid cars have recently been drawn back into political debates as automakers have lobbied the European Union to weaken CO₂ targets. A proposed ban on new combustion engine vehicles in 2035 has faced intense pressure from the car industry and opposition from member states with large automotive industries.

Some senior politicians have proposed plug-in hybrids as a possible “compromise” solution to introduce in the legislation.

One independent energy policy specialist, who was unaffiliated with the research, described the analysis a “highly valuable addition” after years in which parts of the automotive sector argued there was insufficient data to accurately evaluate real-world emissions.

“The results show, without question, that the gap in lab and actual PHEV energy use and CO₂ output is much, much greater than for petrol or conventional cars,” the expert said. “All regulatory adjustments regarding PHEVs should be made with utmost caution and in the light of that data.”