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Plug-in hybrid electric vehicles emit almost 5x more planet-heating pollution than lab-reported figures show, as per a new report.

Widening Gap Between Lab and Real-World Emissions

Data reveals that PHEVs release only one-fifth lower CO₂ than traditional gas and diesel vehicles, according to research carried out by a advocacy organization. That differs significantly with lab estimates, which suggested a 75% decrease in pollution.

Researchers examined data from onboard fuel consumption meters of 800,000 vehicles sold in Europe from 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are falling,” said a senior researcher involved in the report. “That discrepancy is growing and poses a significant problem. As a result, PHEVs emit almost as heavily as petrol cars.”

Key Reasons Behind the Discrepancy

Analysts attributed the majority of the difference to inflated estimates of the “utility factor” – the percentage of miles driven in battery power relative to total mileage. The team determined that only 27% of driving was done in EV mode, while lab estimates suggested over four-fifths.

Even, when running in EV mode, emission levels were well above lab projections. This happened because EV motors were not strong enough to function independently, resulting to combustion motors using fossil fuels for almost a third of the travel covered in EV mode.

Policy and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output allowed several large carmaker groups to avoid over €5bn in penalties from 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend approximately €500 more annually in running expenses than would be assumed under laboratory conditions.

“The strong claims that automakers like to make about their PHEV cars are obviously far from the mark,” commented a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of energy use, CO₂ emissions, and operating expenses.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been drawn back into political debates as carmakers have pressed the EU to relax CO₂ targets. A proposed prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive industry and resistance from member states with large car industries.

Several high-level politicians have suggested plug-in hybrids as a possible “compromise” option to include in the legislation.

One external energy economics expert, who was not involved with the research, called the analysis a “very useful addition” after a long period in which parts of the car industry claimed there was insufficient information to accurately evaluate actual emissions.

“These findings demonstrate, beyond any doubt, that the difference in official and real-world PHEV fuel consumption and CO₂ output is much, much larger than for petrol or diesel cars,” the expert said. “Any regulatory changes regarding PHEVs should be made with utmost caution and considering that evidence.”