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PHEVs emit nearly 5x greater planet-heating pollution than lab-reported data show, according to a new analysis.

Growing Gap In Lab and Real-World CO2 Output

Data shows that PHEVs release just one-fifth less CO₂ than traditional petrol and diesel cars, based on research carried out by a advocacy group. This differs sharply with lab tests, which suggested a three-quarters decrease in pollution.

Researchers examined data from onboard fuel consumption monitors of eight hundred thousand vehicles registered in Europe between 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times greater than lab estimates, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported emissions are falling,” stated a lead analyst involved in the report. “That gap is growing and poses a significant problem. Consequently, PHEVs emit almost as much as petrol vehicles.”

Primary Reasons Driving the Discrepancy

Researchers attributed most of the difference to overestimates of the “utility factor” – the percentage of miles driven in electric mode relative to overall distance. The team found that just a quarter of travel was done in EV mode, whereas lab estimates assumed 84%.

Additionally, when operating in electric mode, pollution levels were significantly higher than official estimates. That occurred because electric motors were insufficiently powerful sufficient to operate independently, leading to combustion motors burning fossil fuels for nearly one-third of the distance covered in EV mode.

Regulatory and Financial Implications

Based on calculations, the lowballing of PHEV emissions enabled several large carmaker groups to escape more than €5bn in fines from 2021 and 2023, by falsely easing adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could pay about €500 extra annually in running expenses than would be assumed under lab conditions.

“The bold claims that manufacturers often promote about their PHEV cars are obviously far from the mark,” commented a automotive expert. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the environment and cutting money. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Policy Debate and Industry Pressure

Plug-in hybrid vehicles have recently been drawn again into political debates as automakers have pressed the EU to weaken CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced heavy lobbying from the car sector and opposition from member states with significant automotive industries.

Some high-level officials have proposed plug-in hybrids as a possible “compromise” solution to introduce in the legislation.

One external energy policy expert, who was unaffiliated with the research, described the analysis a “highly valuable addition” after years in which segments of the automotive sector claimed there was insufficient information to properly assess actual CO2 output.

“These findings show, beyond any doubt, that the gap between lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel cars,” the expert stated. “All policy changes concerning PHEVs should be implemented with extreme care and in the light of that data.”