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Plug-in hybrid electric vehicles emit almost five times more planet-heating pollution than lab-reported figures show, according to a recent analysis.

Widening Gap Between Official and Real-World CO2 Output

Statistics shows that PHEVs release just 19% less CO₂ than traditional petrol and diesel vehicles, according to research carried out by a non-profit group. That differs significantly with lab tests, which assumed a 75% decrease in emissions.

Analysts examined information from onboard energy use monitors of 800,000 cars sold in the EU between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than official estimates, increased from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” stated a lead analyst participating in the study. “This gap is growing and poses a serious issue. As a result, PHEVs pollute almost as heavily as gasoline vehicles.”

Primary Reasons Driving the Discrepancy

Researchers attributed the majority of the gap to overestimates of the “utility factor” – the ratio of miles driven in electric mode relative to total distance. They found that just a quarter of travel was completed in EV mode, while official assumptions suggested 84%.

Additionally, when running in electric mode, emission levels were well above lab estimates. That happened because EV motors were insufficiently powerful enough to function independently, leading to combustion motors using fossil fuels for nearly one-third of the distance covered in EV mode.

Policy and Financial Consequences

Based on estimates, the underestimation of PHEV emissions enabled four major carmaker groups to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could spend about €500 more annually in operating costs than would be assumed under lab tests.

“The strong claims that manufacturers like to make about their PHEV cars are clearly far from the truth,” commented a automotive expert. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and cutting money. In reality, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ production, and operating costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have lately been brought again into policy discussions as carmakers have pressed the EU to weaken CO₂ targets. A proposed ban on new internal combustion vehicles in 2035 has faced intense pressure from the car industry and opposition from EU countries with large car manufacturing.

Some senior politicians have proposed PHEVs as a possible “flexibility” option to include in the legislation.

An external energy policy specialist, who was not involved with the study, called the report a “very useful contribution” after a long period in which segments of the car sector claimed there was insufficient data to accurately assess real-world CO2 output.

“The results demonstrate, without question, that the difference between official and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel vehicles,” they stated. “Any regulatory changes concerning PHEVs should be made with extreme caution and in the light of this data.”