Plug-in Hybrid electric Cars Emit Almost as Much as Gasoline Vehicles, Study Finds

PHEVs emit nearly five times more global warming pollution than official data show, according to a new report.

Widening Discrepancy In Lab and Actual Emissions

Data shows that PHEVs emit just one-fifth lower CO₂ than traditional petrol and diesel vehicles, according to research conducted by a advocacy group. That differs sharply with lab tests, which assumed a three-quarters reduction in emissions.

Researchers examined information from onboard energy use monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, up from 3.5 times in 2021.

“Actual emissions are rising, while lab-reported figures are falling,” said a lead researcher participating in the study. “This gap is growing and creates a serious problem. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Key Reasons Driving the Discrepancy

Analysts attributed most of the gap to overestimates of the “utility factor” – the ratio of kilometers driven in electric mode relative to total distance. They found that just a quarter of driving was completed in EV mode, while lab estimates assumed 84%.

Additionally, when operating in EV mode, emission levels were significantly higher than official estimates. That happened because electric motors were not strong sufficient to operate independently, resulting to engines using fossil fuels for nearly a third of the distance covered in EV mode.

Policy and Financial Implications

According to estimates, the lowballing of PHEV CO2 output allowed four large automaker groups to avoid more than €5bn in fines between 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ standards.

Additionally, drivers of PHEVs could pay approximately €500 extra annually in running expenses than is estimated under lab conditions.

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

Political Debate and Industry Pressure

Plug-in hybrid cars have lately been brought again into policy discussions as automakers have pressed the European Union to relax CO₂ targets. A planned prohibition on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the automotive sector and opposition from member states with large automotive manufacturing.

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

An external energy economics specialist, who was not involved with the study, called the report a “highly valuable contribution” after a long period in which segments of the car industry claimed there was too little data to properly assess actual emissions.

“The results show, without question, that the gap between official and real-world PHEV energy use and CO₂ output is significantly larger than for petrol or conventional vehicles,” they said. “Any policy adjustments concerning PHEVs should be made with extreme caution and considering that data.”