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Plug-in hybrid electric vehicles emit nearly 5x more planet-heating pollution than lab-reported data indicate, according to a recent report.

Growing Gap Between Lab and Actual CO2 Output

Data shows that PHEVs release just 19% lower CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a advocacy organization. This differs significantly with laboratory tests, which suggested a three-quarters reduction in pollution.

Researchers examined data from onboard energy use monitors of 800,000 cars sold in Europe between 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, up from three and a half times in 2021.

“Real-world CO2 output are rising, while official figures are falling,” said a senior researcher participating in the study. “That discrepancy is widening and creates a serious issue. As a result, PHEVs pollute almost as much as gasoline cars.”

Primary Reasons Behind the Emissions Gap

Researchers linked the majority of the gap to inflated estimates of the “utility factor” – the percentage of kilometers driven in battery mode compared to total distance. The team determined that only a quarter of travel was done in EV mode, whereas official assumptions assumed over four-fifths.

Even, when operating in EV mode, pollution levels were well above lab estimates. That happened because electric motors were not strong sufficient to function independently, leading to combustion motors using gasoline for nearly one-third of the distance completed in EV mode.

Policy and Economic Consequences

According to calculations, the lowballing of PHEV CO2 output enabled several major automaker companies to escape more than €5bn in fines from 2021 and 2023, by falsely simplifying adherence with EU average fleet CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 more annually in running expenses than is estimated under lab conditions.

“The bold claims that manufacturers often promote about their PHEV vehicles are clearly way off the mark,” commented a transport expert. “Consumers are being duped into thinking that by buying a PHEV, they are helping the planet and saving money. Actually, PHEVs are little better than regular petrol and diesel cars in terms of fuel use, CO₂ emissions, and running costs.”

Political Debate and Automotive Lobbying

Plug-in hybrid vehicles have recently been drawn back into policy debates as automakers have lobbied the European Union to weaken CO₂ standards. A planned prohibition on new combustion engine cars in 2035 has faced intense lobbying from the car industry and opposition from member states with large automotive industries.

Some senior officials have suggested plug-in hybrids as a possible “flexibility” solution to include in the legislation.

One independent energy policy expert, who was unaffiliated with the study, described the analysis a “very useful contribution” after a long period in which segments of the car industry argued there was too little data to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the difference between lab and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or conventional cars,” they stated. “All regulatory changes regarding PHEVs should be implemented with utmost caution and in the light of this evidence.”