Plug-in Hybrid Cars Pollute Almost as Much as Petrol Cars, Study Finds

Plug-in hybrid electric vehicles emit almost five times more planet-heating pollution than official figures indicate, according to a recent report.

Growing Gap In Official and Real-World Emissions

Data reveals that PHEVs emit only one-fifth lower CO₂ than traditional gas and diesel vehicles, according to analysis carried out by a advocacy group. This contrasts sharply with laboratory tests, which suggested a 75% reduction in pollution.

Researchers studied data from in-vehicle energy use meters of eight hundred thousand vehicles sold in Europe between 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official figures are decreasing,” said a senior researcher participating in the report. “This discrepancy is growing and poses a serious problem. As a result, PHEVs pollute almost as much as gasoline cars.”

Key Factors Driving the Emissions Gap

Analysts attributed most of the gap to inflated estimates of the “utility factor” – the percentage of kilometers driven in electric power compared to total mileage. The team found that only 27% of driving was completed in electric mode, whereas official estimates assumed 84%.

Additionally, when operating in EV mode, pollution levels were significantly higher than official projections. That occurred because electric motors were not strong sufficient to operate alone, leading to combustion motors using fossil fuels for nearly a third of the travel completed in electric mode.

Policy and Economic Implications

According to estimates, the underestimation of PHEV CO2 output enabled four major automaker groups to avoid more than €5bn in fines from 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs would spend about €500 more per year in running costs than would be estimated under lab tests.

“The strong statements that manufacturers like to make about their plug-in hybrid cars are clearly way off the truth,” commented a transport expert. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are only slightly improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating costs.”

Policy Debate and Automotive Pressure

Hybrid vehicles have recently been drawn back into policy debates as carmakers have pressed the European Union to relax CO₂ standards. A proposed prohibition on new internal combustion vehicles in 2035 has faced intense lobbying from the car industry and resistance from EU countries with large automotive industries.

Several senior officials have suggested plug-in hybrids as a potential “flexibility” solution to include in the regulation.

One independent energy policy expert, who was not involved with the research, described the report a “very useful addition” after a long period in which parts of the automotive sector argued there was insufficient data to properly evaluate real-world emissions.

“These findings show, beyond any doubt, that the difference between lab and actual PHEV energy use and CO₂ emissions is significantly greater than for gasoline or conventional vehicles,” they said. “Any regulatory adjustments concerning PHEVs should be made with extreme care and in the light of that evidence.”