Plug-in Hybrid Vehicles Pollute Almost as Heavily as Petrol Vehicles, Study Finds

PHEVs emit almost five times greater planet-heating pollution than lab-reported figures indicate, according to a new analysis.

Growing Gap In Official and Real-World Emissions

Statistics reveals that PHEVs emit only 19% less CO₂ than traditional petrol and diesel vehicles, based on analysis carried out by a advocacy organization. That differs significantly with laboratory tests, which assumed a 75% reduction in pollution.

Analysts studied information from in-vehicle energy use monitors of 800,000 cars registered in Europe between 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, up from three and a half times in 2021.

“Actual emissions are increasing, while lab-reported emissions are falling,” said a senior researcher participating in the study. “This discrepancy is widening and creates a serious problem. As a result, PHEVs emit almost as heavily as gasoline cars.”

Primary Reasons Driving the Emissions Gap

Researchers linked the majority of the gap to overestimates of the “electric driving share” – the percentage of kilometers travelled in battery mode compared to total mileage. The team determined that just 27% of travel was done in electric mode, whereas lab estimates suggested 84%.

Even, when operating in electric mode, emission amounts were significantly higher than lab estimates. That happened because electric motors were insufficiently powerful enough to operate independently, resulting to combustion motors using gasoline for almost one-third of the travel completed in EV mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV CO2 output enabled several major automaker groups to avoid more than €5bn in penalties from 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could spend approximately €500 more annually in running expenses than would be assumed under lab conditions.

“The bold claims that manufacturers like to make about their plug-in hybrid vehicles are clearly far from the mark,” stated a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are helping the environment and cutting money. In reality, PHEVs are little improved than regular petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Political Debate and Industry Pressure

Hybrid cars have recently been drawn back into policy debates as automakers have pressed the EU to relax CO₂ targets. A proposed ban on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the car industry and resistance from EU countries with large car manufacturing.

Several high-level officials have suggested PHEVs as a possible “flexibility” option to introduce in the legislation.

One external energy policy specialist, who was unaffiliated with the study, described the analysis a “very useful addition” after years in which parts of the automotive sector argued there was insufficient information to accurately evaluate actual emissions.

“The results demonstrate, without question, that the gap in lab and actual PHEV energy use and CO₂ emissions is much, much larger than for gasoline or conventional vehicles,” they stated. “Any regulatory changes regarding PHEVs should be made with utmost care and considering that evidence.”