Plug in Hybrid Cars Emit Nearly as Much as Petrol Vehicles, Study Finds

Plug-in hybrid cars release almost five times more planet-heating pollution than lab-reported data indicate, according to a new analysis.

Widening Discrepancy In Lab and Real-World Emissions

Data shows that PHEVs emit only 19% lower CO₂ than traditional petrol and diesel cars, based on analysis conducted by a non-profit group. That differs significantly with lab tests, which assumed a 75% decrease in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of eight hundred thousand vehicles registered in the EU from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab estimates, up from three and a half times in 2021.

“Actual emissions are increasing, while official emissions are decreasing,” said a lead researcher participating in the study. “This gap is widening and creates a serious problem. As a result, PHEVs emit nearly as much as gasoline cars.”

Key Factors Driving the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “utility factor” – the ratio of miles travelled in electric mode compared to total mileage. They determined that just 27% of travel was done in EV mode, while lab estimates suggested over four-fifths.

Additionally, when operating in electric mode, pollution levels were well above official projections. That occurred because EV motors were insufficiently powerful enough to operate independently, leading to engines using gasoline for almost a third of the distance covered in EV mode.

Policy and Economic Implications

Based on calculations, the underestimation of PHEV emissions enabled four large automaker groups to avoid more than €5bn in fines between 2021 and 2023, by artificially easing adherence with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs could pay approximately €500 extra annually in running expenses than would be estimated under lab conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly way off the mark,” stated a transport expert. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and cutting money. Actually, PHEVs are little better than regular gas and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Political Debate and Industry Pressure

Plug-in hybrid vehicles have lately been brought again into policy debates as automakers have pressed the EU to weaken CO₂ standards. A planned prohibition on sales of new internal combustion cars in 2035 has faced heavy pressure from the car sector and resistance from EU countries with significant car manufacturing.

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

One independent energy economics specialist, who was unaffiliated with the research, described the report a “very useful contribution” after a long period in which parts of the car sector argued there was insufficient information to properly assess real-world emissions.

“These findings demonstrate, without question, that the difference in official and real-world PHEV fuel consumption and CO₂ output is much, much greater than for petrol or conventional cars,” they stated. “All regulatory changes concerning PHEVs should be made with utmost care and in the light of that data.”